Incredible images of the swirling clouds of dust produced when NASA‘s Double Asteroid Redirection Test (DART) spacecraft struck an asteroid have been revealed.
The refrigerator-sized spacecraft collided with the 520ft-wide (160m) space rock known as Dimorphos on September 26 last year.
The aim of the mission was to demonstrate that the technology would be able to deflect asteroids that could pose a danger to Earth in the future.
This month, it was revealed that DART shaved 33 minutes off of Dimorphos’ orbit – nearly five times more than predicted – and it was regarded a success.
Scientists at the University of Edinburgh studied the aftermath of the collision, including what was in the debris it left and how it clumped together over time.
Evolution of cloud of debris ejected when the DART spacecraft collided with Dimorphos. The first image was taken just before impact, and the last almost a month later. The white arrow marks the direction of the sun. The streaks in the background are stars. The images were taken with the MUSE instrument at the Very Large Telescope
The refrigerator-sized satellite DART collided with the 520ft-wide (160m) space rock Dimorphos on September 26 last year. The aim of the mission was to demonstrate that the technology would be able to deflect asteroids that could pose a danger to Earth in the future
‘Asteroids are some of the most basic relics of what all the planets and moons in our Solar System were created from,’ said PhD student Brian Murphy.
WHAT WAS DART?
DART was the world’s first planetary defence test mission, launched in November 2021.
It involved crashing a spacecraft into the small moonlet asteroid Dimorphos, which orbits a larger companion asteroid called Didymos.
This was done to slightly change Dimorphos’ orbit.
The moonlet is about 525 feet in diameter, and although it doesn’t pose a danger to Earth, NASA wanted to measure the asteroid’s altered orbit caused by the collision.
Post-impact observations from Earth-based optical telescopes and planetary radars measured the change in Dimorphos’ orbit around Didymos.
Before impact, the time taken for the moonlet to make one circuit of its sibling was 11 hours and 55 minutes, but now it takes 11 hours and 22 minutes.
This demonstration of planetary defence will inform future missions that could one day save Earth from a deadly asteroid impact.
The dust cloud that remained after DART careered into Dimorphos at 14,000 mph (22,000 kph) can tell us about what happened when our Solar System was formed.
It could also provide more information about the chemical composition of these asteroids.
Astronomer Dr Cyrielle Opitom added: ‘Impacts between asteroids happen naturally, but you never know it in advance.
‘DART is a really great opportunity to study a controlled impact, almost as in a laboratory.’
The team used the European Southern Observatory’s Very Large Telescope (VLT) to observe the DART mission as it took place seven million miles (11 million km) away.
For their study, published in Astronomy & Astrophysics, they observed the resulting debris for a month using the Multi Unit Spectroscopic Explorer (MUSE) instrument at the VLT in Chile.
They found that, immediately after the collision, the dust appeared blue in colour, which indicated it was made up of very fine particles.
But as time went on, the particles began to come together and form clumps, spirals and a long tail that extended away from the Sun’s radiation.
The tail and spirals appeared redder than the original cloud of dust, suggesting that they were made up of larger particles.
MUSE also allowed the scientists to study the chemical composition of Dimorphos from the dust it ejected.
This is because certain wavelengths of sunlight are reflected by specific molecules, like water (H₂O) and oxygen (O₂), allowing for their identification.
This artist’s illustration shows the ejection of a cloud of debris after NASA’s DART spacecraft collided with the asteroid Dimorphos
These two molecules in particular would be indicative of the presence of ice within the asteroid, however none could be found.
‘Asteroids are not expected to contain significant amounts of ice, so detecting any trace of water would have been a real surprise,’ said Dr Opitom.
They also looked for traces of propellant from the DART spacecraft, but none of that could be found either.
Dr Opitom added: ‘We knew it was a long shot, as the amount of gas that would be left in the tanks from the propulsion system would not be huge.
‘Furthermore, some of it would have travelled too far to detect it with MUSE by the time we started observing.’
They researchers found that, immediately after the collision, the dust ejected by Dimorphos appeared blue in colour, which indicated it was made up of very fine particles
Light reflected by the Dimorphos’ (pictured) surface became less polarised, so more randomly oriented, immediately after the collision. Researchers suggest this is because it revealed untouched materiel with a more symmetrical molecular structure, which is less polarising
Another team from the Armagh Observatory and Planetarium used another VLT instrument to study what the impact did to the surface of the asteroid.
When objects in space reflect sunlight, it partially polarises it, meaning that the waves change from oscillating in lots of different directions to just one direction.
For their study, published in Astrophysical Journal Letters, the researchers used the FOcal Reducer/low dispersion Spectrograph 2 (FORS2) to observe the polarisation of the light reflected by Dimorphos.
‘Tracking how the polarisation changes with the orientation of the asteroid relative to us and the Sun reveals the structure and composition of its surface,’ said study author Dr Stefano Bagnulo.
They found that the light reflected by the asteroid’s surface became less polarised, so more randomly oriented, immediately after the collision.
They suggest that this is because it revealed untouched materiel with a more symmetrical molecular structure, which is less polarising.
The asteroid also reflected more light after the impact, suggesting this inner materiel is smoother than the rough exterior.
The fact that the interior has a smoother texture and more regular molecular structure than the exterior could be because it had not been exposed to solar wind and radiation.
Another possibility is that DART completely destroyed the top layer of Dimorphos, leading to the production of fine dust particles.
‘We know that under certain circumstances, smaller fragments are more efficient at reflecting light and less efficient at polarising it,’ said PhD student Zuri Gray.
Dr Optiom added: ‘This research took advantage of a unique opportunity when NASA impacted an asteroid, so it cannot be repeated by any future facility.
‘This makes the data obtained with the VLT around the time of impact extremely precious when it comes to better understanding the nature of asteroids.’
NASA’s interactive tool allows users to follow the asteroids racing towards Earth
Earlier thismonth, NASA warned that a city-destroying asteroid the size of the Leaning Tower of Pisa could slam into Earth in a little over 20 years’ time.
It came just two months after another space rock – which was as big as a London bus – made the fourth closest approach to our planet on record.
The good news is that the US space agency, along with scientists from across the globe, are monitoring potential asteroids – and the even better news is that you can too with this interactive tool.
It shows the next five closest approaches to Earth, starting with 2020 FV4 in three days’ time.
The 100ft (30m)-wide object is expected to race past our planet at a distance of some 4.1 million miles (6.7 million km).