MESSENGER to Reveal Mercury

Scientists are eagerly awaiting Monday, Jan. 14, when the MESSENGER spacecraft will make its first flyby over the planet Mercury.

Launched on Aug. 3, 2004, MESSENGER (for MErcury Surface, Space ENvironment, GEochemistry and Ranging) is designed to be the first-ever spacecraft to orbit Mercury, the solar system's smallest planet and the planet closest to the sun. The MESSENGER mission, sponsored by NASA (the National Aeronautics and Space Administration), is aimed at helping scientists better understand how the solar system's planets formed and evolved over time.

One of the solar system's four rocky planets (the others are Venus, Earth and Mars), Mercury orbits the sun about once every 88 days. It's small -- with a diameter of just over 3,031 miles at the equator -- dense, and hard to observe because of its proximity to the sun. It's also the least-explored of the rocky planets, having been only partially mapped by Mariner 10 between 1974 and 1975.

Researchers hope the MESSENGER mission can help answer six important questions about Mercury. They're seeking to understand why the planet is so dense, how it evolved geologically, why it has a magnetic field similar to Earth's and what is the structure of its core. They also hope to learn more about why areas of Mercury's poles are so reflective to radar waves and what gases are most important in the planet's very thin atmosphere.

In an interview with Planetary Radio host Mat Kaplan this week, MESSENGER principal investigator Sean Solomon said the mission aims to fill in many blanks left by the Mariner 10 mission more than 30 years ago.

"I was a very junior assistant professor at MIT (the Massachusetts Institute of Technology) back when Mariner 10 flew by Mercury three times in 1974 and 1975," said Solomon, now with the Carnegie Institution of Washington. "It made some important discoveries that raised some questions that have been with us for three decades. So to be returning to Mercury -- initially with this flyby but ultimately to go into orbit -- with a modern suite of instruments to answer those three-decade-old questions has all of us at the edge of our seats."