Similar to Earth
Viewing MarsThe best Earth-based views of Mars are obtained when Mars is simultaneously at opposition and near perihelionEarth-based observations of Mars are best made during favorable oppositions
Earth-based ObservationsA solar day on Mars is nearly the same length as on EarthMars has polar caps that expand and shrink with the seasonsThe Martian surface undergoes seasonal color changes
Canals?A few observers reported a network of linear features called canalsThese observations, which proved to be illusions, led to many speculations about Martian life Earth-based observations were once thought to show evidence of intelligent life on Mars
Tales of Canals and Life on MarsEarly observers (Schiaparelli, Lowell) believed to see canals on MarsThis, together with growth/shrinking of polar cap, sparked imagination and sci-fi tales of life on Mars.We know today: canals were optical illusion; do not exist!No evidence of life on Mars.
Edgar Rice BurroughsA Princess of Mars is the first adventure of John Carter, a Civil War veteran who unexpectedly find himself transplanted to the planet Mars. Yet this red planet is far more than a dusty, barren place; it's a fantasy world populated with giant green barbarians, beautiful maidens in distress, and weird flora and monstrous fauna the likes of which could only exist in the author's boundless imagination.
Wells and Welles19381898
Seasons of Mars
Seasons of Mars (2)
Ice in the Polar CapPolar cap contains mostly CO2 ice, but also water.Multiple ice regions separated by valleys free of ice.Boundaries of polar caps reveal multiple layers of dust, left behind by repeated growth and melting of polar-cap regions.
Ice in the Polar CapsLeft: Southern polar cap, mostly carbon dioxideRight: Northern polar cap, mostly waterBoth images taken during local summer
Ice in the Polar Cap (2)Here we see cliffs which are almost 2 kilometers high, and the dark material in the caldera-like structures and dune fields could be volcanic ash. These two images of the Martian north polar ice cap show layers of water ice and dust for the first time in perspective view. The close-up view (right) is the upper right section of the image above.
On February 19, 2008, while monitoring the edge of Mars' north polar cap for changes as the spring thaw arrives, Mars Reconnaissance Orbiter was fortunate to catch several avalanches in the act of spilling down the steep slope at the edge of the cap. Two avalanches are visible in this image, one large one near the top and a smaller one near the bottom. The cap is to the left; its steep cliff, running across the center of the image from top to bottom, is approximately 700 meters tall and reaches slopes as steep as 60 degrees. The steep part of the cliff is composed of layered material (the layers are difficult to see in this image) made mostly of water ice with atmospheric dust mixed in. To the right of the image, the cliff flattens out into a still moderate slope of about 20 degrees; this part of the cliff probably has a higher proportion of sand and dust in layers interspersed with ice-rich layers. The avalanches kicked up billowing clouds of dust that rise high into the air, casting shadows to their lower left. Credit: NASA / JPL / U. Arizona
The last image shows two of the four avalanches the HiRISE team spotted in the full image; here's a third.
The Geography of Mars
The Geology of Mars (2)Northern Lowlands: Free of craters; probably re-surfaced a few billion years ago.Southern Highlands: Heavily cratered; probably 2 3 billion years old.Possibly once filled with water.
The Geology of MarsGiant volcanoesValleysImpact cratersVallis MarinerisReddish deserts of broken rock, probably smashed by meteorite impacts.
Valles Marinerishuge canyon, created by crustal forcesTop right: Grand Canyon on same scale 4000 km long Maximum 120 km wide, 7 km deep
Volcanism on MarsVolcanoes on Mars are shield volcanoes. Olympus Mons:Highest and largest volcano in the solar system.
Volcanism on Mars (2)Tharsis rise (volcanic bulge):Nearly as large as the U.S.Rises ~ 10 km above mean radius of Mars.Rising magma has repeatedly broken through crust to form volcanoes.
Water on MarsWas there running water on Mars?Runoff channels resemble those on Earth.Left: MarsRight: Louisiana
Hidden Water on MarsNo liquid water on the surface:Would evaporate due to low pressure.But evidence for liquid water in the past:Outflow channels from sudden, massive floodsCollapsed structures after withdrawal of sub-surface waterSplash craters and valleys resembling meandering river bedsGullies, possibly from debris flowsCentral channel in a valley suggests long-term flowing waterAncient riverbedsTeardrop islands
Hidden Water on Mars (3)Echus Chasma is the source region of the Kasei Valles channel. This perspective image shows that liquid water was present on the surface of Mars thousands of millions of years ago.
Gigantic waterfalls poured over the 4000-meter high cliffs, and fed a lake in the valley. Later, when the planet became cooler, the lakes froze and glaciers formed, carving the giant Kasei Valles. Perspective view of Echus Chasma
Hidden Water on Mars (2)The image above is Kasei Valles, one of the largest outflow channels on Mars, and contains a lot of evidence for glacial and fluvial activity over much of the planet's history. The scour marks in the valley, shown in the image on the right, are most likely due to glacial erosion than by water erosion.
Hidden Water on Mars (4)Gusev Crater and Maadim Vallis: Giant lakes might have drained repeatedly through the Maadim Vallis into the crater.
Water on Mars?Recently, gullies have been seen that seem to indicate the presence of liquid water; interpretation is still in doubtThis set of images shows a comparison of the gully site as it appeared on Dec. 22, 2001 (left), with a mosaic of two images acquired after the change occurred (the two images are from Aug. 26, 2005, and Sept. 25, 2005). Image credit: NASA/JPL
Water on Mars?Recently, gullies have been seen that seem to indicate the presence of liquid water; interpretation is still in doubt
Subsurface Water?In this false-color map of Mars, soil enriched in hydrogen is indicated by deep blue. Source: the neutron spectrometer onboard NASA's 2001 Mars Odyssey spacecraft.
Evidence for Water on MarsLarge impacts may have ejected rocks into space.Galle, the happy face craterMeteorite ALH84001:Identified as ancient rock from Mars.Some minerals in this meteorite were deposited in water Martian crust must have been richer in water than it is today.
Ancient Oceans?Among the important findings of Surveyor, based on altimetry and photographs were: The border between two geologically dissimilar areas in the northern lowlands is nearly level in elevation, suggesting an ancient coastline. The topography below this possible shoreline is much smoother than that of the region above at higher altitudes, which is consistent with smoothing by sedimentation. The volume of the putative sea is within the range of previous estimates of water on Mars. A series of terraces run parallel to the apparent shoreline, bolstering the idea of receding waters. Low areas bear what appear to be mud cracks, like those in dry terrestrial lake beds. Scars from impact craters suggest ground water or ice in the northern lowlands is near the surface.
The Atmosphere of MarsVery thin: Only 1% of pressure on Earths surface95 % CO2Even thin Martian atmosphere evident through haze and clouds covering the planetOccasionally: Strong dust storms that can enshroud the entire planet.Atmosphere probably initially produced through outgassing.
Clouds Above Mars Mountains
The Atmosphere of Mars (2)Most of the Oxygen bound in oxides in rocks Reddish color of the surface
The Martian AtmosphereMartian atmosphere is mostly carbon dioxide, and very thin
Too thin to retain much heat; temperature drops sharply at night
The Martian AtmosphereMars may be victim of runaway greenhouse effect in the opposite sense of Venuss:
As water ice froze, Mars became more and more reflective and its atmosphere thinner and thinner, freezing more and more water and eventually carbon dioxide as well.
Earth and Mars began with similar atmospheresthat evolved very differentlyMarss primordial atmosphere may have been thicker and warmer than the present-day atmosphereIt is unclear whether it contained enough carbon dioxide and water vapor to support a greenhouse effect that would permit liquid water to exist on the planets surfaceThe present Martian atmosphere is composed mostly of carbon dioxideThe atmospheric pressure on the surface is less than 1% that of the Earth and shows seasonal variations as carbon dioxide freezes onto and evaporates from the poles
Why did the climate change?Thicker atmosphere lost?To polar capsTo rocksTo spaceWater lost SubsurfaceBroken by UV and H lost to space while O went to rocks rusty!Change of axis tilt (varies 0-60)
Life on Mars?Many searches have been done for life on Mars, but none has been found.In 1996, scientists claimed to have found such evidence in an Antarctic meteoroid from Mars, but this did not hold up.
Martian Internal Structure No seismic studies have been done From behavior of crust, it is estimated to be 100 km thick No magnetic field, so core is