Out of this world idea

Using a tether system devised by MIT researchers, astronauts could one day stroll across the surface of small asteroids, collecting samples and otherwise exploring these rocks in space.

An asteroid's gravity varies depending on its density and size, which can range from a speck of dust to hundreds of kilometres. On an asteroid that has a diameter larger than eight kilometres, an astronaut who jumps will probably come back to the surface. But if the asteroid is smaller than that, the astronaut may float away.

Now, Christopher Carr, a postdoctoral associate in MIT's Department of Earth, Atmospheric and Planetary Sciences and Ian Garrick-Bethell, a graduate student in the department, say that tying a lightweight rope completely around an asteroid could solve that problem. Once the rope was in place, astronauts could attach themselves to it and manoeuvre or possibly even walk along the surface.

Some people have suggested that astronauts could bolt themselves directly to the asteroid, but the granular material covering the asteroids could prevent this.

'It would be like trying to bolt yourself to a pile of gravel or sand,' Garrick-Bethell said.

The MIT researchers envision deploying their system with an astronaut or a remote-controlled rocket that unwinds a spool of rope while flying around the asteroid. When the craft reaches the starting point, a loop is formed and tightened. Astronauts could then be held to the asteroid using one or more ropes, permitting them to work on the surface.

One unknown is whether the rope would cut into the granular surface of an asteroid, hindering the system's effectiveness. But even if the rope does not allow astronauts to walk on the surface, it could at least give them something to hold onto as they pull themselves along the asteroid without floating away, said Carr.