Image of Dimorphos taken by the DART spacecraft's DRACO imager seconds before the crash. (Image credit: NASA TV / Screenshot)Double Asteroid Redirection Test (DART) Mission: NASA’s DART (Double Asteroid Redirection Test) has successfully crashed into the asteroid Dimorphos. Scientists expect the impact to alter the asteroid’s orbit. However, it will take a few weeks before NASA can determine how much the asteroid’s path was changed due to the impact.
Data obtained from DART’s crash will be compared to the data from various computer simulations run by scientists to ascertain whether this kinetic impactor method will remain a viable option in case of an actual threatening asteroid that does end up coming Earth’s way. Scientists don’t yet know the exact mass of Dimorphos but it is estimated to be around five billion kilograms. The DART spacecraft weighs around 600 kilograms.
By current definitions, the asteroid Bennu is a potentially hazardous asteroid (PHA). It orbits the sun every 1.2 years and gets relatively close to Earth once every six years. It is roughly spherical shaped and has an equatorial bulge. The asteroid’s average diameter is about 492 metres.
A PHA is an asteroid which has an orbit that it will bring it to within 0.05 Astronomical Units of Earth’s orbit. In order to be a PHA, an asteroid also has to be bigger than 50 metres in size since smaller objects that enter Earth’s surface will disintegrate. Just because an asteroid is a PHA does not mean it will impact Earth. Monitoring PHAs and updating their orbits can improve the predictions about their risk of impacting our planet.
The Center for NEO Studies (CNEOS) at NASA’s Jet Propulsion Laboratory has predicted Bennu’s future movements based on 29 radar and 478 optical observations of the asteroid. CNEOS predicts that Bennu will pass close to our planet, within the Moon’s orbit in 2135. This approach could change the asteroid's orbit by a small amount. This introduces uncertainty and could lead to a potential impact on Earth between 2175 and 2199.
But according to CNEOS calculations, the risk of the asteroid striking our planet during that period is a 0.0037, or a one in 2,700 chance. This means that there is a 99.963 per cent probability that the asteroid will not impact our planet during the period.
Here is a recap of the last few seconds before DART crashed into Dimorphos
After NASA’s DART mission, the European Space Agency (ESA) plans to launch the Hera mission in October 2024. Hera is another planetary defence test that is currently under development. It will investigate the Didymos binary asteroid system and measure the outcome of the DART mission in great detail.
The Hera spacecraft will first rendezvous with the target and then it will begin characterising it in detail. It will measure the internal properties of Dimorphos and the crater made by DART to measure the efficiency of the momentum transfer. Hera will also deploy two Cubesats, Milani and Juventas. These CubeSats will operate in the vicinity of the asteroid for a few months to provide scientific measurements.
The Didymos system is within 11 million kilometres of Earth and currently, scientists are using dozens of telescopes stationed around the world and in space to observe the asteroid system. In the coming weeks, they will precisely measure the orbital change that happened to Dimorphos to understand how effectively DART deflected the asteroid. These results will help validate the effectiveness of this technique as a reliable method for asteroid deflection.
ATLAS or Asteroid Terrestrial-impact Last Alert System is an asteroid detection system funded by NASA. It uses three telescopes—one each in Haleakalā and Maunaloa in Hawai’i, and two more in South Africa and Chile—to scan the entire sky every 24 hours to detect near-Earth objects that pose a threat to our planet. Below is ATLAS’ observation of the DART spacecraft impacting the Dimorphos system.
At 8.51 AM IST on September 27, the Artemis 1 mission’s Space Launch System (SLS) rocket and Orion spacecraft left launch pad 39 B and began its 6.4-kilometre journey to the Vehicle Assembly Building at the Kennedy Space Centre. NASA decided to roll back the Artemis 1 stack because of the threat posed by Hurricane Ian.
The kinetic impactor method is not the only trick up scientists’ sleeves. If an asteroid approaching Earth was to be detected early enough, it might be possible to use a method called “gravity tractor,” which involves the use of a spacecraft’s gravity to divert the asteroid.
In this method, instead of crashing into an asteroid, a gravity tractor device would fly along with the asteroid for a long period of time that could last anywhere between years to decades, deviating the path of the asteroid with its own gravitatipnal pull. This technique could potentially work on asteroids of any shape or composition, even if the asteroid in question is just a pile of rubble.
This method offers great control and could even be used to divert approaching asteroids to a separate location where scientists can use them for research or commercial purposes. But the technique is still untested and it could be decades before we can build, launch and carry out a mitigation mission that uses this technique.
As Amitabh Sinha explains one of the reasons scientists chose to target Dimorphos was because of its relatively shorter orbit around Didymos. The two asteroids together orbit the sun. In his explained piece, he notes that "a deviation in this orbit was likely to be more noticeable, and thus easier to measure, than say, if Didymos itself was targeted and an attempt was made to measure the change in its orbit around the Sun." Read our full explained on the NASA Dart mission.
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According to NASA's press statement, its investigation team will now observe the asteroid with relying on ground-based telescopes to confirm and determine just how much DART altered the asteroid's orbit around Didymos. Didymos is a much bigger asteroid and one classified as being a potential threat to Earth, according to the space agency.
NASA notes in its press statement that "researchers expect the impact to shorten Dimorphos’ orbit by about 1%, or roughly 10 minutes; precisely measuring how much the asteroid was deflected is one of the primary purposes of the full-scale test."
“At its core, DART represents an unprecedented success for planetary defense, but it is also a mission of unity with a real benefit for all humanity,” said NASA Administrator Bill Nelson in a press statement. “As NASA studies the cosmos and our home planet, we’re also working to protect that home, and this international collaboration turned science fiction into science fact, demonstrating one way to protect Earth.”
If you search for NASA Dart on Google, you might be in for a surprise. The search results will also show the spacecraft crashing into the page. Check out NASA's tweet on this below:
The DART spacecraft has successfully crashed into the asteroid Dimorphos in what is humanity’s first attempt to test a planetary defence mechanism.
The SMART Nav system has stopped manoeuvring and the DART spacecraft is coasting to its impact with the asteroid Dimorphos. The window for sending any commands to the spacecraft is over.
SMART Nav has precision locked onto Dimorphos and it is no longer tracking Didymos at all. With this, the DART mission has completed its last milestone before impact.
NASA has completed the last Status Poll for the mission ahead of the impact. With all systems working as expected, the mission is on the right track.
The LICIACube, A CubeSat built by the Italian Space Agency, will try to take images of DART's impact with Dimorphos.
Less than 50 minutes before the collision, the DART spacecraft’s SMART Nav is target locked onto Dimorphos.
“We can see Dimorphos and we are on our way. So SMART Nav is looking for bright parts of the image. As Dimorphos gets closer, brighter and bigger, SMART Nav will target it as opposed to Didymos,” said Angela Stickle, planetary geologist and DART Investigation team lead during the NASA livestream.