- Name and appearance: Aris (god
of war) and Mars, from the color; Brighter than many stars, reddish;
From Earth one can sometimes see white (icy) regions near
the poles with a telescope.
- Motion: 1.52 AU from
the Sun on an eccentric, almost 2-year orbit; rotates once
every 24.6 hours, with a tilted axis (it has seasons!).
- Size and Mass: Radius about
half that of Earth [3400 km]; [Mass 11% of Earth's; density 3.9
times that of water, the surface gravity 0.38 g].
Atmosphere and Weather
- Composition: Less than 1% of
Earth's pressure, made of 95%
CO2 [we can see this from Earth]; Little water,
no rain; Dusty and reddish.
- History: The atmosphere was
probably thicker in the past; Was it blown away in an impact?
Gradually lost to space because of a weak gravity? The interior
is not active enough to keep replenishing it with volcano eruptions.
- Effect: The atmosphere is too thin to
protect, to cause greenhouse effect or affect the temperature significantly,
but thick enough to erode features.
- Weather: Winds, dust storms
and cyclones; Mostly colder than Earth, with daily and seasonal
changes [from 150 K (–220°F) to 295 K (70°F)], probably
warmer in the past.
Magnetic field: Almost none,
so there is no protection from the solar wind, which is also continuously
blowing away the atmosphere. (But parts of the crust are
highly magnetized, so Mars does have weak auroras!)
- Early missions: In 1965, after other
attempts failed, Mariner 4 reached Mars, took close-up pictures, and
ended any hopes of finding canals, cities, Martians. 1965-1971, US
Mariner orbiters; 1989, Soviet Phobos 2 orbiter (Phobos 1
was lost); 1971, Soviet Mars 3 lander; 1976, US Viking landers
($3 billion, 8 years to develop!).
- Recent missions: 1997, Mars
Pathfinder [$225 million, 4 years to develop]; Climate Orbiter,
lost 09.99; Polar Lander, lost 12.99; the Japanese Nozomi abandoned
in 2003 due to technical problems; NASA's Mars
Global Surveyor was in orbit from 1999 to 2006.
- Orbiting missions: NASA's Mars Odyssey
has been operational since 2001, ESA's Mars Express since late 2003 (Beagle
2 lander lost during the descent),
and NASA's Mars Reconnaissance Orbiter since early 2006; Why every
- Landing missions: The rovers
Spirit and Opportunity have been on the surface since Jan 2004, the Phoenix
Mars Lander since 2008, Curiosity since 2012.
- Plans: MAVEN (Mars Atmosphere and Volatile Evolution Mission) launch is scheduled for November 2013; More missions are in
the planning stages, including sample returns
to Earth; Issues to consider
are the budget, possible planet contamination; Human missions
are now being considered.
- Color: It really is reddish
(or "butterscotch"!), from rusting iron; Covered
with rocks and sand.
- Northern hemisphere: Younger
(3 Gyr) volcanic plains; Southern
hemisphere: Older (4 Gyr), heavily cratered highlands, higher
and thicker; Polar ice caps; Why the difference? A
collision with a very large (500 miles or so) asteroid is the currently
- Features: Tharsis bulge (4000
km), with 3 prominent volcanos; Mariner valley stretch fracture,
longer than the US; Craters can be used to estimate the age of
the surface; Their shape indicates permafrost underneath.
- Volcanos: There are many, including
the largest in the solar system, Olympus Mons [more than 15 mi
high, 340 mi wide!] How can they be taller that on Earth?
Are some of them active?
- In the past: It definitely existed,
from the runoff channels (highlands) and outflow channels and
islands (equatorial) we see on the surface, and from analysis
of soil by Opportunity and Spirit rovers; Whether water was present
for long or brief periods, and whether there were oceans, is
- Now: It may exist only in a
frozen form, at the poles (both polar caps contain large amounts
of water ice, in addition to carbion dioxide ice), and in permafrost
under the surface, but there is a huge quantity of it; Recent gullies
may indicate that water flowed recently, but they may have
- Situation: Very little known,
no seismic data, some from Global Surveyor, probably inactive.
- Geological activity: None now?
Possibly plate tectonics in the past, and active volcanoes (not
clear how recently the last eruptions occurred).
- Core: Not so hot, from current
absence of geological activity; Long thought to be either not
molten or not metallic, from absence of magnetic field, but years
of spacecraft tracking data indicate molten iron in the core.
- How many? Two, 28 km Phobos
("fear") and 16 km Deimos ("panic"), the
sons of Ares (Mars) and Aphrodite (Venus); [Discovered only in
1877; But Jonathan Swift and Kepler had guessed that Mars had
- Origin: Thought to be captured
asteroid(s), but the details are not clear [they may be fragments
of an old, larger moon]; Made of lighter material than Mars,
which probably includes ice.
- Properties: Small, dark, irregularly
shaped (Why?), and cratered, on very low orbits (Phobos is closer than
Life on Mars?
- 1800's: Schiaparelli ("canali",
1877), Lowell ("canals"), and others.
- 1976: The Viking lander analyzed
samples and found no evidence, but the experiments are still
- 1996: Rock from Mars, meteorite
ALH84001 (left Mars 16 Myr ago, arrived on Earth 13 kyr ago,
found in Antarctica in 1984), showed chemical evidence like carbonate
globules, and tubular fossil-like forms.
- Present: 1996 evidence disputed
(Earth contamination? Carbonates have also been seen in nebulae
around stars); The basic idea remains as a possibility, but studies by
the rovers so far are inconclusive, and currently few people believe
there is life; New studies focus on where and when water existed, and
page by luca bombelli <bombelli at olemiss.edu>,
modified 8 oct 2013