Mars Global Surveyor

Mars Global Surveyor ushered in the modern era of Mars orbital science. Launched by NASA in November 1996, it arrived at Mars in September 1997 and spent nearly a decade mapping the planet in unprecedented detail, becoming one of the most productive and long-lived spacecraft ever sent to Mars.

Its instruments transformed our understanding of the planet. A laser altimeter measured the elevation of the entire surface with remarkable precision, producing the topographic map that revealed the true scale of features like the towering Olympus Mons and the vast Valles Marineris canyon system. Its camera returned images sharp enough to spot features just a few meters across, capturing gullies on crater walls that hinted at the recent movement of water or brine.

Perhaps its most far-reaching discovery came from measurements of remnant magnetism locked in the ancient Martian crust. These findings showed that Mars once had a global magnetic field like Earth's, generated by a churning molten core — a field that died billions of years ago, after which the solar wind stripped away much of the atmosphere. Mars Global Surveyor operated until 2006, far beyond its planned lifetime, and its data underpins much of what we know about the planet's geology and history today.