3 What Is Most Responsible for Changes in Earth's Landforms?
As the smallest planet in the solar system, Mercury often stands in comparison not to other planets but to Earth's moon, which NASA categorizes as only slightly smaller than the first planet from the sun. Mercury and the moon have more in common than their sizes, however. The appearances of their surfaces and the nature of substances found in and on top of those surfaces form the basis of similarities between these two bodies.
People may be tempted to compare Mercury and the moon because one's surface looks much like the other's. Both Mercury and the moon have surfaces, or crusts, composed almost entirely of rock and pocked with craters. Unlike Earth, which has an element-rich atmosphere in which incoming meteorites often burn, Mercury and the moon have thin atmospheres, called exospheres, that hold little gas and offer little insulation. Their craters are considered evidence of numerous meteorite strikes.
Additionally, their surfaces bear other features that, though resembling craters, actually are believed to be long-dormant volcanoes. Different from Earth's tall, mountainous monoliths, many of Mercury's volcanic structures likely resulted from lava oozing from vents in the crust. According to David Blewett of Johns Hopkins University, the lava spread from the vents and settled over Mercury's surface. Volcanoes on the far side of Earth's moon, where steep-sided domes dot the surface, may be the product of similar activity.
Looking at what lies above these bodies' geological markings, scientists have observed evidence of ice at the magnetic poles of both Mercury and the moon. Messenger, an exploratory spacecraft sent to Mercury in 2011, discovered hydrogen at the planet's north and south poles in amounts consistent with frozen water. Recent investigations by NASA's Lunar Reconnaissance Orbiter of the Shackleton Crater at the moon's south pole suggest that ice may lie in the reflective substance lining the crater's floor.
Similarities between Mercury's surface and the moon's extend even to surface composition. Both crusts contain large amounts of silicon and oxygen, together forming mineral silicates. Mercury's composition, in fact, may be 30 percent silicates. Like the moon, Mercury has a reflective surface; on the moon, this quality is traced to the presence of elements like aluminum and titanium. Mercury's crust also contains metals, including aluminum, though here enters one difference: Much of Mercury's metal exists in its dense iron core.
National Aeronautics and Space Administration: How Was Mercury Made?
Space.com: Does Mercury Hold Clues to Birth of Earth's Moon?