The NASA collision that changed the course of an asteroid

By Mark Waghorn via SWNS

Astronomers have captured the aftermath of a NASA collision that changed the course of an asteroid.

A cloud of debris was ejected when NASA's Dart probe struck the 520-foot wide space rock named Coipmorphus in September.

It showed for the first time that humans have the capacity to prevent a potentially catastrophic impact with Earth.

Co-author Brian Murphy, a Ph.D. student at the University of Edinburgh, said: "Asteroids are some of the most basic relics of what all the planets and moons in our Solar System were created from."

The mission was conceived to test a potential strategy. Dart's achievement proves such an idea would work - provided it was initiated early enough and the target wasn't overly massive.

The Double Asteroid Redirection Test (Dart) took place some seven million miles away.

It saw the refrigerator-sized NASA satellite drive straight into Dimorphos at 14,000mph - destroying itself in the process.

Studying material ejected can also tell us about how our Solar System formed.

Lead author Dr. Cyrielle Opitom, also from Edinburgh, said: "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."

Images taken with the MUSE instrument on the European Space Observatory's Very Large Telescope (VLT) show the evolution of the cloud.

Over a month-long period clumps, spirals and a long tail of dust developed - pushed away by the sun's radiation.

Dimorphus orbits a larger asteroid called Didymos.

The researchers found the ejected cloud was bluer than the asteroid itself - indicating very fine particles.

The spirals and tail were reddish - suggesting larger particles.

MUSE mounted on VLT in Chile's Atacama Desert enabled the light to be broken up into a rainbow-like pattern - enabling the identification of chemical fingerprints of different gases.

In particular, they searched for oxygen and water coming from ice - but found nothing.

Dr. Optimum said: "Asteroids are not expected to contain significant amounts of ice, so detecting any trace of water would have been a real surprise."

They also looked in vain for traces of the propellant of the DART spacecraft but found none.

She said: "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 traveled too far to detect it with MUSE by the time we started observing."

Another team led by Dr. Stefano Bagnulo at the Armagh Observatory and Planetarium studied how the DART impact altered the surface of the asteroid.

Dr. Bagnulo said: "When we observe the objects in our Solar System, we are looking at the sunlight that is scattered by their surface or by their atmosphere, which becomes partially polarized."

This means that light waves oscillate along a preferred direction rather than randomly.

He said: "Tracking how the polarization changes with the orientation of the asteroid relative to us and the Sun reveals the structure and composition of its surface."

The researchers used the FORS2 (FOcal Reducer/low dispersion Spectrograph 2) scanner at the VLT to monitor the asteroid.

They found the level of polarization suddenly dropped after the impact. At the same time, the overall brightness of the system increased.

One possible explanation is the impact exposed more pristine material from the interior of the asteroid.

Dr. Bagnulo said: "Maybe the material excavated by the impact was intrinsically brighter and less polarizing than the material on the surface because it was never exposed to solar wind and solar radiation."

Another possibility is the impact destroyed particles on the surface, thus ejecting much smaller ones into the cloud of debris.

Zuri Gray, a Ph.D. student from the same lab, said: "We know that under certain circumstances, smaller fragments are more efficient at reflecting light and less efficient at polarizing it."

The two studies are reported in Astronomy & Astrophysics and Astrophysical Journal Letters.