Friday, 14 December 2012

Future Exploration of the Outer Planets

On Friday December 14th the Royal Astronomical Society hosted a one-day discussion meeting on the future exploration of the outer solar system, organised by myself and Chris Arridge.  The details of the meeting can be found below, along with the list of speakers from the UK and overseas.  More details will appear in this blog after Christmas, and the outcome of the meeting will be described in an article for Astronomy and Geophysics in 2013. The meeting was a great success, with a broad range of topics covered and plenty of discussions over coffee about how we might push for future exploration of the outer solar system!


Exploration of the giant planets of our solar system over the past several decades has revealed four unique, complex and dynamic worlds.  They serve as natural planetary-scale laboratories for the fundamental physics and chemistry at work throughout our solar system, and can be viewed as miniature solar systems in their own right.  Our understanding of these planets remains in its infancy, but the four giants serve as templates for the interpretation of exoplanetary systems being discovered throughout our galaxy.  The purpose of this Royal Astronomical Society Specialist Discussion Meeting on December 14th 2012 is to bring together experts in giant planet systems to identify the key science questions for future exploration of the outer solar system.  The themes of this meeting include:
  1. Drivers for exploration of the Jupiter system by Juno and JUICE – open questions and the scientific potential.
  2. Orbital exploration of an Ice Giant planetary system – science questions and technological feasibility.
  3. In situ exploration of giant planet atmospheres (probes) and satellite surfaces (landers) to provide a window onto the formational history of our solar system.
  4. Future space-telescopic observations of our solar system in the post-Hubble/Spitzer/Herschel era (e.g., capabilities of JWST and the need for planetary spectroscopy).

Abstracts concerning recent research and open questions on the present state of these planets (dynamics, chemistry and vertical structure); their temporal evolution and coupling between their atmosphere, interior, magnetosphere, satellites and ring systems are also welcome.   This meeting will explore the rationale and drivers for outer solar system exploration in the coming decades, and discuss the possibilities for future telescopic and spacecraft missions.   Further information on the meeting (plus details of how to get to Burlington House) can be found at

Keynote Speakers
  1. Mark Hofstadter (JPL) - Missions to the Ice Giants
  2. Michele Dougherty (Imperial) - Exploration of the Jovian System and JUICE
  3. Olivier Mousis (Toulouse) - Formation Processes in the Outer Solar System

Programme:  Friday December 14th 2012
Keynote talks will last 30 minutes (including 5 min discussion), all other talks will last 20 minutes (including 4 min discussion).

10:00 - 10:30 Arrival and Coffee

10:30 - 13:00 Morning Session
10:30 - 10:40 Intro & Aims (10 mins) - Leigh Fletcher, Oxford
10:40 - 11:10 Prospects for a NASA-led Ice Giant Mission (Keynote) - Mark Hofstadter, NASA/JPL
11:10 - 11:30 Uranus Pathfinder - Chris Arridge, MSSL
11:30 - 11:50 Gas Giant Ionospheres and Aurora - Tom Stallard, Leicester
11:50 - 12:20 Origin of Uranus and its Satellite System (Keynote) - Olivier Mousis
12:20 - 12:40 Radioactive Power Sources and Technology Development - Richard Ambrosi, Leicester
12:40 - 13:00 Outer Solar System Technology Development - Matthew Stuttard, Astrium

13:00 - 14:00 Lunch

14:00 - 15:30 Afternoon Session
14:00 - 14:30 Exploration of the Jovian System and JUICE - Michele Dougherty, Imperial
14:30 - 14:50 Future Exploration of Titan - Mark Leese, Open University
14:50 - 15:10 Instrumentation for in-situ measurements of the gas giants and their satellites - Andrew Morse, Open University
15:10 - 15:30 Exploration of Planetary Rings - Carl Murray, QMUL

15:30 - 16:00 Tea at the Geological Society
16:00 - 18:00 RAS Monthly A&G (Ordinary) Meeting
18:00 - 19:00 Drinks Reception (in the RAS' Burlington House Apartments)

Further Details:

Recent observations of the gas and ice giants have revealed complex evolving systems, from (i) short-term variability (comet/asteroidal impacts on Jupiter, giant planetary-scale storms on Saturn, discrete features on Uranus and Neptune, dynamic moon activity at Io and Enceladus), (ii) medium-term changes (the life cycle of Jupiter's South Equatorial Belt, seasonal storms on Saturn, seasonal effects on natural satellites, seasonal changes in ring systems and their atmospheres/ionosphere) and solar cycle variability in the magnetosphere.  The seasonally-induced hemispheric asymmetries, polar vortices and equator-to-pole contrasts on Saturn, Uranus and Neptune allows us to study generalised seasonal and polar phenomena without the complicating terrestrial influence of topography.  Temporal variability within the weather layer may provide key diagnostics of processes occurring in regions inaccessible to remote sensing, within the deep troposphere and planetary interior.   The diverse satellite and ring systems host a plethora of unique environments that have yet to be fully explored, from Io’s volcanoes, the sub-surface oceans of Europa, Ganymede and Callisto, the plumes of Enceladus and Triton and the thick atmosphere of Titan.  And finally, the magnetospheres of the giant planets act as giant particle accelerators (from plasma to dust), exhibit pulsar-like behaviour (Jupiter) and interact with the rest of their planetary environments in complex ways via a range of mass, energy and momentum exchange processes.  This meeting aims to capture each of these diverse planetary exploration fields to discuss the rationale for future missions to the outer solar system.

Saturday, 1 December 2012

Seasons in the Saturn System

Cassini gazing down into Saturn’s spectacular north polar vortex, revealed in reflected sunlight as the north pole enters spring time conditions after years of winter darkness, November 2012. Credit:  NASA/JPL
The EPSC in Madrid in September 2012 featured sessions on giant planets, satellites and seasonal processes in our solar system, all of which provided insights into some of the latest discoveries by Cassini in the Saturn system.  Cassini has been orbiting Saturn since mid winter in the northern hemisphere (when Saturn's northern clouds had a distinctly blue, Neptune like appearance).  The spring equinox was in 2009, when the sun passed from the south into the northern hemisphere for the first time in fifteen years (half of a Saturn year) and the rings were seen edge-on from earth.  Cassini will hopefully remain operating all the way to northern summer solstice in 2017, fully characterising half of a Saturnian year.

Linda Spilker, Cassini project scientist, gave a keynote talk describing some of the latest findings.  During equinox, Saturn's thin F ring remained glowing, revealing that it is slightly inclined compared to the other rings, which were only partially illuminated by Saturn shine (light reflected from the clouds below). Elevated features in the rings cast long shadows, and dusty streaks above the ring plane were evidence of recent impacts, their debris sheared out by keplerian motion and catching the sunlight.  Edge waves on the Keeler Gap, created by the tiny moon Daphnis, cast shadows due to a 4 km lifting out of the ring plane, whereas similar edge waves in the Encke Division, created by tiny Pan, had no similar vertical extension.  Bizarre propeller objects in the rings were also projected above the ring plane.  Thermal mapping showed that the rings were at their coldest at the equinox at 45K, in equilibrium with e thermal radiation from the planet itself.  Intriguingly, the corrugated nature of the rings (ripples observed at equinox) could be modelled and traced all the way back to an impact event in the rings in 1983.  A similar corrugated wave in the Jovian system could be traced back to the collision of comet Shoemaker-Levy 9 in 1994. 

Beyond the rings, the tidally-locked satellite Mimas has been shown to have an unusual interaction between the surface and the magnetospheric environment.  A dark lens shape on the leading face of Mimas coincides with a cold region, bounded by sharp warm edges that give the moon a "pacman" appearance in certain geometries.  Cassini scientists suggest that energetic electrons, travelling retrograde around Saturn, slam into the surface to cate material differences in colour and thermal inertia.  These electrons are mainly funnelled into the corner ansae, creating the lens-shaped appearance.  On the trailing hemisphere, cold plasma and E ring grains cause erosion.  Amanda Hendrix also talked about the UV darkening of water ice due to photolytic creation of hydrogen peroxide, produced in the summer but destroyed in winter by electron bombardment, leading to seasonal asymmetries in UV brightness of the moons.  They predict that the northern hemisphere will darken during southern summer as more and more of this H2O2 is produced.

Alice le Gall reported evidence of seasonal variations on Iapetus, the solar systems most distant tidally-locked moon.  Its inclined orbit makes Iapetus difficult to reach, but also means that the moon passed equinox back in 2007 before the rest of the Saturn system.  Passive radar scans of the Cassini Regio showed that the north was cooler than the south, despite more illumination in the north, and suggestive of heat buried in the upper few centimetres of the moon during the long summer season.  Beneath about 1 m, however, the temperature is just symmetric about the equator.

On Saturn itself, we have been gripped by observations of the gigantic springtime storm system since 2010.  The churning tropospheric storm persisted from December 2010 to July 2011, but produced after effects in the stratosphere that persist to this day, and will be the topic of future posts when the papers are all published.  But Spilker described one interesting development - it was thought that we'd never see lightning on Saturn because of light reflected from the rings.  But the northern storm was so powerful that Cassini could observe the flashes in blue light.  Away from the storm, the slow seasons march on, with Saturn's northern blue hues now completely replaced by the familiar yellow-ochre colours we are all familiar with.  My own work is showing that northern temperatures are warming, as expected, and that the hot south polar stratosphere we reported a few years ago is showing signs of diminishing.

Saturn's enigmatic moon, Titan, continues to undergo severe changes in its atmospheric circulation, as reported by Ralph Lorenz.  When Cassini arrived, the North Pole featured a dramatic vortex, enriched in chemicals due the downward branch of a global circulation system.  That dark north polar hood has now become a distinct dark lane with a detached haze layer.  The height of the detached layer of haze itself seems to change, rising and falling depending on the strength of the meridional circulation. A similar polar hood is now seen to be developing at the South Pole, with recent images showing a dramatic vortex structure reminiscent of Venus' dipole vortex discovered by Venus Express. The whole atmospheric circulation may be shifting direction as spring progresses.

One of the most spectacular Cassini results are the recent observations of specular reflections from Titan's northern lakes, observed by the VIMS instrument at 5 microns.  Glinting sunlight from a titanian sea is a wonderful thought.  

The Cassini spacecraft is still in excellent health, 8 years into the mission and 15 years since launch.  If all goes to plan, the proximal orbits in 2016 will see Cassini closer to Saturn than ever before, flying within the rings themselves as we approach northern summer solstice.  Then, around September 2017 Cassini will plunge to a fiery death, a fitting end to an incredible mission.

Thursday, 15 November 2012

Formation of the Giants

The giant planets Jupiter and Saturn were known to the ancients, and became the first targets of telescopic observations during the renaissance, with Cassini observing a giant red spot and banded structure on Jupiter, and Huygens interpreting the 'ears' of Saturn as a large, flat, inclined ring.  Today, Jupiter has been visited by Pioneer 10 & 11, Voyager 1 & 2, Galileo, Cassini and New Horizons, with Juno expected to arrive in 2016, followed by ESA's JUICE spacecraft in the 2030s.  The Cassini Huygens mission is in its ninth successful year in orbit around Saturn.  

Uranus and Neptune came later.  William Herschel discovered Uranus in 1781 with a 15 cm telescope, Neptune was first observed by J. Galle in 1846 after Le Verrier and J. Adams both predicted the position of the eighth planet.  These ice giant worlds have been visited only once by Voyager 2, and much of what we know about these distant worlds has been revealed by Hubble and ground based observations over the past two decades.

Planet Formation

One of the driving goals behind the exploration of the giant planets is he quest to understand the formation of our solar system.  We know that planets orbit in the same plane (almost), on nearly circular orbits, and that  they rotate anticlockwise just like the Sun.  This suggests that they all formed from a disk of material, an idea supported by the observations of protoplanetary disks around young nearby stars.  Furthermore, there are two types of planets in our solar system: the high density terrestrial planets (3-5 g/cm3) with very few satellites, and the low density giants (0.7-1.7 g/cm3) with extensive satellite systems.

This hierarchy of planets is due to the conditions in the nebula as the planets formed. Embryos of solid particles were embedded in the hydrogen-rich disk, and as more refractory elements (I.e., metals and silicates) were found in the high temperature inner solar system, versus the more icy materials at the cold outer reaches, this explains why the inner and outer solar system look so different from one another.  The available solid mass was lower in the hot inner solar system, whereas abundant ices in the outer solar system produced big embryos of ten earth masses or more.  Once a critical mass for these embryos was reached, the extensive gassy atmospheres of the giants was accreted directly from the gas-rich nebula.  

This core accretion scenario was developed by Mizuno (1980) and Pollack et al. (1996).  More recently, the idea of planetary migration has been added, known as the "Nice model" (A. Morbidelli et al.), where the 2:1 resonance crossing of the Jupiter-Saturn system led to intense perturbations of other bodies in the system and generated the Late Heavy Bombardment, whose impact scars dominate the appearance of rocky bodies in our solar system to this day.  In an earlier phase, Jupiter may have approached the orbit of Mars (stopping its growth) and then receded due to Saturn's interaction (Walsh e al. 2011).

The giant planets can be further subdivided into the gas giants (Jupiter (5 AU) & Saturn (10 AU); 318 and 95 Earth masses, respectively) comprised mostly of hydrogen and helium, and the ice giants enriched in heavier materials (potentially delivered as ices, hence their name).  Uranus and Neptune are smaller (14 and 17 earth masses), and their different atmosphere composition is usually attributed to their formation timescales - they formed after Jupiter and Saturn at a time when there was less gas available in the disk (it was being dissipated). The migration hypothesis suggests that the ice giants formed closer in (10-15 AU) and migrated outward to their present positions (19 and 30 AU). 

Atmospheric Composition

The bulk atmospheric compositions support the idea that the planets formed in a disc with temperatures decreasing with distance from the young sun.  At low temperatures, thermochemical equilibrium implies that the key elements (C, H, O, N) were in hydrogenated, reduced forms of methane, water and ammonia - the key ices thought to have formed the giant planets and still present in their atmospheres.  At the higher temperatures of the inner solar system, those species exist as CO, CO2 and N2, precisely the species found in the terrestrial atmospheres (although these came from later out gassing of secondary atmospheres, rather than accretion of primary atmospheres like the giants).  

Remote sensing of giant planet atmospheres, in addition to the Galileo probe, have provided supporting evidence of the core accretion hypothesis of planetary formation.  Both the carbon and deuterium abundances increase from Jupiter to Neptune, as expected if the ratio of gassy envelope to planetary core decreases with distance from the Sun.  The Galileo in situ entry probe discovered that almost all of the elements making up Jupiter were enriched over solar composition, supporting the existence of planetary embryos enriched in abundance compared to the rest of the gassy nebula.  This direct measurement is something scientists are keen to repeat on the other giant planets in our solar system, particularly an ice giant, to understand the differences in how these bodies formed.  Remote sensing cannot measure the abundances of the noble gases, which are key indicators of the way in which materials like ice and gas were accreted into the giants.

One big mystery about Jupiter's composition remains unanswered - the abundance of oxygen.  If all the other materials were encased in cages of water ice, then there should be lots of it.  Unfortunately Galileo was unable to measure the deep water abundance to confirm this.  The Juno probe, due to arrive in 2016, carried with it a microwave instrument capable of peering beneath the Jovian clouds to sample the deep water abundance.  Scientists wait with baited breath for the answer to this crucial question of how Jupiter formed, with far reaching implications for the evolution of our whole planetary system.

Monday, 5 November 2012

The Galileo Mission to Jupiter

Artist's impression of the Galileo mission to Jupiter.
In a previous post, I summarised some of the stories of Voyager's Grand Tour of the outer solar system, as discussed by John Casani at the Alpbach summer school in 2012.  After the Pioneer missions to Jupiter in the 1970s, NASA began to think about its next voyage to the outer solar system, and conceived the Pioneer-class Jupiter Orbiter with Probe mission, a spin stabilised platform with a despun component to allow remote sensing.  At an early stage, the Galileo project was forced to move away from a Titan launch vehicle like the Voyagers, and were instructed to use the Space Shuttle as the launch system, in a move away from the expendable launch systems of the past to reusable technologies.  From the first planned launch in 1982 to the final launch in 1989, Galileo was continuously delayed by problems with the shuttles launch schedule and deteriorating performance.  When it finally arrived in 1995 to drop its probe into the churning atmosphere of Jupiter, it was ten years later than planned, a lesson for all future planners of outer solar system missions!  To accommodate the space shuttle launch, Galileo went through several costly redesigns, including the introduction of a Probe Carrier, a Mars Flyby Module and a Centaur upper stage which never saw the light of day.  Ultimately, it may have been less costly to stick with the original expendable launch vehicle!

Galileo's main hurdle to overcome was a broken antenna, which failed to unfurl in the early days of the mission, considerably limiting the amount of data returned. For example, remote sensing coverage in the infrared was restricted to small postage stamps of discrete regions if the atmosphere, rather than the global coverage that is still desired by we Jupiter scientists.  In the thermal infrared, the PPR instrument featured a rotating wheel used to change the filter wavelengths, but this got stuck and meant that most of our Jupiter observations are restricted to just two wavelengths.  Indeed, with the exception of the Cassini/CIRS experiment that flew by in 2000, we've never obtained thermal infrared observations of Jupiter sufficient to properly get to grips with Jovian meteorology.  That's something we hope to correct with future missions.

Nevertheless, Galileo provided excellent reconnaissance of Jupiter's churning atmosphere and its diverse satellite system, whetting our appetite for a future return to the gas giant.  Chief among its achievements was the in situ probe, which penetrated deep into the Jovian cloud layers to measure the composition of the planet, providing us with clues to how our solar system formed and evolved from the original protosolar nebula.  Ground based observations by my colleague Glenn Orton (JPL) using the NASA Infrared Telescope Facility showed that the probe had entered a region of unique meteorology known as a hotspot, with powerful down-draughts clearing the air of its main volatile species, ammonia and water.  

The Galileo orbiter was eventually plunged into the atmosphere in 2003 after an 8-year mission.

Thursday, 1 November 2012

NASA's Juno Mission at EPSC 2012

The European planetary science convention (EPSC) took place in September 2012 in Madrid, and for the second year running I was asked to convene the session on the giant planets.  With European activities on JUICE, ESA's proposed mission to Jupiter in the 2030s, in full swing, I hoped to persuade the Juno team to 'cross the pond' to update us on the status of he Juno mission.  Scott Bolton, the mission PI, provided an overview, while Mike Janssen explained the microwave remote sounding of Jupiter's deep interior and Glenn Orton explained the need for coordinated ground based observations in support of these activities.  From the hastily-written notes as the rain fell in Madrid, here's a record of the Juno sessions at EPSC.

Bolton - The Juno Mission

With three solar arrays 8.5 m long, Juno is a big spacecraft, cartwheeling along towards the gas giant.  Juno's science goals at Jupiter will fall into four categories, studying the origin, interior, atmosphere and magnetosphere of the giant planet. The mechanisms by which Jupiter formed are a key question for the origins of our solar system and our habitable planet, and Juno will provide answers to two mysteries - how much oxygen is present, and does Jupiter have a rocky core at its centre? 

The motivation for this is the impasse reached in our understanding of Jupiter's formation since the Galileo probe 17 years ago.  We know that Jupiter is enriched in materials compared to the solar composition, and that all the elements are enriched by roughly the same amount.  Juno will help answer how those materials were incorporated into Jupiter by measuring the abundance of water (molecules were probably delivered trapped in water ice cages), something that escaped Galileo in 1995 when it descended into the Sahara desert of Jupiter (a dry hot spot). 

Probing the core of Jupiter, if one exists at all, will require both precise gravitational measurements as Juno orbits the gas giant, in addition to magnetic field measurements to understand how the interior rotates, where convection occurs, where the magnetic field is generated and why it appears to be asymmetric.   It will help answer how Jupiter's interior rotates, whether as a single solid body, or as a series of concentric cylinders with deep winds.   The polar orbits of Juno will be ideal for such measurements, as well as revealing the unique dynamics and chemistry of the polar atmosphere and auroras for the first time.  The trajectory will take the spacecraft through the regions where particles are accelerated along magnetic field lines.

To achieve its science aims, Juno must get closer to Jupiter than any other spacecraft, within the intense radiation belts.  Those belts, rather like the earth's van Allen belts, contain high energy particles that pour through sensitive detectors and electronics, meaning that Juno will be short-lived, and the prospects for an extended mission slim. There will be 32 primary science orbits roughly 11 days long, starting with the spacecraft close to the equator (perijove at 5000 km above the cloud tops) and distant over the poles, but eventually moving so that Juno enters more and more of the radiation belts as the planet's gravity tweaks the orbit.

Juno features a suite of instruments required to address its four science themes, including a gravity science instrument from JPL, a magnetometer from Goddard space flight center, a microwave radiometer from JPL, energetic particle detectors from APL in Baltimore, a UV spectrometer from SWRI, and a near infrared spectrometer from Italy.  Finally, there's a colour camera on board (JunoCAM, provided by Malin) intended for public outreach activities.  Bolton described Juno as a antenna farm, with more antennae than any other mission.

Juno was launched on schedule (!!) on August 5th 2011, and will return for a swing by of the earth in September 2013.  It will arrive at Jupiter on July 4th 2016 for a year-long mission, at approximately the same time as Cassini will be completing the proximal orbit phase at Saturn (i.e., close inside of the rings).  Juno's main engine was ignited in September for the first time, a correction manoeuvre in deep space, and came as a huge relief to the team.  That engine is needed to insert successfully into Jupiter orbit, without it they'd go sailing right past!

After orbital insertion, Juno will be in a polar orbit, with Jupiter rotating by 192 degrees longitude between each perijove.  For the first 15 orbits, we'll have ground tracks, north to south, spaced every 24 degrees longitude.  After 15 orbits, Juno will shift slightly and fill in the gaps, so the final product will be scans spaced by 12 degrees of longitude around the planet at very close perijove.  When complete, Juno will hopefully have revealed the existence of a core, the deep water abundance, and investigated the structure of the interior and polar regions for the first time.  Finally, Juno carries with it three Lego figurines, of the gods Jupiter and Juno, and Galileo himself, as a fitting tribute to our exploration of the giant planet.

Janssen - Microwave Observations below the Clouds

Microwave radiometry will be used to peer beneath the clouds of Jupiter to measure its internal water abundance and structure.  The MWR on Juno features six antennae from 1.3 to 50 cm in wavelength, with longer wavelengths probing deeper into the planet.  The antennae are huge, with one taking up a whole side of the spacecraft, and the other five mounted together on another side.  The antennae will provide footprints 12 degrees in size from 1.37-11.55 cm, and 20 degrees in size from 20-50 cm.  The longest wavelengths are most likely to probe the water cloud.  This type of science is impossible to do from the earth, as the synchrotron emission from Jupiter's powerful radiation belts hides the atmosphere from view.

The MWR uses a clever technique to calibrate, and get accuracy on the measurements below 0.1%.  Firstly, the spinning of Juno means that the antennae alternately see the synchrotron emission from the radiation belts and the radiance from the planet, meaning that the difference can be used to calibrate.  But the dependence of the radiance on emission angle is independent of the radiometric calibration, allowing the team to achieve high accuracy relative measurements.  This accuracy will allow Juno to peer down below Jupiter's churning clouds for the first time.

Orton - Ground-Based Support during Juno

EPSC had a session devoted to amateur contributions to astronomy, and this year Glenn Orton presented plans for earth based support of Juno in the years preceding the mission.  Juno's suite of eight instruments misses spectral ranges that could provide crucial contextual information. For example, although the near infrared instrument will cover the 2-5 micron range, and the microwave instrument covers beyond 1.3 cm, there's nothing in between (the mid infrared). The visible camera eill have no science-grade calibration.  Furthermore, Juno will be so close to Jupiter that data will come in narrow north-south strips, missing the global spatial context that telescopes on earth could provide. Finally, the Juno mission is short, and given that we know Jupiter's atmosphere varies over long timescales, we may miss the temporal context of our observations.

The Juno team will address these issues via a coordinated campaign of ground-based imaging, from both professional and amateur observatories.  Whole-disk images, at the same time as the microwave observations during orbits 3 through 8 (November 2016 to January 2017), will provide this context for the connection between the lower troposphere and the upper clouds.  Furthermore, ground based images may allow them to predict the location of features, allowing orbits to be tweaked to redirect remote sensing efforts. 

Real time support will be challenges, as Jupiter will be only 35 degrees from the sun in November 2016, so the team emphasises the need for contextual studies during the preceding apparition, before solar conjunction.  Spatially resolved visible and near infrared spectroscopy are desirable, filling in the gaps and calibration of JunoCAM and JIRAM. But the team are aware that all this will be done on a best-effort basis, with no formal contracts for image reduction and calibration, relying on the passion and expertise of amateur observers worldwide to support the Juno mission.

Personally, I don't think they'll have a problem! 

Monday, 29 October 2012

Memories of Voyager

Voyager at Jupiter, Credit: NASA/JPL
The recent Alpbach summer school featured a fascinating presentation from a retired JPL employee, John Casani, who had played a major role in past exploration of the outer solar system.  As his stories included tales I hadn't heard before, about topics that have greatly affected my own research, I've decided to put some of them to paper.  The twin Voyager spacecraft started life in 1961 when Michael A. Minovitch discovered that the gravity of the planets could be used to slingshot spacecraft between different planetary targets.  Four years later, Gary A. Flandro discovered a unique planetary alignment that would recur once every 175 years, which would be ideal fur the use of gravity assists to reach the frigid planets of the outer solar system.  Such an approach would allow robotic explorers to reach Neptune much faster than a direct trajectory.  

The Grand Tour mission was proposed in 1970 for a "new start" in 1971, and originally consisted of two missions: one to the gas giants and Uranus, and one to the gas giants and Neptune.  However, NASA canned this concept due to concerns about its ambitious and costly nature, and JPL re-proposed a more modest mission to Jupiter and Saturn based on the Mariner series of spacecraft (Mariner Jupiter Saturn 1977).  That mission became Voyager in 1978, and the idea that the spacecraft could go on to visit the ice giants after the successful completion of the gas giant studies was introduced.  Casani described Uranus and Neptune as "targets of opportunity", rather than destinations which were required for NASA to consider Voyager a success, and explains why planetary mission goals often seem modest (e.g., mars rovers for 90 days) but go onto achieve great things.  It also meant extended funding would be contingent on the success of the gas giant mission.

The Voyagers were launched by Titan IIIE‐Centaurs on August 20, 1977 (V2) and September 5, 1977 (V1) at a then‐year cost of $320M. The spacecraft carried six RTGs for power, half of the paid for under the “Atoms for Peace” policy.  Major redesigns were required after Pioneer 11 discovered Jupiter's intense radiation belts in 1974, requiring radiation-hard components, a key feature of all Jupiter missions since.  Casani recalled that fumes from facility painting 3 weeks before launch meant that several science instruments required replacement detectors. 

The Voyagers went on to deliver a spectacular mission of discovery in the outer solar system, passing Jupiter in 1979, Saturn and Titan in 1981, and remain the only spa craft to ever visit the ice giants Uranus and Neptune in 1986 and 1989, respectively.  Both spacecraft are now leaving our solar system, with Voyager 1 the most distant human-made object at over 120AU from the sun in February 2012, and adding 3.6AU to that tally every year.  Power from those RTGs is declining, but four of the 11 science instruments are still operating.  By 2020, there'll likely only be enough for one instrument, recording the passage through the heliopause and into interstellar space until around 2025.

Saturday, 27 October 2012

Strange Weather at the Society for Popular Astronomy

At a meeting of the Society for Popular Astronomy in London on 27 October 2012, I gave a presentation explaining how recent spacecraft observations have transformed our understanding of the atmospheres of the giant planets -- Jupiter, Saturn. Uranus and Neptune. Why do the belts of Jupiter sometimes disappear? What causes the storms on Saturn? Even amateur observations are helping to provide some answers..... watch the video below (Vimeo, 74 minutes).

Dr Leigh Fletcher: Strange Weather! Exploring the Giant Planets from Society for Popular Astronomy on Vimeo.

Thursday, 25 October 2012

Saturn's Stratopheric Vortex

VLT image of Saturn's giant vortex at mid-infrared wavelengths, 13.1 ┬Ám, in July 2011.  The vortex formed from the merging of two pockets of warm air in the stratosphere. The two warm air masses, in turn, are an aftereffect of the 'Great Springtime Storm', a turbulent storm that affected Saturn's lower atmosphere from December 2010 until mid-2011.  At its biggest, in late June 2011, the vortex covered about 62 000 km - almost one quarter of the planet's circumference at the mid-northern latitudes affected by the storm.   Image courtesy of L.N. Fletcher, University of Oxford, UK, and ESO
After 18 months of continuous work on this project, I’m happy to say that our paper tracking the evolution of Saturn’s enormous stratospheric vortex (at its formation, the largest vortex in the solar system) is now out in the journal Icarus.  The vortex is an after-effect of the springtime storm on Saturn that I wrote about here, and is still present today.  This ‘beacon of infrared emission’, so called because it dominates the infrared light from the planet, is moving around the springtime hemisphere as regular as clockwork.  The Icarus paper can be found here:

L. N. Fletcher, et al., "The origin and evolution of Saturn's 2011-2012 stratospheric vortex", 2012, Icarus, Volume 221, Issue 2, November-December 2012, Pages 560-586,

Three press-releases are available from ESA and NASA.  The most indepth, by Claudia Mignone on ESA’s SciTech website, is included below, and features some great animations from Chrisophe Carreau. 

Emily Baldwin has written an overview of the discovery for ESA:

Finally, Elizabeth Zubritsky of Goddard Spaceflight Center has written a piece focussing on my colleague Brigette Hesman’s discovery of the gas ethylene within this hot stratospheric vortex:

Copyright: ESA/C. Carreau, full video can be obtained here.

Saturn's giant storm reveals the planet's churning atmosphere
Claudia Mignone, ESA

A recent study of the giant storm whirling on Saturn for the past two years, which became known as the "Great Springtime Storm", has given planetary scientists new clues about the planet's weather. Using a combination of data from the Cassini orbiter and ground-based telescopes, the scientists traced the storm's development from deep within the churning clouds in Saturn's lower atmosphere to altitudes hundreds of kilometres above the cloud decks, in the planet's stratosphere. There, two large pockets of warm air formed and later merged into one gigantic hot vortex that has been travelling around Saturn's northern hemisphere since mid-2011. The study of this storm and its associated vortex, which occurred unusually early in Saturn's 30-year-long weather cycle, suggests that waves play an important role in the energy transfer across the planet's atmosphere.

Storms are large disturbances in a planetary atmosphere. A common phenomenon on Earth, storms are not unique to our planet's weather and may arise on any planet that is surrounded by a thick atmosphere. Astronomical records report similar events on several planets in the Solar System, and recent data hint at possible storms on exoplanets.

A new study, based on data from the NASA/ESA/ASI Cassini-Huygens mission and ground-based telescopes, has looked into one of the largest storms recorded in the Solar System, which started whirling over Saturn's mid-northern latitudes about two years ago. The storm originated in the planet's lower atmosphere, where it was first seen in December 2010, and later grew to encircle the entire planet. The disturbance also propagated to higher atmospheric layers, where its aftermath can still be detected. It is known as the 'Great Springtime Storm' because it took place during the spring season in the planet's northern hemisphere, which started in August 2009 and lasts about seven years.

"Giant storms on Saturn occur regularly and have been observed for over a century, but this is the first time we could follow the temporal evolution of such an event in great detail," notes Leigh Fletcher from the University of Oxford, UK. Fletcher has led an extensive study of the Great Springtime Storm using data gathered in the infrared portion of the electromagnetic spectrum by the Cassini spacecraft, which has been orbiting Saturn since 2004, as well as ESO's Very Large Telescope and NASA's Infrared Telescope Facility.

"The storm was first detected in the planet's lower atmosphere – the troposphere – via optical and radio observations. Then we looked for its signature at mid-infrared wavelengths," explains Fletcher.

"When we look at Saturn's atmosphere in optical wavelengths, we see the sunlight that is reflected by a haze layer located deep down in the troposphere. In the mid-infrared, instead, we directly measure the temperature of the atmosphere for many kilometres above the clouds. This allows us to peer through the three-dimensional structure of the atmosphere," he adds.

Observing at these longer wavelengths provided a drastically different view, and allowed Fletcher and his collaborators to probe how the storm had infiltrated the upper part of the atmosphere – the stratosphere upwards from the troposphere. The presence of Cassini in the saturnian system and its ability to perform mid-infrared observations has allowed the astronomers to monitor the evolution of this unique meteorological event in unprecedented detail.

Mid-infrared images from January 2011 showed that two large pockets of warm air had formed over the storm, in the stratosphere. These warm air masses, also referred to as 'beacons', were both moving westwards, although with different speeds, and remained clearly separated for a few months. Between April and June 2011, the two beacons merged and gave rise to a giant vortex of clockwise-swirling air – an anti-cyclone – with temperatures up to 221 K, hotter than the surrounding air by 70-80 K.

The huge anti-cyclone in Saturn's stratosphere had fully detached from the tropospheric disturbance that caused it in the first place. At its biggest, in late June 2011, the vortex covered about 62 000 km – almost one quarter of the planet's circumference at the mid-northern latitudes affected by the storm. At the same time, the storm in the troposphere, only visible at optical wavelengths, had almost ceased.

"We kept monitoring Saturn during the storm with the help of many small, ground-based telescopes operated by professional and amateur astronomers alike, and found no sign of the giant vortex in the optical data. Although the tropospheric storm was the underlying cause of this enormous vortex, the vortex subsequently evolved independently of events happening deeper down, and was still present long after the tropospheric storm was over," he adds.

Since July 2011, the giant hot vortex has been shrinking and cooling at a very slow pace. It is still present in Saturn's stratosphere, where it has shrunk to less than half of its greatest extent, and is expected to disappear completely in a couple of years.

The data analysed by Fletcher and his collaborators showed how the temperature, wind velocity and chemical composition varied within and around the giant vortex. This allowed them to unveil how the storm had evolved over several months, and to investigate the energy transfer mechanisms at play among the various layers of Saturn's atmosphere.

"We suspected that the weather in the lower atmosphere has an impact on what happens at much higher layers, hundreds of kilometres upwards, just as happens in Earth's atmosphere. Now we have evidence for this on Saturn," says Fletcher.

In Earth's atmosphere, storm-generated waves are known to transport air and energy across the atmosphere, including upwards to the stratosphere. It is possible that a similar mechanism has taken place on Saturn, too: wave-like perturbations, induced by the tropospheric storm, might have made their way upwards to the stratosphere, where they released their energy and caused the formation of the two beacons.

"What is unusual in this particular case is that the two beacons interacted with one another up in the stratosphere, giving rise to the giant vortex. How exactly this happened remains an open question that needs to be tackled via numerical simulations," comments Fletcher.

The timing of the storm is also quite puzzling. Since 1876, large disturbances have been observed on Saturn with striking regularity: once every 'saturnian' year, which lasts about 30 years, and always during the northern hemisphere's summer season. The last such storm on record dates back to 1990, and the next one was expected in 2020.

"The Great Springtime Storm is definitely ahead of schedule with respect to Saturn's standard storm cycle. It is still unclear whether this is an isolated event or a signal that the storm season on the planet started earlier than expected," comments Nicolas Altobelli, Cassini-Huygens Project Scientist at ESA.

"Cassini will keep monitoring Saturn's atmosphere from its vantage point. The mission will be operating until the northern summer solstice, which will take place in May 2017. The storm season on Saturn's northern hemisphere may not be over yet, and in this case we might be able to see other spectacular events in the next few years," Altobelli adds.

"If storms are detected on Saturn in the upcoming future, it will be important to verify whether these will also produce dramatic aftereffects such as the stratospheric vortex from 2011," Fletcher concludes.

Friday, 5 October 2012

Royal Society Fellowship

I won’t lie - the past twelve months have been stressful.  Not only have we had our noses to the grindstone preparing proposals for ESA’s next mission to Jupiter (JUICE), but we’ve also had a flood of data from Cassini and ground-based facilities concerning variability and seasonal processes on all of the giant planets in our solar system.  This was compounded by having to write multiple proposals to funding agencies to try to make sure that my job here in Oxford was secure for the next few years, as my Glasstone Science Fellowship (see my blog entry here) is now coming to an end after three years.

Proposal writing involves reading and re-reading the same motivational/technical text over and over again until you can see the words in your sleep.  Putting together a case for support that not only convinces yourself, but also your reviewers, that this science is timely and worth spending a lifetime on, is no small task. Then comes the lightning-fast interview, with suit and tie facing a large panel of experts looking to see what you’re made of; what your motivations are; and whether you have a future in this field.  So after all this, it’s all-the-sweeter to be finally featured on someone’s list of awarded fellowships, and possibly the most prestigious of them all:  The Royal Society

Royal Society announces prestigious University Research Fellowships for 2012

I am one of 36 new research fellows appointed by the society this year, in fields as diverse as particle physics, cellular biology, ecology and quantum chemistry.  My own research area concerns (yep, you guessed it) the exploration of giant planets, both in our solar system and beyond, specifically looking at seasonal and other time-varying atmospheric phenomena, as well as compositional constraints on the origins and evolution of these planets.  I’m also delighted to say that I’ll remain as a Fellow of University College, Oxford, who were kind enough to offer me a Junior Research Fellowship when I received by Glasstone fellowship in 2009.  

So after months of proposals and interviews, I’m happy to say that you’ll all have to put up with me for a little while longer, as I get to continue studying the solar system from the safe environs of the dreaming spires.

Wednesday, 2 May 2012

JUICE is Go!

The Jupiter Icy Moons Explorer (JUICE) will explore the giant planet and its diverse collection of icy worlds, from volcanic Io, to the waterworlds Europa and Ganymede, to the ancient cratered terrain of Callisto.
Billion euro Jupiter mission approved
Joint release on behalf of Imperial College London, Oxford University, University of Leicester, and University College London; with thanks to Pete Wilton of the Oxford University Press Office.

The European Space Agency (ESA) has approved a new mission to explore Jupiter and its icy moons to reveal fresh insights into the habitability of the ‘waterworlds’ orbiting the giant planets in our solar system and beyond.

On 2 May 2012, at a meeting in Paris, ESA’s Science Program Committee voted to go ahead with the project, the Jupiter Icy Moons Explorer (JUICE), the first European-led mission to the outer solar system, and the first spacecraft destined to orbit an icy moon. The JUICE spacecraft is scheduled to launch in 2022, arriving in the Jupiter system in 2030.

Approval for the estimated billion euro contract for the mission came with UK researchers deeply involved in the leadership and planning for JUICE and playing a vital role in gaining approval for the mission ahead of rival bids. The proposal was led by a UK scientist and UK scientists make up four of the 15 members of the ESA Science Study Team for JUICE with the team including researchers from Imperial College London, Oxford University, University of Leicester, and UCL (University College London). 

The primary target of the mission is the solar system’s largest moon, Ganymede, an icy world 8% larger than the planet Mercury. Ganymede is unique within the solar system – it is thought to harbour a deep ocean under the icy crust, it has its own internally generated magnetic field, and it has an ancient surface littered with more individual types of crater than anywhere else in the solar system. 

If moons are common features of giant planets around other stars, then Ganymede may represent a whole class of potentially habitable environments in our galaxy. JUICE will carry experiments designed to study the sub-surface ocean, the geology and composition of the surface, and its interaction with its plasma environment, to assess its potential as a habitable environment in our solar system. The spacecraft will also investigate Jupiter’s other icy worlds, Callisto and Europa, as well as the giant planet’s complex atmosphere and extended magnetosphere.

Imperial, Oxford, Leicester and UCL will be among the UK institutions working to propose experiments to be carried as part of the spacecraft payload. These instruments will be specifically designed to study the gas giant, its icy moons and charged particle environment to an unprecedented level of detail, giving our most detailed characterisation of the Jovian system ever obtained.

Professor Michele Dougherty of Imperial College London, lead scientist for the JUICE proposal, said: ‘Ever since Galileo’s discovery of the four largest moons of Jupiter, we’ve wondered what it must be like on their icy surfaces, looking into a night sky dominated by the gas giant Jupiter. From the volcanic moon Io, to the potential sub-surface oceans of Europa and Ganymede and the ancient cratered terrain of Callisto, these four moons are fascinating worlds in their own right.’

As well as making close measurements of the surface, sub-surface, magnetic and plasma environment of Ganymede the mission will also focus on the other icy moons; performing multiple flybys of Callisto and two flybys of Europa. By studying all three of these icy environments the mission’s studies of Ganymede will take on a broader significance. 

Dr Leigh Fletcher of Oxford University, a member of the ESA Science Study Team for JUICE, said: ‘Scientists have had a lot of success detecting the giant planets orbiting distant stars, but the really exciting prospect may be the existence of potentially habitable ‘waterworlds’ that could be a lot like Ganymede or Europa. One of the main aims of the mission is to try to understand whether a ‘waterworld’ such as Ganymede might be the sort of environment that could harbour life.’ 

In order to assess whether Jupiter and its moons could provide habitable environments, and provide a model for gas giant systems orbiting other stars, the spacecraft will make an extensive study of the planet’s dynamic, evolving atmosphere, with its belts, zones and gigantic swirling storms, over the 3-year duration of the mission. JUICE will also study the magnetic and charged particle environment of Jupiter, which has the largest magnetosphere in the solar system, and its coupling to the moons (particularly Ganymede).

Dr Emma Bunce of the University of Leicester, deputy lead scientist for the JUICE proposal, said: ‘We need to place the possible habitability of these “waterworlds” into some broader context, and JUICE will do that by also studying the surrounding environment. Ganymede is strongly coupled to its parent Jupiter - through gravitational and electromagnetic forces – studying this interaction gives us further insight into its unique place in the solar system.’

Professor Andrew Coates of UCL, a member of the ESA Science Study Team, said: ‘Studying these watery worlds is the next vital step beyond Mars in the search for the conditions for life in our solar system. Ganymede’s unique magnetic shield helps protect it somewhat from Jupiter’s harsh radiation belts and rapidly rotating magnetosphere, and we want to understand its effectiveness. Europa and Callisto provide key comparisons as we search for the solar system’s ‘sweet spots’ for habitability.’

The data JUICE will send back about the varied environments of Jupiter and its icy moons will benefit many areas of science with geologists, astrobiologists, space and atmospheric physicists all queuing up to see how the mission’s findings will affect their disciplines.

The announcement will lead to further opportunities for British companies as they look to bid for contracts to build elements of the JUICE spacecraft and its instruments. The UK Space Agency estimates that the space industry's overall contribution to UK GDP is £7.9 billion and that it employs nearly 27,000 people, with around 60,000 more jobs enabled by the space sector.

For further information contact:

Professor Michele Dougherty of Imperial College London on mobile; +44 (0)7990 973761 or email OR Simon Levey on +44 (0)207 5946702 or email

Dr Leigh Fletcher of Oxford University on +44 (0)1865 272089 or email

Dr Emma Bunce of the University of Leicester on +44 (0)116 2523541 or email

Professor Andrew Coates of University College London on mobile; +44 (0)7788 448318 or email

Alternatively contact the University of Oxford Press Office on +44 (0)1865 283877 or email

Notes to editors

*The selection of the Jupiter mission is the culmination of five years of hard work by the ESA team of scientists and engineers. ESA’s Cosmic Vision L-class competition started in March 2007 with a call to the scientific community to propose new ideas for future exploration.  A previous incarnation of JUICE was selected as one of three finalists (JUICE, Athena, and NGO), which have been going head-to-head in the ESA studies since 2010. At that time, all three proposals had significant US involvement, and the Jupiter mission was known as the Europa Jupiter System Mission (EJSM/Laplace). However, in March 2011, NASA withdrew from the L Class missions in general, and the reformulation phase began to rework the three proposals into European-led missions, leading to the evolution of the JUICE spacecraft.

*The JUICE mission relies on a strong heritage of outer solar system exploration by UK scientists, such as those involved in the Cassini-Huygens mission to Saturn and Titan.
*For more on how the space industry benefits the UK see: ‘The Size and Health of the UK Space Industry’, November 2012:

Destination: Ganymede

Galileo views Ganymede
Oxford Science Blog By Pete Wilton & Leigh Fletcher, to accompany the press release here.
It’s official: it was announced today that Oxford University scientists will help to prepare a mission to Jupiter and its icy moons.

But whilst the JUICE spacecraft will beam back valuable data on several of the planet’s satellites, it will give special attention to one in particular: Ganymede.

I asked Leigh Fletcher of Oxford University’s Department of Physics, one of the JUICE team, about the appeal of Ganymede, what they hope to find there, and how Oxford scientists will probe the secrets of this enigmatic ‘waterworld’…

OxSciBlog: What makes Ganymede so interesting?
Leigh Fletcher: When people think of moons in our solar system, they often imagine them as being inferior to the main planets, and somehow less interesting. The moons of Jupiter show how wrong that misguided assumption can be - the four largest Jovian moons (Io, Europa, Ganymede, and Callisto) are the size of planets, and each has a fascinating and rich geologic and chemical history. 
These moons truly are worlds in their own right, with a diverse range of unusual landscapes and features that can keep scientists busy for decades. ESA has chosen to focus on Ganymede, the largest example of an icy moon in our solar system. It is thought to be made of roughly equal measures of rocks and water ice, and is likely to harbour a saltwater ocean beneath its icy crust. For those searching for habitable environments in our solar system, the mantra has always been to follow the water, as the vital solvent for the chemical reactions of life.

Ganymede's surface has a mixture of ancient, dark, cratered surfaces, and brighter water-ice-rich regions of ridges. The biggest feature is a dark plain called Galileo Regio, visible from Earth even through amateur telescopes, and may even have polar caps of water frost.  Furthermore, Ganymede has an extremely tenuous oxygen atmosphere, and is the only moon in our solar system with a magnetic field, probably caused by convection within a liquid iron core.

OSB: How does it compare to Jupiter’s other moons?
LF: To better understand Ganymede, it's important to consider the processes which shaped its evolution and surface features by comparing it to the other Galilean moons: although these four worlds of fire and ice probably had the same origins in the Jovian sub-nebula, their present-day structure is the end of product of aeons of subsequent evolution. Jupiter's immense gravity causes tidal flexing of the moons (strongest at Io, weak or absent at Callisto), providing energy to liquefy the water ice crusts and produce internal activity.

Io is mostly rocky, lacking the water ice of the other satellites but featuring hundreds of active volcanoes. Europa is the smallest of the four, with a smooth geologically-young icy surface overlying a water ocean, heated by the tidal flexing from Jupiter. Ganymede's ocean is likely to be deeper than Europa's, under a thicker ice crust. Callisto is further away and experiences less tidal heating, resulting in an ancient terrain, one of the most highly cratered surfaces in the solar system.

OSB: What do we hope JUICE will find out about it?
LF: JUICE will be the first orbiter of an icy moon, and provide a full global characterisation of its surface composition, geology and structure. An ice-penetrating radar will peer through the icy crust for the first time, providing us with our first access to the water ocean of a Galilean moon. Our key goal is to assess the potential habitability of Ganymede as a representative of a whole class of ‘waterworlds’ which may exist around other stars, building upon the discoveries of habitable environments on the Earth's deep ocean ridges.  So JUICE will be looking for key characteristics of habitability on Ganymede - sources of energy, access to crucial chemical elements, liquid water, and stable conditions over long periods of time.

It's a crucial step in our reconnaissance and exploration of our solar system, and towards answering the question of 'What are the necessary conditions that make a planetary body habitable?’ By comparing the three potentially ocean-bearing Galilean moons, we hope to identify the physical and chemical characteristics driving the evolution of this planetary system.
JUICE will study the extent of Ganymede's ocean, its connection to the deep interior and ice shell; the global distribution and evolution of surface materials, geologic features, and present-day surface activity; and the interaction with the local environment and magnetosphere. In addition, JUICE will explore recent activity and composition on Europa, and characterise Callisto as a remnant of the early Jovian system. Finally, JUICE will be capable of exploring the wider Jovian system, from the complex and dynamic Jovian atmosphere, the magnetosphere, the minor satellites and rings.

OSB: What instruments will be needed to study it?
LF: The proposed JUICE payload has cameras to take images of the icy moon surfaces and swirling Jovian clouds; spectrometers covering ultraviolet, near-infrared and sub-millimetre wavelengths to determine moon compositions and temperatures, winds, composition and cloud characteristics on Jupiter; a magnetometer and plasma instruments to conduct an investigation of Jupiter's magnetosphere; and a laser altimeter, ice-penetrating radar and radio science instrument to probe below the surface of the Galilean moons and through the Jovian cloud decks. 

The payload is just a model right now, and other instruments could be added. All this will be launched on a 5 tonne spacecraft in 2022, with solar arrays to provide power and a large high-gain antenna to return the data to Earth. It will take 7.5 years to reach the giant planet, before going into orbit around Jupiter to conduct an extensive survey of the whole planetary system. Then, in the final phase in 2032, it will enter orbit around Ganymede.

OSB: How are Oxford scientists likely to contribute?
LF: Oxford has a strong heritage of contributing instrumentation and data analysis techniques for outer solar system missions, notably with the near infrared mapping spectrometer (NIMS) on Galileo and the composite infrared spectrometer (CIRS) on Cassini.  We also have a long-term campaign of giant planet studies from ground-based observatories in Hawaii and Chile and space-borne telescopes (Spitzer, Herschel, Hubble). This has allowed us to contribute to the science case for a return mission to Jupiter and its icy moons, identifying the key questions and mysteries left unanswered by previous generations of spacecraft.

Oxford, along with many other UK institutions, will hope to contribute instrumentation to fly to Jupiter to address some of these questions. Involvement with Galileo and Cassini enabled Oxford to build up a rich planetary science group, with a broad range of experience from lab spectroscopy to spacecraft hardware, and from icy moons to gas giant dynamics. This expertise will help us to solve the challenges presented by the JUICE mission.

OSB: What is the next big milestone for the JUICE mission?
LF: Now that the mission has been officially selected by ESA as the L-class mission for 2022, the hard work really begins. Industry will be invited to design and build the spacecraft systems, and an announcement of opportunity will be issued to call for instrument designs. Teams will be assembled to thrash out ideas for instruments that address key scientific questions, all hoping to see their particular design on the launch pad when we lift off for Jupiter in a decade's time.  The final go-ahead for the mission from ESA, known as 'adoption', should come in the next 2-3 years.

Tuesday, 1 May 2012

Pythagora's Trousers

At the end of April, Chris North (University of Cardiff, BBC Sky at Night, @chrisenorth) interviewed me for the Pythagoras’ Trousers radio podcast, which was broadcast on Monday April 30th on Radio Cardiff.  We spent 20 minutes discussing the outer solar system, with themes ranging from the formation of the giant planets and why the gas and ice giants appear so different; future missions to explore the giant planets and their icy moons; and professional-amateur collaborations on giant planet storm tracking.  We focussed for a while on future Jupiter missions, including Juno (en route and due to arrive in 2016) and JUICE (the ESA Jupiter Icy Moons Explorer, due to arrive in 2030).

The podcast can be downloaded from the following website.  Here’s their write-up:

Small businesses in Wales and astronomy
On this week’s programme, Rhys talks to Peter King from DPI Limited about job opportunities for science and engineering graduates amongst small businesses in Wales and our STEM Ambassador of the Week is Brij Geerjanan from Tata Steel. Later on, Chris North talks to Leigh Fletcher from the University of Oxford about the outer solar system and Hugh Lang guides us through the night sky throughout May. Finally, this week’s Subject of Science looks at the history of the zip.

Pythagoras’ Trousers is a radio show from the South Wales Networks of theInstitution of Engineering & Technology and Radio Cardiff. Each week, presenter Rhys Phillips takes a look at stories of interest from the worlds of science, technology, engineering and mathematics, bringing these fields to a wider audience and promoting these subject areas to school pupils.
The show is broadcast on Radio Cardiff every Monday evening 8-8:30pm and repeated Tuesday nights 11-11:30pm.

Wednesday, 18 April 2012

University College Movies

Back in February I was visited by a film crew working for University College Oxford to showcase some of the work we do in Atmospheric Physics here in Oxford.  You can see the finished product on  Hats off to Kerry Harrison of for some great footage!

Dr Leigh Fletcher from University College Oxford on Vimeo.

At Univ... from University College Oxford on Vimeo.

Monday, 27 February 2012

Long Distance Storm Chasing - A Plea for Help!

Last spring, Saturn’s gigantic springtime disturbance was characterised for the first time in the infrared, allowing us to measure the vertical temperature structure of a Saturnian storm system.  Our paper (Fletcher et al., 2011, Thermal Structure and Dynamics of Saturn’s Northern Springtime Disturbance, Science, 332, 1413--1417,, showed that the thermal infrared imaging yielded some surprises - not least was the dramatic effect that this churning, tropospheric storm system had on the usually calm and quiescent stratosphere (see Saturn image on the far right).  It spawned two warm airmasses, which we termed ‘beacons’ because of their impressive emission at infrared wavelengths.  These heated airmasses were tracked throughout 2011 by Cassini, the Very Large Telescope in Chile, and the Infrared Telescope Facility in Hawai’i.

Today (February 2012), a single large hot airmass remains in Saturn’s stratosphere, but there’s a big question remaining - does this have any impact on the visible cloud tops?  Indeed, one of the big challenges for giant planet science is relating visible changes in albedo and cloud colouration to environmental changes (e.g., changes in temperature, cloud formation or chemistry).  So far, our comparisons with visible light observations have suggested that the effects of the hot stratospheric beacon are completely invisible.  The chart above shows the expected longitude (System III West) of the beacon, and an Excel spreadsheet listing the longitude on each date through the rest of 2012 can be found here:  

As Saturn reaches opposition on April 16th 2012, the next few months provides an excellent opportunity to search for any unusual goings-on beneath the hot beacon.  To find the System III Longitude visible from Earth at any time, use the JPL Horizons Ephemeris Generator (with option 14 for the table settings).

Wishing you clear skies and happy storm chasing!


Tuesday, 21 February 2012

Becoming a Planetary Scientist

In 2012, I was asked a series of questions about how I became a planetary scientist, and what advice I’d give to school students wanting to get involved in this exciting field.  I’ve reproduced my answers here, just in case it serves to help any visitors to this site!

Job Title: Planetary Scientist

What do you actually do? 
I’m a planetary weather man, studying the physics and chemistry of all the atmospheres in our solar system to better understand the worlds around us.

What did you choose to do once you could leave school, ie at age 16?
Stay on at sixth form college to study A Levels – Maths, Further Maths, Physics, Chemistry, Biology and General Studies

What did you choose to do next?
Went to University:  Emmanuel College Cambridge to study for a BA and MSci in Natural Science, specialising in Physics.

How did you get to where you are now?  
When I left University, I really wanted to study a topic that I felt was close to home, that some day we could reach out and touch with our own hands, see with our own eyes.   Despite an interest in astronomy, I decided against studying the far reaches of our universe and chose instead to explore the planets of our own solar system.  In 2004, the Cassini-Huygens spacecraft was about to arrive at Saturn, and Oxford were looking for research students to help analyse the first data from the ringed world.  I spent my PhD characterising Saturn’s dynamic atmosphere, which then set me on a course to study all of the giant planets in our solar system in a series of short fellowships at NASA’s Jet Propulsion Laboratory and Oxford’s Planetary Physics department.  Today I use a variety of interplanetary spacecraft, orbital telescopes and giant ground-based observatories to learn more about the planets.

Were there other routes you could have taken to get this job?
Planetary science requires you to be a jack of all trades:  being a planetary scientist requires an excellent knowledge of physics, computing, maths and chemistry, so each of these topics would have allowed me to work in this exciting field, provided they’d been studied to degree level.

What do you like best about your job?  
Things can change quickly, and we have to be responsive to that.  If an asteroid strikes Jupiter, or a storm explodes in the atmosphere of Saturn, we have to bring all our experience to try to understand what’s happening.   So the days are never dull, and you rarely do the same thing from one day to the next!  I get to work as part of an international team of scientists, which means I get to travel far and wide to communicate my research and forge new collaborations.  Finally, we find ourselves in a revolution in this subject, with more missions and telescopes in flight than at any point in humankinds history – that means that the potential for new discoveries is enormous, and you never know when you might be the first human to observe a new phenomenon in our solar system.  The old adage is true – when you love what you do, you never work a day in your life!

What would your top tips be to a 16-year old considering working in this field?  
For any scientific subject, it’s essential to get a good grounding in maths and computing, as these topics go hand in hand.  So much of what we do requires the ability to write computer code and solve mathematical problems, that you really can’t escape it!  Without a doubt, you should forge ahead with A-levels, but never forget the bigger picture – there’s so much exciting science happening out there; if you read widely you might just stumble across a topic that really excites you.  That’s what happened to me with planetary exploration.

What would your top tips be to an 18 year old considering working in this field?
Think carefully about where you’d like to go for your degree, and make sure that the institution provides a good balance between science, maths and computing.  All three are needed to be a successful atmospheric scientist or meteorologist.  It’s all about building up a toolkit of experience, which you can then apply to new problems as they’re presented to you.  So be curious, don’t be satisfied with explanations that are unclear, and experiment for yourself.  Curiosity and the ability to solve problems are the traits that are essential in any independent research scientist, and will be vital as you head to university.

Tell us something about yourself.  
In the summer of 2009, I was having a barbeque on a sunny California day with my wife.  My boss called to say that an Australian amateur astronomer had spotted something rather odd near Jupiter’s south pole.  I raced to the office, where we could remotely use the telescopes in Hawaii to figure out what was going on, and we were in for a massive surprise.  A huge, super-heated plume of aerosols and debris had been lofted into Jupiter’s atmosphere by an asteroidal collision.  Without the data we took that Californian evening, we might never have been able to unravel the mystery of what had happened up there on Jupiter.  It was the chance of a lifetime, a stroke of luck, and provided us with fascinating scientific results for years to come.  It shows just how exciting this field is, and that there are so many surprises and marvels out there for us to explore.

Saturday, 21 January 2012

Stargazing Oxford

Oxford's physics department opened its doors to the public on a cold Saturday in January, inviting the local community into the lab to catch a glimpse of some of the exciting ideas we spend our days working on.  With over a thousand people through the doors, and lots of happy memories, I think we can call it a runaway success!  Designed to tie in with the BBC's Stargazing Live, the Stargazing:Oxford event was the first of its type.  As organisers, we wanted a village-fete style of event, allowing the public to mix and interact with the scientists to see some of the passion and enthusiasm we have for our subject.

We had the Philip Wetton telescope on the roof open for visitors; an inflatable planetarium dome; rapid-fire talks on all manner of topics from planetary exploration to galactic evolution and beyond; our own version of University Challenge; plus the Science Cafe, where we got to exhibit some of the neat toys we get to play with!  The event was a tremendous experience for us, not least because it brought together the atmospheric physicists from the East Physics with the astronomers of West Physics, forming new links between us that will hopefully pave the way for even bigger events in the future.


The planetary group were primarily involved in the Science Cafe, with a stand devoted to exploring planets both in our solar system and beyond.  We ran a great comet demonstration, using a mix of dry ice, soil, water, smelling salts and Worcestershire sauce to replicate the icy mixture of a comet.  We made a great mess, but it was worth it to see the jaws of our guests dropping as the freezing cold comet nucleus emerged, jets of cold carbon dioxide streaming away from it.  Oxford works on a mission called Rosetta, currently on its way to rendezvous with a comet in 2014, so watch this space for future discoveries...

All this cometary fun was monitored by a thermal infrared camera, sensitive to the heat energy being given off by an object, rather like firefighters would use to see body heat in a disaster zone.   The camera can be used to take the temperature of an object without touching it, something we call remote sensing.  Infrared light is just like any other, giving reflections and appearing brighter from some objects (my warm hand) than others (the cold comet nucleus), it's just at a longer wavelength, meaning the light has less energy than the visible light you’re used to.  The planetary group measures infrared light from all the planets in our solar system, using the measurements to literally 'take the temperature' of another planet, without having to actually go there with a thermometer.   The camera was hooked up to a big 50" LCD screen, so we had a great time taking photos of families, emailing them them later with these great infrared souvenirs.

We also had a host of other things on show - pieces of equipment known as flight spares (i.e., there are two in existence, one on a spacecraft somewhere in the solar system, and the other sat in our lab in Oxford).  This included the detector assembly for the instrument we work with on Cassini (CIRS, an infrared instrument to measure Saturn and Titan's temperature and composition); the wind sensor for Beagle 2 (the ill-fated mission that crashed on Mars in 2003); a new design for wind sensors measuring the speed of sound (something being worked on in Oxford right now); plus lots more.   We played with a giant inflatable solar system, gave away 'Top Trumps' solar system cards, showed 3D movies of NASA and ESA missions to the planets, and generally had a great time showing off our science to the interested public.


The feedback was superb - one of the great side-effects of the village fete style was that people were quite happy to come and ask lots of questions.  The BBC shows had ignited a real passion, and we had people from far and wide - I remember talking to one family that'd come all the way from Bristol to see inside our Physics department, and one mother of a 7-year old who was astonished to be told 'I want to be an astrophysicist when I grow up....'!  Here are some more messages we received later on:

"The open day was excellent - apart from the range off interesting activities, we were overwhelmed by the enthusiasm of the staff."

From a 9 year old:  "I really enjoyed the lego build your own universe, looking at the stars through telescopes, the milky way poster and being able to talk to the staff when we were in the queue. Also I could stay late and have my supper there too."

"This is ace!  Thank you for an excellent day, 5 hours went in a flash."

"Thanks for cool look into the fantastic world of astronomy/cosmology/and physics and from the length of the queues outside I'd say that the day was a big success i wish i could have stayed longer to look at the main telescope in the roof top observatory."

"Thank you so much for this. My son is thrilled with the infrared image and took it in to show his class at school today.  Your event was really lovely and beautifully executed. It’s no wonder so many people came!   Many many thanks, and if you ever do anything similar, please do let us know as we’d love to come."

So despite 10 hours on my feet and a totally exhausted voice, I got back home absolutely buzzing.  I'd managed to get my first ever glimpse of the Andromeda galaxy through a telescope on the roof (we had local amateur astronomy societies there to help); and I'd held a real chunk of Mars (a meteorite) in the palm of my hand!   An open event like this serves to remind us of why we spend hours in front of our computers to study the universe we live in, and how lucky we all are to be paid to do our hobby!  It's got to be one of the best jobs in the world.  Everyone benefited, the planetary group had a great time meeting the rest of the Astrophysics department, and I can safely say we'd be happy to do it again sometime soon!