All right, sure – there are a lot of asteroids that don’t hit us. And of course quite a few that do… Earth is impacted by around 100 tons of space debris every day (although that oft-stated estimate is still being researched.) But on March 10, 2015, a 12–28 meter asteroid dubbed 2015 ET cosmically “just missed us,” zipping past Earth at 0.3 lunar distances – 115,200 kilometers, or 71, 580 miles.*
The video above shows the passage of 2015 ET across the sky on the night of March 11–12, tracked on camera from the Crni Vrh Observatory in Slovenia. It’s a time-lapse video (the time is noted along the bottom) so the effect is really neat to watch the asteroid “racing along” in front of the stars… but then, it was traveling a relative 12.4 km/second!
UPDATE 3/14: As it turns out the object in the video above is not 2015 ET; it is a still-undesignated NEO. (My original source had noted this incorrectly as well.) Regardless, it was an almost equally close pass not 24 hours after 2015 ET’s! Double tap. (ht to Gerald in the comments.) UPDATE #2: The designation for the object above is now 2015 EO6.
The slim crescent of Ceres smiles back as the dwarf planet awaits the arrival of an emissary from Earth. This image was taken by NASA’s Dawn spacecraft on March 1, 2015, just a few days before the mission achieved orbit around the dwarf planet. Because of its angle of approach (see video above) Dawn saw Ceres from its backside, which from its perspective, was mostly in darkness. Credit: NASA/JPL
Dawn’s approach and trajectory as it begins its orbital “dance” with Ceres. As you watch, note the timeline at upper right.
Dawn made it! After a 14-month tour of the asteroid Vesta and 2 1/2 years en route to Ceres, the spacecraft felt the gentle tug of Ceres gravity and slipped into orbit around the dwarf planet at 6:39 a.m. (CST) Friday morning.
“We feel exhilarated,” said lead researcher Chris Russell at the University of California, Los Angeles, after Dawn radioed back the good news.
Not only is this humankind’s first probe to orbit a dwarf planet, Dawn is the only spacecraft to fly missions to two different planetary bodies. Dawn’s initial orbit places it 38,000 miles (61,000 km) from Ceres with a view of the opposite side of Ceres from the Sun. That’s why we’ll be seeing photos of the dwarf planet as a crescent for the time being. If you watch the video, you’ll notice that Dawn won’t see Ceres’ fully sunlit hemisphere until early-mid April.
Dawn’s spiral descent from survey orbit to the high altitude mapping orbit. The trajectory progresses from blue to red over the course of the six weeks. The red dashed segments are where the spacecraft is not thrusting with its ion propulsion system. Credit: NASA/JPL
The spacecraft will spend the next month gradually spiraling down to Ceres to reach its “survey orbit” of 2,730 miles in April. From there it will train its science camera and visible and infrared mapping spectrometer to gather pictures and data. The leisurely pace of the orbit will allow Dawn to spend more than 37 hours examining Ceres’ dayside per revolution. NASA will continue to lower the spacecraft throughout the year until it reaches its minimum altitude of 235 miles.
As Dawn maneuvers into orbit, its trajectory takes it to the opposite side of Ceres from the sun, providing these crescent views. These additional pictures were taken on March 1 at a distance of 30,000 miles (49,000 km). Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
“Since its discovery in 1801, Ceres was known as a planet, then an asteroid and later a dwarf planet,” said Marc Rayman, Dawn chief engineer and mission director at JPL. “Now, after a journey of 3.1 billion miles (4.9 billion kilometers) and 7.5 years, Dawn calls Ceres, home.”
More about Dawn’s incredible accomplishment can be found in the excellent Dawn Journal, written by Dawn chief engineer and mission director Marc Rayman.
There’s a famous line from Shakespeare’s Hamlet that says “There are more things in heaven and Earth, Horatio, than are dreamt of in your philosophy,” and the same now holds true for brave new worlds for humans to explore.
This result was published earlier this week courtesy of the NASA/JPL Near-Earth Program Office. The study found that the number of possible asteroid targets for human exploration has now doubled from the 666 known in the first study, completed in late 2010.
NHATS NEO asteroid discoveries by year. Credit: NASA/GFSC/Brent Barbee
This information comes from NHATS, which stands for the Near Earth Object Human Spaceflight Accessible Targets Study. Yes, it’s an acronym containing acronyms. NHATS is an automated system based out of Greenbelt, Maryland which monitors and periodically updates its list of potential target candidates for accessibility. The NHATS system data is readily accessible to the public online, and as of February 11th 2015, 1346 NHATS compliant asteroids are known.
This is the Holy Grail for the future of manned spaceflight, and will represent a good stepping stone (bad pun intended) for future crewed missions to Mars. Several hundred NHATS asteroids require less time and energy to reach than the Red Planet, and a few dozen even require less energy to reach than it does to enter lunar orbit.
Relative delta-V and return velocity is crucial. Apollo astronauts were subject to a blistering 11 kilometre per second reentry velocity on their return from the Moon, and future asteroid missions would be subject to the same style of trajectory on return to Earth from a solar orbit.
Mission to an NEO: a typical orbital profile. Credit: Brent Barbee/NASA/GSFC
The test of the Orion heat shield on reentry during last year’s EFT-1 flight was a step in this direction, and the next test will be an uncrewed launch atop an SLS rocket in September 2018. If all goes according to schedule — and NASA can successfully weather the ever-shifting political winds of multiple future changes of administration — expect to see astronauts exploring an NHATS asteroid placed in lunar orbit sometime around late 2023.
I know. “When I was a kid back in the 70’s…” we expected to be vacationing on Callisto by 2015, as well.
Brent Barbee at NASA’s Goddard Space Flight Center designed the automated NHATS system. It pulls data from a source that many comet and asteroid hunters are familiar with: JPL’s Small Bodies Database. The NHATS system then makes trajectory calculations and patches in conical solutions for possible spacecraft trajectories and actually gives potential launch window dates for future missions. Seriously, its fun to play with… you can even tailor and filter these by target dates versus maximum velocity constraints and the length of stays.
The orbit of asteroid 1943 Anteros. Credit: NASA/JPL.
The first discovered NHATS-compliant NEO was 2.3 kilometre 1943 Anteros way back in 1973, and famous alumni on the NHATS list also include 10 metre asteroid 2011 MD, which passed 12,000 kilometres from the Earth on June 27th, 2011. 2011 MD is on NASA’s short list of asteroids ideal for human exploration. Another famous asteroid on the NHATS list is 99942 Apophis which — triskaidekaphobics take note — will safely miss the Earth by 31,300 kilometres on Friday the 13th, April 2029. More are added every day, and the growing curve of discoveries also closely mirrors the rise of automated all-sky surveys such as LINEAR, PanSTARRS and the Catalina Sky Survey, though dedicated amateurs do get in on the act occasionally as well.
To date, over 12,000 NEA asteroids are now known, and you can expect future surveys such as the Large Synoptic Survey Telescope set to see first light in 2021 to add to their ranks. The Sentinel space telescope set to launch in 2017 will also boost the known number of NEOs as it covers our sunward blind spot from an orbit interior to the Earth’s. Remember Chelyabinsk? That could actually be a great rallying cry for Sentinel’s cause, as the asteroid came at the Earth from a sunward direction and avoided the sky sweeping robotic eyes of astronomers.
Sometimes, NEOs turn out to be returning space junk from the early Space Age (a low relative velocity and low orbital inclination is often a dead giveaway). Earth has also been known to capture an NEO as an occasional temporary second Moon, as occurred in 2006 in the case of asteroid 2006 RH120.
The LSST mirror in the Tuscon Mirror Lab. Photo by author.
But beyond just creating a database, the NHATS system also presents key opportunities for astronomers to perform follow-up observations of NEO asteroids, which is vital for precisely characterizing their orbits. Two future missions are also planned to return samples from NHATS asteroids: Hayabusa 2, which launched on December 3rd 2014 headed for asteroid 1999 JU3 in July 2018, and the OSIRIS-REx mission, set to launch in late 2016 headed for asteroid 101955 Bennu in 2018.
NHATS is providing a crucial target list for that day when first human footfall on an asteroid occurs… or should we say docking?
One several images NASA's Dawn spacecraft took on approach to Ceres on Feb. 4, 2015 at a distance of about 90,000 miles (145,000 kilometers) from the dwarf planet. Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
NASA’s Dawn spacecraft has acquired its latest and closest-yet snapshot of the mysterious dwarf planet world Ceres. These latest images, taken on Feb. 4, from a distance of about 90,000 miles (145,000 km) clearly show craters – including a couple with central peaks – and a clearer though still ambiguous view of that wild white spot that has so many of us scratching our heads as to its nature.
Get ready to scratch some more. The mystery spot has plenty of company.
Take a look at some still images I grabbed from the video which NASA made available today. In several of the photos, the white spot clearly looks like a depression, possibly an impact site. In others, it appears more like a rise or mountaintop. But perhaps the most amazing thing is that there appear to be not one but many white dabs and splashes on Ceres’ 590-mile-wide globe. I’ve toned the images to bring out more details:
Here the spot appears more like a depression. Frost? Ice? Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDAHere the white spot is at the asteroid’s left limb. You can also see lots of additional smaller spots that remind me of rayed lunar craters. Of course, they may be something else entirely. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDALook down along the lower limb to spot a crater with a cool central peak. Note also how many white spots are now visible on Ceres. The mystery spot is a little right of center in this view. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDAOur mystery white spot is further right of center. Is it a rise or a hole?Are the streaks rays for fresh material from an impact the way the lunar crater Tycho appears from Earth? Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDAYet another view of the mystery spot. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Animation made from images taken by Dawn on Feb. 4. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Now let’s take a look at an additional NASA animation of Ceres made using processed images. As the spot first rounds the limb it looks like a depression. But just before it disappears around the backside a pointed peak seems to appear. Intriguing, isn’t it?
Individual radar images of 2004 BL86 and its moon. The asteroid appears very lumpy, possibly from unresolved crater rims. The moon appears elongated but that may be an artifact and not its true shape. Credit: NASA
New video of 2004 BL86 and its moon
Newly processed images of asteroid 2004 BL86 made during its brush with Earth Monday night reveal fresh details of its lumpy surface and orbiting moon. We’ve learned from both optical and radar data that Alpha, the main body, spins once every 2.6 hours. Beta (the moon) spins more slowly.
The images were made by bouncing radio waves off the surface of the bodies using NASA’s 230-foot-wide (70-meter) Deep Space Network antenna at Goldstone, Calif. Radar “pinging” reveals information about the shape, velocity, rotation rate and surface features of close-approaching asteroids. But the resulting images can be confusing to interpret. Why? Because they’re not really photos as we know it.
For one, the moon appears to be revolving perpendicular to the main body which would be very unusual. Most moons orbit their primary approximately in the plane of its equator like Earth’s moon and Jupiter’s four Galilean moons. That’s almost certainly the case with Beta. Radar imagery is assembled from echoes or radio signals returned from the asteroid after bouncing off its surface. Unlike an optical image, we see the asteroid by reflected pulses of radio energy beamed from the antenna. To interpret them, we’ll need to put on our radar glasses.
Bright areas don’t necessarily appear bright to the eye because radar sees the world differently. Metallic asteroids appear much brighter than stony types; rougher surfaces also look brighter than smooth ones. In a sense these aren’t pictures at all but graphs of the radar pulse’s time delay, Doppler shift and intensity that have been converted into an image.
Another set of images of 2004 BL86 and its moon. Credit: NAIC Observatory / Arecibo Observatory
In the images above, the left to right direction or x-axis in the photo plots the toward and away motion or Doppler shift of the asteroid. You’ll recall that light from an object approaching Earth gets bunched up into shorter wavelengths or blue-shifted compared to red-shifted light given off by an object moving away from Earth. A more rapidly rotating object will appear larger than one spinning slowly. The moon appears elongated probably because it’s rotating more slowly than the Alpha primary.
Meanwhile, the up and down direction or y-axis in the images shows the time delay in the reflected radar pulse on its return trip to the transmitter. Movement up and down indicates a change in 2004 BL86’s distance from the transmitter, and movement left to right indicates rotation. Brightness variations depend on the strength of the returned signal with more radar-reflective areas appearing brighter. The moon appears quite bright because – assuming it’s rotating more slowly – the total signal strength is concentrated in one small area compared to being spread out by the faster-spinning main body.
If that’s not enough to wrap your brain around, consider that any particular point in the image maps to multiple points on the real asteroid. That means no matter how oddly shaped 2004 BL86 is in real life, it appears round or oval in radar images. Only multiple observations over time can help us learn the true shape of the asteroid.
You’ll often notice that radar images of asteroids appear to be lighted from directly above or below. The brighter edge indicates the radar pulse is returning from the leading edge of the object, the region closest to the dish. The further down you go in the image, the farther away that part of the asteroid is from the radar and the darker it appears.
Imagine for a moment an asteroid that’s either not rotating or rotating with one of its poles pointed exactly toward Earth. In radar images it would appear as a vertical line!
If you’re curious to learn more about the nature of radar images, here are two great resources:
Computer generated simulation of an asteroid strike on the Earth. Credit: Don Davis/AFP/Getty Images
For decades, scientists have debated the cause of the mass extinction that wiped out the dinosaurs and other life 65 million years ago. While the majority of researchers agree that a massive asteroid impact at Chicxulub, Mexico is the culprit, there have been some dissenters. Now, new research is questioning just a portion of the asteroid/Cretaceous-Paleogene extinction scenario. While the scientists involved in the study don’t doubt that such an asteroid impact actually happened, their research shows it is just not possible that vast global firestorms could have ravaged our planet and be the main cause of the extinction.
Researchers from the University of Exeter, University of Edinburgh and Imperial College London recreated the vast energy released from a 15-km wide asteroid slamming into Earth, which occurred around the time that dinosaurs became extinct.
They found that close to the impact site — a 180 km wide crater in Mexico — the heat pulse would have lasted for less than a minute. This intense but short-lived heat, the team says, could not have ignited live plants, challenging the idea that the impact led to global firestorms.
However, they did find that the effects of the impact would actually be worse on the other side of the planet, where less intense but longer periods of heat could have ignited live plant matter.
“By combining computer simulations of the impact with methods from engineering we have been able to recreate the enormous heat of the impact in the laboratory,” said Dr. Claire Belcher from the University of Exeter. “This has shown us that the heat was more likely to severely affect ecosystems a long distance away, such that forests in New Zealand would have had more chance of suffering major wildfires than forests in North America that were close to the impact. This flips our understanding of the effects of the impact on its head and means that palaeontologists may need to look for new clues from fossils found a long way from the impact to better understand the mass extinction event.”
The Cretaceous-Paleogene extinction was one of the biggest in Earth’s history and geologic evidence of the impact has been discovered in rock layers around the world from this time period. Some critics of the asteroid impact theory as a cause of the extinction have pointed to some of the microfossils from the Gulf of Mexico that show the impact occurred well before the extinction and could not have been its primary cause. Others point to volcanism that produced the Deccan traps of India around this time as a possible cause of the extinction.
But multiple models have showed such an impact would have instantly caused devastating shock waves, tsunamis, and the release of large amounts of dust, debris and gases that would have led to a low light levels and a prolonged cooling of Earth’s surface. The darkness and a global winter would have decimated the planet life and the dependent animals.
So while fire and brimstone may not have played a big role in the Cretaceous-Paleogene extinction, there was plenty of destruction and mayhem for the resulting extinction of more than 70% of known species.
Here’s a video from the researchers that shows their findings that close to the impact site, the heat pulse was too short to ignite live plant material.
Toes of a pahoehoe flow advance across a road in Kalapana on the east rift zone of Kilauea Volcano, Hawaii and the binary asteroid 2004 BL86. Credit: U.S. Geological Survey (left) and NASA/JPL-Caltech
At first glance, you wouldn’t think Hawaii has any connection at all with asteroid 2004 BL86, the one that missed Earth by 750,000 miles (1.2 million km) just 3 days ago. One’s a tropical paradise with nightly pig roasts, beaches and shave ice; the other an uninhabitable ball of bare rock untouched by floral print swimsuits.
But Planetary Science Institute researchers Vishnu Reddy and Driss Takir would beg to differ.
Using NASA’sInfrared Telescope Facility on Mauna Kea, Hawaii they discovered that the speedy “space mountain” has a composition similar to the very island from which they made their observations – basalt.
“Our observations show that this asteroid has a spectrum similar to V-type asteroids,” said Reddy. “V-type asteroids are basalt, similar in composition to lava flows we see in Hawaii.
Minerals on the surface of an object like the moon or an asteroid absorb wavelengths of light to create a series of “blank spaces” or absorption lines that are unique to a particular element or compound. Credit: NASA
The researchers used a spectrograph to study infrared sunlight reflected from 2004 BL86 during the flyby. A spectrograph splits light into its component colors like the deli guy slicing up a nice salami. Among the colors are occasional empty spaces or what astronomers call absorption lines, where minerals such as olivine, pyroxene and plagioclase on the asteroid’s surface have removed or absorbed particular slices of sunlight.
You’re looking straight down into the 310-mile-wide (500 km) Rheasilvea crater / impact basin on the asteroid Vesta. It’s though that many of the Vesta-like asteroids, including 2004 BL86, originated from the impact. It Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
These are the same materials that not only compose earthly basalts – all that dark volcanic rock that underlies Hawaii’s reefs and resorts – but also Vesta, considered the source of V-type asteroids. It’s thought that the impact that hollowed out the vast Rheasilvia crater at Vesta’s south pole blasted chunks of mama asteroid into space to create a family of smaller siblings called vestoids.
This animation, created from individual radar images, shows the binary asteroid 2004 BL86 on January 26th. The moon’s orbital period is about 13.8 hours. Credit: NASA/JPL-Caltech
So it would appear that 2004 BL86 could be a long-lost daughter born through impact and released into space to later be perturbed by Jupiter into an orbit that periodically brings it near Earth. Close enough to watch in wonder as it inches across the field of view of our telescopes like it did earlier this week.
The little moonlet may or may not be related to Vesta, but its presence makes 2004 BL86 a binary asteroid, where each object revolves about their common center of gravity. While the asteroid is unlikely to become future vacation destination, there will always be Hawaii to satisfy our longings for basalt.
A triple crater in Elysium Planitia on Mars. Credit: NASA/JPL/University of Arizona.
At first glance, you many not guess that this feature on Mars is an impact crater. The reason it looks so unusual is that it likely is a triple impact crater, formed when three asteroids struck all at once in the Elysium Planitia region.
Why do planetary scientists think the three craters did not form independently at different times?
“The ejecta blanket appears to be uniform around the triple-crater showing no signs of burial or overlapping ejecta from overprinting craters,” write scientists Eric Pilles, Livio Tornabene, Ryan Hopkins, and Kayle Hansen on the HiRISE website. “The crater rims are significantly stunted where the craters overlap.”
This oblong-shaped crater could have been created from a triple asteroid, or it could have been a binary asteroid, and one broke apart, creating the three overlapping craters. The team says the two larger craters must have been produced by asteroids of approximately the same size, probably on the order of a few hundred meters across.
“The northern crater might have been created by a smaller asteroid, which was orbiting the larger binary pair, or when one of the binary asteroids broke up upon entering the atmosphere,” the team explained. “The shape of the triple-crater is oblong, suggesting an oblique impact; therefore, another alternative would be that the asteroid split upon impact and ricocheted across the surface, creating additional craters.”
Studying craters on Mars — and there are lots of them, thanks to Mars’ sparse atmosphere — can help estimate the ages of different terrains, as well as revealing materials such as ice or minerals that get exposed from the impact.
Animation of Ceres made from images acquired by Dawn on Jan. 25, 2015. (NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)
This is the second animation from Dawn this year showing Ceres rotating, and at 43 pixels across the images are officially the best ever obtained!
NASA’s Dawn spacecraft is now on final approach to the 950 km (590 mile) dwarf planet Ceres, the largest world in the main asteroid belt and the biggest object in the inner Solar System that has yet to be explored closely. And, based on what one Dawn mission scientist has said, Ceres could very well be called the Solar System’s “hipster planet.”
“Ceres is a ‘planet’ that you’ve probably never heard of,” said Robert Mase, Dawn project manager at NASA’s Jet Propulsion Laboratory in Pasadena, California. “We’re excited to learn all about it with Dawn and share our discoveries with the world.”
Originally classified as a planet, Ceres was later categorized as an asteroid and then reclassified as a dwarf planet in 2006 (controversially along with far-flung Pluto.) Ceres was first observed in 1801 by astronomer Giuseppe Piazzi who named the object after the Roman goddess of agriculture, grain crops, fertility and motherly relationships. (Its orbit would later be calculated by German mathematician Carl Gauss.)
“You may not realize that the word ‘cereal’ comes from the name Ceres,” said Marc Rayman, mission director and chief engineer of the Dawn mission at JPL. “Perhaps you already connected with the dwarf planet at breakfast today.”
Ceres: part of this nutritionally-balanced Solar System!
Comparison of HST and Dawn FC images of Ceres taken nearly 11 years apart. Credit: NASA.
The animation above was made from images taken by Dawn framing camera on January 25, 2015 from a distance of about 237,000 km (147,000 miles). These are now the highest-resolution views to date of the dwarf planet, 30% more detailed than those obtained by Hubble in January 2004.
And there’s that northern white spot again too… seen in observations from earlier this month and in the 2003-04 HST images, scientists still aren’t quite sure what it is. A crater wall? An exposed ice deposit? Something else entirely? We will soon find out.
“We are already seeing areas and details on Ceres popping out that had not been seen before. For instance, there are several dark features in the southern hemisphere that might be craters within a region that is darker overall,” said Carol Raymond, Dawn deputy principal investigator at JPL.
Full-frame image from Dawn of Ceres on approach, acquired Jan. 25, 2015. (NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)
From now on, every observation of Ceres by Dawn will be the best we’ve ever seen! This new chapter of the spacecraft’s adventure has only just begun.
The asteroid Vesta as seen by the Dawn spacecraft. Credit: NASA/JPL-Caltech/UCAL/MPS/DLR/IDA
I don’t think I ever learned one of those little rhymes – My Very Educated Mother Just Served Us Nine Pizzas – to memorize the order of the planets, but if I had, it would’ve painted for me a minimalist picture of the solar system. (Side question: what is my Very Educated Mother serving now that we only have Dwarf Pizzas?) After all, much of the most exciting work in planetary science today happens not at the planets, but around them.
Ask an astronomer where in the solar system she’d like to visit next and you’re just as likely to hear Europa, Enceladus, Titan, or Triton as you are Venus, Mars, or Neptune. Our solar system hosts eight planets but nearly 200 known moons. And moons, it turns out, are just the start. We’ve detected more than a million asteroids; surely that’s just a fraction of what’s lurking beyond our limits of observation. Let’s not even think about the billions, perhaps even trillions, of Kuiper belt and Oort cloud objects – we could be here all day! So, while the planets may dominate the solar system gravitationally, they are pitiful numerically.
If there is one thing that the study of exoplanets has taught us in the last twenty years, it’s that the Universe thrives on chance. Given enough planets (and there appear to be gazillions out there!), practically anything can happen. Want a planet with a double sunset? We’ve got that, but perhaps you’d prefer one with three! How about a planet whose temperature is nearly half that of the surface of the Sun? No problem there. I can even offer you a planet ten times more massive than Jupiter, but nearly 20 times closer to its star than Mercury (probably not the best place for your first off-world vacation home…). The point is, with only a few thousand planets discovered, what we’ve seen already is astonishing. Imagine what those million asteroids could be hiding.
In fact, asteroids might be the next great frontier in planetary science. Let’s find out why.
An artist’s impression of the rings around Chariklo. Credit: ESO/L. Calçada/M. Kornmesser/Nick Risinger (skysurvey.org)
Suppose I ask you to think about the planet Saturn. What’s the first thing that jumps to mind? Probably its rings. And, if you were paying attention around the time you learned one of those nifty rhymes, you might recall that Jupiter, Uranus, and Neptune also have rings. But, did you know that at least one asteroid is also home to a ring system? Called Chariklo, it’s the largest known of a family of asteroids trapped between the orbits of the outer planets. Early last year, astronomers reported the detection of a ring system about this 250-kilometer sized object. I say a ring system because there appear to be at least two distinct rings encircling Chariklo. Discovering this new system is more than just an additional data point. Perhaps the paramount question facing the field of planetary rings today is how they formed and how long they can last; the existence of rings around a tiny asteroid tells a very different story than that implied by the giant planets.
Of course, rings haven’t been the biggest planetary science story of the last decade (much to my chagrin as a rings researcher!). That honor might instead lie with geysers. The 2005 discovery of an enormous water plume emanating from the surface of Saturn’s moon Enceladus changed the way we looked at the icy moons of the solar system. Eight years later, astronomers using Hubble claimed to have found a similar phenomenon at Jupiter’s moon Europa (now they’re not so sure). But geysers, too, might not be the sole province of planetary moons. Just last year, researchers with the Herschel Space Telescope found the first evidence for water vapor emanating from the surface of the enormous asteroid Ceres! There’s more good news: unlike Europa, with its off-in-the-future mission, the Dawn spacecraft is on its way to Ceres right now. It will arrive in just under two months and provide a close-up look at the second confirmed off-world geyser.
Speaking of moons, it probably won’t surprise you to learn that asteroids have those, too! In fact, the number of asteroids with known satellites is far too long to enumerate here. But, they are not merely numerous; the variety of asteroid moons seems to be nearly as large as the variety of asteroids themselves. Like with the planets, many asteroids dwarf their moons. Others, though, are more like binary systems in which both bodies are approximately the same size. And, although we generally know little about their shape, the variety in this realm also appears tremendous.
An artist’s conception of how an unmanned spacecraft might redirect an asteroid into lunar orbit. Credit: NASA
Ultimately, though, it’s not their number or their variety that might make asteroids the future of planetary science; the laws of physics are on their side. It’s no accident that NASA intends to send astronauts to land on an asteroid long before they attempt to touch down on Mars. Neither is it a coincidence that at least three missions (Hayabusa, Hayabusa 2, and OSIRIS-REx) will have returned, or at least attempted to, samples from an asteroid to the Earth before NASA’s ambitious plan to do the same at Mars. The gravitational tug on the surface of the Red Planet is more than thirteen times more powerful than that of even the largest asteroid.
We’re seeing this accessibility in action already. Hayabusa returned a sample of asteroid Itokawa back in 2010 and its successor is already on its way. And, remember Dawn on its way to Ceres? It turns out that wasn’t its first stop. Before setting out for the solar system’s largest asteroid, the mission spent fourteen months in orbit about the asteroid Vesta. When it arrives at Ceres in March, Dawn will become the first spacecraft in history to orbit two extraterrestrial bodies.
Dawn is, I think, a signal of things to come. Asteroids, in general, and the main asteroid belt, in particular, offer the tantalizing opportunity to visit a variety of different worlds in one fell swoop. These are places that are closer to us, easier to approach, and just as scientifically interesting as the classical celestial worlds. Does this mean that the world’s science agencies will or even should abandon the study of the planets? Of course not. No asteroid looks like the cloud tops of Jupiter or the methane lakes of Titan or the intense heat of Venus. I’m not at all trying to limit the worlds which we visit. Quite the opposite, in fact: we’ve suddenly found a million new places to go!
