GETTING READY FOR THE DART MISSION
We speak to planetary scientist Nancy Chabot from Johns Hopkins University’s Applied Physics Laboratory (APL) about DART “DART is just one part of a larger planetary defence strategy”
What will the DART mission tell us about the viability of asteroid deflection?
One of the major challenges is targeting a small asteroid in space at very high speed when that asteroid has never been imaged by spacecraft previously. It is only within the last hour of the spacecraft’s approach to Dimorphos that the onboard camera can distinguish it from Didymos, the larger asteroid that Dimorphos orbits. The DART team at APL developed the SMART Nav [Small-body Maneuvering Autonomous Real Time Navigation] algorithms that autonomously navigate it to impact Dimorphos. Demonstrating this capability in space at high speed is challenging, but it’s also an important technology demonstration for planetary defence. DART’S demonstration of this technology will be a major result to inform future planetary defence activities.
Assuming the impact is successful, why is there uncertainty over how much the orbit will change?
How the asteroid reacts to the kinetic impact of the DART spacecraft is one of the main objectives to be investigated. We know from other asteroids that have been explored that they have a range of shapes, internal structures, surface properties and strengths, and these characteristics will influence how much the asteroid Dimorphos is deflected in its orbit around Didymos.
After DART, what’s the next step?
DART is just one part of a larger planetary defence strategy led by NASA’S Planetary Defense Coordination Office. Finding, tracking and characterising the near-earth object population is crucially important to the success of any future planetary defence mitigation efforts, of which DART is just the first test. Future planetary defence missions currently in the pre-launch development phase include the European Space Agency’s Hera mission, which will explore DART’S target asteroid system in 2026 and see the crater left by DART’S collision, and NASA’S NEO Surveyor mission to find near-earth objects.
Discovered in 1949, asteroid Icarus takes 409 days to complete an orbit around the Sun. Since that’s 12 per cent longer than Earth’s year of 365 days, you might think it puts it safely outside our own orbit. But Icarus travels on a very elliptical orbit, the outermost point of which is outside the orbit of Mars, but at its innermost point is closer to the Sun than the planet Mercury. Between those two extremes there’s a point where its orbit intersects Earth’s. Every so often – most recently in 2015 – Icarus reaches this intersection point at roughly the same time Earth does, posing the small but real possibility of a collision. This possibility gained attention in 1967 when a study at the Massachusetts Institute of Technology, called Project Icarus investigated technological ways that such a collision might be prevented.
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Generally, when astronomers talk about potentially hazardous asteroids the stress is on ‘potentially’. They don’t pose a threat for the foreseeable future, but they travel on orbits that might lead to a collision in the more distant future. But when Apophis was first discovered, it was believed to have a real possibility of impacting Earth in April 2029. Fortunately, it’s now known this won’t happen. Apophis will whizz past at very close range – even closer than some communications satellites – but it won’t hit us. The same is true of other close encounters for at least the next hundred years.
Toutatis travels on an eccentric orbit, taking it all the way from the main asteroid belt between Mars and
Jupiter at its outermost point to within Earth’s orbit at its innermost. This orbit takes just over four years to complete, and almost every orbit since it was first discovered in 1989 has involved a relatively close pass of Earth. But even the closest of these, such as those in 2004 or 2012, couldn’t be classed as near collisions since the minimum distances were still as large as 4 and 18 times the distance from Earth to the Moon respectively. During the 2012 encounter, the first really clear pictures of the asteroid were obtained in two different ways: by radar imagery using NASA’S Deep Space Network antenna in Goldstone, California, and by China’s Chang’e 2 space probe, which was specially diverted to fly past the asteroid.
Bennu is another asteroid that makes occasional close passes of Earth and is large enough to cause serious devastation if it were to hit the planet. As with Apophis, that’s not going to happen in the foreseeable future, but even so it helps to understand such objects as thoroughly as possible.
That was the rationale behind NASA’S OSIRIS-REX (Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer) mission, which visited Bennu in 2021 and is now en route back to Earth with a sample of rock collected from it.