Object: asteroid 16 Psyche
Alter ego: naked metal core
If Jules Verne were alive, he鈥檇 raise a toast. In a twist on his notion to journey to the centre of the Earth, a proposed spacecraft may get to visit the core of a proto-planet that was long ago stripped of its rocky outsides and cast adrift in the solar system.
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Asteroid was discovered in 1852, but it was not until the 1980s that it was recognised as an oddball. Radar observations made from Earth revealed that Psyche is about 200 kilometres across and is made of 90 per cent iron and nickel, with 10 per cent silicate rock.
This composition is strikingly similar to that of Earth鈥檚 metal core. That means Psyche could have started life as a small rocky world with a metal core and a silicate mantle, similar to the large asteroid Vesta. And astronomers think larger planets like Earth and Venus could have formed when such nascent worlds collided and merged.
But other times, incoming asteroids might have stripped a proto-planet of its soft outer layers. Psyche could have fallen victim to a series of hit-and-runs that robbed it of its mantle, leaving just the metallic core behind. If that core had been liquid at some point, it would have given the object a strong magnetic field. In fact, Psyche could still have a remnant field almost as strong as the Earth鈥檚.
Unique core sample
鈥淚t could be like a little refrigerator magnet in space,鈥� says of the Carnegie Institution in Washington DC, who presented an idea for a mission to Psyche at a meeting of the American Geophysical Union in San Francisco last week.
鈥淎 mission there is the only way that humankind will ever visit the core of any body,鈥� says Elkins-Tanton. 鈥淲e can learn about the building blocks of the planets in the first million years of the solar system in a way that we can鈥檛 do any other way.鈥� Her team鈥檚 proposed spacecraft would orbit the asteroid for about six months, making measurements of the metal world鈥檚 gravity, composition and topography.
Physically, Psyche could look quite different from any other space object we鈥檝e yet seen. Physicists have run laboratory experiments on how impact craters form on metal surfaces, and they suggest that Psyche鈥檚 craters could have dramatic rims that froze in splash-like patterns.
鈥淏ut here鈥檚 the thing: we don鈥檛 know what we鈥檙e going to see,鈥� says Elkins-Tanton. 鈥淲e鈥檝e seen rock worlds and ice worlds and gas worlds, but we鈥檝e never visited a metal world. We have no idea what it will look like. We only know we鈥檙e going to be surprised.鈥�
