Sunset on Mars - Image from NASA
Mars is a little over half the size of Earth, with a diameter of 6788 km (4218 miles) at its equator. Mars has two small moons in orbit around it, named Phobos and Deimos.
Scientists believe that Mars is about the same age as Earth (4.6 billion years old). The length of one day on Mars is similar to that on Earth. Mars makes one complete rotation on its axis every 24 hours and 40 minutes.
Mars is the fourth planet from the sun. It is a terrestrial planet, like Earth. In fact, out of all of the planets in our solar system, the environment on Mars is most like Earth's. However, Mars certainly isn't the oasis that Earth is.
Mars has changing seasons like Earth does and it also has a thin atmosphere that contains 0.13% oxygen. Earth's atmosphere contains 21% oxygen and so we would suffocate on Mars, unless we brought along additional oxygen to breathe.
Mars thin atmosphere is capable of producing clouds and wind. In fact, Mars has very strong winds that often create major dust storms.
The image of the stratus clouds on Mars was taken by Mars Pathfinder. The clouds consist of water ice and red dust particles from the surface that give the clouds their pink color.
Scientists believe that at one time the atmosphere on Mars may have been much thicker than it is now, but was lost due to several factors (e.g., asteroid impacts).
Scientists know a lot about the surface of Mars because of the robotic probes that have been sent there. Mars seems to be a dry, dusty world. There is a lot of iron in its soil and that is responsible for the reddish color of the surface.
Mars has large volcanoes and mountains. Scientists are uncertain whether or not the Martian volcanoes are still active. No one has seen any evidence of recent volcanic activity, but it could be that there is a lot of time between eruptions and we just haven't seen one yet.
The surface of Mars also has numerous impact craters. Because of its thin atmosphere, most meteoroids and asteroids don't disintegrate on their way to the surface as they usually do here on Earth. There are also lots of lava rocks on the surface as seen in the photo.
Mars is believed to have an iron sulfide core.
Evidence of Flowing Water on Mars
Scientists believe that at one time Mars had flowing water on its surface, however, there doesn't seem to be liquid water there now. Mars does have water ice at its polar caps, but the temperature on Mars at the poles is too cold for this ice to melt. At Mars equator it does get to a comfortable daytime temperature that is slightly above 60 °F (16°C) but there isn't ice or water at the equator and Mars equator gets very cold during the nighttime, below -200 °F (-129 °C). The polar caps also contain dry ice (frozen carbon dioxide).
Scientists believe that water flowed on Mars in the not too distant past. In fact, there is evidence that some water flowed on Mars within the last 10 years. Scientists have also found evidence of dried up river beds, lakes, and oceans on the surface of Mars. There is also evidence that major flooding of the surface occurred at some point in the past.
If all of this water was on Mars at one time, where is all of the water now?
Scientists believe that the water may be frozen under Mars surface and at the poles. Scientists have found evidence of large amounts of water ice under the surface. Scientists believe this happened when Mars lost most of its atmosphere and the temperature became much colder, causing the water on Mars to either freeze or evaporate. Scientists believe that there is enough water ice at Mars poles to flood the entire planet if it all melted.
Evidence for Life on Mars
Because the environment on Mars isn't too extreme or hostile, it has an atmosphere, evidence of water, and other compounds that suggest Mars could support life, scientists have investigated whether or not life exists on Mars now or in the past. So far, no conclusive evidence of life on Mars has been found.
Image of Mars surface: Courtesy of NASA Glenn Research Center.
Image of Mars sunset and Mars clouds: Courtesy of NASA/JPL-Caltech.