The spherical robots called hedgehogs are spiky to better cope with rolling and hopping across the surface of Phobos with its very low gravity.
Marco Pavone, an assistant professor in Stanford University in collaboration with NASA's Jet Propulsion Laboratory and Massachusetts Institute of Technology developed the hedgehog which is a sort of 'hybrid' machine - part flying spacecraft and part rover.
Phobos is small with a diameter of approximately 22.2 kilometres and since its discovery and that of its sister moon Deimos in 1877, very little has been learned about the nature of Phobos, website Gizmag reported.
It may be a captured asteroid or a chunk of Mars knocked off by an ancient impact. If it's the latter, then Phobos could provide a lot of information about Mars.
It's also a very good place to test technologies needed to explore Mars.
The problem is that Phobos' gravity is only 1/1000th that of Earth. This makes getting around on wheels, treads or legs extremely difficult because the low gravity means little or no traction, so building a rover for Phobos presents a challenge.
More From This Section
The hedgehog robot is roughly spherical, made up of many facets covered in solar panels and spikes. Inside the shell of the hedgehog are three rotating discs set at right angles to one another.
As these spin, the spikes dig in and the hedgehog rolls, hops, tumbles and bounds in ten-metre arcs over the Phoboian surface.
However, the hedgehogs will be accompanied by the Phobos Surveyor orbiting spacecraft. About the size of a coffee table and powered by two solar panels, it will act as the mother ship for up to six hedgehogs.
Both the Phobos Surveyor and the hedgehogs are designed to be largely autonomous due to being hundreds of millions of miles from mission control.
The Phobos exploration mission will take up to three years including the two-year journey from Earth. Once at Phobos, Surveyor will conduct scans from orbit, mapping the topography. It will then release one hedgehog at a time several days apart for close up surveys.
Surveyor and the hedgehogs work together to determine the spherical robots' locations and orientations and steer them toward targets. The hedgehogs then beam data to Surveyor for relay to Earth.
A prototype of the Phobos Surveyor has already been constructed and two generations of hedgehog prototypes have been built. Though no official go ahead has been given for the mission, Pavone hopes to see the hedgehogs deployed to Phobos within the next twenty years.