Later today, NASA’s DART spacecraft will attempt to smash into a non-threatening asteroid. It’s one of the most important things we’ve done in space — if not the most important thing — as this experiment to deflect a non-threatening asteroid could eventually result in a robust and effective planetary defence strategy for protecting life on Earth.
We’ve landed humans on the Moon, transported rovers to Mars, and sent spacecraft to interstellar space, yet nothing compares to what might happen today when NASA’s DART spacecraft smashes into Dimorphos, the smaller member of the Didymos binary asteroid system. Should all go according to plan, DART will smash directly into the 160-metre wide asteroid at 9:14 a.m. AEST (watch it live here) and change the rock’s speed by around 1%. That’s a small orbital adjustment for an asteroid, but a giant leap for humankind.
NASA’s DART mission, short for Double Asteroid Redirection Test, won’t mean that we suddenly have a defence against threatening asteroids, but it could demonstrate a viable strategy for steering dangerous asteroids away from Earth. It’ll be many more years before our competency in this area fully matures, but it all starts today with DART.
Existential implications
At a NASA press briefing on September 22, Lindley Johnson, manager of NASA’s Near-Earth Object Observations program, described DART as “one of the most important missions in space history” but also in the “history of humankind.” I wholeheartedly agree. Missions to the Moon, Mars, and Pluto are important and monumental in their own right, but this proof-of-concept experiment could literally lead to defensive measures against an existential threat. So yeah, pretty damned important.
The dino-extinguishing asteroid measured somewhere between 10-15 kilometres wide and was travelling around 13 km per second when it struck Mexico’s Yucatan Peninsula some 66 million years ago. The collision wiped out 75% of all species on Earth, including every animal larger than a cat. And of course, it ended the 165-million-year reign of non-avian dinosaurs.
Asteroids of that size don’t come around very often, but that’s not to say our planet is immune from plus-sized space rocks. Recent research estimates that somewhere between 16 and 32 asteroids larger than 5 km wide strike Earth once every billion years. That’s about once every 30 million to 65 million years. That said, impacts with asteroids wider than 10 km are exceptionally rare, happening once every 250 million to 500 million years.
Despite the infrequency of these events, it’s the kind of impact that would wipe out our civilisation. Developing the means to defend ourselves is obviously a smart idea, but the threat of colossal asteroids isn’t what keeps me up at night — it’s the smaller ones that are much more likely to strike our planet.
Smaller but still deadly
The Southwest Research Institute says our atmosphere shreds most incoming asteroids smaller than 50 metres in diameter. Objects that reach the surface, including objects smaller than 2 km in size, can cause tremendous damage at local scales, such as wiping out an entire city or unleashing a catastrophic tsunami. As Johnson explained during the DART press briefing, asteroids the size of Dimorphos strike Earth about once every 1,000 years. The solar system is home about a million asteroid larger than 49.99 m wide. An estimated 2,000 near-Earth objects (NEOs) are larger than 2 km wide. Impacting asteroids at sizes around 2 km “will produce severe environmental damage on a global scale,” according to SWRI. And as noted, impacting asteroids wider than 10 km can induce mass extinctions.
NASA categorizes asteroids as being potentially hazardous if they’re 30 to 50 metres in diameter or larger and their orbit around the Sun brings them to within 8 million km of Earth’s orbit. The space agency works to detect and track these objects with ground- and space-based telescopes, and its Centre for Near Earth Object Studies keeps track of all known NEOs to assess potential impact risks.
‘Planetary defence is applied planetary science’
As it stands, no known threat to Earth exists within the next 100 years. NASA is currently monitoring 28,000 NEOs, but astronomers detect around 3,000 each year. There’s a chance that a newly detected asteroid is on a collision course with Earth, in which case a DART-like mitigation would come in handy. But as Johnson explained, this type of scenario and our ensuing response won’t likely resemble the way they’re depicted in Hollywood films, in which we typically have only a few days or months to react. More plausibly, we’d have a few years or decades to mount a response, he said.
To protect our planet against these threats, Johnson pointed to two key strategies: detection and mitigation. NASA’s upcoming Near-Earth Object Surveyor, or NEO Surveyor, will certainly help with detection, with the asteroid-hunting spacecraft expected to launch in 2026. DART is the first of hopefully many mitigation experiments to develop a planetary shield against hazardous objects.
DART is a test of a kinetic impactor, but scientists could develop a host of other strategies, such as using gravity tractors or nuclear devices, the latter of which could be surprisingly effective — at least according to simulations. The type of technique employed will largely depend on factors having to do with the specific asteroid in question, such as its size and density. Kinetic impactors, for example, may be useless against so-called “rubble pile asteroids,” which feature loose conglomerations of surface material. Dimorphos is not expected to be a rubble pile, but we won’t know until DART smashes into it. As Johnson said, “planetary defence is applied planetary science.”
Safeguarding humanity from multiple threats
A case can be made that space experiments to help us live off-planet are more important than asteroid deflection schemes. Indeed, we currently lack the ability to live anywhere other than Earth, which limits our ability to save ourselves from emerging existential risks, such as run-away global warming, malign artificial superintelligence, or molecular nanotechnology run amok.
Yes, it’s important that we strive to become a multi-planet species and not have all our eggs in one basket, but that’s going to take a very long time for us to realise, while the threat of an incoming asteroid could emerge at any time. We’d best be ready to meet that sort of threat, while steadily developing our capacity to live off-planet.
Rework the solar system
More conceptually, the DART experiment is our introduction to solar system re-engineering. Subtly altering the orbit of a tiny asteroid is a puny first step, but our civilisation is poised to engage in more impactful interventions, as we re-architect our immediate celestial surroundings to make it safer or find better ways of exploiting all that our solar system has to offer. These more meaningful interventions, in addition to removing asteroid threats, could involve the geoengineering of planets and moons or even tweaking the Sun to make it last longer.
But I’m getting a bit ahead of myself. First things first — and fingers firmly crossed — that DART will successfully smash into its unsuspecting target later today.