Mars has had its share of mechanical visitors from Earth. But as of today, NASA's Mars Odyssey orbiter has officially been the red planet's longest-staying guest.
Dec. 15 marks the 3,340th day since the satellite entered orbit around Mars, passing the record previously set by the Mars Global Surveyor, another orbiting satellite. And Mars Odyssey hasn't been idling in space, either. Since its 2001 launch, Odyssey has made a fantastic contribution to our understanding of our fellow planet, scientists say.
"Our picture of Mars has changed over the past ten years," Odyssey project scientist Jeffrey Plaut of NASA's Jet Propulsion Laboratory in Pasadena, Calif., told SPACE.com. "And it's due in part to what Odyssey has discovered."
The orbiter's most famous discovery came a few months into the mission, when Odyssey found evidence for water ice under the Red Planet's rocky surface. This evidence led to the Phoenix mission, a Mars lander that touched down on the planet's surface in May 2008, and later confirmed the presence of water there.
As part of its stated mission, Odyssey also monitored the radiation levels on Mars to determine how safe the planet would be for human exploration. The atmosphere on Mars is considerably thinner than that of Earth, and it lacks magnetic shielding, both of which protect humans from solar flares and cosmic radiation. Odyssey determined that the Martian radiation levels are 2 percent to 3 percent higher than those on our planet. If astronauts were to visit the planet, they would have to take precautions, such as limiting the time they spend outside and the distance they would travel from protective habitats.
Scientists' understanding of Martian weather has also improved significantly since Odyssey set its sights on the planet. Over the spring and summer, dust storms criss-cross the landscape. Occasionally, they evolve into planet-engulfing storms, visible by Earth-bound telescopes.
Monitoring these storms and other weather patterns over several years has increased the store of knowledge available, giving climate modelers more information to work with as they try to determine their causes and effects.
The Mars Odyssey probe completed these official tasks by 2004, when its prime mission ended. Yet its work continues today.
"We have met all of our official requirements for the mission, but there are scientific goals we had from the outset that we continue to pursue," Plaut said.
One of the most important goals is the creation of a complete high-resolution global map of the planet. Odyssey's orbit was adjusted years ago so it could capture images of the ground directly beneath it in the late afternoon. The minerals and rocks in the soil give off the best thermal signal between 3:30 and 4 (Martian time), so the orbiter maps the areas at this time of day, moving slightly with each pass to create a mosaic.
"It's like wrapping string around a ball of yarn," Plaut explained. "You put each string next to the previous one." The pictures overlap only slightly with their neighbors, creating an in-depth map.
Odyssey is also continuing to pursue climate research. Over the course of several years scientists have monitored long-term climate patterns on Mars using data from the probe. Neutron detectors on Odyssey monitor the amount of carbon dioxide cycling from the ice on Mars' poles.
And Odyssey doesn't operate in a vacuum ? it often partners with other spacecraft near Mars. Its location high above the surface has allowed it to serve as the primary communication relay for Spirit and Opportunity, two exploration rovers on the surface of Mars.
Odyssey also served as a hub for the Phoenix Mars Lander, broadcasting data back to Earth from the craft on the ground. It has also worked with NASA's Mars Global Surveyor and Mars Reconnaissance Orbiter to observe weather changes over the years.
Odyssey's teamwork will continue in 2012, when NASA?s next rover, Curiosity, lands. Its position may be tweaked to observe the landing, and afterward, it will serve along with the Mars Reconnaissance Orbiter to send data from Curiosity back to Earth.
After almost a decade in space, Odyssey is holding up surprisingly well, scientists say. After an intense solar storm in 2003, the Martian Radiation Environment Experiment (MARIE) shut down. Also, one of the components in the gamma ray spectrometer (GRS) no longer functions.
However, most instruments are still functioning and Odyssey continues to gather an abundance of scientific data. In fact, the spacecraft still has a backup subsystem that has yet to be utilized because the primary systems still work so well.
Odyssey is part of a partnership between NASA, JPL, and Lockheed Martin Space Systems, with Lockheed responsible for its production, as well as continuously monitoring communications from Odyssey.
"The success and durability is a real tribute to the way (Lockheed) built the craft," Plaut said.
So how much longer will Odyssey continue to send information to earth?
"If you had asked me 10 years ago," Plaut said, "I would have said four or five years max."
That guess obviously would have fallen short. Plaut cautioned about the fallibility inherent in such predictions before adding, "I don't see any reason we won't go another 10 years ? as long as we don't run out of fuel or funding."
- Special Report: Odyssey Mission to Mars
- Gallery: Latest Mars Photos from Rovers Spirit and Opportunity
- Best Map of Mars Ever Made Hits Internet