The planet Mars is the fourth planet from the sun. The diameter
is 6,794 km (compared to Earth's 12,756.3 km) and a mass of 6.4219 x 1023
kg about 1/10th
of that of Earth. This results in a surface gravity
of 0.38 that of Earth (3.69 m/s-2
) and an escape velocity
of 5.027 km/s-1 Pluto
are the only planets smaller than Mars.
At aphelion Mars is at a distance of 249,200,000 km from the sun. Perihelion is at 206,600,000 km. This is a much more eccentric (0.09) orbit than that of Earth which has a nearly perfect circular orbit (only 0.01 eccentricity - 0.00 is a perfect circle). The length of a Martin day is 24.622962 hours, a Martian year is 686.98 earth days or 667.76 Martian days.
The effect of this eccentricity is that the seasons are very uneven in length. Northern spring lasts 371 Martian days (more than half the Martian year), and summer solstice (separating spring from summer) occurs significantly later than halfway between spring and fall. The result of this is that the southern summer is short and warm while the northern summer is long and cool. This also creates differences in the composition of the polar caps. The southern cap is formed in the southern winter which is long and cold and is thought to be mostly dry ice. The northern polar cap is formed in the northern winter which is much warmer and thus would be made of water ice.
At an mean distance of 1.52 AU from the sun, this means that the planet gets much less sunlight. Earth receives 1370 watts/m2 while Mars receives only 445 watts/m2. This is known as the solar constant. This combined with the elliptical orbit results in large temperature fluctuations. The lowest temperature recorded was in northern hemisphere winter -124 C. The highest recorded temperature was -31 C. It is believed that temperatures may get as high as 20 C at the equator and -140 C at the poles.
The atmosphere of Mars has a mean pressure of 7 millibars
at sea level on Earth is 1 about bar or 1000 millibars) and is primarily
composed of CO2 (95.3%), N2
(2.7%), Ar (1.6%),
and trace O2 (0.15%) and H2O
(0.03%). At the
deepest basin this goes up to 9 millibars, while the top of Olympus Mons
is only 1 millibar. This atmosphere provides very little
greenhouse effect and only raises the surface temperature about 7 degrees.
The total land surface area of Mars is about the same as that the
land surface area of Earth. Of notable interest
- Olympus Mons: Largest mountain in the Solar System rising 24km above the surrounding plane. The base of this ancient volcano is 500km in diameter and has a cliff 6km high. It is about as large as the state of Texas.
- Tharsias: A huge bulge on the surface about 4000 km across (similar to the size width of the United States) and 10 km high.
- Valles Marineris: A system of canyons 4000 km long and 2 to 7 km deep (again, similar in length to the width of the United States)
- Hellas Planitia: The largest known impact crater in the Solar System over 6 km deep and 2000 km in diameter.
Mars was first successfuly visited in 1965 by the Mariner 4 spacecraft. Mars 2 was the first spacecraft to land on Mars, which was followed by the Viking landers in 1976. Twenty years later, Mars Pathfinder landed on July 4, 1997.
All missions are American unless otherwise mentioned.
- Mars 1 - Soviet - flyby - Launch November 1, 1962 - lost contact
on March 21, 1963. Closest approach 193,000 km June 19, 1963
- Mariner 3 - flyby - (launched) November 5, 1964 - shroud which encased
the spacecraft failed to open properly
- Mariner 4 - flyby - July 14, 1965
- Mariner 6 - flyby - July 31, 1969
- Mariner 7 - flyby - August 5, 1969
- Mariner 8 - (launched) May 8, 1971 - failed at launch
- Mariner 9 - orbiter - November 13, 1971
- Mars 2 - Soviet - lander/orbiter - (landed) November 27, 1971 -
No data from lander retrieved. First landing on Mars.
- Mars 3 - Soviet - lander/orbiter - (landed) December 2, 1971 - Signals for 20 seconds after landing
- Mars 4 - Soviet - orbiter - (launched) May 28, 1971 - failed orbital insertion
- Mars 5 - Soviet - orbiter - February 2, 1974 - The only complete success of the Soviet Mars Program
- Mars 6 - Soviet - lander - March 12, 1974 - only 148 seconds of data after
- Mars 7 - Soviet - lander - (flyby) March 9, 1974 - retrorocket failure and missed Mars by 1,300 km.
- Viking 1 - lander - June 19, 1976
- Viking 2 - lander - August 7, 1976
- Mars 96 - Russian - (launched) November 16, 1996 - fell back to Earth
- Mars Observer - orbiter -(last transmission) August 22, 1993
- Mars Pathfinder - lander - July 4, 1997 - now known as Sagan Memorial Station in memory of Carl Sagan
- Mars Global Surveyor - orbiter - September 13, 1997
- Mars Climate Orbiter - orbiter - September 23, 1999 - entered atmosphere too low and burned up
- Mars Polar Lander/Deep Space 2 - lander - December 3, 1999 - lost upon arrival
- Mars Odyssey - (launched) April 7, 2001 - arrived October 23, 2001
- Mars Express - European Space Agency and Italian space agency (support from NASA Deep Space Network) - launch June 2, 2003 and December 2003 arrival. Some science equipment heritage from the Mars 96 mission. The lander (inserted on December 25, 2003) failed to respond so far (see http://www.beagle2.com/ for more info on this lander).
- 2003 Mars Exploration Rovers (Spirit and Opportunity ) - launched June 10 and July 7, 2003. Spirit landed on Mars in Gusev Crater on January 3, 2004. Opportunity landed on January 24, 2004.
There is evidence that at one time, Mars had running water on the surface. This would have required a much thicker atmosphere. Some even theorize that life could have evolved on Mars first because it cooled off earlier due to its small size. This life would then have been ejected into space on a meteorite that could have fallen on Earth.