An early morning launch is planned for the Lucy spacecraft, the first space mission to study Jupiter’s Trojan asteroids. Tomorrow, October 16 at 5:34 a.m. EDT is the first day and time in Lucy’s 21-day launch window, and current weather conditions show a 90% chance of favorable conditions for liftoff from Cape Canaveral Space Force Station in Florida. The launch window remains open for 75 minutes.
Lucy will embark on a 12-year mission to explore the “fossils of planet formation,” Jupiter’s Trojan asteroid swarms. This mission provides the first opportunity to observe these intriguing objects close-up.
In astronomy, comets and asteroids are defined very differently. Comets have a “nucleus,” usually made of ice and dust, and a tail when they get near the sun, which is the nucleus material shedding off from the comet itself. Asteroids, on the other hand, are small balls of rock orbiting the sun. Occasionally though, some objects meet the criteria to be both an asteroid and a comet – and a team from the Planetary Science Institute (PSI) think they have found a new one.
How do you track an asteroid that hit the Earth over 60 million years ago? By using a combination of geology and computer simulations, at least according to a team of scientists from the Southwest Research Institute (SwRI). Those methods might have let them solve a long-standing mystery of both archeology and astronomy – where did the asteroid that killed the dinosaurs come from?
If asked to pick what color asteroids in the asteroid belt would be, red is likely not one that would come to mind for most people. But that is exactly the color of two new asteroids found by Hasegawa Sunao of JAXA and an international team of researchers. The catch is the objects don’t appear to be from the asteroid belt at all, but are most likely Trans-Neptunian objects that were somehow transported into what is commonly thought of as the asteroid belt. How exactly they got there is still up for debate.
Astronomers have painstakingly built models of the asteroid population, and those models predict that there will be ~1 km sized asteroids that orbit closer to the Sun than Venus does. The problem is, nobody’s been able to find one. Until now.
Astronomers working with the Zwicky Transient Facility say they’ve finally found one. But this one’s bigger, at about 2 km. If its existence can be confirmed, then asteroid population models may have to be updated.
In March of 2015, NASA’s Dawn mission arrived around Ceres, a protoplanet that is the largest object in the Asteroid Belt. Along with Vesta, the Dawn mission seeks to characterize the conditions and processes of the early Solar System by studying some of its oldest objects. One thing Dawn has determined since its arrival is that water-bearing minerals are widespread on Ceres, an indication that the protoplanet once had a global ocean.
Naturally, this has raised many questions, such as what happened to this ocean, and could Ceres still have water today? Towards this end, the Dawn mission team recently conducted two studies that shed some light on these questions. Whereas the former used gravity measurements to characterize the interior of the protoplanet, the latter sought to determine its interior structure by studying its topography.
Together, the team relied on gravity measurements of the protoplanet, which the Dawn probe has been collecting since it established orbit around Ceres. Using the Deep Space Network to track small changes in the spacecraft’s orbit, Ermakov and his colleagues were able to conduct shape and gravity data measurements of Ceres to determine the internal structure and composition.
What they found was that Ceres shows signs of being geologically active; if not today, than certainly in the recent past. This is indicated by the presence of three craters – Occator, Kerwan and Yalode – and Ceres’ single tall mountain, Ahuna Mons. All of these are associated with “gravity anomalies”, which refers to discrepancies between the way scientists have modeled Ceres’ gravity and what Dawn observed in these four locations.
The team concluded that these four features and other outstanding geological formations, are therefore indications of cryovolcanism or subsurface structures. What’s more, they determined that the crust’s density was relatively low, being closer to that of ice than solid rock. This, however, was inconsistent with a previous study performed by Dawn guest investigator Michael Bland of the U.S. Geological Survey.
Bland’s study, which was published in Nature Geoscience back in 2016, indicated that ice is not likely to be the dominant component of Ceres strong crust, on a count of it being too soft. Naturally, this raises the question of how the crust could be light as ice in terms of density, but also much stronger. To answer this, the second team attempted to model how Ceres’ surface evolved over time.
Their study, titled “The Interior Structure of Ceres as Revealed by Surface Topography and Gravity“, was published in the journal Earth and Planetary Science Letters. Led by Roger Fu, an assistant professor with the Department of Earth, Atmospheric and Planetary Sciences at MIT, this team consisted of members from Virginia Tech, Caltech, the Southwest Research Institute (SwRI), the US Geological Survey, and the INAF.
Together, they investigated the strength and composition of Ceres’ crust and deeper interior by studying the dwarf planet’s topography. By modeling how the protoplanet’s crust flows, Fu and colleagues determined that it is likely a mixture of ice, salts, rock, and likely clathrate hydrate. This type of structure, which is composed of a gas molecule surrounded by water molecules, is 100 to 1,000 times stronger than water ice.
This high-strength crust, they theorize, could rest on a softer layer that contains some liquid. This would have allowed Ceres’ topography to deform over time, smoothing down features that were once more pronounced. It would also account for its possible ancient ocean, which would have frozen and become bound up with the crust. Nevertheless, some of its water would still exist in a liquid state underneath the surface.
This theory is consistent with several thermal evolution models which were published before the Dawn mission arrived at Ceres. These models contend that Ceres’ interior contains liquid water, similar to what has been found on Jupiter’s moon Europa and Saturn’s moon Enceladus. But in Ceres’ case, this liquid could be what is left over from its ancient ocean rather than the result of present-day geological activity in the interior.
Taken together, these studies indicate that Ceres has had a long and turbulent history. While the first study found that Ceres’ crust is a mixture of ice, salts and hydrated materials – which represents most of its ancient ocean – the second study suggests there is a softer layer beneath Ceres’ rigid surface crust, which could be the signature of residual liquid left over from the ocean.
As Julie Castillo-Rogez, the Dawn project scientist at JPL and a co-author on both studies, explained, “More and more, we are learning that Ceres is a complex, dynamic world that may have hosted a lot of liquid water in the past, and may still have some underground.”
On October 19, 2017, NASA announced that the Dawn mission would be extended until its fuel runs out, which is expected to happen in the latter half of 2018. This extension means that the Dawn probe will be in orbit around Ceres as it goes through perihelion in April 2018. At this time, surface ice will start to evaporate to form a transient atmosphere around the body.
During this period and long after, the spacecraft is likely to remain in a stable orbit around Ceres, where it will continue to send back information on this protoplanet/large asteroid. What it teaches us will also go a long way towards informing our understanding of the early Solar System and how it evolved over the past few billion years.
In the future, it is possible that a mission will be sent to Ceres that is capable of landing on its surface and exploring its topography directly. With any luck, future missions will also be able to explore the interior of Ceres, and other “ocean worlds” like Europa and Enceladus, and find out what lurks beneath their icy surfaces!
According to current estimates, there could be as many as 100 billion planets in the Milky Way Galaxy alone. Unfortunately, finding evidence of these planets is tough, time-consuming work. For the most part, astronomers are forced to rely on indirect methods that measure dips in a star’s brightness (the Transit Method) of Doppler measurements of the star’s own motion (the Radial Velocity Method).
Direct imaging is very difficult because of the cancelling effect stars have, where their brightness makes it difficult to spot planets orbiting them. Luckily a new study led by the Infrared Processing and Analysis Center (IPAC) at Caltech has determined that there may be a shortcut to finding exoplanets using direct imaging. The solution, they claim, is to look for systems with a circumstellar debris disk, for they are sure to have at least one giant planet.
For the sake of this study, Dr. Meshkat and her colleagues examined data on 130 different single-star systems with debris disks, which they then compared to 277 stars that do not appear to host disks. These stars were all observed by NASA’s Spitzer Space Telescope and were all relatively young in age (less than 1 billion years). Of these 130 systems, 100 had previously been studied for the sake of finding exoplanets.
Dr. Meshkat and her team then followed up on the remaining 30 systems using data from the W.M. Keck Observatory in Hawaii and the European Southern Observatory’s (ESO) Very Large Telescope (VLT) in Chile. While they did not detect any new planets in these systems, their examinations helped characterize the abundance of planets in systems that had disks.
What they found was that young stars with debris disks are more likely to also have giant exoplanets with wide orbits than those that do not. These planets were also likely to have five times the mass of Jupiter, thus making them “Super-Jupiters”. As Dr. Meshkat explained in a recent NASA press release, this study will be of assistance when it comes time for exoplanet-hunters to select their targets:
“Our research is important for how future missions will plan which stars to observe. Many planets that have been found through direct imaging have been in systems that had debris disks, and now we know the dust could be indicators of undiscovered worlds.”
This study, which was the largest examination of stars with dusty debris disks, also provided the best evidence to date that giant planets are responsible for keeping debris disks in check. While the research did not directly resolve why the presence of a giant planet would cause debris disks to form, the authors indicate that their results are consistent with predictions that debris disks are the products of giant planets stirring up and causing dust collisions.
In other words, they believe that the gravity of a giant planet would cause planestimals to collide, thus preventing them from forming additional planets. As study co-author Dimitri Mawet, who is also a JPL senior research scientist, explained:
“It’s possible we don’t find small planets in these systems because, early on, these massive bodies destroyed the building blocks of rocky planets, sending them smashing into each other at high speeds instead of gently combining.”
Within the Solar System, the giant planets create debris belts of sorts. For example, between Mars and Jupiter, you have the Main Asteroid Belt, while beyond Neptune lies the Kuiper Belt. Many of the systems examined in this study also have two belts, though they are significantly younger than the Solar System’s own belts – roughly 1 billion years old compared to 4.5 billion years old.
One of the systems examined in the study was Beta Pictoris, a system that has a debris disk, comets, and one confirmed exoplanet. This planet, designated Beta Pictoris b, which has 7 Jupiter masses and orbits the star at a distance of 9 AUs – i.e. nine times the distance between the Earth and the Sun. This system has been directly imaged by astronomers in the past using ground-based telescopes.
Interestingly enough, astronomers predicted the existence of this exoplanet well before it was confirmed, based on the presence and structure of the system’s debris disk. Another system that was studied was HR8799, a system with a debris disk that has two prominent dust belts. In these sorts of systems, the presence of more giant planets is inferred based on the need for these dust belts to be maintained.
This is believed to be case for our own Solar System, where 4 billion years ago, the giant planets diverted passing comets towards the Sun. This resulted in the Late Heavy Bombardment, where the inner planets were subject to countless impacts that are still visible today. Scientists also believe that it was during this period that the migrations of Jupiter, Saturn, Uranus and Neptune deflected dust and small bodies to form the Kuiper Belt and Asteroid Belt.
Dr. Meshkat and her team also noted that the systems they examined contained much more dust than our Solar System, which could be attributable to their differences in age. In the case of systems that are around 1 billion years old, the increased presence of dust could be the result of small bodies that have not yet formed larger bodies colliding. From this, it can be inferred that our Solar System was once much dustier as well.
However, the authors note is also possible that the systems they observed – which have one giant planet and a debris disk – may contain more planets that simply have not been discovered yet. In the end, they concede that more data is needed before these results can be considered conclusive. But in the meantime, this study could serve as an guide as to where exoplanets might be found.
“By showing astronomers where future missions such as NASA’s James Webb Space Telescope have their best chance to find giant exoplanets, this research paves the way to future discoveries.”
In addition, this study could help inform our own understanding of how the Solar System evolved over the course of billions of years. For some time, astronomers have been debating whether or not planets like Jupiter migrated to their current positions, and how this affected the Solar System’s evolution. And there continues to be debate about how the Main Belt formed (i.e. empty of full).
Last, but not least, it could inform future surveys, letting astronomers know which star systems are developing along the same lines as our own did, billions of years ago. Wherever star systems have debris disks, they an infer the presence of a particularly massive gas giant. And where they have a disk with two prominent dust belts, they can infer that it too will become a system containing many planets and and two belts.
The latest discovery was made by a team of international astronomers led by the Max Planck Institute for Solar System Research. Using Hubble, they spotted a unique object in the Main Asteroid Belt – a binary asteroid known as 288P – which also behaves like a comet. According to the team’s study, this binary asteroid experiences sublimation as it nears the Sun, which causes comet-like tails to form.
Using the Hubble telescope, the team first observed 288P in September 2016, when it was making its closest approach to Earth. The images they took revealed that this object was not a single asteroid, but two asteroids of similar size and mass that orbit each other at a distance of about 100 km. Beyond that, the team also noted some ongoing activity in the binary system that was unexpected.
As Jessica Agarwal explained in a Hubble press statement, this makes 288P the first known binary asteroid that is also classified as a main-belt comet. “We detected strong indications of the sublimation of water ice due to the increased solar heating – similar to how the tail of a comet is created,” she said. In addition to being a pleasant surprise, these findings are also highly significant when it comes to the study of the Solar System.
Since only a few objects of this type are known, 288P is an extremely important target for future asteroid studies. The various features of 288P also make it unique among the few known wide asteroid binaries in the Solar System. Basically, other binary asteroids that have been observed orbited closer together, were different in size and mass, had less eccentric orbits, and did not form comet-like tails.
The observed activity of 288P also revealed a great deal about the binary asteroids past. From their observations, the team concluded that 288P has existed as a binary system for the past 5000 years and must have accumulated ice since the earliest periods of the Solar System. As Agarwal explained:
“Surface ice cannot survive in the asteroid belt for the age of the Solar System but can be protected for billions of years by a refractory dust mantle, only a few meters thick… The most probable formation scenario of 288P is a breakup due to fast rotation. After that, the two fragments may have been moved further apart by sublimation torques.”
Naturally, there are many unresolved questions about 288P, most of which stem from its unique behavior. Given that it is so different from other binary asteroids, scientists are forced to wonder if it merely coincidental that it presents such unique properties. And given that it was found largely by chance, it is unlikely that any other binaries that have similar properties will be found anytime soon.
“We need more theoretical and observational work, as well as more objects similar to 288P, to find an answer to this question,” said Agarwal. In the meantime, this unique binary asteroid is sure to provide astronomers with many interesting opportunities to study the origin and evolution of asteroids orbiting between Mars and Jupiter.
In particular, the study of those asteroids that show comet-like activity (aka. main-belt comets) is crucial to our understanding of how the Solar System formed and evolved. According to contrasting theories of its formation, the Asteroid Belt is either populated by planetesimals that failed to become a planet, or began empty and gradually filled with planetesimals over time.
In either case, studying its current population can tell us much about how the planets formed billions of years ago, and how water was distributed throughout the Solar System afterwards. This, in turn, is crucial to determining how and where life began to emerge on Earth, and perhaps elsewhere!
Be sure to check out this animation of the 288P binary asteroid too, courtesy of the ESA and Hubble:
By popular request, Isaac Arthur and I have teamed up again to bring you a vision of the future of human space exploration. This time, we bring you practical construction tips from a pair of Type 2 Civilization engineers.
To make this collaboration even better, we’ve teamed up with two artists, Kevin Gill and Sergio Botero. They’re going to help create some special art, just for this episode, to help show what some of these megaprojects might look like.
As the single-largest body in the Asteroid Belt, Ceres has long been a source of fascination to astronomers. In addition to being the only asteroid large enough to become rounded under its own gravity, it is also the only minor planet to be found within the orbit of Neptune. And with the arrival of the Dawn probe around Ceres in March of 2015, we have been treated to a steady stream of scientific finds about this protoplanet.
The latest find, which has come as something of a surprise, has to do with the composition of the planet. Contrary to what was previously suspected, new evidence shows that Ceres has large deposits of water ice near its surface. This and other evidence suggests that beneath its rocky, icy surface, Ceres has deposits of liquid water that could have played a major role in its evolution.
This evidence were presented at the 2016 American Geophysical Union meeting, which kicked off on Monday, Dec. 12th, in San Fransisco. Amid the thousands of seminars that detailed the biggest findings made during the past year in the fields of space and Earth science – which included updates from the Curiosity mission – members of the Dawn mission team shared the results of their research, which were recently published in Science.
In short, the GRaND instrument detected high levels of hydrogen in Ceres’ uppermost structure (10% by weight), which appeared most prominently around the mid-latitudes. These readings were consistent with broad expanses of water ice. The GRaND data also showed that rather than consisting of a solid ice layer, the ice was likely to take the form of a porous mixture of rocky materials (in which ice fills the pores).
Previously, ice was thought to only exist within certain cratered regions on Ceres, and was thought to be the result of impacts that deposited water ice over the course of Ceres’ long history. But as Thomas Prettyman – the principal investigator of Dawn’s GRaND instrument – said in a NASA press release, scientists are now rethinking this position:
“On Ceres, ice is not just localized to a few craters. It’s everywhere, and nearer to the surface with higher latitudes. These results confirm predictions made nearly three decades ago that ice can survive for billions of years just beneath the surface of Ceres. The evidence strengthens the case for the presence of near-surface water ice on other main belt asteroids.”
The concentrations of iron, potassium and carbon detected by the GRaND instrument also supports the theory that Ceres’ surface was altered by liquid water in the interior. Basically, scientists theorize that the decay of radioactive elements within Ceres created enough heat to cause the protoplanet’s structure to differentiate between a rocky interior and icy outer shell – which also allowed minerals like those observed to be deposited in the surface.
Similarly, a second study produced by researchers from the Max Planck Institute for Solar Research examined hundreds of permanently-shadowed craters located in Ceres’ northern hemisphere. According to this study, which appeared recently in Nature Astronomy, these craters are “cold traps”, where temperatures drop to less than 11o K (-163 °C; -260 °F), thus preventing all but the tiniest amounts of ice from turning into vapor and escaping.
Within ten of these craters, the researcher team found deposits of bright material, reminiscent to what Dawn spotted in the Occator Crater. And in one that was partially sunlit, Dawn’s infrared mapping spectrometer confirmed the presence of ice. This suggests that water ice is being stored in Ceres darker craters in a way that is similar to what has been observed around the polar regions of both Mercury and the Moon.
Where this water came from (i.e. whether or not it was deposited by meteors) remains something of a mystery. But regardless, it shows that water molecules on Ceres could be moving from warmer mid-latitudes to the colder, darker polar regions. This lends further weight to the theory that Ceres might have a tenuous water vapor atmosphere, which was suggested back in 2012-13 based on evidence obtained by the Herschel Space Observatory.
All of this adds up to Ceres being a watery and geologically active protoplanet, one which could hold clues as to how life existed billions of years ago. As Carol Raymond, deputy principal investigator of the Dawn mission, also explained in the NASA press release:
“These studies support the idea that ice separated from rock early in Ceres’ history, forming an ice-rich crustal layer, and that ice has remained near the surface over the history of the solar system. By finding bodies that were water-rich in the distant past, we can discover clues as to where life may have existed in the early solar system.”
Back in July Dawn began its extended mission phase, which consists of it conducting several more orbits of Ceres. At present, it is flying in an elliptical orbit at a distance of more than 7,200 km (4,500 mi) from the protoplanet. The spacecraft is expected to operate until 2017, remaining a perpetual satellite of Ceres until the end.