We’ve had an unbroken presence at Mars for a quarter of a century. It started with Mars Global Surveyor, which began settling into orbit 25 years ago today. Before Global Surveyor, it had been 15 years since there was a fully successful Mars probe. The United States and Russia both launched missions during the interim, but they all failed. Global Surveyor orbited Mars from pole to pole. It spent a year and a half dipping deeper into the upper atmosphere to sculpt its orbit. So it began full science operations in early 1999. The craft mapped all of Mars many times over. That allowed scientists to study changes on the surface caused by winds, meteorite impacts, and outbursts of water or gases from below the surface. It also watched the weather. Its pictures showed frontal systems, dust storms, and cloud formations. And the probe measured Mars’s gravitational and magnetic fields, revealing details about its interior. Global Surveyor’s original mission called for one Mars year of observati
