The DART mission — which was launched in late November last year — will test whether a simple, kinetic impact based on the transfer of momentum could provide a viable means of deflecting asteroids found to be on a collision course with our planet. The target asteroid for the test, Dimorphos, is a 560-foot-diameter “minor-planet moon” in orbit around a larger asteroid, 65803 Didymos, both of which are in the asteroid belt between Mars and Jupiter, some 6.8 million miles from the Earth. The pair were chosen by NASA for the DART test for a number of reasons, including both their relative closeness to Earth, and the fact that, being part of a binary system, one can calculate any changes to Dimorphos’s velocity by tracking how often the light from Didymos dims when its satellite passes in front of it.
Furthermore, NASA have explained, Dimorphos’s scale of what may need to be deflected in a future apocalyptic collision-course-with-Earth scenario.
As the Didymos system’s orbit does not cross that of our own, however, neither presently pose a threat to life on Earth, with the DART mission simply being an experiment. According to NASA, there is also no risk that tomorrow’s deflection experiment could cause either body to become an impact hazard.
Insead, the impact of the 1,000 lbs spacecraft into Dimorphos at some 14,760 mph — providing the equivalent energy of three tonnes of TNT explosives — is expected to reduce the asteroid’s velocity by around 0.4 millimetres per second, bringing it in closer to Didymos and reducing its orbital period by around ten minutes.
While this change in velocity may seem minor, if induced early enough on an asteroid on a collision course with Earth, the impact on its trajectory over the span of years should be enough to push it onto a safer course.
In an advisory statement, the space agency explained that “this test will show a spacecraft can autonomously navigate to a target asteroid and intentionally collide with it to change the asteroid’s motion in a way that can be measured using ground-based telescopes.
“DART will provide important data to help better prepare for an asteroid that might pose an impact hazard to Earth, should one ever be discovered.”
NASA planetary defence officer Lindley Johnson added: “This is an exciting time, not only for the agency, but in space history and in the history of humankind quite frankly.”
Live coverage of the impact will be provided by NASA TV, beginning at 6.00pm ET (11.00pm BST) tonight on the space agency’s website, as well as their Facebook, Twitter and YouTube accounts.
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Closer to Dimorphos, the impact of the DART spacecraft will also be witnessed by the Italian Space Agency’s Light Italian CubeSat for Imaging of Asteroids (LICIACube).
The tiny craft, which will perform a flyby of the Didymos system at a distance of around 34 miles some 165 seconds after the collision, will send images of Dimorphos as well as the impact ejecta and plume back to Earth for analysis.
And in October next year, the European Space Agency (ESA) will launch its Hera mission, which will arrive at Dimorphos in 2026 to determine exactly what effect DART’s impact had.
The craft, which will sport cameras, spectrometers, radar and even toaster-sized support satellites to help it measure the asteroid’s shape, mass and both chemical and physical makeup.
At the International Astronautical Congress in Paris last week, NASA administrator Dr Bhavya Lal said: “”If an asteroid is made up of, for example, loose gravel, approaches to disrupt it may be different than if it was metal or some other kind of rock.”
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Astrophysicist Professor Alan Fitzsimmons of Queen’s University Belfast is a member of both the NASA DART Investigation Team and the ESA Hera Science Management Board.
He said: “I’ve been waiting 20 years to see a Planetary Defence test to be performed.
“DART will give us our first proof that we have the technology to prevent a small asteroid hitting Earth. The teams at NASA and APL are doing exactly what we need to do.
“Once the DART and follow-up Hera mission have been successfully completed, we’ll have a much better idea how to protect ourselves against a catastrophic impact.”
Referencing Netflix’s recent apocalyptic black comedy, Prof. Fitzsimmons quipped: “The film may have been called ‘Don’t Look Up’, but it’s a good job we are!”