Sunday, 10 January 2021

Embarking on the Bryson Line

Locked down again and going mad.  I'm not particularly good at sticking to an exercise routine - seem to get bored too easily with running (after a couch-to-5km) and cycling (which I tend to do with the kids).  But I do enjoy walking, whatever the weather, headphones in and listening to an audiobook or podcast.  Anyone that lives near me will probably spot me doing laps of the village every few days - we have an old railway line near our home that's a good straight line for several kilometres, some good cross-field footpaths with views towards Leicester city centre, and a nearby hill looking down into a quarry. But with the lockdowns and homeworking of 2020, I've done these loops around the villages many times.... so I wondered about a change.  Not that there's anything I can do right now, in the middle of #Lockdown3.

One of the amazing audiobooks I listened to in 2020 was Bill Bryson's Road to Little Dribbling, which saw him taking the route from Bognor Regis to Cape Wrath, a straight-line route that spans England and Scotland (the longest straight line one can travel in the UK without crossing any part of the sea, which he calls the Bryson Line).  If you draw a straight line between the two (916 km), it passes within 2.8 km of the very centre of England.  

That's right here in Leicestershire, at Lindley Hall Farm, 1.5 km east of Fenny Drayton and 5 km north of Nuneaton.   The farm is part of the former RAF Lindley (1943-46) airfield, named after the farm which itself was named after the former Lindley Hall.  According to Wikipedia, a plaque denoting this point, and disputing England's "traditional" centre as being Meriden in the West Midlands, was erected by Ordnance Survey on 14 June 2013.  This also right next to MIRA, the Motor Industry Research Association, an automotive engineering and development consultancy company that uses the old airfield.

It's also only 7.3 km from where I grew up, in Hinckley in Leicestershire.  

So that feels like a meaningful-enough starting point for this fairly pointless blog post.  Armed with Strava recording my movements, Google Maps as a guide to the Bryson Line from Lindley Hall Farm, and Wikipedia for place names, I wondered how far I would get without actually leaving Leicestershire.

Jan 3rd: 6.45 km from Lindley Hall to Sheepy
Past Sibson, ending up in a field between Sheepy Magna and Wellsborough at 52.62015, -1.49456.  I'm in the civil parish of Sheepy, created in 1935 from the merger of the four civil parishes of Sheepy Magna, Sheepy Parva, Sibson and Upton.

Jan 9th: 6.24 km. Twycross
Right through the centre of Twycross, home to the incredible Zoo that I've visited many times with my family, and which has the largest collection of monkeys and apes in the Western World.  Still in Leicestershire for now.  I end up outside a place called the Upper Rectory Farm Cottages in Appleby Magna, which (according to Wikipedia) lies on the edge of the ancient boundary between the kingdom of Mercia and the Danelaw.

Jan 10th:  6.79 km. Leaving Leicestershire 
Appleby Magna to Shortheath, near to the Forestry Commission's Hicks Lodge (good for cycling) and Conkers, in the middle of the National Forest (200 square miles of north Leicestershire, south Derbyshire and southeast Staffordshire planted in an attempt to blend ancient woodlands together into a new forest).  Also passed close to Moira Furnace, a nineteenth-century iron-making blast furnace.  The Leicestershire county line follows the Hooborough Brook here, so I guess I've officially left Leicestershire and arrived in Derbyshire.

Jan 12th:  4.52 km. To Swadlingcote
Properly passing into Derbyshire now, and heading for the centre of Swadlingcote, still within the National Forest.  According to Wikipedia, shallow valleys and ridges, shaped particularly by the mining activity which once dominated the area as the Leicestershire and South Derbyshire Coalfield, seams from the Upper Carboniferous age.

Jan 17th: 7.6 km Walking and 7.3 km Cycling
Northwest from Swadlingcote towards Burton-on-Trent, crossing the River Trent and the River Dove near to where the two rivers meet, during a 7.6 km walk in the morning. Finished just past a railway line, then a 7.3-km cycle onwards across Derby Airfield, to the east side of Hilton, through the Hilton Gravel Pits Nature Reserve, to finish in fields near Sutton on the Hill.

Friday, 18 December 2020

Saying Goodbye to the Royal Society

Last day of "School", and a bittersweet ending for me - after 8 years, my @royalsociety research fellowship is coming to an end.  The URF picked me up at a desperate point in 2012 (I was a new Dad, with no job beyond the end of that year), and I can't overstate my gratitude.  

Some highlights of working with @royalsociety during this time: funding two superb PhD students (@RohiniGiles and @ortk95), summer students, and giving me the flexibility to manage an ERC-funded planetary atmospheres research team at Leicester. 

Running the @IcyGiants discussion meeting in 2020, along with a photo I'll treasure from the Marble Hall.  Participating in the #SummerScience exhibition in 2018.  'Meet the press' events at Carlton House.  Just sitting in the fellows room with a coffee.

Judging the 2018 Investment Science Book prize, working with an amazing panel, being invited to the Hay festival, then meeting all the authors on the shortlist.  A trip to St. James' Palace with the other URFs and DHFs. 

And being allowed to view the planetary and astronomy treasures (Newton's death mask, books by Galileo, Cassini, Herschel, Huygens...) in their archives, showcasing them to amateur Jupiter observers after a Juno meeting in 2018. 

But of course the biggest thing to be grateful for - giving me the opportunity to move from Oxford to Leicester five years ago.  Felt like an enormous decision at the time, but no regrets. So, raising a mulled wine to @royalsociety today, and let's see what 2021 brings.

Tuesday, 13 October 2020

On ESO and TIMMI for Jupiter

H/T to Ulli Kaufl for showing this quote from Low&Rieke (1974) on early thermal-IR @ESO_IR2020: "Observing at 10 µm has been likened to observing visually through a telescope lined with luminescent panels and surrounded by flickering light as though the telescope were on fire..." 

I also never knew that the TIMMI instrument on @ESO's 3.6-m telescope observed the Shoemaker-Levy 9 comet collision with Jupiter at 10 µm back in 1994, sensing ammonia gas and debris lofted into the stratosphere (Credit:ESO)

...and I didn't know that the successor TIMMI2 was also observing Jupiter in 2000 (left, showing thermal waves later seen by Cassini) and 2004 (right). Seems we have more archival Jupiter thermal-IR data than I realised... (Credit:ESO)…ImageImage

Tuesday, 22 September 2020

#PlanetBites: On Ice Giants as Laboratories for Convection

This blog post is based on a White Paper and #EPSC2020 presentation by Tristan Guillot, available on Vimeo.  Uranus and Neptune are key to the understanding of planets with hydrogen atmospheres. These are the last worlds never to have been visited by an orbiter, and are probably the building blocks for formation of giant planets.  Their interiors and evolution, and hence their composition, are poorly constrained.  They are unique laboratories for understanding heat transfer, compositional variations and temporal variations.  These planets are active, with methane clouds, seasonal variations, and activity most probably linked to convective phenomena.  

What have we learned from the other giants, like Juno at Jupiter?  Equilibrium cloud structures have methane clouds near the top of the observable atmosphere, where the optical depth is relatively low.  This is opposite for the water clouds in Jupiter and Saturn.  Juno has shown that the atmosphere is not as simple as we expected.  Ammonia is varying in altitude and latitude down to great depths, tens of bars or more.  The presence of water storms lofting ice crystals, that dissolve ammonia, and then bring down ammonia and water gas down to great depth.  This precipitation forms intense cold downdrafts that can penetrate deep.  How deep to they fall with no surface?  Hydrogen atmospheres always have heavy condensates, contrary to the earth case.  Downdrafts in the Sun are important for the solar convective zone.

Moist convection can be inhibited by composition.  The molecular weight effect inhibits convection locally, and this occurs when water is more abundant than 10x solar, and methane more abundant than 40x solar, so should occur on Saturn and the Ice Giants.  Furthermore, we don't know what the temperature profiles look like below the 1-bar level - what sort of adiabats should they follow, and what are the implications for interior modelling?

We need to evolve from a standard picture of uniform clouds based on equilibrium, to something that is more variable with strong updrafts, precipitation, and downdrafts.  We know that clouds are extremely important for understanding hot and warm Jupiters and their compositions, and also important for brown dwarfs.  A mission is sorely needed, with an orbiter and a probe.

#PlanetBites: On ESA's Jupiter Icy Moons Explorer

At #EPSC2020, Olivier Witasse described the JUICE mission to Jupiter, a European mission to explore the emergence of habitable worlds around gas giants.  The mission will explore the icy moons Europa, Callisto and Ganymede, particularly their internal oceans, as well as the Jupiter system globally (the atmosphere, interior, and magnetosphere).  The aurora of Jupiter show the invisible link between the planet and its wider system, the moons and rings.  

Olivier showed schematics of the spacecraft.  We have almost 90 m2 of solar panels, with a complex deployment sequence.  The optical bench is on the top, with the remote sensing instruments.  On the bottom is the 10-m magnetometer boom, with magnetic and plasma sensors.  There is a long boom for the radar, and smaller booms for plasma parameters.  Two antennas, the high gain antenna and medium-gain antenna will be used for the radio science subsystem, and there are ten instruments in total.  

The video shows movies from Airbus in Germany.  All instrument teams are working hard to build, test and deliver the flight models to the industrial contractors - so far two are delivered to Airbus (UVS from San Antonio, and RPWI from Uppsala), with thermal vacuum tests due at ESTEC in January 2021 being the next big milestone.  COVID has reduced the margins, with still one month in reserve for a launch in May 2022 from Kourou with Ariane 5.  Backup launches in Sep 2022 and Aug 2023 have also been studied.

JUICE has a complex and interesting mission profile, 7.5 years to Jupiter, arriving in 2029 for a 2.5 year orbital tour around Jupiter, making flybys of the icy moons.  In Sep 2032 JUICE will end up in Ganymede orbit, to study the largest satellite of Jupiter down to 500 km above the surface.  

JUICE is a challenging mission - the mission lifetime; the radiation environment requiring shielding; the thermal environment from the hot Venus to cold Jupiter; the power is an issue far from the Sun even with large solar arrays producing 1000 W; and some strong EM requirements, making the design complex.

Navigation is also challenging with two orbit insertions, and many flybys.  We have to address planetary protection, never impacting Europe, plus some power and data rate constraints.  Lastly, for a mission lasting 30 years from idea to the end of mission, we need to ensure we have all the knowledge available throughout.

Olivier shows some images of the spacecraft, with the tanks being inserted at the end of 2019 and the high-gain antenna undergoing tests, showing the size of this enormous spacecraft.  The spacecraft is really taking shape now, waiting for the instruments to be integrated.  

Pro-Am Support for Juno

This workshop, organised by Ricardo Hueso, is a continuation of previous meetings in Nice (2016) and London (2018), making stronger links between the Juno mission and the efforts by the amateur community to produce a near-continuous record of atmospheric activity on Jupiter.  EPSC meetings have always had an amateur astronomy contribution, making it unique amongst planetary conferences - it's just a shame we were not able to meet again in person!

Image Processing for Jupiter

Christopher Go started proceedings on how to improve planetary image processing, describing his basic workflow and new techniques in processing.  An exciting new development for planetary imaging is the Sony IMX462C back-illuminated CMOS chip, with very high sensitivity in the infrared, allowing them to capture very high-resolution methane band observations compared to the older IMX290M.  Chris recommends "taking care of the little things" - seeing is the most important thing, which requires location, location, location.  Local conditions can affect this, such as heat sources nearby (the warmth of the cement near his home), so Chris sprays the floor with water a few hours before imaging.  He recommends watching the jetstream, using - if you're underneath it, it might not be worth going out imaging.  Set up the OTA early and cool it down, using a cooling fan to reduce tube currents (e.g., Chris uses a vacuum cleaner!).    The mirror needs to be locked after focussing to prevent focus shifts, never over-tightening the bolts, which would distort the mirror.  Collimation needs to be done with a camera on, not with the eyepiece in, as a slight shift can occur.  Chris is often asked what settings he uses for his camera, like exposure time and gain.  These are immaterial, as he changes them depending on transparency and seeing - he uses the histogram close to 90% with FireCapture gain control.  For high-quality captures, he emphasises the need to find the sweetspot of the system, use the fastest frame-rate possible, spend time to focus, don't be gain-shy, and capture a lot of data.  For Jupiter, he focusses using Io or Europa. 

Once he has the images, he performs derotation with WinJupos, which allows observers to stack beyond the time limit set by the rotation of the planet.  This derotation is so good, Chris even uses it to process Hubble images, even though a typical Hubble image is only 15 minutes long.   He uses something called Topaz Labs in Photoshop in methane-band images to pull out the details.  Finally, Chris states that "the goal of planetary imaging, is not to acquire beautiful images, but to provide useful data."

Current Events on Jupiter

North Temperate Belt:  John Rogers picks up the reigns with a review of current phenomena on Jupiter in 2020, and how it fits in with the long-term patterns of Jupiter's climate (cyclic patterns of events, sometimes regularly, sometimes irregularly).  The most recent is the NTB south jet outbreaks, which usually occur every five years, but this one has erupted after only four years.  One or more brilliant plumes erupts at the latitude of this jet, spreading a disturbance all around the planet.  The first plume erupted on August 18th, the brightest feature on the planet in the visible and methane band, showing that it had punched up above the usual cloud deck.  It has developed and expanded since, with two further plumes erupting in the weeks that follow at completely different longitudes.  Animations over several weeks show the plumes moving eastward, with a wake of dark spots and chaotic regions behind it.  One big dark spot - an anticyclonic vortex - appears roughly every five days.  On September 1st, a second outbreak appeared, expanding in the same way as the first.  On September 8th, a third one appeared.  We expect each one to collapse and decay when it catches up with the tail of the previous one, and Shinji Mizumoto at ALPO-Japan has been doing some very careful tracking of this process.  Plume 3 already appears to be disappearing, and we expect Plume 2 to disappear in late September, and Plume 1 by mid-October.  The turbulent wakes them coalesce into a dark NTB south component, which will then become orange over time.  Juno's PJ29 passed just a few days ago, but sadly did not cover the current outbreak.

North Tropical Domain:  In the North Tropical Domain we observe NEB expansion events (where the brown belt expands northwards) every 3-5 years.  The most recent one was in 2017, and a new event started in April 2020, possibly initiated in February from a bright rift around "White Spot Z" (a large white anticyclone).  In the wake of the rifted region, some sections of the NEB were drifting northward.  The belt had big dark patches, and some brighter cyclonic areas.  By September the belt has expanded all the way around the planet.  From here on, we expect a series of barges and Anticyclonic White Ovals (AWOs) all around the expanded northern NEB, but at the moment the NTB south outbreak could be disturbing this process.

Equatorial Zone:  This typically-white zone has been vividly coloured over the past couple of years.  This event began in 2018, peaked last year, but is still there today.  As of this summer, it looks stable and distinct as an ochre belt.  Maybe things are being brought up from the deeper atmosphere and "being cooked" by UV light to create the ochre colour. 

South Tropical Domain:  In the South Tropical Domain, the SEB is the only belt not undergoing any special cycles right now.  It is unusually pale in the northern half, but there remains plenty of convective disturbance in the wake of the Great Red Spot, so no evidence of a fade any time soon.  Its always possible that a new mid-SEB outbreak can occur at any time.  Right now, some little vortices entering Red Spot Hollow are still pulling flakes out of the Red Spot, continuing the activity seen in 2019.  It's still happening, and was observed again this month.  The GRS has begin shrinking again this year, even though the flaking events haven't been quite so impressive, so will this be a stable decline or will it recover again?

Finally, the South Temperate Domain, which consists of structured sectors that appear and propagate around the planet on an otherwise blank domain.  There's always two or three of these, one at the moment adjacent to Oval BA, and another at the following end of the STB spectre.  We are expecting a new structure to arise preceding Oval BA, arising from cyclonic vortices.  The appearance of "Clyde's Spot" from the small white spot in STB latitudes might be a precursor of this, and was observed by JunoCam during PJ27.  This short-lived plume left a darker spot that has continued to be turbulent, and maybe the dark spot will evolve into a new structured sector.

Juno and JunoCam

Glenn Orton from JPL joined from California, mentioning that they finally have clear air after the winds have shifted from the Bobcat fire, and the Mount Wilson observatory has been saved.  Glenn's role on the Juno mission was to provide ground-based observations to support the mission.  These are needed to improve the spatial coverage over the globe where Juno is not observing; to provide context in time to track the evolution of features; to provide spectral coverage in ranges that are not covered by Juno instrumentation, and to provide simultaneous coverage of multiple components of the jovian system (e.g., Io).

The nominal mission ends at PJ34, in June 2021, but a proposal will soon be submitted for an extended mission, with a maximum of 76 orbits up to May 2025, providing high resolution coverage of Jupiter's northern hemisphere and pole, with multiple flybys of Io, Europa, Ganymede, as well as a characterisation of the ring system.  Supposedly we'll know the outcome towards the end of this year.  Very late on, there'll also be opportunities for radio occultations of the jovian atmosphere.  One caveat is that we'll be going into a treacherous part of the magnetosphere, an increasing challenge for the spacecraft.

Candy Hansen emphasises that the Juno mission also has artists involved, and not just scientists and engineers.  JunoCam, a push-frame imager built by Malin Space Science Systems, is on the payload to allow the public to participate in a planetary mission, and the great science is a bonus.  At the closest point, JunoCam is observing the storms from just a few thousand kilometres up.   JunoCam collects data for only 2 hours out of a 53-day orbits, so amateur observations are essential to fill in the gaps.  Lighting is everything to an imaging experiment.  When Juno arrived, the orientation of the orbit meant we were looking at the terminator region.  As time went on, it became more challenging to observe, but now the orbit is evolving, and we'll come over onto the dusk side of Jupiter, allowing us to get great images with nice shadows.  The orbit is evolving into a more southerly orientation, getting close to the north pole, with a long period to image the southern hemisphere (albeit at worsening resolution).  The closest approach will be at a latitude of 28N by the nominal end of mission on PJ34, reaching 63N by the end of PJ75.   For a little outreach camera, there's an awful lot of science being done.

To monitor the health of the camera, one image is taken every PJ pass with all the same settings, so we have a record as the orbit evolves to show how the camera is changing.  Up to now, there is no sign of permanent damage, just a little more radiation noise, so they expect to survive right to the end of the mission.

Kevin Gill then described the image processing pipeline he uses for JunoCam images.  Kevin is one of many people who process these images.  He's an engineer at JPL, but does the processing on an amateur basis.  The raw data has long framelets, used to produce the map-projected colour images.  Kevin takes the raw framelets, as it provides better options for colour calibration.  His pipeline produces maps, which then inform wide-angle perspective views, cylindrical projected detailed shots with some enhancening and sharpening; fish-eye composites (ultra-wide angle views that makes it look like you're seeing the full disc).  His code also outputs meshes for 3D programmes like Blender.  He's also working on stereographic images, as best he can given the dynamic nature of Juno's orbit and the interval between observations, as well as fly-over movies.  The automated pipeline is open source and can be found on his github, uses ISIS3 and Spice.  He then uses manual processing for the reprojection and combination if he's making a composite of multiple observations, using the ISIS3 suite.  Blender, Photoshop, Topaz Denoise (very carefully!) and Lightroom are then used to produce his output products.  This not a scientific approach, but provides a visually pleasant view (Ed: that's an understatement!).  

The Value of Long Term Monitoring of Jupiter

Finally, Arrate Antunano gives a presentation on how the data you're taking today might be of value to those researching Jupiter in the decades to come.  Different planets display diverse cyclic activity in their weather and climate patterns.  Jupiter has dramatic planetary-scale disturbances that completely alter the planet's appearance.  Most studies deal with just snapshots of observations, usually as a result of one phenomenon that captures the imagination at the time.  But what is the big picture here?  How do things change in the long term?  How cyclic are these events?  Are there correlations between different events?

Long-term monitoring of Jupiter's atmosphere, highlighting the expansion and contraction of the north equatorial belt - credit: Fletcher et al. (2017)

Ground-based observations are a goldmine for researchers.  At infrared wavelengths, we have around 40 years of observations available since the early 1980s, providing great temporal coverage.  Checking the Planetary Virtual Observatory and Laboratory (PVOL), the amateur observations span 2000 to 2020, and even older observations are present in the ALPO-Japan directory.  These long-term observations at multiple wavelengths allows them to characterise temperature, composition, and aerosol changes.  

Examples of these cyclic activities include the cloud-clearing events at the equator, where the equator brightened at 5 microns with a period of 7-years or so.  This brightening h appens at the same time as the visible coloration events at the equator.  The aerosol opacity decreases at the 400-600 mbar level, where the ammonia clouds are. However, we didn't see any change in ammonia or temperature, so this rejects the idea that the cloud-clearing is due to warming and evaporation of clouds. Maybe changes in the deep ammonia gas are responsible, but this is something that Juno has not yet investigated.  Also using 5-micron data, some changes in the bands are observed to be anticorrelated, particularly between changes in brightness of the NEB and SEB.  Finally, looking at 7.9 microns, which senses Jupiter's stratospheric temperatures, reveals how Jupiter's equatorial stratospheric winds change with time.  We've known this for 30 years, but new results published in Nature Astronomy show that Jupiter's equatorial stratospheric oscillation has been disrupted twice, completely switching into a new period, and these changes coincide with substantial disturbances in the deeper atmosphere.  This is unexpected, and hasn't been observed on Earth or Saturn, which have similar equatorial stratospheric oscillations.  

The long-term Jupiter observations are critical for this exploration of natural jovian cycles, and Arrate would like to continue this study with reflected sunlight observations, to understand the vertical extent of the events and their interconnectivity with the deeper atmosphere,  so that we can maybe predict these events in advance to be ready with our telescopes.

The Pro-Am community at the 2018 meeting at the Royal Astronomical Society in London.

Monday, 21 September 2020

Ice Giant Science at EPSC 2020

This blog post has been written in preparation for the 2020 Europlanet Society Congress, which will be held virtually from September 21st.  Contributors were asked to submit pre-recorded video presentations or 6-slide virtual posters, which would be viewed asynchronously at a time convenient for the audience.  Each presentation and poster was accompanied by a text-based chat for questions, allowing for asynchronous discussion of the various presentations.  However, in an effort to advertise the individual sessions and to ensure a lively discussion, the EPSC 2020 organisers scheduled short 20-minute science showcases, to be delivered by the session conveners or a selected presenter.  This blog represents a summary of the Ice Giant science being presented at EPSC2020, grouping the abstracts into themes.  We urge you to visit and participate in the discussion of the individual contributions, and hope for a lively meeting.

1. Ice Giant Atmospheres

Guillot (514) discusses how the Ice Giants can be used as a laboratory for methane-driven convection and storms, providing insights into how moist convection works in atmospheres where the condensates are heavier than the surrounding air.  They point out that the methane clouds are more readily accessible than the water clouds of Jupiter and Saturn, making this a fascinating regime to study via future missions.

Sticking with this theme, Hueso et al. (354) describe a programme of Earth-based observations of Neptune in 2019, using contributions from amateur observers to fill time-gaps between large-class facilities like Hubble.  The data suggest more variability but less cloud activity in 2019 than previously, and the team uses the observed cloud features to reassess Neptune’s zonal winds.  In addition, Sato et al. (080) study the evolution of dark spots and storms on Neptune via the 1.6-m Pirka telescope of Hokkaido University in 2018, using the spectrum in the near-infrared to estimate the drift rate of a storm.

The nature of the clouds themselves are explored by Toledo et al. (593), who present constraints on the formation of hazes and clouds from a coupled cloud-haze microphysical model, used to understand the vertical structure and evolutionary timescales of ice giant aerosols.  Irwin et al. (241) describe observational constraints on clouds and methane in Neptune’s atmosphere, via fitting visible-light spectroscopy acquired by the VLT MUSE instrument in 2018, using the observed limb-darkening to discriminate between methane and aerosol contributions to the spectrum, and confirming the strong equator-to-pole gradient in methane gas on Neptune.

Moving into the stratosphere, Rowe-Gurney et al. (244) use Spitzer observations to reveal the properties of Uranus’ stratosphere, discovering a variation in emission as a function of longitude as the planet rotated in 2007.  They demonstrate that these changes are the result of stratospheric temperature variations, and relate it to small-scale structures in bands of warm mid-latitude emission on Uranus.  Roman et al. (471) use thermal infrared observations of Neptune over the past two decades to reveal surprising changes in emission, implying that processes occurring much faster than a Neptunian season are significantly modifying the temperature and/or chemistry of the stratosphere, with a substantial change occurring between 2006 and 2008.

Finally, Milcareck et al. (297) describe the development of a general circulation model for Uranus and Neptune, using state-of-the-art radiative-equilibrium models (Vatant d’Ollone, (292)) and reproducing the broad structure of Ice Giant wind fields, but generating a number of open questions concerning differences between the two planets.

2. Planetary Origins and Interiors

Turning to the bulk composition of the Ice Giants, Cavalie et al. (053) explore Ice Giant chemistry via a combination of chemical modelling and Earth-based compositional measurements, concluding that a combination of in situ atmospheric probes and remote sensing are required to understand Ice Giant composition.  Mousis et al. (613) describe a model of the outer region of the proto-solar nebula to understand how materials might have been delivered to the Ice Giants to explain the observed elemental enrichments of Uranus and Neptune.  They suggest that these planets accreted from building blocks of grains and pebbles that condensed in the vicinity of the N2 and CO ice lines.

Scheibe et al. (640) attempt to reconcile thermal evolution models with the extreme differences in intrinsic heat flux between Uranus and Neptune, proposing and studying a conducting interface that inhibits energy transport between the ice-rich interior and the outer atmosphere.

Moving from the planets to the satellites, Li & Christou (769) revisit the idea that Triton and Nereid, by virtue of their peculiar orbits, must have been captured by Neptune.  By assuming instead that the satellites formed in situ around Neptune, but were then perturbed during the period of instability suggested by the Nice Model, a small number of satellites survive the encounter and can gain Triton-like or Nereid-like orbits, challenging the conventional capture model.

3. Magnetospheres and Upper Atmosphere

Gershman & DiBraccio (258) study how the solar wind couples to the Ice Giant magnetospheres, showing how solar wind magnetic pressure changes influence the strength of the coupling, and therefore hinting that magnetospheric dynamics may have a strong dependence on the solar cycle, being strongest at solar maximum.

Two techniques are explored for studying the upper atmospheric emission.   Melin et al. (268) continue to monitor the long-term cooling trend of Uranus’ upper atmosphere using near-infrared emission from the H3+ ion, showing cooling by 8 K per year since records began in 1992 that they relate to the changing geometry of Uranus’ magnetic field and the solar wind over the past three decades.  And Thomas et al. (797) report on the ongoing attempts to detect Uranian auroras via emission from H3+, to supplement previous detections in the ultraviolet.  They used NIRSPEC on Keck in 2006 to identify fast changes in intensity that are suggestive of auroral processes, potentially the first spatially resolved infrared images of Uranian auroras.

Finally, Dunn et al. (1028) also continue to search for X-ray emissions from the Ice Giants, using Chandra observations of Uranus to show two non-detections during solar minimum and one statistically significant detection during solar maximum consistent with an X-ray emission from charge exchange or scattering of solar photons.

4. Future Missions and Instruments

The final theme of this EPSC session concerns a look ahead to future missions.  Blanc et al. (984) describe the outcomes of the “Horizon 2061” foresight exercise, suggesting questions that could be addressed via a long-term plan for Ice Giant exploration, potentially with one or more spacecraft and making use of gravity assists in the 2030s.  Costa Sitjà et al. (878) consider the opportunities that a long cruise to Uranus and Neptune might provide, by developing a tool to assess potential flyby encounters enroute to Neptune, searching for Jupiter Trojans, Centaurs, Trans Neptunian Objects and Jupiter Family Comets, with the aim of ultimately optimising trajectory designs.

Probst et al. (435) introduces a tool that investigates the feasibility for planetary entry probes accessing different latitudes on Saturn, Uranus and Neptune, looking at how different trajectories, approach angles, and probe designs impact the available probe sites, which will provide crucial insights for mission development.  For such an atmospheric probe, Irwin et al. (306) describe the needs for a net flux radiometer instrument, able to measure the upward and downward fluxes of solar and thermal radiation as the probe descends.  They evaluate how such an instrument would constrain both the radiation energy budget and the properties of the clouds and haze layers.

In addition, Molina-Cuberos et al. (523) discuss the potential for in situ probes measuring electrical properties of Ice Giant atmospheres during the probe descent.  Using a model developed for Mars and Titan, the authors show how important aerosol properties are to the observed ionisation and electrical conductivity.

Tortora et al. (1042) describe the proposed Discovery-class Trident mission to Triton, specifically focussing on the capabilities of the radio science instrument to study electron densities, neutral atmospheric temperatures, and the thickness of Triton’s hydrosphere.  And Lamy et al. (941) discuss the variety of radio emissions from the “radio twins” Uranus and Neptune, and how a digital high-frequency receiver could provide a low-resource instrument to study auroral and atmospheric radio and plasma waves or dust impacts.