Mission to Mercury: Just the Facts


—Image courtesy NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

NASA’s MESSENGER space probe sent some postcards home this morning from its second jaunt past Mercury, that tiny planet nearest to the sun.

The flyby is part of some maneuvering MESSENGER has to do to ease itself from orbiting the sun to orbiting Mercury.

Using the gravity of other planets helps the orbiter reach Mercury while saving on fuel, a bit of technique that was not even feasible until the 1980s.

MESSENGER’s entire trajectory, looking down on Earth’s orbit plane


—Image courtesy NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

NatGeo News reporter Anne Minard has the skinny on what scientists are saying about the new images, including the implication that geologic processes on Mercury might be an awful lot like those on the moon.

Minard also collected a great set of facts and figures about Mercury and its exploration that didn’t make the cut for the news story, but that I think deserve a bit of airtime:

  • Mercury has a metal-rich core 60 percent denser than Earth’s.
  • The planet’s thin atmosphere is contains sodium, calcium, potassium, and, surprisingly, water vapor.
  • Mercury’s daytime surface temperatures can reach over 800 degrees Fahrenheit (426 degrees Celsius), but it looks like the planet still manages to have ice in some of its craters.
  • Mariner 10 flew by Mercury three times in 1974 and 1975, capturing images of about 45 percent of the planet’s cratered surface.
  • MESSENGER launched on August 3, 2004. It carried about 1,323 pounds (600 kilograms) of liquid chemical propellant at launch, nearly 55 percent of its total launch weight.


  • The spacecraft conducted an Earth flyby in 2005 and two Venus flybys in 2006 and 2007 on its way to Mercury.
  • MESSENGER first flew by Mercury in January of this year, imaging a further 20 percent of the surface.
  • On its second flyby, MESSENGER flew 124 miles (200 kilometers) above Mercury’s surface during its closest approach on October 6, 2008.
  • The craft imaged 30 percent of the surface not seen during previous space-based missions.
  • As of today [October 7, 2008] MESSENGER is about 61million miles (99 million kilometers) from Earth.
  • The craft is halfway through a 4.9-billion-mile (7.9-billion-kilometer) journey into Mercury’s orbit that includes more than 15 trips around the sun.

—Image courtesy NASA

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