Watching the Asteroids

Asteroids are always intriguing. Little planetoids that fly around the solar system in mysterious orbits, often swinging dangerously close to Earth. It’s that element of the unknown as well as the potential threat to life on Earth that always ensures their popularity.

There is a lot of work going on behind the scenes in modelling asteroid orbits and tracking them. The NASA Near-Earth Object Observations Program – dubbed Spaceguard – detects, tracks characterises both asteroids and comets passing by Earth (anything inside 28 million miles of Earth is regarded as Near-Earth). It uses both ground and space-based telescopes. This information is used to predict their paths, and to determine any potential hazard.  At any given moment some of the world’s most massive radar dishes are on the case.

A new space-based asteroid-hunting telescope is being planned. NASA scientists recently tested the Near-Earth Object Camera – a key instrument. That will be interesting to watch for, potentially doing for asteroids what Kepler did for planet-hunting.

One favourite way to get to know an asteroid is hitting it hard with another object (not recommended in personal relationships). Those collisions can tell us a lot about their structural integrity and composition. Trying to get that little probe to actually hit anything travelling at hypervelocity (11,000 km/h or above) is a feat in itself.

Knowing where an asteroid will be, and its structure and composition are vitally important things to know if we plan to move asteroids around or want to explore them for valuable materials.

Potential targets can be quite small – as tiny as 50 metres wide. One little-known complication of creating a scientifically significant impact is that they can also have their own little family of tiny moons orbiting around them. Trying to track down those secondary orbiting bodies can be a challenge, but critical to the success of any ultimate impact.

At least with asteroids you do not have the complication of jets of material firing into space, which you have with comets. These can upset imaging and guidance systems.

One likely candidate is the asteroid 1999 RQ36, which is the target of a NASA mission called OSIRIS-Rex. The currently slated launch date is September 2016, with the ‘landing’ in 2023 (now that’s long-term planning). Not only do the NASA scientists need to co-ordinate the impact, they have to ensure that the OSIRIS-REx spacecraft, with its crucial observing instruments, can monitor the results of the impact from a safe distance. This little craft will do a loop around Mars then close with its target at the rate of 49,000 km/h (8.4 mi/s). Needless to say mission scientists will be executing several deep space manoeuvres to refine its position during its approach. The spacecraft’s own automatic navigation system will take control only two hours from impact, executing three planned corrections at 90min, 30min and 3min from the impactor ‘landing’. At this point the spacecraft will be a mere 2,400 km away from RQ36. Cosmic spitting distance!

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