NASA's Mars exploration rover, Spirit, has reached the summit of a hill it first spied in the distance when it landed on the red planet in January 2004.  Astronomers say the perch is not only giving them a spectacular view of the martian horizon, but valuable scientific data. 

It has taken Spirit 590 days to reach the summit known as Husband Hill, part of a mountainous range known as the Columbia Hills.  Columbia Hills are named for the ill-fated space shuttle Columbia and Husband Hill honors the ship's commander, Rick Husband.

The crest of Husband Hill is 106 meters above the site where the space rover landed in Gusev crater.  The crater is a bowel about 150 kilometers in diameter that scientists selected as a landing site because the terrain suggested it once held a lake.

During it's slow, rocky climb up the hill, Spirit has found mineral deposits suggesting that water once flowed on the red planet.  From the top of Husband Hill, the rover is sending back images of layered outcrops to the south of the crater which scientists now believe are the remnants of water flowing out of the crater.

Steve Squyres is principal investigator for the Mars mission involving Spirit and its twin rover, Opportunity.  Mr. Squyres says the rocks encountered in Columbia Hills are so far the oldest on the planet.

"They provide a wonderful glimpse into what Mars was like in the earliest part of its history," said Mr. Squyres.  "It was a violent place.  It was a place where meteorite impacts were happening frequently.  It was a place where there volcanic explosions happening frequently.   Hot stuff was raining from the skies.  There was water.  When rocks were deposited, water would flow through those rocks and change their chemistry.  This is a glimpse into the ancient past of Mars."

Mission scientists say Spirit will remain atop Husband Hill for about a month analyzing mineral samples.

The Mars rover team says the vehicles are in superb shape almost a year longer than scientists expected the mission to last given the planet's harsh conditions.