NASA’s DART mission (Double Asteroid Redirection Test) collided with the asteroid Dimorphos in September 2022, changing its orbital period. Ground- and space-based telescopes will be used not only to study what happened to the asteroid, but also for planetary defense efforts that may someday be needed to reduce the possibility of a collision with Earth. I turned to watch this event unfold in order to provide information.
Astronomers continued to observe and study Dimorphos long after the collision. However, Dimorphos is a small asteroid in this binary system, being only a small moon orbiting the larger asteroid Didymos.
The James Webb Space Telescope (JWST) is the only telescope that can visually distinguish between two closely orbiting asteroids. Astronomers are now using JWST to make follow-up observations of the system to see what happened to Didymos after the dust cleared.
in new preprinted paper, A team of scientists led by Andrew Rivkin DART’s head of research explained how they used two instruments on JWST to measure Didymos’ spectrum about two months after the DART impact. One of their biggest conclusions is that Didymos and Dimorphos appear to have the same composition, that of a normal chondrite. This is a class of stony meteorites that accounts for more than 80% of all meteorites that fall to Earth. This means that the DART test was a very good proxy for the types of asteroids that could one day pose a threat.
“One of the benefits of using the Didymos system was definitely that it was considered representative of most of what was on the property,” Rivkin told Universe Today in an email. “People working on planetary defense often point out that ‘the asteroid is choosing us, rather than the other way around,’ but it’s very important to show that what we did with Dimorphos is broadly applicable.” It is important.”
For the new observations, scientists used NIRSpec, a near-infrared spectrometer, and MIRI, a mid-infrared instrument, on November 28, 2022.
At the time of observation, the centers of Didymos and Dimorphos were no more than 0.1 inch apart from each other from JWST’s perspective. However, the research team took advantage of the fact that Dimorpho was obscured by Didymos during MIRI observations.
“Didimos is about five times larger in diameter than Dimorphos, so its cross-sectional area is about 25 times larger than Dimorphos,” the researchers wrote. “This size difference between the components means that about 96% of the luminous flux from the system typically comes from Didymos.”
The researchers say that several lines of evidence suggest that the asteroid and its moons have similar compositions, and that the research team is able to “reasonably estimate the composition of Dimorphos from measurements of the Didymos-dominated flux.” “It can be done,” he concluded.
Considering how difficult it is to distinguish between Didymos and Dimorphos in long-range observations, there is a noticeable change in observations of Didymos after the impact with Dimorphos, given all the dust and debris from the impact. I asked Rivkin. The results seem to indicate that Didymos escaped the DART asteroid moon impact largely unscathed.
“Many new results from observations of the Didymos system have been published (Including this preprint paper led by Theodore Caleta) talking about the development and evolution of the tail. It shows that after about 25 days, the extra brightness from debris within the Didymos system has dissipated, and by November 2022, observations of this system (including those from JWST!) Almost everything will return to the Didymos system. ”
Rivkin has made some puzzling observations using polarized light, suggesting that Didymos’ average particle size or average reflectance may have changed slightly, but further observations could yield He added that he is waiting for the spring of 2024 to be ready.
An interesting (and fun!) comparison made by Rivkin and his team is how similar Didymos’ composition is to the Chelyabinsk meteor, a famous meteor that caused a massive airburst event over Russia in February 2013. I mean, are you doing it? The Chelyabinsk meteor is considered to be the largest. Since the Tunguska incident in 1908, natural space objects have entered the Earth’s atmosphere. Therefore, it also plays a representative role as a near-Earth asteroid.
“Yes, I thought that comparison was particularly apt!” Rivkin said. “The composition of Didymos and Dimorphos is very common in near-Earth asteroids, so even randomly chosen meteorites have a good chance of being a match.”
Other asteroids that have been studied in more detail, such as Eros and Itokawa, have similar compositions, although they likely did not come from the same source object, Rivkin said. However, all the asteroids mentioned here belong to the same class of S-type asteroids (siliceous or stony).
Eros was the first asteroid to be orbited by a spacecraft (NEAR in 2000) and the first asteroid to land on a spacecraft. It was also the first near-Earth asteroid (NEA) discovered in 1898. Itokawa was the first asteroid visited, sampled and brought to Earth for analysis by her JAXA Hayabusa mission.
Rivkin said remote sensing of distant objects like Didymos and Dimorphos is encouraged by their success, especially despite the great difficulty of accurately determining the composition of asteroids.
“We’ve spent more than 50 years trying to sort out some very detailed questions and solutions,” he says. “Studies like the JWST observations and all the other great work that’s been done over the years to observe Didymos, and the fact that they agree on the big picture, makes us take a step back and look at the It gives us the opportunity to realize how much we are now capable of.” It allows us to remotely tell what something is made of. ”
But observations of Dimorphos and Didymos will continue, and astronomers look forward to learning more in the near future. ESA’s Hera Mission is expected to arrive on the Didymos system at the end of 2026, and the researchers said they will be able to follow up on or extend some of the results found with JWST.
Hera, in particular, has a higher spatial resolution than was possible from DART (and the Light Italian CubeSat for Asteroid Imaging, LICIACube, a cubic satellite that was part of the DART mission and sent back images of the asteroid). It becomes possible to image the surface of Didymos. Hera will be able to perform tests to estimate regolith particle size derived from mid-infrared spectroscopy and confirmation of measured thermal inertia.
“We continue our efforts to understand the population of potential asteroid impact sources, to help inform planetary defense efforts to redirect science and reduce the likelihood of impact. We look forward to future JWST measurements of Hera and additional S-complex asteroids,” the researchers said. .
