Icehenge by Kim Stanley Robinson:
It stands at the north pole of the planet Pluto - a giants dance of ice frozen harder than stone, harder than steel. Each slab towers two hundred feet above the crater-pocked surface; the one in the center bears an inscription in Sanskrit. The first mission to Pluto found it there already, waiting for them. Is it a starlit message from an alien race? Or does it mark a human mystery? For there was one ship that might have passed this way, forgotten decades ago - if the crew survived. If the ship existed at all...