Leonard David's INSIDE OUTER SPACE

This image is one of the highest resolution images taken to date by the MESSENGER spacecraft. It features a field of secondary craters in Mercury’s northern smooth plains. Secondary craters are formed by the re-impact of debris strewn from a larger crater. The largest secondary craters in this image are roughly a few hundred meters across. If you look closely, you can see some small craters that are only tens of meters across.
Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

NASA’s MESSENGER – short for MErcury Surface, Space ENvironment, GEochemistry, and Ranging – has moved closer to Mercury than any spacecraft has before.

The spacecraft has been maneuvered to an altitude at closest approach of only 100 kilometers (62 miles) above the planet’s surface.

“This dip in altitude is allowing us to see Mercury up close and personal for the first time,” said Ralph McNutt, MESSENGER project scientist at Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland.

Doing so means closer looks at polar ice deposits, unusual geological features, and the planet’s gravity and magnetic fields, McNutt said in an APL press statement.

How low can you go?

Because of progressive changes to the orbit over time, MESSENGER’s minimum altitude will continue to decrease.

On August 19, the spacecraft’s minimum altitude will be cut in half, to 50 kilometers.

Closest approach will be halved again to 25 kilometers on September 12, noted MESSENGER Mission Design Lead Engineer Jim McAdams, also of APL.

Because of progressive changes to the orbit over time, MESSENGER’s minimum altitude will continue to decrease.

On August 19, the minimum altitude will be cut in half, to 30 miles (50 kilometers). Closest approach will be halved again to 15 miles (25 kilometers) on September 12, noted MESSENGER Mission Design Lead Engineer Jim McAdams, also of APL.

“Soon after reaching 25 kilometers above Mercury, an orbit-correction maneuver (OCM-10) will raise this minimum altitude to about 56 miles (94 kilometers),” noted McAdams.

“Two more maneuvers, on October 24 and January 21, 2015, will raise the minimum altitude sufficiently to delay the inevitable – impact onto Mercury’s surface – until March 2015,” McAdams said.

Extended mission

As the first space mission designed to orbit the planet closest to the Sun, the MESSENGER spacecraft was launched on August 3, 2004, and entered orbit about Mercury on March 18, 2011 (UTC), to begin its primary mission – a yearlong study of its target planet.

MESSENGER’s first extended mission began on March 18, 2012, and ended one year later.

MESSENGER is now in a second extended mission, which is scheduled to conclude in March 2015.