Editor’s note: We’re wrapping up a busy summer with one last conference: the EPSC-DPS joint meeting in Geneva, Switzerland. To celebrate the announcement of AAS Publishing’s new Planetary Science Journal, we’ll be bringing you some highlights from this planetary science conference all week!

Press Conference: Akatsuki Mission Results, 2020 Coordinated Venus Observations, and Science at Venus

Today’s press conference was a celebration of Venus, covering both current and future missions and theory.

Akatsuki

Masato Nakamura (ISAS/JAXA) opened the session by providing us with an update on Akatsuki, the only operational spacecraft currently in orbit around Venus. Akatsuki was launched in 2010 and arrived in orbit at Venus in 2015. Since then, it’s been using its five different cameras to image Venus in wavelengths from infrared to ultraviolet.

Akatsuki’s primary objective is to help us understand the differences between Venus’s atmosphere and Earth’s. Besides a difference in composition and thickness, Venus’s atmosphere also has the peculiar property of rotating an astonishing 60 times faster than the planet itself (something we call “superrotation”). What causes this? How is it sustained? Akatsuki’s pictures are slowly helping us to better understand the dynamics and 3D structure of the atmosphere to answer these questions.

One way Akatsuki is studying Venus’s atmosphere is by making infrared observations of the planet’s cloud tops. It’s a challenging process, says Takeshi Imamura (University of Tokyo), because the thermal images taken at 10 µm appear to be fairly featureless. By averaging images together within the coordinate system that moves with the superrotating wind frame, however, the team is able to extract detail from the images, identifying small-scale, turbulent features, spirals, and streaks. These complicated structures reflect dynamics in the clouds.

In addition to the thermal imaging, ultraviolet imaging is used to track Venus’s clouds and identify wind motions. Takeshi Horinouchi (Hokkaido University) presented on the surprising variety of motions these observations have revealed, from turbulent motions to planetary-scale waves. The ultraviolet observations also revealed an apparent asymmetry in wind speeds between Venus’s northern and southern hemispheres; Horinouchi suggests that this may be due to an asymmetric distribution of as-yet unidentified particles that absorb ultraviolet light. We clearly still have a lot to learn!

Joint Observations of Venus in 2020

Akatsuki won’t be alone next year! BepiColombo, a joint ESA/JAXA mission, will pass close to Venus in 2020 during a flyby. During this time, BepiColombo, Akatsuki, and ground-based telescopes will join their powers for a combined observational campaign of Venus.

Valeria Mangano (INAF-IAPS) was at today’s press conference to tell us more about BepiColombo’s role in this. BepiColombo is a Mercury magnetospheric orbiter — but on its way to Mercury, it will conduct two Venus flybys: one in October 2020 and one in August 2021. During the flybys, it will coordinate with Akatsuki to produce joint observations of Venus from multiple different viewing angles.

BepiColombo has two different components: ESA’s Mercury Planetary Orbiter (MPO) and JAXA’s Mercury Magnetospheric Orbiter (MMO). During the Venus flyby, 8 of 11 instruments will operate on MPO and 3 of 5 instruments will operate on MMO, measuring Venus’s atmosphere, tenuous exosphere, and its magnetosphere and plasma environment. The first flyby will be at 10,000 km altitude, and the second one will be just 1,000 km above Venus’s surface!

In addition to Akatsuki and BepiColombo, Earth-based telescopes like the Canada France Hawaii Telescope (CHFT) and the NASA Infrared Telescope Facility (IRTF) will be able to provide an additional angle during the coordinated campaign, explains Yeon Joo Lee (Technical University of Berlin). The multiple perspectives will enable global mapping of Venus’s atmospheric features.

Science at Venus

Last up, we heard from the theory side: Michael Way (NASA Goddard Institute for Space Studies) presented on modeling work exploring the possible habitability of ancient Venus. We think that early Venus conditions likely mirrored early conditions on Earth. By conducting a series of simulations with different topographies, land seed masses, etc., Way and collaborators explored the Venus’s atmospheric evolution over time to determine whether Venus very rapidly became the hostile environment it is today, or whether it may have been more welcoming for a long period of its history.

They find that conditions on Venus were likely very similar to those on Earth up until about 1 billion years ago. At that point, Way says, it appears that a catastrophic “intrusive volcanism” event of some kind occurred, in which magma traveled through the crust and led to resurfacing. This process released into the atmosphere carbon dioxide that was locked up in Venus’s surface, leading to the runaway greenhouse effect that turned the planet into the hellish world it is today. In this scenario, Venus could indeed have had a habitable surface for most of its history.

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EPEC Science Flash

Present your work in a fun and original way! You have exactly 180 seconds of time supported by one slide and/or small additional equipment.

I was intrigued by the above description of this Europlanet Early Career Network event, because it sounded very similar to 60-second Pop Talks — one of my favorite components of ComSciCon, a science communication workshop for grad students. How would the early-career planetary scientists who signed up for this do, trying to explain their research in a succinct (and hopefully accessible) way?

I dropped in for a while to find out; here are some very rapid takeaways! These researchers are working on:

• studying occultations. I learned something new: did you know that if you’re in the exact center of an occultation path, you might see what’s known as a “central flash”, caused by focusing of the background starlight by the foreground object’s atmosphere?
• exploring the properties of Mercury-analog matter in a laboratory
• the WISDOM GPR instrument on the Rosalind Franklin (previously called ExoMars) rover, which will be used to explore the underground structure of Mars using radar observations
• the conundrum of life on Mars … will we find evidence for (simple) life when we finally arrive at Mars?
• exploring Pluto’s atmosphere and aerosols via laboratory experiments.

One presentation was especially unique: Eleanor Armstrong (University College London, UK) gave a blind presentation, taking only 15 seconds to look at someone else’s slide and then give a presentation related to it. She absolutely killed the talk, pointing out that in most of the images on the slide, “science” is represented as a sterile process with no human involvement (“Here we have experiments apparently running themselves, and a completely uninhabited planetary base…”). Her doctoral research focuses on how scientists are represented in museums — something that can certainly stand improvement!

I really enjoyed attending this session and seeing scientists challenge themselves to explain their research succinctly and clearly — and I hope to see more programs encouraging this sort of development in the future! Shameless plug: if you’re a STEM grad student and want to push yourself to do the same, do consider checking out the AAS-sponsored ComSciCon workshop series; there are ComSciCon workshop events all across the U.S. (and one now in Canada), they’re all free or very low-cost to attend, and they’re a great way of learning more about effective science communication.

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Session: Ocean Worlds and Icy Moons

We’ve heard a lot about rocky bodies this week, but what’s going on with ocean and icy worlds? We stopped by the end of this session to catch a few updates.

Marc Rovira-Navarro (Utrecht University and TU Delft, the Netherlands) presented a new tool that can be used to model tides in subsurface oceans on icy moons. In particular, this tool allows researchers to explore the dissipation of tides in oceans that don’t have a uniform depth — because it’s likely, of course, that real oceans in our solar system and beyond are going to have varying seafloor topography. As an example, he demonstrated the use of this tool for modeling the suspected subsurface ocean below the southern pole of Saturn’s icy moon Enceladus.

Observations of Enceladus have captured plumes of ice grains and vapor coming from fractures near its southern pole — and analysis of these plumes have revealed evidence of volatile organic material. Nozair Khawaja (Free University Berlin and Heidelberg University, Germany) presented new work suggesting that Enceladus’s core may be an enormous factory for organic compounds, and this material can be efficiently transported from deep within the proposed subsurface ocean to the planet’s surface and expelled into space via the plume.

What are we seeing in observations of Jupiter’s icy Galilean moons from the Voyager flyby? Our best guess is that these moons are covered in a combination of water ice and salty ices. In order to better interpret these observations and future observations from missions like JUICE and Europa Clipper, Romain Cerubini (University of Bern, Switzerland) and collaborators are conducting laboratory experiments on salty ices — ices prepared from brines of NaCl and MgSO₄ that were flash-frozen — to characterize the particles that form.

Subsurface oceans on ice satellites may not be well-mixed. Teresa Wong (Westfälische Wilhelms-Universität Münster, Germany) asks whether layers can exist in these oceans — and if so, how long can they persist, and what implications might this have? Her work indicates that such layers aren’t stable, but when they exist, they can inhibit heat and material transport through the ocean. This would alter the dynamics of the ocean and how the properties at the seafloor relate to those at the icy shell at the top of the ocean.

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Unfortunately, we’re unable to attend the last day of the meeting — so with that, we’re officially signing off! Thanks, EPSC/DPS attendees, for sharing with us what’s going on in planetary science at the moment and what upcoming missions we can expect soon. We’re looking forward to seeing all the exciting results that come out of this field in the near future — and of course, we’re hoping we’ll get to publish it in AAS journals!

Editor’s note: We’re wrapping up a busy summer with one last conference: the EPSC-DPS joint meeting in Geneva, Switzerland. To celebrate the announcement of AAS Publishing’s new Planetary Science Journal, we’ll be bringing you some highlights from this planetary science conference all week!

Session: Leveraging Outreach in Planetary Defense

Communication about planetary defense efforts is a tricky game. Of course it’s important to share the information that scientists obtain about near-Earth asteroids and close approaches of small bodies from our solar system — but it’s also very easy for that information to take on a life of its own, leading to sensationalism and fear-mongering. We dropped in on this morning’s session on planetary defense outreach to learn more about its inherent challenges.

Patrick Michel (Observatoire de la Côte d’Azur, CNRS) pointed out an interesting problem: due to improvements in observational techniques, the number of newly detected near-Earth asteroids keeps increasing. As a result, reports of these objects enter into the news cycle more and more often — and to the public, this gives the appearance that the risk is inexplicably increasing.

To combat this effect, it’s important that scientists engage more effectively both with the media and with the public directly about planetary defense. According to Michel, the primary message should be that impact hazard is the least likely hazard, as compared to other natural disasters like tsunamis or earthquakes — and yet it’s also the only one that we have reasonable and feasible means to predict (by taking inventory of near-Earth objects) and mitigate (by developing and testing asteroid deflection tactics).

Conveniently, though interest in near-Earth asteroids is broad — for reasons of planetary defense, scientific study, resource mining, and more — all facets rely on gathering the same scientific information now. Understanding asteroid properties like composition, dynamics, response to impacts and stressors, etc., is a crucial first step, and communicating what we learn from this process will help to decrease misinformation about asteroid threats.

Speakers Regina Rudawska and Bernard Foing (ESA) and Phil Davis (NASA/JPL) described some of the ways that the U.S.’s and Europe’s major space agencies are working on planetary defense, and how this information is communicated.

According to a recent study, Davis told us, roughly 6 out of 10 Americans view planetary defense as a top priority. The interest is there — but people have a lot of questions, and it would be better if answers came from us, rather than from “killer asteroid” misinformed news stories. Davis manages several major websites for NASA, so his web experience informs his perspective. “We know what questions people are asking; Google tells us! We just need to answer them, and to make sure our answers get out there [on the internet].”

Both NASA and ESA are working on this through website development and production and dissemination of engaging visuals (think NASA/JPL’s stunning space tourism posters or ESA’s lovely space safety program posters, also seen at right). Other institutes, like the Lunar and Planetary Science Institute, are working on engaging the public via interactive means, said Christine Shupla. She described games and activities that provided a broader and more positive view of asteroids, to counteract the bad rap these objects usually get.

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Press Conference: Future Mission Updates

AIDA: DART and Hera

So, all that said, what are our major space agencies doing on the planetary defense front? Today’s press conference gave us an inside look at one major collaborative program: the Asteroid Impact and Deflection Assessment (AIDA) project. Patrick Michel (Observatoire de la Côte d’Azur, CNRS) opened by giving us an overview of the international program, which marks our first attempt to deliberately change the orbit of an asteroid (and learn as much as possible in the process!).

AIDA will target nearby asteroid Didymos, a binary asteroid (binaries account for ~15% of the asteroid population) made up of a primary body, Didymos A, that’s about 800 meters across and its moon, Didymos B, that is just 160 meters in diameter. Note that though Didymos is a near-Earth asteroid, it is not on a collision course with Earth; the goal of altering this asteroid’s orbit is purely for educational reasons, and not out of necessity!

The AIDA project consists of two major components:

1. NASA’s Double Asteroid Redirection Test (DART) mission, which will aim a kinetic impactor at Didymos’s smaller, secondary asteroid, attempting to alter its orbit; and
2. ESA’s follow-up Hera mission, which will arrive at the system a few years later and make detailed observations of Didymos, determining the consequences of DART’s impact.

While the most unique goal of the program is testing asteroid deflection tactics, there will be a number of other firsts! Didymos B will be the smallest asteroid we’ve ever studied, and this will also mark the first time we’ve used a radar to probe the subsurface structure of an asteroid.

Why was Didymos selected? Didymos B is roughly in the size range we worry about for planetary defense, so it’s a useful target to understand the response when a body of this size is struck. What’s more, the fact that this system is an eclipsing binary means that we can measure its orbital period very well using ground-based telescopes — and we’ll be able to use the same approach after DART’s impact to see exactly how the period changed.

So where does this mission stand? Nancy Chabot (Johns Hopkins Applied Physics Lab) reports that everything is on schedule for DART’s launch in July 2021, with impact occurring in September 2022.

The impact itself is a fascinating challenge. DART will be coming in at 6.6 km/s (that’s 14,800 mph!), and the Didymos system is a small target. In fact, DART won’t be able to distinguish between Didymos A and B until it’s within an hour of impact — yet it somehow needs to aim for the exact center of the tiny, 160-m moon! The DART team has addressed this challenge by equipping DART with a SMARTNav system — it will use its camera to autonomously distinguish between the two bodies, lock onto Didymos B, and aim itself at its center without any human intervention.

On its way in, DART will release a cubesat (a small satellite) with a camera that will observe the moment of impact. Important observations of the collision and the aftermath, however, will also come from ground-based telescopes on Earth — 11 million kilometers away.

So will this cause a spectacular deflection of the asteroid? Definitely not … watch the animation below for a rough idea of what we can expect. The goal is not to disrupt this asteroid or drastically alter its course, but rather to change its orbital period by a mere 10 minutes or so (that’s a ~1% change). Sounds minuscule, but that change of course is all that may be needed to deflect an asteroid past the Earth if we discover it while it’s still far enough away!

DART might seem like the main event of the AIDA project, but this mission will be greatly enhanced by follow-up observations after the dust has literally settled. Michael Küppers (European Space Astronomy Centre (ESA/ESAC) described plans for the Hera mission, the intended means of undertaking this follow-up.

Hera will be launched in 2024 and arrive at the Didymos system in early 2027. It will orbit around the system, taking images and doing detailed crater investigation as it spirals progressively closer. At the end of the mission, it will attempt to land either on the primary or the secondary asteroid (depending upon what we’ve learned about the bodies by that time).

Hera will carry two cubesats (small satellites) — the most advanced interplanetary cubesats yet. One of them will be responsible for conducting the first-ever radar subsurface exploration of an asteroid, which is sure to provide us with a wealth of information about this asteroid’s structure. All of the data Hera gathers will help us to better understand the system and how Didymos B responded to DART’s impact, further preparing us for the future possibility of undertaking a similar program in a case of planetary-defense necessity.

EnVision

Why are the Earth and Venus so different? Venus, Earth, and Mars are basically a Goldilocks story: though they may have started out similarly, Mars ended up too cold for life, Venus too hot, and the Earth just right. Colin Wilson (University of Oxford) introduced the EnVision mission, a proposed orbiter mission to Venus that will study its structure and atmosphere, helping us to understand what shaped Venus into the hostile environment it is today.

Venus is a relatively unexplored planet — though dozens of Venus missions were launched in the 1970s and early 1980s (including 10 successful or semi-successful landers, none of which lasted more than 2 hours on Venus’s extreme surface), there have not been many missions to Venus since. EnVision would therefore provide important insight that we’ve been lacking.

This orbiter would come equipped with instruments allowing it to image Venus at resolutions down to < 5m, measure magnetic fields, detect volcanic activity via thermal emission, measure subsurface structures down to 1 km in depth via radar, and map out Venus’s lithospheric/crust structure. It could also make detailed measurements of various species in Venus’s atmosphere.

EnVision’s goal is to address three main science themes:

• Activity: How geologically active is Venus today?
• History: How have Venus’s surface and interior evolved?
• Climate: How did Venus’s atmosphere become so hostile?

The EnVision mission hasn’t yet been approved, but it’s a finalist in ESA’s M5 Space Science mission competition. If selected, it would launch in 2032 and conduct its science mission 2035–2038. Keep an eye out for more developments from this project in the future!

Mars Sample Return

Like looking at long goals? Kelly Geelen (European Space Agency) rounded out the press conference with an overview of the proposed joint NASA/ESA Mars Sample Return mission, which would return the first sample from Mars to Earth in 2032.

This campaign has four distinct components:

1. The Mars 2020 rover collects samples and caches them, leaving them on Mars’s surface for later retrieval. (NASA)
2. A lander arrives on Mars’s surface in 2028 and collects the samples left behind, delivering them to an ascent rocket. The ascent rocket launches to a low Mars orbit in spring of 2029. (NASA)
3. An Earth return orbiter then captures the canisters with the sample, returning to Earth in 2031. (ESA)
4. The sample return canister, enclosed in an Earth re-entry module, arrives at Earth in spring 2032 and the sample is then received, curated, and investigated. (international)

This mission is still in the planning stages, and it’s clearly a huge cooperative effort. But Geelen hopes that in 10 years’ time we’ll have a sample getting ready to head back to us!

Editor’s note: We’re wrapping up a busy summer with one last conference: the EPSC-DPS joint meeting in Geneva, Switzerland. To celebrate the announcement of AAS Publishing’s new Planetary Science Journal, we’ll be bringing you some highlights from this planetary science conference all week!

Press Conference: Asteroid Sample Return Mission: Hayabusa2

It’s pretty exciting that, in recent years, we’ve been able to send spacecraft to directly explore a number of the small bodies in our solar system, learning more about these objects’ composition, formation, evolution — and even their role in the formation of life on Earth. Two of these recent missions, Hayabusa2 and OSIRIS-REx, are visiting nearby asteroids — and they have the added goal of returning samples of these asteroids to Earth. In today’s press conference, we got to hear more about one of these endeavors.

The Hayabusa2 mission follows on the heels of Hayabusa, a spacecraft developed by the Japan Aerospace Exploration Agency (JAXA) that, in 2003, traveled to small near-Earth asteroid 25143 Itokawa and returned a sample to Earth in 2010. Hayabusa2 hopes to build on that success, providing additional clues to the origin and evolution of the inner, terrestrial planets in our solar system, as well as to the origin of water and organic compounds — precursors to life — on Earth.

Like all missions that include actual contact with a solar-system body, Hayabusa2’s operations are incredibly complex. After launching in 2014 and arriving at its target — the asteroid 162173 Ryugu — in 2018, Hayabusa2 began a multi-step process to gather information about this primitive near-Earth asteroid. Several rovers were deployed to the asteroid, an impactor was fired at Ryugu’s surface, and the spacecraft completed two touchdowns, briefly tapping the asteroid’s surface before lifting off again.

So how’s the mission going so far? Makoto Yoshikawa (ISAS/JAXA) shared more about the impact experiment and Hayabusa2’s second touchdown.

In April 2019, Hayabusa2 deployed what is basically a space gun: a system that could fire a single 2.5-kg copper projectile into Ryugu’s surface at a speed of ~2 km/s (about 4,500 mph). After deploying a camera to watch, Hayabusa2 hid out of reach of debris and waited for the results. We expected the formation of a crater of perhaps 2 or 3 meters — but the actual crater that formed is larger than 10 meters! This suggests that Ryugu’s material is of lower density and higher porosity than we thought.

The next step was to sample Ryugu’s subsurface material, kicked up by the impact and deposited around the crater region. Hayabusa2’s second touchdown occurred roughly 20 meters from the crater site, giving the spacecraft an opportunity to gather a quick sample of the ejected material before returning to orbit. We don’t yet know how much material was gathered — and, in fact, we won’t know until we open the sample container once it’s returned to Earth at the end of next year! — but we don’t need much: all the sample analysis can be completed if we’ve gathered as little as 0.1 grams.

Even before we consider the upcoming sample return, we’ve already learned a lot about Ryugu from Hayabusa2’s imaging observations! Antonella Barucci (Observatoire de Paris) detailed how advanced statistics have allowed us to explore the reflected light from Ryugu, mapping out the asteroid’s surface and gathering detailed information from its spectrum. The spectral variation on Ryugu’s surface reveals information about space weathering and the grains of its surface material (its regolith). It also provides constraints on how this rubble-pile asteroid formed, reaccumulating from the wreckage of its parent asteroid.

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Changing gears, Franck Marchis (SETI Institute) discussed recent work that will advance another asteroid mission: Lucy. NASA’s Lucy space probe will launch in 2021 and journey to Jupiter’s trojan asteroids, likely flying by six of them on its tour. Before the spacecraft undertakes this voyage, however, it would be helpful for us to learn everything we can about its targets. This, according to Marchis, is where eVscope can be useful.

Unistellar’s enhanced vision telescope (eVscope) is a backyard telescope that began as a kickstarter project and has now gone into production. This unique telescope is designed to reduce the entry barrier to amateur astronomical observation, making it easy for anyone to observe the night sky. The telescope is highly portable, easily and quickly set up and initiated, and accumulates light over short periods rather than passing it directly through to an eyepiece, providing an immediate deeper view.

Perhaps most intriguing of eVscope’s features is the fact that it comes with an app that allows the user to connect to world-wide observing campaigns. The app is able to send out alerts about upcoming transient events (perhaps an asteroid flyby, a supernova, or a comet) and, if the user accepts the observation request, it can transmit instructions to automatically point the user’s eVscope to observe the event. The observations from all users are then combined and shared, allowing scientists to build a much more complete picture of the event than could be obtained through a single observation. The added benefit of this eVscope brand of citizen science is that the network of amateur astronomers making observations are all doing so with the exact same equipment, vastly simplifying the process of combining the data.

One of the ways in which we can take advantage of this benefit is with occultations — events where a nearby, solar-system body passes in front of a distant star, briefly blocking the star’s light and allowing us to learn more about the properties of the occulting object. More than 40 occultations will be observable per day with the eVscope network, according to Marchis, and if as many people participate as they hope, eVscopes could provide an ideal world-wide network for hunting down occultations.

As a proof of concept, the eVscope team has tested this in Oman by using these telescopes to make the first occultation observation of asteroid 21900 Orus, one of the Lucy mission’s upcoming targets. To catch a glimpse of Orus’s shadow as it passed in front of a star, teams were stationed at different locations near the predicted path the shadow would take. The successful observation of the occultation by one team (and the non-observation by the other!) confirmed Orus’s orbit and provided an independent measurement of its size.

The eVscope team plans to do this again the next time Orus passes in front of a background star, on 4 November — this time with more people and more telescopes involved. From this, Marchis hopes that we’ll be able to learn even more about the asteroid — from its size and shape to whether it has any moons — thereby improving science planning for Lucy’s flyby.

Editor’s note: We’re wrapping up a busy summer with one last conference: the EPSC-DPS joint meeting in Geneva, Switzerland. To celebrate the announcement of AAS Publishing’s new Planetary Science Journal, we’ll be bringing you some highlights from this planetary science conference all week!

DPS Kuiper Prize Lecture: Inside the Moon Fifty Years After Apollo

The DPS’s 2019 Gerard P. Kuiper Prize for outstanding contributions to the field of planetary science has been awarded to Maria Zuber (MIT) “for her contributions to advancements in geophysics, planetary gravity mapping, and laser altimetry.”

Zuber opened her prize lecture by pointing out how much we didn’t know about the Moon before the first lunar landing fifty years ago. We weren’t sure what to expect regarding the Moon’s structure and composition, nor how that could influence the landing — was the lunar dust so soft and thick that it would swallow the lander like quicksand? Fortunately, none of our uncertainties about the Moon derailed the landing — and with research since then, we now much better understand the lunar crust and interior.

An important means by which we’ve learned about the Moon’s structure is the Gravity Recovery and Interior Laboratory (GRAIL) mission, led by Zuber, which lasted from 2011 to 2012. By flying two spacecraft close over the Moon’s surface and measuring minute changes in the distance between them, the GRAIL team was able to construct an extremely detailed map of the Moon’s gravitational field, thereby revealing its internal geological structure.

GRAIL’s data produced many important results, including detailed maps of the lunar crust and lithosphere, insight into the subsurface structure of the Moon’s 74 impact basins with diameters greater than 200 km, and constraints on the presence of a core at the Moon’s center. One of the biggest surprises from the mission, says Zuber, was the discovery of the Moon’s fractured crust: even beneath the lunar surface, the Moon’s crust is broken up. GRAIL’s insights provide a record of massive impacts in the inner solar system early in its history, as well as a look at some of the formation processes that were at work during the Moon’s birth.

Could a mission like GRAIL be applied to other solar-system bodies in the future? In order to build its detailed maps, GRAIL dropped to within a handful of kilometers of the lunar surface — a feat that wouldn’t be possible around any of our solar system’s planets. If we tried that with a spacecraft around Mercury, for instance, the thermal radiation would destroy the spacecraft.

But perhaps a mission like GRAIL could be used to map other satellites in our solar system, such as Jupiter’s Galilean moons? Fifty years after we first landed on the Moon, it’s exciting to see how much we’ve learned since then — as well as how much we still stand to learn, both about Earth’s only natural satellite and about other, similar bodies in our solar system.

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DPS Urey Prize Lecture: New Horizons: Exploration of Distant Worlds in the Kuiper Belt

In a transition from nearby bodies, our next speaker took us to the outer reaches of the solar system with the New Horizons mission. Kelsi Singer (Southwest Research Institute), this year’s DPS Urey Prize winner for outstanding achievement in planetary research by a young scientist, gave us an update on this intrepid little explorer’s latest adventures.

New Horizons launched in January 2006, and after a gravity assist from Jupiter, it arrived at the Pluto system in July of 2015. After flying by Pluto and taking detailed images of the former planet and its moon Charon, New Horizons then continued onward, later buzzing the Kuiper belt object 2014 MU₆₉ in January of this year.

New Horizons’s images have been nothing short of spectacular (see, for instance, the incredible detail in the image of Pluto that’s on The Planetary Science Journal‘s cover and shown at the top of the page. No seriously, check out the high-res version. Zoom in. It’s unreal!). Singer showed us some of the images of Charon that reveal a whole host of features: a mountain surrounded by a moat, ropey structures from icy volcanic eruptions, wide flat plains. All of these features are clues that can be used to piece together Charon’s past — in this case indicating that the moon was resurfaced long ago, and it has been sitting gathering crater impacts since.

The craters, however, raise another new puzzle. Singer highlighted the lack of small (< 10 km in diameter) craters relative to what we expected to see, and showed the same missing-crater trend in New Horizons’s images of MU_69. As these craters should have been caused by Kuiper belt objects of < 1 km in size, their dearth suggests there may be far fewer small Kuiper belt objects than we thought. This suggests one of the following:

1. Fewer small objects tend to form in the Kuiper belt than we initially thought, or
2. Small objects do form, but they somehow get preferentially removed.

Either explanation would have important implications for how our solar system formed and evolved, and more observations like those of New Horizons will prove invaluable in puzzling out this mystery!

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EPSC Farinella Prize Lectures: Completing the Inventory of the Solar System

The 2019 Farinella prize was awarded for the first time to a team of people rather than to a single individual. Scott Sheppard (Carnegie Institution for Science) and Chad Trujillo (Northern Arizona University) jointly received the award for their collaborative work observationally characterizing the Kuiper belt and Neptune-trojan population.

Neptune Trojans

What are trojans? These small celestial bodies (mostly asteroids) orbit the Sun along the same path as the planet with which they’re associated, but they either lead 60° ahead or trail 60° behind the planet at so-called stable Lagrange points. The Jovian trojans are perhaps the most well known — there are more than 7,000 known asteroids that move in these two clumps ahead of and behind Jupiter. But other planets have trojans as well: we’ve spotted four around Mars, a pair around Uranus, and even one around Earth.

Neptune, at current count, has 23 known — and Sheppard and Trujillo have discovered a number of them. When the duo first started looking for Neptune trojans, it was unclear whether the majority of these bodies would be on high- or low-inclination orbits. Sheppard and Trujillo’s work, however, suggests that the vast majority of Neptune trojans are high-inclination (high-inclination orbits dominate by a ratio of 4 to 1!). This puffed-up population points to an interesting origin: they were likely captured by Neptune from elsewhere in the solar system during a period of migration for the giant planets.

As Neptune trojans share a lot of similar properties with Jupiter trojans, we can guess that these two populations may have similar histories. With any luck, we’ll be able to test this theory soon: in 2021, NASA plans to launch a space probe called Lucy to visit six different Jupiter trojans. This mission is sure to reveal more about these intriguing bodies.

Extreme TNOs

What other unexpected objects lurk deep in the outer reaches of our solar system? The minor planet Sedna, which lies at a distance of about 86 AU (three times the distance to Neptune), poses an interesting riddle with its extremely eccentric orbit. With a number of plausible formation scenarios proposed — each with different implications for the solar system’s formation environment and subsequent evolution — Sheppard and Trujillo determined that the best way to understand Sedna was to find more bodies like it!

Thus began an extensive deep solar system survey, using the CTIO 4-m telescope with the Dark Energy Camera in the southern hemisphere and the Subaru 8-m telescope with HyperSuprimeCam in the northern hemisphere. This large uniform survey has covered 3,000 square degrees, or about 20% of the sky, to 24th magnitude — and through this search, Sheppard and Trujillo have discovered roughly 80% of the known objects beyond 60 AU.

The survey revealed two Sedna-like objects — 2012 VP₁₁₃, a distant minor planet with a whopping perihelion of ~80 AU; and “The Goblin”, 2015 TG₃₈₇, which has an orbital period of more than 11,000 years — as well as a number of additional extreme trans-Neptunian objects (eTNOs), bodies with perihelions of >40 AU and semimajor axes of >150 AU. Intriguingly, a pattern appeared in the data: all of the orbits of the eTNOs appeared to cluster in approximate alignment, rather than being randomly distributed around the Sun.

Could a distant, massive, as-yet undiscovered planet in our solar system be influencing these bodies’ orbits, shepherding them into a cluster? That’s what Sheppard and Trujillo proposed, and this theory has been supported by additional eTNOs that have been found since.

The distant-object discoveries continue to pour in — two of the latest are FarOut (2018 VG₁₈), which currently lies at ~120 AU and FarFarOut (no designation yet), which is estimated to be at a whopping near-140-AU distance! These continued discoveries bring us ever closer to understanding our outer solar system — and possibly finding any hidden planets that may lurk there.

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Splinter Session: Status Report on Planning for the Next Planetary Science Decadal Survey

What’s planned for the next decade of planetary science? That’s exactly what needs to be decided via the next Planetary Science Decadal Survey, a review process in which the community comes together to define and prioritize the key scientific questions that could potentially be addressed in the next decade, as well as prioritize the possible missions that might address these questions.

You may have thought we just went through this whole process recently — but it turns out planetary science has its own overview, which occurs completely independently of the astronomy decadal survey (Astro 2020 is currently underway). The planetary science decadal is offset by a few years, so the field is only just starting to gear up for this review.

In this session, David Smith (Space Studies Board, NAS Engineering and Medicine), Lori Glaze (director of NASA’s Science Mission Directorate’s Planetary Science Division), and Linda French (program director at NSF) were on hand to discuss plans and processes for the upcoming planetary science decadal. The estimated timeline, as it currently stands:

• 2/2020: Opening of the website through which scientists can submit white papers, short papers that describe important science questions, missions, or the state of the field
• 5/2020: White paper submission deadline
• 6/2020: The decadal survey committee and panels, made up of members of the planetary science community, begin meetings to consider the white papers and mission studies
• 10/2021: The survey committee compiles their recommendations into the first draft of a report with recommendations for the coming decade
• 3/2022: The final survey report is released

Keep an eye out next year for the start of this important process!

Greetings from the EPSC-DPS meeting in Geneva, Switzerland! We’re wrapping up a busy summer of conferences with this meeting, jointly hosted by the European Planetary Science Congress and the American Astronomical Society’s Division for Planetary Sciences. The normal posting schedule for AAS Nova will resume next week.

Why are we here? AAS publishing recently announced a brand new journal, the Planetary Science Journal. In honor of this exciting news, we’re here at EPSC-DPS 2019 to celebrate the latest research from the field of planetary science (and to bring you some of the highlights)!

This year marks the third joint meeting between EPSC and DPS — and with more than 1,500 participants from around the world registered, this promises to be the largest gathering of planetary scientists held in Europe to date! More than 1,000 oral presentations and nearly as many posters are scheduled over the course of this week, with presentations broken into parallel sessions spanning six broad topics:

• Terrestrial planets
• Outer planet systems
• Missions, instrumentation, techniques
• Small bodies (comets, Kuiper-belt objects, rings, asteroids, meteorites, dust)
• Exoplanets and origins
• Outreach, diversity, astronomy

We’re looking forward to hearing about some of the latest news from this community!