For more than a decade, Mars Odyssey has been circling the Red Planet. The NASA spacecraft broke a record in 2010 for being the longest-serving piece of machinery to work at Mars.
Mars Odyssey has been making discoveries of its own – such as finding extensive water ice under the surface of Mars — but it also plays an important part in the ever-growing network of Martian rovers. It has served as a communications relay for the now-dead Spirit rover and current Opportunity and Curiosity rovers. Odyssey is also expected to assist with the 2018 European-Russian ExoMars rover mission.
Channeling Clarke and sailing to Mars
Because Mars Odyssey was launching in 2001, NASA chose to name its orbiter after the book "2001: A Space Odyssey," which also spawned a movie in 1968 just ahead of the Apollo moon landings that began a year later. According to NASA, author Arthur C. Clarke (who was still alive at the time) "enthusiastically endorsed" the name for the mission.
Mapping was one of the main goals for the $297-million spacecraft. Odyssey was supposed to look at the chemical and mineralogical composition of Mars' surface in visual and infrared wavelengths. Additionally, it was supposed to keep an eye out for hydrogen (a likely indicator of water ice) and serve as a communications relay for the Spirit and Opportunity rovers that would land on Mars in 2004.
The 1,600-pound Odyssey launched April 7, 2001, without major incident and reached Mars on Oct. 23, 2001. To finalize its orbit, Odyssey used an "aerobraking" technique pioneered at the Red Planet by Mars Global Surveyor in 1997.
Essentially, Odyssey gradually used the friction of the Martian atmosphere to slow itself down. That maneuver saves on fuel and overall mission cost. This process, which took several weeks, put Odyssey into its final orbit in January.
Mapping Mars, better than before
With a few high-power cameras in orbit, Mars Odyssey could keep track of global weather conditions on the Martian surface. Some of its most spectacular examples were its pictures of Martian dust storms in 2007 and 2009. Odyssey's far-reaching eyes, NASA stated at the time, would be an early warning system to NASA mission planners concerned about protecting Spirit and Opportunity from any dust storms coming their way.
In 2008, Odyssey spotted evidence of salt deposits across about 200 places in the south of Mars. NASA considers these areas to be signs of where abundant water used to sit. Scientists theorized the deposits could come from groundwater, which evaporated and left deposits of mineral behind. Since the sites are not connected with each other, they are unlikely to be signs of an ancient global ocean, NASA added.
More unusually, in 2007 NASA sent out pictures of seven possible caves snapped by Mars Odyssey. The find, dubbed the "Seven Sisters," excited researchers because the caves could contain underground hiding spots for life. Scientists spotted the caves by mapping unusually warm spots that showed up at night. This was courtesy of Odyssey's Thermal Emission Imaging System (THEMIS), which can take pictures in the visual and infrared bands.
Mars Odyssey's greatest legacy is a complete map of the Martian surface. The entire planet was mapped in the highest resolution ever, at the time. In 2010, NASA released a global map stitched together from 21,000 THEMIS images taken over eight years. This map showed features of as small as 330 feet (100 meters) in size, although NASA said Odyssey has mapped certain areas at an even higher resolution. [Gallery: Pictures from Longest Mars Mission]
Other major discoveries: Odyssey found evidence of water ice lying beneath Mars' surface, a finding that was confirmed by Phoenix when it arrived on Mars. With regard to habitability, Mars Odyssey has also finished a radiation safety study with an eye to helping future astronauts walking on the Red Planet.
Working with other spacecraft
The spacecraft sometimes teams up with the Mars Reconnaissance Orbiter (MRO), which arrived in 2006, and the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft, which arrived in 2014, to perform work. One case was the search for a signal from the Phoenix Mars lander after a cold Martian winter.
NASA did not expect the lander to survive, but just in case, spent weeks hailing the lander with Mars Odyssey. MRO then took a picture of the Phoenix landing site and spotted damage using its High Resolution Imaging Science Experiment (HiRISE) camera. At that point, NASA declared Phoenix dead.
The rovers Spirit, Opportunity and Curiosity all have used Mars Odyssey to send data back to Earth. The orbiter can send information back much more quickly than the rovers. Having Odyssey handle the data transfer frees up more time for the rovers to wander around the surface and perform science experiments.
Additionally, Mars Odyssey's high-flying eyes can provide global context for any local findings the rovers scoop up. This is especially important for long-term investigations such as Mars Curiosity's search for habitable conditions. If Curiosity spots an environment on the ground that could sustain life, Mars Odyssey can search for the same phenomenon from up above.
More recently, Odyssey worked MAVEN and MRO to examine Comet Siding Spring. The comet passed within close reach of Mars in October 2014, providing a unique opportunity for spacecraft in that area to look at the visitor from the outer solar system.
The spacecraft made optical observations with its Thermal Emission Imaging System (THEMIS) and also looked for effects on Mars' atmosphere (particularly regarding the dust) with the neutron spectrometer and high-energy neutron instruments on board. Along with MAVEN observations, NASA concluded there was a possible Martian meteor shower when the comet went by, and the dust created vaporized metal in the planet's atmosphere.
Like any aging piece of machinery, Mars Odyssey has its cranky moments. It has entered "safe mode" temporarily several times during its mission, but has remained in contact with Earth through these incidents.
A 2007 update from NASA said safe mode incidents in 2005, 2006 and 2007 all came from the same root cause. "When the onboard flight computer could not get a routine response from the system that monitors the spacecraft's orientation, a fault protection feature in the software told the flight computer to reboot and put the spacecraft into the standby status," the status update read.
Safe modes occurred again in June 2008 and also, November 2009, because of a memory error. NASA briefly shelved normal science operations for Mars Odyssey following the latter incident, but a press release noted that controllers knew how to help the spacecraft as the same behavior happened in 2008.
Another safe mode occurred in 2010 when Mars Odyssey encountered a problem with its electronic encoder that controls a device designed to move Odyssey's solar arrays. NASA switched to a backup unit and essentially carried on. Mars Odyssey also had two brief safe mode incidents in 2012, including one a few weeks ahead of the Curiosity landing.
In June 2015, however, Odyssey finished 60,000 orbits around Mars and was reported to still be scientifically productive and working well. It already has one notch in the history books: on Dec. 15, 2010, Odyssey's 3,340 Earth days in orbit made it the longest-running Mars mission. The previous record was Mars Global Surveyor, which flew around Mars from Sept. 11, 1997 to Nov. 2, 2006.
As of November 2015, Odyssey was maneuvered into a new orbit to observe the "terminator," or the day-night line. This is expected to provide information on fog, haze, clouds and especially frosts that could disappear when the sun gets higher.