The tiny planet is made up of a single continental plate over a cooling iron core. By comparison: 0.459 times that of EarthĪs if Mercury isn't small enough, it not only shrank in its past but is continuing to shrink today, according to a 2016 report. By comparison: 0.313 times that of EarthĪphelion (farthest distance from sun): 43,380,000 miles (69,820,000 km).
By comparison: 0.38 Earth's distance from the sun Comets or meteorites may have delivered ice there, or water vapor may have outgassed from the planet's interior and frozen out at the poles.Īverage distance from the sun: 35,983,095 miles (57,909,175 km). The southern pole may also contain icy pockets, but MESSENGER's orbit did not allow scientists to probe the area. Another large impact may have helped create the planet's odd spin, according to research in 2011.Īs close to the sun as Mercury is, in 2012, NASA's MESSENGER spacecraft discovered water ice in the craters around its north pole in 2017, where regions may be permanently shaded from the heat of the sun. Known as the Caloris Basin, this crater could hold the entire state of Texas. About 4 billion years ago, an asteroid roughly 60 miles (100 km) wide struck Mercury with an impact equal to 1 trillion 1-megaton bombs, creating a vast impact crater roughly 960 miles (1,550 km) wide. Since it has no significant atmosphere to stop impacts, the planet is pockmarked with craters.
Mercury is the smallest planet - it is only slightly larger than Earth's moon. – Mercury-bound spacecraft snaps selfie with Venus in close flyby (photo) – Fly by Mercury with this stunning video from the BepiColombo spacecraft – What is a 'morning star,' and what is an 'evening star'?
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