Mercury

The Swiftest Planet
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    IntroductionThe Latest: Like the waistband of a couch potato in midlife, the orbits of planets in our solar system are expanding. It happens because the Sun’s gravitational grip gradually weakens as our star ages and loses mass. Recently, a team of NASA and MIT scientists indirectly measured the Sun's mass loss and other solar parameters by looking at changes in Mercury’s orbit.

    The smallest planet in our solar system and nearest to the Sun, Mercury is only slightly larger than Earth's moon. From the surface of Mercury, the Sun would appear more than three times as large as it does when viewed from Earth, and the sunlight would be as much as 11 times brighter.

    Despite its proximity to the Sun, Mercury is not the hottest planet in our solar system—that title belongs to nearby Venus—but it is the fastest, zipping around the Sun every 88 Earth days. Explore Mercury ›

    Ten Things to Know About Mercury

    10 Things to Know About Mercury

    1

    Smallest

    Mercury is the smallest planet in our solar system - only slightly larger than the Earth's moon. If the sun were as tall as a typical front door, Earth would be the size of a nickel and Mercury would be about as big as a green pea.

    2

    Insider

     

    It is the closest planet to the sun at a distance of about 58 million km (36 million miles) or 0.39 AU.

    3

    Long Days, Short Years

    One day on Mercury (the time it takes for Mercury to rotate or spin once with respect to the stars) takes 59 Earth days. One day-night cycle on Mercury takes 175.97 Earth days. Mercury makes a complete orbit around the sun (a year in Mercury time) in just 88 Earth days.

    Mercury Transit - November 2006

    4

    Rough Surface

    Mercury is a rocky planet, also known as a terrestrial planet. Mercury has a solid, cratered surface, much like the Earth's moon.

    5

    Can't Breathe It

    Mercury's thin atmosphere, or exosphere, is composed mostly of oxygen (O2), sodium (Na), hydrogen (H2), helium (He), and potassium (K). Atoms that are blasted off the surface by the solar wind and micrometeoroid impacts create Mercury's exosphere.

    6

    Moonless

    Mercury has no moons. 

    7

    Ringless

    There are no rings around Mercury. 

    8

    Tough Place to Live

    No evidence for life has been found on Mercury. Daytime Temperatures can reach 430 degrees Celsius (800 degrees Fahrenheit) and drop to -180 degrees Celsius (-290 degrees Fahrenheit) at night. It is unlikely life (as we know it) could survive on this planet.

    9

    Big Sun

    Standing on Mercury's surface at its closest point to the sun, the sun would appear more than three times larger than it does on Earth.

    10

    Robotic Visitors

    Only two missions have visited this rocky planet: Mariner 10 in 1974-5 and MESSENGER, which flew past Mercury three times before going into orbit around Mercury in 2011.

    Hollows on Mercury

    Did You Know?

    Did You Know?

    Because of Mercury's elliptical—egg-shaped—orbit and sluggish rotation, the morning sun appears to rise briefly, set and rise again from some parts of the planet's surface. The same thing happens in reverse at sunset.

    Pop Culture

    Pop Culture

    The smallest planet in our solar system has a big presence in our collective imagination. Scores of science fiction writers have been inspired by Mercury, including Isaac Asimov, C. S. Lewis, Ray Bradbury, Arthur C. Clarke and H. P. Lovecraft. Television and film writers, too, have found the planet an ideal location for storytelling. In the animated television show Invader Zim, Mercury is turned into a prototype giant spaceship by the extinct Martians. And in the 2007 film Sunshine, the Icarus II spacecraft goes into orbit around Mercury to rendezvous with the Icarus I.

    In the comic strip Calvin and Hobbes, Calvin and his classmate Susie give a presentation about Mercury, in which Calvin's contribution is full of questionable information: "The planet Mercury was named after a Roman god with winged feet," says Calvin. "Mercury was the god of flowers and bouquets, which is why today he is a registered trademark of FTD florists. Why they named a planet after this guy, I can't imagine."

    Solar System in My Neighborhood

    Solar System Activity

    In this 1-hour activity, students shrink the scale of the vast solar system to the size of their neighborhood.

    Resources

    Resources

    Planetary Photojournal: Mercury

    Johns Hopkins University MESSENGER Mission Site

    Solar System News