Mars is a cold desert world. It is half the diameter of Earth and has the same amount of dry land. Like Earth, Mars has seasons, polar ice caps, volcanoes, canyons and weather, but its atmosphere is too thin for liquid water to exist for long on the surface. There are signs of ancient floods on Mars, but evidence for water now exists mainly in icy soil and thin clouds.

Mars__atmosphere_708Mars lost much of its atmosphere over time. Where did the atmosphere–and the water–go? The MAVEN mission’s hunt for answers will help us understand when and for how long Mars might have had an environment that could have supported microbial life in its ancient past.

10 Need-to-Know Things About Mars

  1. If the sun were as tall as a typical front door, Earth would be the size of a nickel, and Mars would be about as big as an aspirin tablet.
  2. Mars orbits our sun, a star. Mars is the fourth planet from the sun at a distance of about 228 million km (142 million miles) or 1.52 AU.
  3. One day on Mars takes just a little over 24 hours (the time it takes for Mars to rotate or spin once). Mars makes a complete orbit around the sun (a year in Martian time) in 687 Earth days.
  4. Mars is a rocky planet, also known as a terrestrial planet. Mars’ solid surface has been altered by volcanoes, impacts, crustal movement, and atmospheric effects such as dust storms.
  5. Mars has a thin atmosphere made up mostly of carbon dioxide (CO2), nitrogen (N2) and argon (Ar).
  6. Mars has two moons named Phobos and Deimos.
  7. There are no rings around Mars.
  8. More than 40 spacecraft have been launched for Mars, from flybys and orbiters to rovers and landers that touched surface of the Red Planet. The first true Mars mission success was Mariner 4 in 1965.
  9. At this time in the planet’s history, Mars’ surface cannot support life as we know it. A key science goal is determining Mars’ past and future potential for life.
  10. Mars is known as the Red Planet because iron minerals in the Martian soil oxidize, or rust, causing the soil — and the dusty atmosphere — to look red.

IDL TIFF fileA Martian panorama taken by the Mars Exploration Rover Opportunity.

Though details of Mars’ surface are difficult to see from Earth, telescope observations show seasonally changing features and white patches at the poles. For decades, people speculated that bright and dark areas on Mars were patches of vegetation, Mars was a likely place for advanced life forms, and water might exist in the polar caps. When the Mariner 4 spacecraft flew by Mars in 1965, photographs of a bleak, cratered surface shocked many – Mars seemed to be a dead planet. Later missions, however, showed that Mars is a complex planet and holds many mysteries yet to be solved. Chief among them is whether Mars ever had the right conditions to support small life forms called microbes.

Mars is a rocky body about half the size of Earth. As with the other terrestrial planets – Mercury, Venus, and Earth – volcanoes, impact craters, crustal movement, and atmospheric conditions such as dust storms have altered the surface of Mars.

ESP_020914_0930Mars is not all red dust and rocks.

Mars has two small moons, Phobos and Deimos, that may be captured asteroids. Potato-shaped, they have too little mass for gravity to make them spherical. Phobos, the innermost moon, is heavily cratered, with deep grooves on its surface.

Like Earth, Mars experiences seasons due to the tilt of its rotational axis. Mars’ orbit is about 1.5 times farther from the sun than Earth’s and is slightly elliptical, so its distance from the sun changes. That affects the length of Martian seasons, which vary in length. The polar ice caps on Mars grow and recede with the seasons. Layered areas near the poles suggest that the planet’s climate has changed more than once. Volcanism in the highlands and plains was active more than 3 billion years ago. Some of the giant shield volcanoes are younger, having formed between 1 and 2 billion years ago. Mars has the largest volcano in the solar system, Olympus Mons, as well as a spectacular equatorial canyon system, Valles Marineris.

Mars has no global magnetic field today. However, NASA’s Mars Global Surveyor orbiter found that areas of the Martian crust in the southern hemisphere are highly magnetized, indicating traces of a magnetic field from 4 billion years ago that remain.

nssdc_vo1_mg07s078Valles Marineris is more than 3,000 km long and 8 km deep.

Scientists believe that Mars experienced huge floods about 3.5 billion years ago. Though we do not know where the ancient flood water came from, how long it lasted, or where it went, recent missions to Mars have uncovered intriguing hints. In 2002, NASA’s Mars Odyssey orbiter detected hydrogen-rich polar deposits, indicating large quantities of water ice close to the surface. Further observations found hydrogen in other areas as well. If water ice permeated the entire planet, Mars could have substantial subsurface layers of frozen water. In 2004, Mars Exploration Rover Opportunity found structures and minerals indicating that liquid water once existed at its landing site. The rover’s twin, Spirit, also found the signature of ancient water near its landing site, halfway around Mars from Opportunity’s location.

The cold temperatures and thin atmosphere on Mars do not allow liquid water to exist at the surface for long. The quantity of water required to carve Mars’ great channels and flood plains is not evident today. Unraveling the story of water on Mars is important to unlocking its climate history, which will help us understand the evolution of all the planets. Water is an essential ingredient for life as we know it. Evidence of long-term past or present water on Mars holds clues about whether Mars could ever have been a habitat for life.

In 2008, NASA’s Phoenix Mars lander was the first mission to touch water ice in the Martian arctic. Phoenix also observed precipitation (snow falling from clouds), as confirmed by Mars Reconnaissance Orbiter. Soil chemistry experiments led scientists to believe that the Phoenix landing site had a wetter and warmer climate in the recent past (the last few million years). NASA’s Mars Science Laboratory mission, with its large rover Curiosity, is examining Martian rocks and soil at Gale Crater, looking for minerals that formed in water, signs of subsurface water, and carbon-based molecules called organics, the chemical building blocks of life. That information will reveal more about the present and past habitability of Mars, as well as whether humans could survive on Mars some day.

vasavada-4stormcloseup(hi-res)Close-up image of a dust storm on Mars.

How Mars Got its Name
Mars was named by the Romans for their god of war because of its red, bloodlike color. Other civilizations also named this planet from this attribute; for example, the Egyptians named it “Her Desher,” meaning “the red one.”

Significant Dates

  • 1877: Asaph Hall discovers the two moons of Mars, Phobos and Deimos.
  • 1965: NASA’s Mariner 4 sends back 22 photos of Mars, the world’s first close-up photos of a planet beyond Earth.
  • 1976: Viking 1 and 2 land on the surface of Mars.
  • 1997: Mars Pathfinder lands and dispatches Sojourner, the first wheeled rover to explore the surface of another planet.
  • 2002: Mars Odyssey begins its mission to make global observations and find buried water ice on Mars.
  • 2004: Twin Mars Exploration Rovers named Spirit and Opportunity find strong evidence that Mars once had long-term liquid water on the surface.
  • 2006: Mars Reconnaissance Orbiter begins returning high-resolution images as it studies the history of water on Mars and seasonal changes.
  • 2008: Phoenix finds signs of possible habitability, including the occasional presence of liquid water and potentially favorable soil chemistry.
  • 2012: NASA’s Mars rover Curiosity lands in Gale Crater and finds conditions once suited for ancient microbial life on Mars.