MESSENGER spacraft MESSENGER spacecraft Why Mercury? The Mission Education News Center Mission Operations Science Operations Who We Are Frequently Asked Questions MESSENGER Webcam Related Links Contacts Home
MESSENGER BannerThe NASA LogoThe Carnegie Institution of Washington LogoThe John Hopkins University Logo
bannerleft side of the Education and Public Outreach BannerRight side of the Education and Public Outreach BannerRight side of the Education and Public Outreach Banner

Core

The Mariner 10 mission sent back more than just pictures of Mercury's surface. On-board instruments detected a weak magnetic field - about 100 times weaker than Earth's. This came as a surprise, since the photographs from this mission showed a Moon-like surface, and the Moon's magnetic field is about 100 times weaker yet. A planet's magnetic field shields it from constant bombardment of charged particles streaming outward from the Sun - the solar wind.

Mercury’s magnetic field and high density both indicate that the planet has a large, iron-rich core, probably about 3600 kilometers in diameter. This core takes up a large fraction of the planet's volume, since Mercury's total diameter is only 4880 kilometers. Mercury’s ratio of core size to planet size is the largest of any planet in the solar system. Mercury prbably has only a thin lunar-like silicate mantle.

Learn about the Surface of Mercury

The Elusive Planet banner
 
Inside and Out
 
Mercury's iron core is thought to extend from the planet's center to nearly three quarters of the way to the surface, making it about the size of our Moon.