"We are still ironing out the funding details, but we are pleased to be able to support the continued exploration of Mercury," NASA MESSENGER program scientist Ed Grayzeck said.
The extension will mean the unmanned spacecraft will continue to perform science beyond the planned end of its primary mission March 17.
"The extended mission guarantees that the best is indeed 'yet to be' on the MESSENGER mission, as this old-world Mercury, seen in a very new light, continues to give up its secrets," project scientist Ralph McNutt of the Johns Hopkins University Applied Physics Laboratory said in a release Tuesday.
The laboratory built and operates the MESSENGER spacecraft and manages the mission for NASA.
MESSENGER launched Aug. 3, 2004, and entered orbit around Mercury on March 18, 2011, to begin its primary mission -- a year-long study of the planet.