On July 25, MESSENGER moved closer to Mercury than any spacecraft has before, dropping to an altitude at closest approach of only 100 kilometers (62 miles) above the planet's surface.

"The science team is implementing a remarkable campaign that takes full advantage of MESSENGER's orbital geometry, and the spacecraft continues to execute its command sequences flawlessly as the 14th Mercury year of the orbit phase comes to a close," said MESSENGER Mission Operations Manager Andy Calloway, of the Johns Hopkins University Applied Physics Laboratory (APL).

The latest observational campaign includes closer looks at polar ice deposits, unusual geological features, and the planet's gravity and magnetic fields "in ways that have never been possible," said APL's Ralph McNutt, MESSENGER's Project Scientist.

"This dip in altitude is allowing us to see Mercury up close and personal for the first time."

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 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.

"Soon after reaching 25 kilometers above Mercury, an orbit-correction maneuver (OCM-10) will raise this minimum altitude to about 94 kilometers," he said.

"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."