A spacecraft colliding with an asteroid isn’t NASA’s usual approach to planetary science, but it was certainly an opportunity nonetheless.
NASA’s Double Asteroid Redirection Test (Arrow) A spacecraft collided with a small asteroid called Demorphos on September 26 to test a potential technology to protect Earth, if we find ourselves on a collision course with a large space rock. But the impact has also given planetary scientists a close, if fleeting, view of the smallest asteroid No spacecraft you’ve visited so far.
“It was exciting to see the data come in,” Carolyn Ernst, a planetary scientist at Johns Hopkins University’s Applied Physics Laboratory and instrument scientist for the only DART instrument, told Space.com. “Everyone was filling it with passion and busy working on it.”
Related: Asteroid collision: This is the last thing NASA’s DART spacecraft saw before it crashed
It’s still early days to learn about the asteroid itself; Scientists only have the DART data on hand for a few weeks, and they’ll run countless analyzes before saying anything with great confidence. “There are a lot of spot notes you can make, but there are a lot of subtle things you have to put together before you go too far down any road,” said Ernst.
Demorphos is 525 feet (160 meters) wide and orbits a larger asteroid called Didymus, which is probably 2,560 feet (780 meters) wide. Before the launch of DART in November 2021, scientists got a feel for the shapes of both rocks thanks to planetary radar, in which a beam of radio waves bounced off the asteroids.
As the DART spacecraft was sailing toward its final destination, that was all scientists knew about the pair of rocks.
DART’s only tool, the Didymos Reconnaissance and Asteroid Optical Navigation Camera (DRACO), was able to change that. During most of the DART flight, asteroids appeared as a single bright spot, but about 10 minutes before the collision, that point began to transform into two small but unique worlds.
One of the characteristics of Demorphos jumped out as soon as scientists saw the last DART images before the impact: Its rocky surface is covered in boulders, dust, and everything in between. Spacecraft have seen this type of surface before: Japan’s Hayabusa 2 mission to Ryugu and NASA’s OSIRIS-REx mission to Determine Both found themselves exploring rock conglomerates, worlds that scientists call “rubble pile” asteroids.
“Because it looks so dirty and because of what we know about those other asteroids, I think a lot of people imagine it’s some kind of rubble pile or some kind of loose group of rocks,” Ernst said.
However, DART has not revealed the interior of the Dimorphos, so the appearance of the rubble pile may not hold up. “We don’t have a direct way to measure the interior,” Ernst said. “Could it be that the interior is a bunch of bigger things with smaller stuff on top of it? Could it have its shape on the surface all the way to the end? We have no direct idea of that.”
The second characteristic of Dimorphos that hit Ernst during the DART approach was their egg-like shape, at least as seen from the angle of the DART approach. “It was less abnormal than I expected,” she said. “People often call asteroids big potatoes because they have a lot of irregular shapes. So, in that sense, I think they were shaped more regularly than I expected.”
As the analysis continues, Ernst added, scientists will look for clues about whether material on Demorphos’ surface appears to be moving, which could make the asteroid relatively round.
Scientists can also look forward to insight from the European Space Agency Hera’s missionscheduled for release in 2024 On a SpaceX Falcon 9 rocket She arrives at Demorphos two years later. Hera will explore the asteroid and its impact in three dimensions and without DART acceleration.
DART’s view of the Dimorphos’ biggest companion, Didymos, was even more fleeting, because towards the end of the approach it slid out of the spacecraft’s field of view. But planetary scientists are studying Didymus with the data DART sent home.
“We have some really interesting and interesting looks at Didymus that we will definitely be able to do some science with,” said Ernst.
Even a passing view showed Didymus and Demorphus to be two distinct bodies, despite their close proximity. “The surface definitely looks different from Dimorphos,” Ernst said. “You can certainly see some big boulders, especially on the edges. But it doesn’t look like a huge pile of boulders, as Demorphos does.”
In particular, I note that Didymus appears to show a greater contrast in terrain between smooth and rough patches than did the regular rocky surface of Demorphos.
The differences between Didymus and Demorphos could affect how scientists try to explain the formation of binary asteroids. one idea It is suggested that the main body could rotate so rapidly that material would fly out of it, eventually coalescing into the shape of a moon; second sight He hypothesizes that if an asteroid got too far from a large planet, the planet’s gravity could rip the material that becomes the young moon.
Scientists believe about 15% Of the near-Earth asteroids are actually binary systems, where the three-piece transverse asteroids are thrown.
Meaning in chaos
Thanks to the design of the DART mission, the spacecraft’s sudden demise didn’t mark the end of the data scientists can use to understand Dimorphos.
First, DART carried with it a small companion called the Light Italian Cubesat to photograph asteroids (LICIACube) that was published two weeks before the effect. Equipped with two cameras, LICIACube bypassed the impact site about three minutes after DART arrived in hopes of spotting a crater or perhaps some debris.
“We didn’t know what they were going to show when they set out to do that,” said Ernst. But the LICIACube photos showed the debris flying off of Dimorphos at the banners. “Those pictures, they were absolutely amazing and amazing.”
These large amounts of debris indicate that Dimorphos consists of a material that is relatively weakly cohesive; Consider throwing a tennis ball into a sandbox compared to throwing it off the sidewalk. But there’s a downside to effect clutter, too. The LICIACube images are so filled with debris that scientists can’t decipher much of the asteroid’s natural surface from the images.
But LICIACube wasn’t the only DART witness. In addition, the expedition recruited Telescopes on Earth And the in the space Watch the effects of a DART collision.
The mission’s planetary defense objective led the primary duty of these observers. Planetary defense experts say that if humans discover an asteroid that threatens to collide with Earth, shortening the asteroid’s orbit around the sun can ensure that the two objects do not run the risk of being in the same place at the same time.
To this end, telescopes have focused on the goal of recording the time it now takes Demorphos to orbit Didymus. Demorphos’ orbit previously lasted 11 hours 55 minutes; Following the impact, that period was Decreased by 32 minutes. This was the highest expectations scientists had before the launch. Because the debris flyby of Demorphos would have contributed to the orbital change, the large dip highlights the amount of debris created by DART.
But constant observations also tell scientists a lot about asteroids as space rocks, as well as about what happens when asteroids collide naturally.
The Didymos system is usually the single bright spot for telescopes on Earth. But just two days after the collision, the pair of asteroids possessed a long, bright tail similar to a comet spanned 6000 miles (10,000 km) in space.
Like the LICIACube images, the tail notes indicate that DART left a big mess. Radiative pressure from the sun also pushed the debris into the tail; This debris also reflects sunlight, hence the bright smudge.
“It’s basically like a little comet, a temporary comet,” said Ernst.
The scientists were able to watch the tail change during the weeks after the DART effect. The Hubble Space Telescope It was especially important on that front, where the asteroid has been observed 18 times since the collision and caught Demorphos with a second tail bud, comets Sometimes you do as well.
Demorphos is not the first asteroid to dress up as a comet. Around 1 in 10,000 A space rock is an “active asteroid” with comet-like features such as a tail. Interestingly, scientists have already thought that these confusing scenes may occur when a natural impact throws debris off the asteroid’s surface.
But there is a lot more work to be done before scientists are ready to draw any major conclusions about asteroids from their profiles at Didymos and Demorphos. “I think it’s honestly going to take a long time for people to be able to reconstruct everything around what that means,” Ernst said of the tail.
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