Mars•Mars is a dry dead world.

•There are no Martian transits.

• Semi-major axis-1.52 A.U.

• Eccentricity-0.093 Only Mercury and Pluto have a greater eccentricity.

• Perihelion-1.38 A.U.

• Aphelion-1.66 A.U.

The sunlight intensity is 45% greater at perihelion than at aphelion.

Mars’ orbital period is 687 Earth days.

As observed from Earth, Mars is considerably fainter than Venus.

Three main reasons:• 1. Mars is greater than twice

as far from the Sun, less light.

• 2. The surface area is only 30% that of Venus.

• 3. Mars’ albedo is 0.15. (Venus’ albedo is 0.7.)

Diameter - 6800 km0.53 of Earth’s

Mass - 6.4 x 1026 g0.11 of Earth’s

Density - 3.9 g/cm3

Rotation - once every 24.6 hours

Mars is tilted on its axis 25.2° (Earth is 23.4°)

Therefore, Mars has daily and seasonal cycles.

Earth-Observations The surface features of Mars change from season to season.

Mars has bright polar ice caps made up primarily of frozen CO2.

Mars has “canals”. They are highly cratered and eroded areas. Surface dust occasionally blows over and obscures these areas. Percival Lowell thought the canals were changing and suspected life.

The dust on Mars is blown by strong winds often reaching 100’s of km/hr (hurricane force).

Mariner 9 visited Mars in 1971. When it arrived there was a planet-wide dust storm. If it had been a fly-by mission it would have been a failure.

Mars also has dust devils: small, tornado-like weather events

The atmosphere is primarily CO2.

Spacecraft ExplorationMariner 4 in July 1965. Mariner 6 & 7 in 1969. They all found Mars to be geologically dead and heavily cratered.

Mariner 9 mapped the entire surface in Nov of 1971.It found vast plains, volcanoes, drainage channels, and canyons.

Viking 1 & 2 visited Mars in mid-1976. They mapped the surface and had a lander.

Viking

Mariner 1 was scheduled to touchdown on July 4, 1976. It actually landed July 20.

Mariner 2 landed in September of 1976. The landing area was strewn with rocks and boulders. The lander could have been destroyed on landing.

Mars has no plate-tectonic activity. It is geologically dead.

The Northern Hemisphere is composed of rolling volcanic plains (like lunar maria).

The Southern Hemisphere is composed of heavily cratered highlands, several km above the level of the lowland north.

The highland-lowland boundary can be sharp with a surface drop of 4 km over a distance of 100 km.

The major geological feature is the Tharsis Bulge. It is the size of North America and is located on the Martian equator. It is 10 km higher than the rest of the Martian surface.

The Chryse Planitia (Plains of Gold) is east of the Tharsis Bulge. The Isidis Planitia (Plains of Isis) is west of the Tharsis Bulge. These are wide depressions, 100’s of km across, and up to 3 km deeper than the surrounding areas.

The Tharsis Bulge is even less heavily cratered than the northern hemisphere (therefore, younger).

The Tharsis Bulge is the only “continent” on Mars (but there is no plate tectonics).

VolcanismMars has the largest known volcanoes in the solar system. There are four very large ones on the Tharsis Bulge. The largest is Olympus Mons (Mount Olympus).

Olympus Mons is 700 km in diameter at the base (slightly smaller than TX). It stands 25 km above the plains with a caldera 80 km across. In comparison, the largest mountain on Earth is Mauna Loa in Hawaii (120 km across, 9km above ocean floor).

There are three smaller volcanoes (only 18 km high) near the top of the Tharsis Bulge. All are shield volcanoes. They all show lava channels and other flow features.

The Viking images show many hundreds of volcanoes. Most of the largest are on the Tharsis Bulge, but many smaller volcanoes are in the northern plains.

The great height is a result of Mars’ low gravity. The gravity is only 40% of that on Earth, so the volcanoes can rise 2.5 times as high. There is no direct evidence of any active volcanoes.

Impact Craters Mars and its two moons are pitted with impact craters. The smaller craters are filled with dust-like surface matter (much like our Moon).

But the craters are filled faster than on the Moon. This is due to the fact that Mars’ atmosphere is much more highly erosive than the meteoric erosion on the Moon. So, craters must be larger to still be seen on Mars.

Ejecta blankets around Martian craters indicate that the ejecta was fluid rather than solid like on the Moon. (A “splosh” crater).

Geologists believe a layer of permafrost, or water ice, lies just under the surface. Meteorites heat and melt the ice, causing the fluid appearance of the ejecta.

Martian Grand Canyon“Valles Marineris” (Mariner Valley) on the Tharsis Bulge. It was not formed by running water. Believed to be a tectonic fracture (found all around the Tharsis Bulge).

The Valles Marineris is 4000 km long (one fifth of the way around the planet). It is 120 km across at its widest, 7 km deep at its deepest.

Colorado’s Grand Canyon would fit in one “side crack” of the Valles Marineris. It is large enough to be observed from Earth.

Mars was visited by the Pathfinder mission in 1998.