Mars Reconnaissance Orbiter (MRO) has collected more scientific data on Mars than any other spacecraft. MRO has orbited Mars since 2006, photographing virtually the entire planet every day. Scientists use MRO photos and other data to understand Martian weather, climate, and geology. The National Aeronautics and Space Administration (NASA) manages MRO. 
MRO carries several cameras. The HiRISE camera takes highly detailed images of the planet’s surface. It can resolve (distinguish) objects smaller than 1 meter (3 feet). HiRISE has produced over 1 million images. Another camera, called MARCI, captures daily photos of the weather across the planet. MARCI images show clouds, dust storms, and frost forming and changing.
MRO also carries a spectrometer, which no longer works. The spectrometer analyzed sunlight reflected from the planet’s surface to identify minerals. Data from the spectrometer enabled scientists to create detailed maps showing where certain minerals occur. The mineral maps help scientists decide where to send landers and rovers. To function, the spectrometer needed to be cooled. The instrument’s cooling devices eventually stopped working, and NASA retired the spectrometer in 2023.
The spacecraft’s other instruments include a device called a sounder, which measures humidity, temperature, and dust in the Martian atmosphere. A radar instrument, built by the Italian Space Agency, can detect layered rocks and ice beneath the planet’s surface.
An important function of MRO is to help rovers and other surface probes communicate with NASA on Earth. A rover can send data directly to Earth when it is on the side of Mars that is facing Earth. But Mars constantly rotates, and a long transmission would be interrupted when the rover’s position turned away from Earth. An orbiter, however, is not blocked as often by the planet’s rotation. MRO can maintain long, uninterrupted transmissions to send large amounts of data. NASA’s Curiosity and Perseverance rovers send scientific data to MRO, which then transmits the data to Earth. MRO can also receive instructions and software updates from Earth and transmit them to the rovers. MRO sometimes shares these duties with two other NASA orbiters—MAVEN and Mars Odyssey—and orbiters managed by the European Space Agency. Together, these spacecraft make up the Mars Relay Network. 
MRO launched on Aug. 12, 2005, and entered Mars orbit on March 10, 2006. MRO replaced the Mars Global Surveyor, a NASA orbiter that took daily pictures of the surface from 1999 to 2006.
See also Space exploration (Exploring Mars).
