In a remarkable discovery 126 million miles from Earth, the Mars rover Opportunity has found a second large iron meteorite sitting just a half mile from its twin sibling where they both landed on Mars within seconds of each other 3 billion years ago.

The new "Sheltered Rock" meteorite discovered by Opportunity Oct. 2, lies only 2,300 feet away from the "Block Island" meteorite that the rover discovered in July and examined for six weeks.

Cornell Pancam mosaic prepared exclusively for Spaceflight Now, shows the area between Block Island and the new Sheltered Rock meteorite has some dangerous terrain including small young craters deep sand dunes. See larger image here

Designated "Sheltered Rock" by the rover team, the new meteorite almost certainly came from the same body as Block Island that was discovered July 18. They both laid undisturbed at the same spot until Opportunity stumbled across them while driving west across the Meridiani plain.

Sheltered Rock is about 18.5 inches long compared with about two feet for Block Island. Each weighs several hundred pounds and are quite similar to each other.

Analysis indicates both fell about 3 billion years ago when Mars had a much thicker atmosphere that slowed impact velocity so the rocks did not explode and dig craters when they hit the planet.

An inspection plan is being drawn up at Cornell University and Jet Propulsion Laboratory to use the rover's robotic arm to place its spectrometers and microscopic imager on Sheltered Rock for a direct comparison with data from Block Island.

Pancam image of new Sheltered Rock iron-nickel meteorite shows where it has sat for 3 billion years. Compare this view of Sheltered Rock with false color view of Block Island final image below. Credit: NASA/JPL/Cornell University

Discovery of the second body will also provide new data on both the meteorite and early Martian atmosphere since it is likely whatever aerodynamic forces it did encounter, resulted in separation of the pair at a low enough altitude for both of them to hit so close together.

It is not unusual on Earth to find multiple pieces from the same meteorite event. But on Mars with a single rover, driving in a specific direction, it is remarkable that Opportunity encountered a second meteorite related to the first.

The new discovery is also the third meteorite found by Opportunity since it discovered a much smaller basketball sized meteorite lying near its heat shield ten months after landing in January, 2004.

In addition to being smaller, that initial meteorite dubbed Heat Shield Rock looks more rounded and polished than the more rectangular Block Island and Sheltered Rocks. Data from all three will be compared to see if Heat Shield rock could also be related to the original body that spawned the more recent finds. All three fell relatively close together with Heat Shield rock only about 11 miles away from the other two.

Opportunity's top right solar array is in foreground as rover makes a slow pass to left of Sheltered Rock. Credit: NASA/JPL/Cornell University

Opportunity had been driving west for three weeks after it left Block Island to continue its journey toward Endeavour crater, still more than a years drive time away to the south. The jog west was to avoid dangerous terrain. Images taken on about sol (Martian day) 2,020 of its mission spotted something unusual ahead. On sol 2,022 Opportunity completed a drive of 94 feet to pull up beside what turned out to be the Sheltered Rock meteorite.

While Opportunity continues to score scientifically on its marathon traverse to Endeavour crater, the rover Spirit on the opposite side of Mars remain stuck in powdery volcanic material where it was halted in early May. JPL computer runs using physical data from two test rovers in a JPL sand box continue to asses escape techniques. But it looks increasingly likely that Spirit's driving days are over although it's Cornell University Athena science package will continue to return valuable data even if it is stuck for good.

Steve Squyres rover principal investigator at Cornell has also just won a prestigious award for communicating the rover story to the public.

For his work making NASA's Mars Exploration Rover mission a compelling saga for millions of people, Steven W. Squyres has received the 2009 Carl Sagan Medal from the American Astronomical Society.

Controllers have deployed rover's arm with sensors as Opportunity moves in closer to meteorite. Credit: NASA/JPL/Cornell University

The Sagan medal recognizes a planetary scientist for excellence in public communication. Squyres received the medal during the AAS's Division for Planetary Sciences annual meeting, Oct. 4 to Oct. 9, in Puerto Rico.

In addition to heading rover science operations Squyres is also the Goldwin Smith Professor of Astronomy at Cornell where he was quick to share credit with the entire Mars rover mission team there and at JPL. Squyres said he has always taken seriously the responsibility of giving people -- the taxpayers who have bankrolled the mission -- a clear window into what they are doing on Mars.

"We feel very strongly that the people who pay have a real right to find out in very clear, simple terms what they're getting for their $900 million," Squyres said.

Since January, 2004, when Spirit and Opportunity landed, the rover team has maintained a publicly accessible database of images taken by the spacecraft. Atypical of most NASA missions, the rover project has allowed people to access data almost immediately. It was a conscious decision by the rover team, Squyres said, to pipeline the data straight to the Web. Squyres told Spaceflight Now that some senior NASA managers were against this approach early on.

False color image of Block Island meteorite allows comparison with new Sheltered Rock meteorite shown in pictures above. Credit: NASA/JPL/Cornell University

"If I'm asleep and you're awake, you can see the pictures from the rover before I do," Squyres said. "And what that has done is it's really enabled people to share in this voyage of exploration."

Squyres hopes these efforts, including the Web site that provides updates of rover activities, has inspired young people to pursue careers in science and engineering.

As a Cornell graduate student in the early 1980s Squyres began working closely with Sagan who died in 1996. "Carl really pioneered, in a very important way, the way in which scientists interact with the media and the public," Squyres said. "To receive an award that's named after him for trying to do the same sort of thing that he did so brilliantly is a real honor."