Click for Live Display showing the current positions of the moons of Mars.
Mars is the fourth closest planet to the Sun and orbits in an fairly eccentric orbit at around 230 (+-20) million km.
Similarities to Earth
Mars takes about 686 Earth days to orbit the Sun. It has a tilt (25.1 degrees) and rotational period (24 hour 37 minutes) which are both similar to the Earth with a day (sunrise to sunrise) lasting 24 hours, 39 mins. Because of the tilt it also has seasons in the same way as the Earth does.
Second Smallest Planet
Mars is about half the size of the Earth with a diameter of 6,792km. However its mass is only a tenth of Earth’s with gravity on the surface being around 37% that of Earth’s.
Because Mars no longer has a magnetic field to protect it, Mars has lost its original atmosphere due to the effects of the solar wind interacting with the atmosphere causing atoms to be lost into space. Spacecraft have detected streams of atoms trailing off into space behind Mars. As a result the atmospheric pressure on Mars is 1% that on Earth. It is comprised of mostly (95%) carbon dioxide.
Coldest of the Inner Planets
Mars is very cold. Not only is it about 1.5 times further from the Sun than Earth, it also has a thin atmosphere which cannot store much heat. Because of this the temperature ranges from about -143 degrees C in winter up to a maximum of 35 degrees C in summer.
Mars is very dusty and prone to huge dust storms which can envelop the entire planet. These are more likely to occur when the planet is closest to the Sun.
A Map of Mars - Click to go to NASA's interactive map
Signs of Liquid Water
Evidence has been increasing that liquid water has sculpted the landscape of Mars in the past and is probably flowing, or rather seeping through the rocks during periods within salts called perchlorate salts. The video below talks about the details of this discovery.
Skip the first ten minutes to avoid the NASA hard sell, and hang in there with the poor quality sound on Luju's report from France.
Moons : Phobos and Deimos
Mars is lucky enough to have 2 small moons - both discovered in August 1877 by Asaph Hall. Phobos is tiny - only about 22km across- orbiting very close to Mars (9300km from its centre or 6000km above its surface) every 7 hours. It can be described as a non symmetrical, heavily cratered, dirty rock. Deimos however, is even smaller. It is only 12km across and orbits at 23,000 km every 30 hours. The origins of the moons are disputed but it is likely they are captured asteroids. However their near perfect circular orbits which align with the planets equator could point toward them originating on or with Mars. For more information on the moons, click here.
Mars and Man
Mars is named after the Roman god of war and has been known since before Babylonian times where it was associated with Nergul, a god of war, fire and destruction - possibly inspired by its red colour.
Possibly because Mars has a more benign environment than that of any of the other inner planets (other than Earth of course) it has received quite a few robotic explorers.
The first successful fly-by of Mars was performed by Mariner 4 in 1965. Mariner 9 in 1971 became the first probe to orbit another planet when it entered Mars orbit. Shortly after 2 Soviet probes Mars2 and Mars3 became the first to successfully land on another planet - even though they ceased functioning very shortly after. 1976 saw the US Viking mission with two orbiters and two landers. The landers successfully relayed images of the Mars surface and other measurements and continued working for up to 6 years.
In 1988 the soviets sent 2 probes (phobos 1 and 2) to photograph and land on the moons. One lost communications in transit and the other successfully photographed the phobos but failed before deploying its landers. Mars Global Surveyor entered the Mars orbit in 1997 and spent 4 years mapping Mars in detail. Also in 1997 Mars Pathfinder landed on the surface with its robotic vehicle Sojourner which was able to wander up to 0.5 km from the lander and took many photographs and measurements from the rocks and soil. Another lander, Phoenix, landed in the polar regions of Mars and confirmed the presence of water on Mars.
Since the year 2000, many additional probes have reached Mars and now provide detailed monitoring of the planets atmosphere and geography. The Mars Exploration Rovers, Spirit and Opportunity landed in 2004 for their 90 day mission. They both exceeded their mission objectives with Spirit eventually failing in March 2010 and Opportunity being declared dead in February 2019 after contact was lost in July 2018 when a huge planet wide dust storm blocked it's energy source - the Sun. End of Opportunity Mission Article.
Near future missions include a whole host of spacecraft to arrive 2020 to 2021:
NASA's Mars 2020 Mission - a lander, and surprisingly (because the atmosphere is so thin) a solar powered drone to help with navigation.(Mars Helicopter Links: Mars Helicopter Article, NASA Video, JPL Video). ExoMars 2020 - the second part of ESA's ExoMars mission to search for life. It comprises a rover to land in 2021. A public competition is open to name the rover (link), 2020 Chinese Mars Mission - An orbiter and lander to arrive in 2021. Hope Mars Mission or 'Al-Amal' - A United Arab Emirates orbiter to arrive in 2021. India's Mars Orbiter Mission 2 - from the Indian Space Research Organisation. An orbiter and possible lander (2021-2022).
Defunct spacecraft on the surface include MER-A Spirit and several other inert landers and rovers such as the Phoenix lander, which completed its mission in 2008. Observations by the Mars Reconnaissance Orbiter have revealed possible flowing water during the warmest months on Mars.
Above is one of those most rarest of media - live video (even only at four frames a second) from another planet. This video follows the landing of Curiosity - from the ejection of it's heat shield, falling (on parachute) and then being lowered to the surface from the sky crane (a hovering rocket powered structure that kicks up a lot of dust in the video).
Above is a remarkable animation (made before Curiosity even left earth) showing Curiosity's exciting arrival and then the rover going about it's business. Strangely, it brings home the loneliness of the life of a Mars Rover.