In 1971, Mariner 9 became the first spacecraft to orbit Mars. It found the planet shrouded in a global dust storm that obstructed the view of all but the tallest surface features. As the dust cleared, Mariner 9 mapped volcanoes, canyons, and polar caps.
From 1976 to 1980, the Viking Orbiters gave us our first global view of Mars. They revealed a diversity of landforms related to impact, volcanic, and other geological processes, and strong evidence that water carved many large features in the distant past.
The summit of the Ascraeus Mons volcano pokes through the dust storm in this Mariner 9 image (above).
Mariner 9
NASA/JPL image
Mars Orbiters
Orbiters have arrived at Mars with increasing frequency in recent decades. Over 100 Viking Orbiter images were pieced together to produce this global view of Mars (left). A deep canyon called Valles Marineris extends more than 3,000 kilometers (1,900 miles) across the center of the image.
Viking Orbiter
NASA/USGS image
Mars Global Surveyor
Mars Global Surveyor studied Mars from 1997 to 2006. The long duration of its mission allowed it to observe ongoing surface processes. Its Mars Orbiter Camera (MOC) provided both high-resolution images and a long-term record of lower-resolution global views. The spacecraft also produced a planet-wide topographic map and provided evidence of an early magnetic field.
Mars Orbiter Camera view of wind-eroded sedimentary rock terraces in Gale Crater.
Mars Global Surveyor, MOC
NASA/JPL/MSSS image
Mars Odyssey
Mars Odyssey began mapping Mars in 2002 and has provided data on its surface composition and radiation environment. It discovered large amounts of near-surface water ice around the poles, determined the radiation hazards for future human explorers, and has served as a communication relay for the two Mars Exploration Rovers.
Mars Odyssey's Thermal Emission Imaging System (THEMIS) produces both visible and infrared images. This visible-light image shows part of Mangala Vallis. Flowing water shaped the streamlined "islands" billions of years ago.
Mars Odyssey, THEMIS
NASA/JPL/Arizona State University image
The THEMIS infrared camera imaged the same impact craters in both daytime and nighttime. Infrared images depict the heat materials emit. Warmer areas appear brighter and cooler areas darker. Fine-grained materials like dust cool quickly after sundown, so they appear dark in the nighttime image, while rocky areas cool slowly and appear lighter. The extent of rocky material ejected from the craters can be clearly mapped. The daytime image resembles one taken in visible light, because Sun-facing slopes are warmer and shaded areas cooler.
Mars Odyssey, THEMIS
NASA/JPL/Arizona State University image
Mars Express
Europe's Mars Express orbiter arrived at the planet in 2003. It carries seven instruments that map surface terrain and composition and study the subsurface and atmosphere.
The spacecraft's High Resolution Stereo Camera (HRSC) produced this image of the Solis Planum region.
Mars Express, HRSC
ESA image
The MARSIS radar instrument sends radio waves to an area and analyzes the echoes that bounce back. It can look beneath the surface and detect rock layers or the presence of water. MARSIS also provides data on surface roughness and on the interaction of the atmosphere and solar wind.
NASA/JPL drawing
Mars Reconnaissance Orbiter
Since 2006, the Mars Reconnaissance Orbiter has studied the Martian surface, subsurface, and atmosphere. Its high-resolution camera (HiRISE) images the surface with greater detail than has ever been seen before from orbit. The Shallow Subsurface Radar (SHARAD) reveals geologic layering as deep as 2 kilometers (1.2 miles) underground. Other instruments study mineralogy, global weather, and atmospheric properties.
The HiRISE Camera on the Mars Reconnaissance Orbiter has a telescopic lens that produces images with such amazing detail that scientists can distinguish features as small as 1 meter (about 3 feet) across.
NASA/JPL/University of Arizona images
Instruments on the Mars Reconnaissance Orbiter use the visible, infrared, and radio ranges of the electromagnetic spectrum to measure water in the atmosphere, on the surface, and below the surface. Blue arrows show how water may cycle slowly between the Martian poles and lower latitudes.
NASA/JPL-Caltech image
