Tharsis begins with an event of astronomical improbability. Somewhere in the interplanetary medium, a meteoroid floating through space at 25 miles a second occupies the same bit of spacetime as the spaceship Inktomi, which is hurtling towards Mars at 11 miles a second. The ship and its crew have been travelling for weeks; the meteoroid, millenia. And there, in the emptiness of the cosmic void, they somehow meet. An impact; a burst of compressed air; a body blown into space; a crippled vessel drifting toward Mars. What remains is a quartet of crew and a fistful of dice to navigate…