|Mars as Percival Lowell might have seen it. This is typical of what the best observatory photographs of Mars once looked like.|
|Thanks to improvements in imaging technology, Earth-based photos of Mars now look like this. In fact, amateur astronomers armed with small telescopes and off the shelf webcams now routinely take better photographs of Mars than the largest telescopes on Earth once did.|
|Of course, for really detailed imagery, you have to get out there physically. This is a computer generated mosaic of spacecraft imagery.|
|The biggest surprise of the first Martian flyby mission, Mariner IV in 1964, was the extensive cratering on Mars. One half of Mars consists of ancient, cratered crust and purely by chance, the spacecraft imaged only that side. In this view, crater floors are covered with frost or low-lying haze, and several layers of haze are visible above the surface.|
|Craters like the one at left are found only on Mars and are called rampart craters. The ejecta doesn't taper off gradually but consists of sharp-edged lobes. These look so much like large mudflows that most planetary geologists believe that's what they are. The impact probably melted subsurface ice, and the water mixed with ejecta to make mudflows, actually a coarse slurry of debris of all sizes. The ejecta filled the crater below the large crater to the brim. You can almost hear it go "splat."|
|This small crater, dubbed "Beagle", has a rim of shattered rock and sand dunes on its floor.|
|This crater in Mars' polar regions is dusted with frost but also has a large patch of permanent ice on its floor.|
|The only one of Percival Lowell's "canals" that has definitely been identified is this one, now called Vallis Marineris. It is a vast rift valley wider and deeper than anything on Earth. It would span the U.S.|
|Mars has a number of huge shield volcanoes. The largest, Olympus
Mons, was called "Nix Olympica" by Lowell. "Nix" is Latin for snow and
Lowell though a bright patch here was snow on a high peak. We now
believe he was seeing a cloud cap over the summit.
Olympus Mons is 500 kilometers across and 25 kilometers high.
|Left: the summit caldera of Olympus Mons.
Below: large lobes of ragged terrain are probably gigantic landslides from the collapse of the base of the volcano.
|The polar caps on Mars are thin layers of frost, including both ice and frozen carbon dioxide. They expand and contract dramatically with the Martian seasons. If they were on earth, it would be the equivalent of the Antarctic ice cap nearly vanishing in the summer and expanding to New Zealand in the winter. So they cannot be thick ice sheets.|
|A winter view taken by Viking, showing frost.|
|The Pathfinder mission pioneered the use of air bags for landing and also deployed the first rover on Mars, named Sojourner (after Sojourner Truth, a black woman who guided escaped slaves before the Civil War). At left is a view from Pathfinder, bleow left is Sojourner in its stored configuration, while at right it is fully deployed.|
|This sort of scalloped pitting is very typical of wind-abraded rocks.|
|Left and below: layered rocks are very abundant on Mars and there is mounting evidence that many of them were deposited by water.|
|Spirit and Opportunity have something no previous mission had - the ability to see things larger than life.|
|A Martian sunset.|
|Since Mars lacks oceans, we don't see the dramatic differences in heating and cooling that drive terrestrial weather. There is no rain. There may be snow. We never see thick, vertical clouds like on Earth. But occasionally we do see rotating weather disturbances like this and the one below.|
|Note the frost filled craters in both images.|
|Left: A dust devil sweeps a track across a crater and casts a shadow
(right edge of picture).
Below: dust devil tracks.
|Just about every imaginable dune form is found on Mars.|
|Left: a cliff in the polar region of Mars rises above a large dune field.|
|This crater was buried by the flat layers that underlie the mesa,
then uncovered by erosion. Geologists call this an exhumed
Below: Intersecting dunes create a network dubbed the "Inca City,: although there is no evidence the Incas ever got beyond the Moon.
|On a world where water erosion is minimal, many years of wind erosion can have dramatic effects. Streamlined hills like these occur on Earth and are called yardangs, but on Mars they are larger and more smoothly sculpted.|
|Above: Dendritic channels, certainly water eroded, on Mars. Since the channels do not completely dissect the landscape, the channel incision episode must have been fairly brief. Also, from the degree of cratering, the channeling happened some time ago.|
|Left: A recently discovered mystery on Mars is recent gullying in craters. It seems hard to imagine anything but water doing this, but the gullies are in craters in the polar regions. One theory is that heat from Mars' interior melts ice at the bottom of the permafrost and that pent-up water occasionally discharges to the surface. On the surface it will quickly evaporate or freeze.|
|These features certainly look like springs.|
|Left: A montage of Mars' two tiny moons. Phobos, left, is the larger and more interesting of the two. Deimos, at right is smaller and more distant.|
|Left: Deimos passing over the summit of Olympus Mons. Fairly extreme contrast enhancement is needed to bring out the bright surface of Mars and details on much darker Deimos. That's why the apparent relief around Deimos.|
The satellites of Mars don't so much eclipse the Sun as transit it. Above is a transit of Phobos, at right is a transit of Deimos.
|At left, the shadow of Phobos on the surface of Mars.|
Created 20 May 1997, Last Update 14 December 2009
Not an official UW Green Bay site