The Exploration of Mars
- Mars attracted attention in the night sky since even before the invention of the telescope.
- It has a distinctly red color.
- It varies tremendously in brightness as its distance from Earth
- Telescopic observations revealed
- It is similar in size to Earth -- although somewhat smaller.
- Its rotation period is just over 24 hours.
- It has an inclined rotation axis like Earth and thus seasons.
- Unlike Earth, the orbit of Mars is quite eccentric and varying distance from the Sun is a factor in its seasons in addition to its tilt.
- Clouds occasionally are visible in the atmosphere.
- It has polar caps that change in size with season.
- It is thought to have a metallic core like Earth.
- Although its lower overall density (3.9 grams/cc) suggests that the core may be mainly iron sulfide, which was thought to be more common than iron in the cooler regions of the solar nebula.
- These intriguing similarities to Earth led some astronomers to see
evidence of civilization
in the fuzzy shimmering
view of Mars as seen from Earth!
- The green-hued surface features on Mars even appear to change
with time suggesting (incorrectly we now know) vegetation.
- All of this provided tremendous fuel for science fiction
- Orson Welles Haloween broadcast of a dramatization of H.G. Wells
War of the Worlds in 1938 incited real terror in people who did not realize it was radio theater.
- Telescopic observations later in the 20th century, however, revealed
major differences between Earth and Mars which probably
make Mars currently inhospitable to life...
- The atmosphere is very thin (about 1% of
Earth's) and is composed of mainly carbon dioxide.
- This thin atmosphere provides a poor blanket. The
temperature is well below freezing nearly
everywhere all of the time.
- It is so cold at the poles that CO2
can solidify. The polar caps are largely made of a layer of
CO2 frost (dry ice) .
- In the Martian summer the CO2 frost
retreats exposing small residual water ice caps.
- The atmospheric pressure on Mars actually rises and
falls as more or less atmosphere becomes frozen at the poles.
- In the early 1960's NASA accomplished the first spacecraft flyby's
- The images returned were disappointing. Mars looked more
like the Moon.
- Mars is about half the size of the Earth.
- Its crust solidified and thickened long ago
and it is geologically dead today.
- Mars is heavily cratered due to lack of
resurfacing and strong erosion.
- Some light erosion does take place due to
- In the 1970's orbiters and landers were sent to Mars. Our view
of the planet was transformed overnight.
- The 1960's flybys, as luck would have it, had imaged
the "boring" side of Mars!
- Mars was sufficiently large to have
had an interesting past.
- A number of large volcanoes can be found on Mars.
- Some of these volcanoes may have been active in the
past few hundred million years (there are few craters on their
- The biggest, Olympus Mons, is the
largest volcano in the Solar System.
- These volcanoes are reminiscent of "hot spot" volcanism where volcanoes form over a particularly active and persistent plume of
- Motion of the crust over the plume changes the center
of volcanic activity.
- The Hawaiian Islands are a good example on Earth.
- Valles Marineris is a vast fissure spanning 5000 km.
- The fissure is likely the result of crustal movement/rifting and
similar to rift valleys on Earth.
- These facts combined suggest that Mars had a brief period of
"plate tectonic" activity before its crust thickened and activity ceased.
- Most of this activity occurred early in Martian history - maybe the first 1/2 billion years.
- Geolgical activity implies outgassing and a thicker atmosphere around the early Mars.
- A thicker CO2 atmosphere suggests greenhouse warming and thus a
warmer early Mars.
- This view is supported by evidence that liquid water once flowed on the surface of Mars.
- Mars may very well have had an "earthlike" beginning.
Revised November 26, 2007