Astro Glossary

Mars Polar Lander

A spacecraft that was designed to land in the polar regions of Mars. It failed during final descent when its on-board computer interpreted the jolt of an engine firing as contact with the ground and shut down the engine, causing the probe to crash.

Mars Reconnaissance Orbiter

The Mars Reconnaissance Orbiter’s main instrument is a telescopic camera, which will map parts of the Martian surface with unprecedented clarity. Scientists will use the pictures to plot the landing sites for future robotic and manned missions.The pictures and other observations also are providing new data in the search for water on Mars. The observations have helped locate minerals that formed in a watery environment. MRO also carries a radar system that discovered deposits of frozen water below the surface.

Mars Rovers Spirit and Opportunity

Building on the success of the 1997 Sojourner rover, the Spirit and Opportunity rovers landed on Mars in 2004. Although their planned mission was just 90 Mars days long (about 92 Earth days), Spirit continued until March 2010, while Opportunity was still operating in 2011. Both found evidence that water had helped shape the Martian landscape in the distant past.

Mars Science Laboratory, Curiosity

Scheduled to launch in fall 2011 and land on Mars in August 2012, Curiosity is the largest rover ever sent to the Red Planet. It will carry 10 instruments that will help search Mars for environments where life might have existed and the capacity of those environments to preserve evidence of past life.

Mars' Atmosphere

The atmosphere of Mars is thin and cold. The average density is 0.7 percent the density of Earth, with average temperatures far below zero. The atmosphere consists almost entirely of carbon dioxide, with only a tiny amount of other elements and compounds. The atmosphere supports clouds of both water and carbon dioxide. The clouds sometimes produce snow. When Mars was young, its atmosphere was much thicker and warmer than it is today, allowing liquid water to flow and stand on the surface. During the last four billion years, though, most of that atmosphere has been lost. Much of it escaped into space, while some of the compounds in the atmosphere combined with others to form rocks at the Martian surface. Several spacecraft have studied the planet's atmosphere and continue to do so today.

Mars' Moons

Mars has two small moons, Phobos and Deimos. Phobos is the larger of the two. It is shaped like a potato, about 15 miles long by 10 miles wide. One end is scarred by a giant crater. The impact that created it may have fractured the entire moon, leaving big cracks that travel from one end to the other. Phobos is in such a low orbit that it circles Mars about three times per day. It rises in the west, then sets in the east just a few hours later. As seen from the equator it looks less than half as big as our Moon looks from Earth. Deimos is both smaller and farther out. It takes almost three days to complete one orbit. From the Martian surface, it looks about like Venus looks from Earth.

Martian Surface

The fourth planet from the Sun in the solar system. Mars orbits the Sun at an average distance of 1.52 AU. The planet has a mass 0.1 times the mass of Earth and a radius 0.5 times the radius of Earth. It is made of solid, rocky material, and has a thin atmosphere of carbon dioxide. Iron oxide, or rust, on the surface of Mars gives it its characteristic red color. The planet has bright polar ice caps made of frozen water and carbon dioxide. Mars also has two small moons, Phobos and Deimos.

Mathematics and Physics

Maya Astronomy and Folklore

McDonald Observatory

McDonald Observatory, a research unit of The University of Texas at Austin, is one of the world’s leading centers for astronomical research, teaching, and public education and outreach. Observatory facilities are located atop Mount Locke and Mount Fowlkes in the Davis Mountains of West Texas, which offer some of the darkest night skies in the continental United States.