Recent asteroid tests have resounded the need for international space agencies to team up and smash a craft into space rock. Scientists at NASA have said that the time has come when they are preparing to do just that.
The target asteroid is Didymos B, the smaller of the two rocks in the Didymos binary asteroid system and the spacecraft will be NASA’s Double Asteroid Redirection Test aka DART. The mission is to test whether a spacecraft impact can truly deflect an asteroid’s trajectory as a contingency plan to protect Earth from rogue space rocks.
The combined AIDA that stands for ‘Asteroid Impact and Deflection Assessment’ project was announced by the European Space Agency (ESA) and NASA in 2015, but recent surprise findings from ensuing asteroid missions may have significance for the test.
For instance, when Japanese JAXA’s Hayabusa2 bombed asteroid Ryugu in April this year, its impact made a much larger crater than expected. In addition, the rocky material on the asteroid’s surface behaves a lot like sand which could influence the effectiveness of kinetic impact deflection.
Planetary scientist Patrick Michel of CNRS explained, “The impact with Hayabusa2 showed that there was no cohesion on the surface and the regolith behaved like pure sand. Gravity was dominating the process, rather than the intrinsic strength of the material from which the asteroid is made. If gravity is also dominant at Didymos B, even though it is much smaller, we could end up with a much bigger crater than our models and lab-based experiments to date have shown. Ultimately, very little is known about the behaviour of these small bodies during impacts and this could have big consequences for planetary defence.”
After an AIDA workshop last week in Rome, scientists have come together at the EPS-DPS Joint Meeting 2019 in Geneva to pursue the project further.
Astronomer Ian Carnelli of the ESA told Technology Review, “Today, we’re the first humans in history to have the technology to potentially deflect an asteroid from impacting the Earth. The key question that remains to be answered is, are the technologies and models that we have good enough to actually work? Before you drive a car, you need to have an insurance policy. Well, AIDA is the insurance policy for planet Earth.”
The Didymos system provides the perfect testbed for this mission as it is a near-Earth object but not too far away. Also, as at present, it isn’t on a collision course with Earth so our tests are unlikely to backfire.
Planetary scientist Nancy Chabot of Johns Hopkins University Applied Physics Laboratory said, “DART’s target, Didymos, is an ideal candidate for humankind’s first planetary defense experiment. It is not on a path to collide with Earth and therefore poses no current threat to the planet. However, its binary nature enables DART to trial and evaluate the effects of a kinetic impactor.”
In this asteroid binary, the larger object of Didymos A measures around 780 meters across while the smaller Didymos B measures 160 meters. It is sometimes called “Didymoon” as it orbits the larger asteroid every 11.92 hours.
When DART smashes into Didymos B at a speed of 23,760 kilometers per hour (14,760 miles per hour) as per plan, it is expected to only change the asteroid’s speed very slightly i.e. just a centimeter per second or so.
This might not be detectable in a single asteroid but in the binary Didymos system, the impact is anticipated to slightly change the orbital period. From its original 11.92 hours, Didymos B may take a few minutes more to go around Didymos A.
Although it doesn’t sound like much, if we are able to intercept an Earth-bound asteroid early enough, even the slightest velocity change could make all the difference.
DART is scheduled to launch in July 2021, for an impact targeted in September 2022. A small cubesat named the LICIAcube will separate from the spacecraft just before impact to take photos of the ‘smash’ and beam them back to Earth. Then Earth-based telescopes will constantly observe Didymos check if the transit times change by tracking the regular dips in the system’s light curve.
The second part of the joint mission will be ESA’s Hera, a small observation spacecraft that will launch in 2023 to reach and observe Didymos B in 2027. As the asteroid system can’t be clearly seen from Earth, Hera is intended for providing all the finer details like whether the DART impact makes Didymos B wobble longitudinally, etc.
Hera has already passed its system requirements review and is presently proceeding into the development stage.
Carnelli told Technology Review, “Planetary defence is really a worldwide endeavor. Besides just the technology and the science, AIDA is also a really good experiment in terms of collaboration between scientists and agencies around the world. It’s the sort of thing that would be needed were an asteroid on a collision course for Earth.”