Photo: "Supergiant" Asteroid Shut Down Mars's Magnetic Field



A "supergiant" asteroid several times larger than the one that likely killed the dinosaurs struck Mars with such force that it shut down the planet's magnetic field, scientists said in May 2009.

That impact created the 2,000-mile-wide (3,300-kilometer-wide) Utopia crater (dark-blue circle, pictured), which dates back roughly 4.1 billion years.

Photograph courtesy NASA


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