Mercury is our solar system's closet planet to the Sun. Because it is so close to the Sun, Mercury is difficult to observe and can only be seen during twilight.
Orbiting the Sun in just over 88 days, Mercury is never more than 28° away from the Sun.
Mercury is a very dense planet and has a strong magnetic field which implies a solid metal core.
The surface of the planet is heavily cratered with several that exhibit prominent "rays" from the impact.
The largest crater on Mercury is the Caloris Basin which formed from an ancient impact and is about 1300 km across.
There is little evidence of an atmosphere, so the nighttime temperature drops 600°C from the daytime temperature.
There have been only two major NASA missions to Mercury.
Mariner 10
The Mariner 10 mission to Mercury launched on November 3, 1973 and
arrived at Mercury on March 29, 1974. The spacecraft flew by the planet
on March 29, 1974, September 21, 1974 and March 16, 1975 and took images
covering about 57% of the planet surface. Mariner 10 was the first spacecraft
to use “gravity assist” to alter its trajectory.
Mercury Surface, Space Environment, Geochemistry and Ranging (MESSENGER)
Messenger is slated to be the first Mercury Orbiter.
Launched on Aug 3, 2004, it is scheduled to go into orbit on March 18, 2011.
Messenger contains two imagers, one wide field and one narrow field,
a Gamma ray detector, a magnetometer, a laser altimeter and other instruments.
These instruments will be uses to study Mercury’s surface, geology and magnetosphere.
Since Mercury is so close to the Sun, if we send a probe there directly,
it will be moving too fast to be captured by Mercury’s gravity and will be a “fly-by” mission.
By using a roundabout path, Messenger approaches Mercury slowly so it can achieve an orbit.
The path chosen for Messenger uses “gravity assist” to slow the spacecraft by flying past
Venus, Mercury and the Earth several times on the way to its final approach into orbit.
For more information about Messenger, please visit
Messenger site.