NASA's Mars Reconnaissance Orbiter passes over the planet's south polar region in this artist's concept illustration. The orbiter's shallow radar experiment, one of six science instruments on board, is designed to probe the internal structure of Mars' polar ice caps, as well as to gather information planet-wide about underground layers of ice, rock and, perhaps, liquid water that might be accessible from the surface. Phobos, one of Mars' two moons, appears in the upper left corner of the illustration. Image
Credit: NASA/JPL/Corby Waste
The Mars Reconnaissance Orbiter (MRO) has beamed back fascinating images from Mars and has made some startling discoveries. The spacecraft carries NASA's most powerful orbital cameras, as well as radar and other instruments.
MRO will probably be best remembered for finding ice and other evidence of water on Mars, and its imagery of Comet Siding Spring in 2014. Its powerful camera also watched dust devils go across the surface, and sand dunes change in real time.
The orbiter also spent months searching for a suitable landing spot for the Mars Curiosity rover; today, it serves as a communications relay for Curiosity and another rover, Opportunity.
However, the spacecraft has also had multiple problems, including an incident in 2009 that saw all science stop for several months.
MRO launched Aug. 12, 2005, on top of an Atlas V rocket with a suite of science instruments on board. The HiRISE camera (High-Resolution Imaging Science Experiment) would peer at things on the surface, while the Mars Color Imager (MARCI) would watch over storms and clouds. Also on board were items such as radar, a spectrometer and a gravity field investigation package.
While pictures and video and searches for water are what tend to get the public excited about Mars, the scientists were also salivating about something different with MRO: its data capability.
Before launch, NASA promised that the spacecraft would beam back information three times faster than a conventional broadband telephone connection. This meant that scientists would receive information faster than ever before — which would be especially important when sending back data from rovers and other spacecraft on the surface of the Red Planet.
MRO tested out its super-speed capabilities in September, when it snapped some pictures of Earth's moon from 6 million miles (10 million kilometers) away. It then sent back 75 gigabits of data to Earth, which is the equivalent of about 13 CDs of information. That was a record amount of data at the time.
Aerobraking and money shots
The spacecraft made it into Martian orbit on March 10, 2006, and began beaming back images right away while putting itself into the correct orbit. MRO used a technique called aerobraking — brushing against the Martian atmosphere — to adjust its orbit. This process saves fuel and money, but takes a lot of time. MRO completed the challenging maneuvers successfully in September, after six months of adjustments.
One of MRO's first targets was the Opportunity rover. Opportunity, which had outlasted its 90-day mission by more than two years in October 2006, was on the edge of the Victoria crater. MRO sent a high-resolution picture not only showing the rover and its tracks, but also a shadow cast by the golf-cart sized vehicle on Mars.
After snapping some pictures of Opportunity's twin, Spirit, as well as the two Viking landers that arrived in 1976 — some obvious public relations shots — MRO's team then had progressed far enough to begin releasing science results.
In December 2006, some of MRO's first radar observations and pictures focused on layers of ice near the poles. "These deposits record relatively recent climate variations on Mars, like recent ice ages on Earth," said Ken Herkenhoff, from the U.S. Geological Survey, in a press release issued that month.
Safe mode scrapes
But MRO's high-resolution pictures briefly came under threat. In February 2007, NASA reported that the HiRISE camera was experiencing problems with "bad pixels" and other image noise in some of the camera detectors. The problem appeared to be worsening with time, which could impact the mission down the road. Another instrument also had trouble that appeared to be resolved at that time.
Later that year, the camera problem appeared to be holding steady and not getting any worse. NASA traced the problem to a design flaw and noted that it successfully took steps to address it.
In March 2007, MRO put itself into safe mode and switched itself to a backup computer. The spacecraft has done that occasionally in the years since then, but has always remained in contact with Earth for reboots and remote repairs.
The worst incident occurred in 2009, when NASA suspended science operations for months while making fixes in an attempt to resolve the issue. Frequent orbital computer resets prompted NASA to send a software upgrade to the ailing craft. Then, managers carefully brought MRO out of safe mode to resume work Dec. 16.
"It's good to have the instruments back on," said MRO mission manager Dan Johnston of NASA's Jet Propulsion Laboratory in December 2009. "This has been a long stand-down. Now we're ready to resume our science and relay mission."
MRO underwent another glitch in March 2014 after it unexpectedly swapped computers, triggering an automatic safe mode. The spacecraft was considered successfully recovered in about a week, and resumed regular science operations shortly afterwards.
Part of MRO's work involved searching for suitable Curiosity landing sites, as well as relaying information from the Spirit, Opportunity and Phoenix spacecraft. When Phoenix went out of contact with Earth, MRO snapped a picture showing ice and damage on the spacecraft. In general, MRO is a powerful tool in helping spacecraft roaming on the surface stay in touch with Earth.
Additionally, MRO has spent several years charting the effect of wind and water on the Red Planet — as well as giving clues into Mars' wet past.
In 2007, MRO scrutinized two Martian gullies previously imaged by Mars Global Surveyor. Researchers earlier speculated that changes in the gullies came from flowing water, but the new, sharper MRO images revealed these are likely from "landslides of loose, dry materials."
Later that year, MRO beamed back pictures of puzzling features on Mars that scientists dubbed "spiders" and "lizard skin." Researchers said the strange shapes were probably due to carbon dioxide gas popping out in the spring and shaping the terrain. Bright "fans" of material spotted on the surface were likely carbon dioxide frost.
One of MRO's greatest finds came in 2008, when the orbiter spotted clay-rich rock in Mawrth Vallis. This channel, in the northern hemisphere of the Red Planet, has several different types of clay overlying each other. Scientists said this probably happened when water mixed with the basalt that the northern highlands are known for.
Later that year, the spacecraft beamed back evidence of opal (or hydrated silica) sprawling across Mars — a big calling card for water. According to scientists, water on the Red Planet was present as recently as 2 billion years ago, which is a billion years later than previously believed.
Water, wind and carbon dioxide
In later years, MRO has seen avalanches, dust devils and rock fractures from orbit, giving close-up views of changes on Mars over several years. The spacecraft found other signs of water as well, with buried glaciers as well as ice poking around meteorite craters.
We've also learned new things about the atmosphere of Mars courtesy of the spacecraft. As the planet's tilt changes, liquid water on the surface is also affected as well as the number and severity of Mars' famous dust storms. A 2010 discovery of massive frozen carbon dioxide deposits at the south pole led scientists to believe that dry ice enters the atmosphere when Mars increases the tilt of its axis.
High-resolution imagery of the surface continues to come back from MRO, including observations of “ice spiders” and sand dunes in 2014. The spacecraft also beamed back stunning imagery of Comet Siding Spring when the celestial visitor flew relatively close to the planet in October 2014. Its pictures of the comet, which whizzed by 86,000 miles (138,000 kilometers) away, were described by NASA at the time as “the highest-resolution views ever acquired of a comet coming from the Oort Cloud at the fringes of the solar system.”
MRO's prime mission ended in December 2010, but NASA believes the spacecraft can still perform well until at least 2015. That will be important given the increased science that Curiosity is performing with its high-resolution cameras and roving science laboratory. The rover mission will beam back massive amounts of data through MRO for years to come.
- NASA Solar System Exploration: Mars Reconnaissance Orbiter mission
- NASA: MRO Multimedia Gallery: Images, videos & diagrams of the mission
- NASA: Comet Siding Spring overview