Eyes in the Martian Sky
By: Nicole Willett
While rovers on the Martian surface capture the public imagination with their close-up images of rocks and landscapes, the orbiters circling Mars above are equally essential to our understanding of the Red Planet. These eyes in the Martian sky provide global perspectives that no surface mission can achieve, mapping the entire planet, monitoring weather patterns, and serving as vital communication relays for rovers and landers below.
The Current Fleet
As of this writing, several active orbiters are studying Mars from above:
Mars Odyssey
Launched in 2001, Mars Odyssey is the longest-serving spacecraft at Mars. Its instruments have mapped the distribution of water ice beneath the Martian surface, identified minerals, and monitored radiation levels. Odyssey’s Thermal Emission Imaging System (THEMIS) has provided detailed maps of surface temperature and mineralogy across the entire planet.
Mars Express
The European Space Agency’s Mars Express, launched in 2003, carries a suite of instruments including the High Resolution Stereo Camera (HRSC), which has produced stunning three-dimensional images of the Martian surface. Mars Express also carries a radar instrument, MARSIS, that has detected subsurface water ice and even a possible subsurface lake beneath the south polar ice cap.
Mars Reconnaissance Orbiter (MRO)
MRO, launched in 2005, carries the HiRISE camera, the most powerful camera ever sent to another planet. HiRISE can resolve objects as small as a desk on the Martian surface, providing unprecedented detail for studying geological features, monitoring active surface processes, and scouting landing sites for future missions. MRO also carries the CRISM spectrometer, which has mapped the mineral composition of the surface with remarkable precision.
MAVEN
NASA’s Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, launched in 2013, is dedicated to studying Mars’ upper atmosphere and its interaction with the solar wind. MAVEN has provided crucial data on how Mars lost most of its atmosphere over billions of years, transforming from a warm, wet world to the cold, dry planet we see today.
Mars Orbiter Mission (Mangalyaan)
India’s Mars Orbiter Mission, launched in 2013, made India the first Asian nation to reach Mars orbit. The spacecraft carried instruments for studying the Martian surface, atmosphere, and mineral composition.
The Role of Orbiters
Mars orbiters serve several critical functions:
Global mapping: Orbiters can image the entire planet, providing context that surface missions cannot. This global perspective is essential for understanding planetary-scale processes like dust storms, seasonal ice cap changes, and atmospheric dynamics.
Site selection: High-resolution orbital imagery is crucial for selecting safe and scientifically interesting landing sites for rovers and future human missions. HiRISE images have been used to evaluate candidate landing sites for missions including Curiosity and Perseverance.
Communication relay: Orbiters serve as communication relays between surface missions and Earth. The vast distance between Earth and Mars means that direct communication with rovers and landers is limited; orbiters overhead can receive data from surface missions and relay it to Earth at much higher data rates.
Atmospheric monitoring: Orbiters continuously monitor Mars’ atmosphere, tracking dust storms, water vapor, carbon dioxide cycles, and seasonal changes. This data is essential for understanding Mars’ climate and for planning future surface operations.
Looking Ahead
As Mars exploration intensifies in the coming decades, orbiters will continue to play a vital role. New missions will carry even more capable instruments, building on the discoveries of the current fleet. When humans eventually travel to Mars, the orbital infrastructure established by these robotic pioneers will be essential for communication, navigation, weather monitoring, and emergency response.
The eyes in the Martian sky remind us that exploration is not just about what is at our feet, but about understanding the big picture — the entirety of a world that may one day become our second home.