N EW YORK CITY — Tucked away in a building on the corner of 72nd Street and York Avenue in Lenox Hill, an extraterrestrial marvel sits sturdily on a white pedestal. It's the largest Mars rock on planet Earth — and it turns out its 54-pound (25-kilogram), ashy terracotta structure isn't as priceless as you'd expect.

A chunk of the Martian surface that made an unlikely voyage to Earth will be available to the highest bidder at Sotheby's auction in New York.