The New Horizons spacecraft is heading towards a mystery rock

Milky Way: view from the Karoo desert of Pluto and MU69

Milky Way: view from the Karoo desert of Pluto and MU69

NASA/JHUAPL/SwRI/Henry Throop

The thrusters have fired, the clock is ticking. Humanity’s envoy to the outer solar system, the same New Horizons probe that flew over Pluto in the summer of 2015, will meet a faint speck of light called MU69 on New Year’s Day, 2019.

There’s just one problem: we still don’t know what MU69 looks like. It might be a misshapen potato, two rocks touching each other like Chinese stress balls, or even a binary, a pair of objects separated by a wide gap.

Last month, this seemingly innocuous question ate up seven straight presentations at the annual meeting of the American Astronomical Society’s Division for Planetary Sciences in Provo, Utah – and for good reason.

If MU69 is a binary, that would be exciting because it would quite literally offer two space rocks