It’s not the space rock NASA is looking to target for its Asteroid Redirect Mission, but if an asteroid dubbed 2004 BL86 was just a few years later it might have been. On January 26, the half-kilometer asteroid will pass within 1.2 million kilometers of Earth — the closest any major stellar object will come for 12 more years. It’s a unique opportunity since this is an asteroid of meaningful size passing usefully close to the Earth, but it poses absolutely no threat to the Earth. Astronomers can watch and collect information at their leisure, as the space rock passes just four times further from the Earth’s surface than our own Moon. It’s such a close pass that if the night sky is clear you ought to be able to see it with a small telescope or strong binoculars.
1.2 million kilometers might seem like a long way for an object to pass, and it’s certainly a sizable miss for those of you worried about an asteroid-borne apocalypse, but in the context of super-powered optical telescopes, a million kilometers is a just stone’s throw. With such powerful spyglasses astronomers should be able to resolve all manner of interesting details about its structure and composition, perhaps even collecting some of the information projected to come from a (decreasingly likely) asteroid capture. At the very least, it should give astronomers the opportunity to gaze at a stellar time capsule bringing us information from a distant area of the galaxy — or at least, of our own solar system.
NASA will look at the asteroid first with microwaves, via its Deep Space Network of satellites, and attempt to collect some radar data. This should provide not just insights about the surface, but also the internal structure of the rock, about which astronomers currently know almost nothing. Asteroids are small and dark, meaning that astronomers rarely get the chance for a detailed look. Even their shapes make them difficult to study, as the jagged, erosion-free surfaces often cast long, jet-black shadows that render the majority functionally invisible.
An asteroid roughly ten times the size of 2004 BL86 passed about the same distance from Earth in 1967, but we only know about that close pass by tracking its path backward; tragically, this wonderful opportunity was totally missed at the time, and the mega-asteroid was only discovered in 1999. The danger posed by this asteroid, 1999 RD32, was only appreciated more than 30 years after it had already passed, and it stands as one of the best examples of the necessity of defensive star-gazing. The asteroid that killed off the dinosaurs and reshaped out planet some 65 million years ago was probably only about twice as large as 1999 RD32, so don’t dismiss the danger.
— Asteroid Watch (@AsteroidWatch) January 14, 2015
Asteroids have a lot of potential for future space science; they carry the majority of all evidence we have from other systems that doesn’t come in the form of light, and according to one NASA researcher they could represent cosmic “refueling stations” for long term missions. They are more accessible than planets and moons, more plentiful than comets, and they are often broken-off bits of larger bodies we can track back for insight.
Close passes like this should be able to offset any potential failures in asteroid redirection, granting some insight into the nature of space rocks even if we can’t use ion thrusters to push one into a stable lunar orbit. Though they are often thought of as little more than dead rocks, large bits of space debris with little function other than causing randomized extinction events, asteroids hold marvelous potential to reform the scientific understanding of space.