Earth-based observations prepare Juno for the Great Red Spot Encounter

In just a few days time, on July 11th 2017, NASA's Juno spacecraft will perform the closest-ever views of the swirling maelstrom known as Jupiter's Great Red Spot.  It was always hoped that the pre-planned polar orbit and close perijove passes would take the spacecraft over the storm, but the slow and somewhat unpredictable westward motion of the gigantic vortex meant that a little luck would be required.  That luck comes in on Perijove 7, and we'll be rewarded by breathtaking views - so close that the vortex will stretch from jovian horizon to jovian horizon.

In preparation for that encounter, myself and others have been collaborating on an Earth-based support campaign, capturing multi-wavelength views of the jovian atmosphere to provide spatial, temporal and spectral context for Juno's close-in encounters.  Today, two of the telescopes we've been using released some of our imagery from May 19th 2017, acquired during Juno's last perijove 6.  These images show the Great Red Spot as it was just a few weeks ago, and prepare us for Juno's close-in views.

Thermal Emission from Jupiter

Both observatories are located on the peak of Mauna Kea on the Big Island of Hawaii.  We have been working with the Subaru Telescope (the National Observatory of Japan) and the Gemini-North telescope.  The COMICS instrument on Subaru provides mid-infrared (7-25 µm) observations that reveal the temperature structure, gaseous composition and cloud opacity within the Great Red Spot.  The Subaru telescope has released an image at 8.8 µm, which primarily senses temperatures and aerosols, showing the planet's white zones as cold and cloudy (i.e., dark) and the brown belts as warm and cloud-free (bright).  The Great Red Spot can also be seen as cold and cloudy, something that we studied at length (using both Subaru data and those from ESO's Very Large Telescope VISIR instrument) in an Icarus paper in 2010.

Jupiter's thermal emission at 8.8 µm obtained by the Subaru/COMICS instrument on May 18th 2017.  A video created from a series of observations with the same settings on January 14th 2017 is also available. Credit:  NAOJ and JPL.

Glenn Orton was the PI of Keck exchange time to use the Subaru facilities, and said this in the press release:  "During our May 2017 observations that provided real-time support for Juno's sixth perijove, we obtained images and spectra of the Great Red Spot and its surroundings.  Our observations showed that the Great Red Spot had a cold and cloudy interior increasing towards it centre, with a periphery that was warmer and clearer.  This implied that winds were upwelling more vigorously towards its centre and subsiding at the periphery.  A region to its northwest was unusually turbulent and chaotic.... this region is where air is heading east towards the GRS and flows around it to the north, where it encounters a stream of air flowing over it from the east."  Crucially, observations of this kind, from the VLT and from Subaru, are capable of resolving 1000-km length scales on Jupiter that are comparable to Juno's microwave experiment, which will sound the deep atmospheric processes underlying those that we can see in this thermal image.

Jupiter in Reflected Sunlight

At shorter wavelengths, the NIRI instrument on the Gemini-North observatory captured the reflected sunlight from the Great Red Spot and its surroundings, as explained in their press release.  These observations required Adaptive Optics, using observations of a nearby satellite to observe and correct for the distortions caused by our own atmosphere.  Orton explains: “Back in May, Gemini zoomed in on intriguing features in and around Jupiter’s Great Red Spot: including a swirling structure on the inside of the spot, a curious hook-like cloud feature on its western side and a lengthy, and a fine-structured wave extending off from its eastern side.”  By observing Jupiter in a variety of different near-infrared wavelengths, which sense differing amounts of methane absorption, we're able to reconstruct the three-dimensional cloud structure within Jupiter's upper troposphere.

A composite colour infrared image of Jupiter reveals haze particles over a range of altitudes, as seen in reflected sunlight. The image was taken using the Gemini North telescope with the Near-InfraRed Imager (NIRI) on May 18, 2017, one day before the Juno mission’s sixth close passage (“perijove”) of the planet.  Credit: Gemini Observatory/AURA/NSF/JPL-Caltech/NASA

Version of the image above labelled by Dr. John Rogers of the British Astronomical Association.

From the Gemini press release:  The colour filters cover wavelengths between 1.69 to 2.275 microns and are sensitive to pressures of 10 millibars to 2 bars. The Great Red Spot (GRS) appears as the brightest (white) region at these wavelengths, which are primarily sensitive to high-altitude clouds and hazes near and above the top of Jupiter’s convective region – revealing that the GRS is one of the highest-altitude features in Jupiter’s atmosphere. The features that appear yellow/orange at Jupiter’s poles arise from the reflection of sunlight from high-altitude hazes that are the products of auroral-related chemistry in the planet’s upper stratosphere.

Narrow spiral streaks that appear to lead into it or out of it from surrounding regions probably represent atmospheric features being stretched by the intense winds within the GRS, such as the hook-like structure on its western edge (left side). Some are being swept off its eastern edge (right side) and into an extensive wave-like flow pattern; and there is even a trace of flow from its north. Other features near the GRS include the dark block and dark oval to the south and the north of the eastern flow pattern, respectively, indicating a lower density of cloud and haze particles in those locations. Both are long-lived cyclonic circulations, rotating clockwise - in the opposite direction as the counterclockwise rotation of the GRS. A prominent wave pattern is evident north of the equator, along with two bright ovals; these are anticyclones that appeared in January. Both the wave pattern and the ovals may be associated with an impressive upsurge in stormy activity that has been observed in these latitudes this year. Another bright anticyclonic oval is seen further north. Juno may pass over these ovals during its July 11 closest approach. High hazes are evident over both polar regions with much spatial structure that has never been seen quite so clearly in ground-based images, with substantial variability in their spatial structure. The central wavelengths and colors assigned to the filters are:1.69 microns (blue), 2.045 microns (cyan), 2.169 microns (green), 2.124 microns (yellow), and 2.275 microns (red).

Jupiter's Deep Glow

Supplementing the two investigations above, a ground-based programme is also under way to observe the deep thermal emission of Jupiter near 5 µm.  We released images from ESO's Very Large Telescope last year, and this programme has continued for each of Juno's perijoves. A parallel Gemini programme headed by Michael Wong of the University of California, Berkeley, used an approach commonly called “lucky imaging” to obtain sharp images of Jupiter at 5 µm. Images obtained with this filter are mainly sensitive to cloud opacity (blocks light) in the pressure range of 0.5 to 3 bar. “These observations trace vertical flows that cannot be measured any other way, illuminating the weather, climate and general circulation in Jupiter’s atmosphere,” notes Wong.

Jupiter glows with thermal (heat) emission at 5 µm, thick clouds block the emission from the deeper atmosphere. The Great Red Spot is visible just below centre. This image, obtained with the Gemini North telescope’s Near-InfraRed Imager (NIRI), was obtained on January 11, 2017, so the relative positions of discrete features have changed with respect to the near-infrared image above.  Credit: Gemini Observatory/AURA/NSF/UC Berkeley 

For more information about the National Astronomical Observatory of Japan's Subaru Telescope, visit:  https://subarutelescope.org/  For more information about the Gemini Observatory, a partnership of the United States, Canada, Brazil, Argentina and Chile, visit:  https://www.gemini.edu/

For the Subaru Image:  Orton (Jet Propulsion Laboratory) and Yasumasa Kasaba (Yohuku University, Japan) led the team, with Takuya Gujiyoshi (Subaru Telescope astronomer) operating the telescope.  Other team members included James Sinclair, Anna Payne (JPL), Joshua Fernandes (California State University, Long Beach), Leigh Fletcher (University of Leicester), Patrick Irwin (University of Oxford), Padma Yanamandra Fisher (Space Science Institute), Takao Sato (JAXA), Davide Grassi (IAPS/INAF), Shohei Aoki (IASB, Belgium), Tomoki Kimura (RIKEN), Chihiro Tao, Takeshi Kuroda (NICT)l Takeshi Sakanoi, Hajime Kita, Hiromu Nakagawa (Tohuku University), Hideo Sagawa (Kyoto Sangyo University) and Joana Bulger (Subaru Telescope).

For the NIRI Image:  Orton leads the observing team for the adaptive-optics imaging and Wong heads the observing team for the thermal imaging. Additional team members include Andrew Stephens (Gemini Observatory); Thomas Momary, James Sinclair (JPL); Kevin Baines (JPL, University of Wisconsin), Michael Wong, Imke de Pater (University of California, Berkeley); Patrick Irwin (University of Oxford); Leigh Fletcher (University of Leicester); Gordon Bjoraker (NASA Goddard Space Flight Center); and John Rogers (British Astronomical Association).

Saving Cassini - ESA and NASA in 1994

In June 1994, as a result of threatened cuts during Dan Goldin's tenure as NASA administrator, our epic mission to the Saturn system was under extreme threat of cancellation.  The background to these decisions is covered in Michael Meltzer's excellent book, but I'd always heard of the striking letter sent directly to Vice President Al Gore (i.e., bypassing Goldin) from ESA's Director General, Jean-Marie Luton.  I managed to track this letter down in an appendix to a 1998 book from the National Academic Press on U.S.-European Collaboration In Space Science, and it's reproduced here.  Further background can be found in the NASA in the World book.

Letter from the European Space Agency to the Vice President of the United States, June 13, 1994

european space agency

agence spatiale européenne

D.SCI/RMB/db/3948

Paris, 13 JUNE 1994

Jean-Marie Luton
Director General

The Honorable Albert Gore, Jr.
Vice President of the United States
Old Executive Office Building
Washington, DC 20501
USA

Dear Mr. Vice President,

I have recently received a number of disturbing reports that suggest that the continuation of the joint U.S./European CASSINI mission could be threatened by ongoing Congressional deliberations on NASA's FY95 Appropriations Bill.

I am aware that the House version of the Bill, as marked up by the House VA-HUD and Independent Agencies Subcommittee on June 9, retains the necessary funding for NASA's portion of the mission. However, I am also aware that the House Subcommittee's Senate counterpart is faced with a more stringent budget allocation. I am told that the Subcommittee Chair, Senator Mikuiski, has indicated that without an increase in said allocation, termination of a major NASA programme would have to be contemplated, with specific reference being made to the CASSINI mission.

In the field of space science, CASSINI is the most significant planetary mission presently being undertaken by either the European Space Agency (ESA) or NASA, involving the exploration of Saturn, the most complex planet in the solar system and of its Moon, Titan. It is expected to provide at least a ten-fold increase in our knowledge of both bodies as compared to NASA's highly successful Voyager mission.

In making the commitment to participate with the U.S. in 1989, ESA oriented its overall space science programme in order to select this cooperative project, rather than opt for one of a number of purely European alternatives that were proposed at the same time. This decision was taken on the basis of scientific merit and in the belief that the cooperation would be of major benefit to both the U.S. and European scientific communities as well as the international science community in general. Over the past five years, while ESA's Long-Term Space Plan has been forced to undergo a series of significant revisions, driven primarily by our own budget limitations, the Member States have maintained a full commitment to the space science portion of the plan, of which CASSINI is an essential component.

To date, the Member State governments of ESA have committed around $300 Million to our portion of the mission (the Huygens Probe that will descend into the atmosphere of Saturn's Moon Titan, and several elements of the Saturn Orbiter Payload), of which two-thirds have already been spent, and have committed to a further expenditure of around $100 Million to see the mission through to completion. These figures do not include the approximately $100 Million contribution of Italy via a NASA/Italian Space Agency bilateral agreement.

The HUYGENS programme has been in the hardware phase for the past four years, with probe delivery to NASA due to take place in two years time. The hardware integration and testing phase started in early May this year.

The CASSINI mission has generated intense interest in Europe, both within the scientific and engineering community and from the public at large. Approximately 900 European scientists and engineers are working on the programme with more than 30 European institutes and universities involved in the preparation of CASSINI/HUYGENS science.

Europe therefore views any prospect of a unilateral withdrawal from the cooperation on the part of the United States as totally unacceptable. Such an action would call into question the reliability of the U.S. as a partner in any future major scientific and technological cooperation.

I urge the Administration to take all necessary steps to ensure that the U.S. commitment to this important cooperative programme is maintained so that we shall be able to look forward to many more years of fruitful cooperation in the field of space science.

Respectfully,

J.M. Luton

Wilton Exoplanet Fellowships at Leicester

A recent advertisement to come and join our team in exoplanet science at Leicester!  In particular, if you're interested in the characterisation of exoplanetary atmospheres via spectral inversion techniques, please do get in touch.

Exoplanetary research is one of the most rapidly developing fields in modern science, with the discovery of thousands of worlds beyond the confines of our own Solar System.  Drawing upon the breadth of expertise in the Physics and Astronomy Department of the University of Leicester, the Exoplanet Research Team is involved in a wide-ranging scientific programme at the forefront of this field.

Winton Philanthropies (www.winton.com/philanthropies/the-winton-exoplanet-fellowship) have recently announced a number of new exoplanet fellowships to be held at a university within the UK.

We therefore invite applications from young scientists with PhDs (obtained by September 30th, 2017) and no more than 5 years’ postdoctoral experience (exceptions will be made for periods of extended leave), to apply to join the exoplanetary research team at the University of Leicester.

The University of Leicester has 7 academic members of staff (2 of whom hold ERC consolidator grants), 4 postdoctoral researchers and 10 PhD students working in fields related to exoplanetary science. We are one of the founding members of  the Next Generation Transit Survey (NGTS), and are part of the JWST MIRI instrument team. Our expertise includes planet formation and migration, protoplanetary discs and dynamics of planetary systems, the detection and characterisation of exoplanets using photometry, characterisation of exoplanet atmospheres via spectral inversion; and aurora and magnetic fields.

To apply, please send Sarah Casewell (slc25@le.ac.uk) a pdf by Friday 21 July, containing:

1. Curriculum Vitae 
2. 1 page concise research proposal indicating how your research aims complement and extend the existing exoplanetary research at Leicester and identifies one or more suitable academic hosts.
3. Publication list

Each institution may only submit 2 candidates, and we will invite our selected applicants to make a full proposal at the start of August, with the final submission date of September 1st, 2017. Candidates will not be permitted to participate in multiple applications with different institutions and must be in a position to hold the Fellowship at a UK university.  In October 2017 Winton Philanthropies will announce awardees and the fellowships must commence within six months of the award.

Research topics include:

• Formation and evolution of exoplanets looking in particular at how protoplanetary discs shape young planetary systems. (contact: Dr Richard Alexander PI of the ERC Consolidator Grant project "Building planetary systems: linking architectures with formation (BuildingPlanS)”).
• Brown Dwarf observations and theory, in particular irradiated brown dwarfs (contact: Dr. Sarah Casewell)
• Numerical simulations exploring the dynamics of protoplanetary discs, and how planets form and evolve within them (contact: Dr. Chris Nixon)
• Planets around white dwarfs (contact: Dr Matt Burleigh)
• Detection and Characterisation of exoplanets using photometry, particularly using NGTS. (contact: Dr Mike Goad, Dr Matt Burleigh).
• Exoplanet atmospheres characterisation:  Inversion of spectroscopy from exoplanet transits and directly-imaged worlds to characterise their thermal structure, global composition and aerosol properties (contact:  Dr Leigh Fletcher)
• Exoplanetary Magnetospheres and Aurorae (contact: Dr Jonathan Nichols)
• Gravitational Instability theory of planet formation and super-migration of planets from ~ 100 au down to 0.1 au, including population synthesis models for the upcoming PLATO mission (contact: Prof. Sergei Nayakshin).

Advanced Study Projects at Leicester

In their fourth year of undergraduate studies, Leicester's Physics and Astronomy students undertake a supervised reading project with an academic supervisor, helping them to develop critical evaluation skills for assessing scientific literature.  As planetary atmospheres is a relatively new discipline for Leicester, I've been offering a range of topics that take the students from Earth-based phenomena to my own work in solar system science.  Some of the projects on offer are listed below.

Climate Oscillations in Earth’s Atmosphere
Our planet’s atmosphere exhibits cycles of activity that operate over annual and multi-year timescales.  Prominent examples include the El Nino Southern Oscillation (ENSO), the Madden-Julian Oscillation (MJO), the North Atlantic Oscillation (NAO, which helps to modulate the weather patterns over the British Isles), and the Quasi-Biennial Oscillation (QBO) in the equatorial stratosphere.  These atmospheric cycles have only been identified by long-term tracking of meteorological phenomena, such as patterns or rainfall or sea-surface temperatures.  The underlying causes of some of these oscillations remain poorly understood, but there is evidence of connectivity, via teleconnections, between the different cycles.  This project will review the variety of long-term climate cycles, connections to anthropogenic climate change, and implications for cyclic activity on other worlds in our solar system.  You will gain an understanding of the forces influencing UK weather patterns, and the implications for global climate of disruptions to these delicate atmospheric balances.

Suggested Reading:
• El Nino’s Extended Family:  From NASA’s Earth Observatory: https://earthobservatory.nasa.gov/Features/Oscillations/
• NOAA Website on El Nino and El Nina https://www.climate.gov/enso
• North Atlantic Oscillation from UK Met Office: http://www.metoffice.gov.uk/learning/learn-about-the-weather/north-atlantic-oscillation


Alien Skies:  Clouds from Ice Giants to Hot Jupiters
The bewildering variety of planetary environments discovered in the past two decades have provided an extreme test of our understanding of planetary atmospheric chemistry and cloud formation.  Models of planetary clouds are required to explain what the skies might look like on a hot roasting Jupiter, orbiting so close to its star that the temperatures soar to 3000K, and what they might be like on the coldest ice giant like Uranus or Neptune, at a frigid 50K.  This project will introduce you to the physics and chemistry of cloud formation, showing how condensation is influenced by the availability of volatile species and the temperature structure of an atmosphere.  It will take you from familiar clouds of water, to methane raindrops and hazes of iron and titanium.  We’ll conduct a thought experiment for how Jupiter’s cloud structure would change if it migrated inwards, closer and closer to the Sun, and use this to predict what the spectra of exoplanets might look like.

Suggested Reading:
• Fletcher et al., 2014, Exploring the Diversity of Jupiter-Class Planets, https://arxiv.org/abs/1403.4436
• Sanchez-Lavega et al., 2004, Clouds in planetary atmospheres: A useful application of the Clausius-Clapeyron equation, https://www.researchgate.net/publication/243492714
• Marley et al., 2013, Clouds and Hazes in Exoplanet Atmospheres, https://arxiv.org/abs/1301.5627

To the Surface of Europa
The next decade will see two ambitious missions providing new, close-in reconnaissance of Jupiter’s most enigmatic moon, Europa.  Europe’s Jupiter Icy Moons Explorer (JUICE) will conduct two close flybys of Europa, whereas NASA’s Europa Clipper will swing by more than 45 times.  These missions will pave the way for future landings on the surface, and will assess the capability of the Europan surface to host life.  This project will review our current understanding of the surface composition of Europa, its relation to the deep water-ice interior and the action of irradiation of surface materials.  You will look at the evidence for and against different surface acids, sulphates and salts, and their implications for the habitability of the surface.  You will develop an understanding of planetary ice spectroscopy, and the difficulties associated with distinguishing a unique composition from remote planetary measurements.  You will also assess the technological challenges associated with a mission to Jupiter’s moons, both in terms of available power, the harsh radiation environment, and the descent and landing concepts.

Suggested reading:
• JUICE Red Book study report: http://sci.esa.int/juice/54994-juice-definition-study-report/
• Greeley et al., 2004, The Geology of Europa (Chapter 15 of Jupiter. The planet, satellites and magnetosphere), http://adsabs.harvard.edu/abs/2004jpsm.book..329G
• Phillips and Pappalardo, 2014, Europa Clipper Mission Concept, EOS 95, p165-167, http://adsabs.harvard.edu/abs/2014EOSTr..95..165P

Anatomy of a Storm: From Earth to the Giant Planets
Planetary atmospheres serve as global-scale conveyor belts for heat, redistributing energy around the globe and influencing the pattern of weather and seasons.  On the giant planets, thundercloud systems produce lighting 10000x more intense than on Earth, and yet the same physics governs the formation of storm systems on all of the planets in our solar system, albeit under very different environmental conditions.  On Earth and on the giant planets, moist convection driven by the condensation of water (and the release of latent heat) controls this atmospheric heat engine, and shapes the appearance of a planet's atmosphere.  This project will compare and contrast evolving storm systems on terrestrial worlds and giant planets, identifying common processes and key differences between each world.  In particular, you will explore recent planetary-scale events (such as the disappearance and reappearance of Jupiter’s broad dark belts and the eruption of seasonal, globe-encircling storms on Saturn) and the importance of continuous versus triggered convective activity in planetary atmospheres.  You will develop an understanding of how satellite imaging and spectroscopy, either from Earth-orbiting satellites or planetary spaceprobes, contribute to our understanding of storm anatomy, and consider future measurement techniques to explore planetary atmospheric processes.

Suggested reading:
• Introduction to Planetary Atmospheres, Agustin Sanchez-Lavega, CRC Press, 2011.
• Dynamics of Jupiter’s Atmosphere, http://adsabs.harvard.edu/abs/2004jpsm.book..105I
• Cloud Dynamics, Robert Houze, Academic Press, 1993.

Realm of the Giants: Influence of Migration
The formation of the four giant planets shaped the architecture of our entire planetary system, both by providing the bombardment that delivered water and organic materials to our forming planet, and by shielding us from further cataclysmic impacts.  Recent simulations of planetary dynamics suggest that giant planets, once formed in the cold outer solar system beyond the snow line, migrate inwards towards the host star.  You will explore the consequences for such an inward motion, both in terms of the chemical and climatic conditions on the giant planets themselves (e.g., the evaporation of cloud decks) as they evolve the ‘hot Jupiters’, and on the evolution of forming terrestrial worlds.  This will help you to understand the key differences in the atmospheric structure of the four giant planets and, potentially, the hypothesised Planet Nine.  You will also investigate why the inward migration of Jupiter was halted, and outward migration began (the Grand Tack hypothesis), and the implications of this for the evolution of our planetary system.

Suggested reading:
• The Grand Tack Hypothesis, https://en.wikipedia.org/wiki/Grand_tack_hypothesis
• Diversity of Jupiter-Class planets, http://adsabs.harvard.edu/abs/2014arXiv1403.4436F
• Planetary Sciences, de Pater and Lissauer, http://adsabs.harvard.edu/abs/2015plsc.book.....D

Uranus from Hubble

Whoever said that Uranus was the boring planet?  Here is Erich Karkoschka's time-lapse movie of Uranus over four years between 1994 and 1998 from the Hubble Space Telescope, as the south pole swings out of view and we head towards the 2007 equinox.  You can see considerable activity in the northern hemisphere as it becomes visible later in the sequence, and the dance of the satellites in the plane of the sky due to Uranus' weird axial tilt.  This movie was first published back in 1999
(http://hubblesite.org/video/175/news_release/1999-11).