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Mars is the fourth planet from the Sun and the seventh largest:
orbit: 227,940,000 km (1.52 AU) from Sun
Mars (Greek: Ares) is the god of War. The planet probably got this name
due to its red color; Mars is
Mars has been known since prehistoric times. It is still a favorite of
science fiction writers as the most
The first spacecraft to visit Mars was Mariner 4 in 1965. Several others
followed including the two Viking
Though Mars is much smaller than Earth, its surface area is about the same
as the land surface area of
Except for Earth, Mars has the most highly varied and interesting terrain
of any of the terrestrial planets,
- Olympus Mons: the largest mountain in the Solar System rising 24 km (78,000
ft.) above the surrounding
- Tharsis: a huge bulge on the Martian surface that is about 4000 km across
and 10 km high.
- Valles Marineris: a system of canyons 4000 km long and from 2 to 7 km
deep.
- Hellas Planitia: an impact crater in the southern hemisphere over 6 km
deep and 2000 km in diameter.
Like Mercury and the Moon, Mars appears to lack active plate tectonics;
there is no evidence of horizontal
There is very clear evidence of erosion in many places on Mars including
large floods and small river
Mars has a very thin atmosphere composed mostly of the tiny amount of remaining
carbon dioxide (95.3%)
Mars has permanent ice caps at both poles composed mostly of solid carbon
dioxide ("dry ice"). The ice
Recent observations with the Hubble Space Telescope have revealed that
the conditions during the Viking
The Viking landers performed experiments to determine the existence of
life on Mars. The results were
On 1996 Aug 6, David McKay et al announced the first identification of
organic compounds in a Martian
Exciting as this is, it is important to note while this evidence is strong
it by no means establishes the fact of
Mars has no global magnetic field.
When it is in the nighttime sky, Mars is easily visible with the naked
eye. Its apparent brightness varies
Planet
Profile
Mass
6.42 x 10^23 km
Martian
Atmosphere
Surface Pressure:
6.9 mb to 9 mb (Viking Lander 1 site)
Major : Carbon Dioxide (CO2) - 95.32% , Nitrogen
(N2) - 2.7%, Argon (Ar) - 1.6%,
Minor (ppm): Water (H2O) - 210, Nitrogen Oxide (NO) - 100, Neon
(Ne) - 2.5,
Orbital
parameters
diameter: 6,794 km
mass: 6.4219e23 kg
sometimes referred to as the Red Planet. (An interesting side note: the
Roman god Mars was a god of
agriculture before becoming associated with the Greek Ares; those in favor
of colonizing and terraforming
Mars may prefer this symbolism.) The name of the month March derives from
Mars.
favorable place in the Solar System (other than Earth!) for human habitation.
But the famous "canals" "seen"
by Lowell and others were, unfortunately, just as imaginary as Barsoomian
princesses.
landers in 1976. Ending a long 20 year hiatus, three new spacecraft will
arrive at Mars in 1997. Mars'
orbit is significantly elliptical. One result of this is a temperature
variation of about 30 C at the subsolar point
between aphelion and perihelion. This has a major influence on Mars' climate.
Overall, the Viking landers
found that Martian temperatures vary from 150 K (-220 F) to 295 K (70 F).
Earth.
some of it quite spectacular:
plain. Its base is more than 500 km in diameter and is rimmed by a cliff
6 km (20,000 ft) high.
Much of the Martian surface is very old and cratered, but there are also
much younger rift valleys, ridges, hills
and plains. The southern hemisphere of Mars is predominantly ancient cratered
highlands somewhat similar
to the Moon. In contrast, most of the northern hemisphere consists of plains
which are much younger, lower in
elevation and have a much more complex history. An abrupt elevation change
of several kilometers seems
to occur at the boundary. The reasons for this global dichotomy and abrupt
boundary are unknown (some
speculate that they are due to a very large impact shortly after Mars'
accretion). Recently, some scientists
have begun to question whether the abrupt elevation is real in the first
place. Mars Global Surveyor should
resolve the issue.
The interior of Mars is known only by inference from data about the surface
and the bulk statistics of the
planet. The most likely scenario is a dense core about 1700 km in radius,
a molten rocky mantle somewhat
denser than the Earth's and a thin crust. The lack of a global magnetic
field indicates that Mars' core is
probably solid. Mars' relatively low density compared to the other terrestrial
planets indicates that its core
probably contains a relatively large fraction of sulfur in addition to
iron (iron and iron sulfide).
motion of the surface such as the folded mountains so common on Earth.
With no lateral plate motion,
hot-spots under the crust stay in a fixed position relative to the surface.
This, along with the lower surface
gravity, may account for the Tharis bulge and its enormous volcanoes.
systems. At some time in the past there was clearly water on the surface
There may have been large lakes
or even oceans. But it seems that this occurred only briefly. (Valles Marineris
was NOT created by running
water. It was formed by the stretching and cracking of the crust associated
with the creation of the Tharsis
bulge.)
plus nitrogen (2.7%), argon (1.6%) and traces of oxygen (0.15%) and water
(0.03%). The average pressure
on the surface of Mars is only about 7 millibars (less than 1% of Earth's),
but it varies greatly with altitude
from almost 9 millibars in the deepest basins to about 1 millibar at the
top of Olympus Mons. But it is thick
enough to support very strong winds and vast dust storms that on occasion
engulf the entire planet for
months. Although its atmosphere is mostly carbon dioxide (like Venus'),
the greenhouse effect on Mars is
strong enough to raise the surface temperature by only 5 degrees (K).
caps exhibit a layered structure with alternating layers of ice with varying
concentrations of dark dust. In the
northern summer the carbon dioxide completely sublimes, leaving a residual
layer of water ice. It's not known
if a similar layer of water ice exists below the southern cap since its
carbon dioxide layer never completely
disappears. The mechanism responsible for the layering is unknown but may
be due to climatic changes
related to long-term changes in the inclination of Mars' equator to the
plane of its orbit. There may also be
water ice hidden below the surface at lower latitudes. The seasonal changes
in the extent of the polar caps
changes the global atmospheric pressure by about 25% (as measured at the
Viking lander sites).
missions may not have been typical. Mars' atmosphere now seems to be both
colder and dryer than
measured by the Viking landers.
negative. Optimists point out that only two tiny samples were measured
and not from the most favorable
locations. More experiments will be done by future missions to Mars.
A small number of meteorites (the SNC meteorites) are believed to have
originated on Mars.
meteorite. The authors further suggest that these compounds, in conjunction
with a number of other
mineralogical features observed in the rock, may be evidence of ancient
Martian microorganisms.
extraterrestrial life. Remember, "extraordinary claims require extraordinary
evidence." Much work remains to
be done before we can be confident of this most extraordinary claim.
greatly according to its relative position to the Earth.
Diameter
6787 km
Mean density
3940 kg/m^3
Escape velocity
5000 m/s
Average distance from Sun
1.524 AU
Rotation period (length of day in Earth days)
1.026 Days
Revolution period (length of year in Earth days) 686.98 Days
Obliquity (tilt of axis in degrees)
25
Orbit inclination (degrees)
1.85
Orbit eccentricity (deviation from circular)
0.093
Maximum surface temperature
310 K
Minimum surface temperature
150 K
Visual geometric albedo (reflectivity)
0.15
Highest point on surface
- Olympus Mons 24 km above surrounding lava plains
Atmospheric components
95% carbon dioxide
3% nitrogen,
1.6% argon
Surface materials
basaltic rock and altered materials
Surface Density:
~0.020 kg/m3
Scale height:
11.1 km
Average temperature: ~210 K
Mean molecular weight: 43.34 g/mole
Diurnal temperature range: 184 K to 242 K (Viking Lander 1 site)
Wind speeds: 2-7 m/s (summer)
5-10 m/s (fall)
17-30 m/s (dust storm) (Viking Lander sites)
Atmospheric composition (by volume):
Oxygen (O2) - 0.13%, Carbon Monoxide (CO)
- 0.08%
Hydrogen-Deuterium-Oxygen (HOD)- 0.85, Krypton
(Kr) - 0.3, Xenon (Ex) - 0.08
| Mars | |
|---|---|
| Semi major axis (106 km) | 227.9 |
| Sidereal orbit period (days) | 686.980 |
| Tropical orbit period (days) | 686.930 |
| Perihelion (106 km) | 206.6 |
| Aphelion (106 km) | 249.2 |
| Synodic period (days) | 779.94 |
| Mean orbital velocity (km/s) | 24.13 |
| Orbit inclination (deg) | 1.85 |
| Orbit eccentricity | 0.0934 |
| Sidereal rotation period (hr.) | 24.6229 |
| Obliquity to orbit (deg) | 25.19 |
Satellites of Mars
Mars has two tiny satellites which orbit very close to the surface.
|
|
Phobos | Deimos |
|---|---|---|
| Distance from Mars (km) | 9000 | 23000 |
| Radius (km) | 11 | 6 |
| Mass (kg) | 1.08e16 | 1.80e15 |
| Discoverer | Hall | Hall |
| Discovery Date | 1877 | 1877 |
| Mean distance from Mars (km) | 9377 | 23436 |
| Sidereal orbit period (days) | 0.31891 | 1.26244 |
| Orbital inclination (deg) | 1.08 | 1.79 |
| Orbital eccentricity | 0.0151 | 0.00033 |
| Major axis radius (km) | 13 | 8 |
| Minor axis radius (km) | 9 | 5 |
| Mass (1015 kg) | 10.8 | 1.8 |
| Mean density (kg/m3) | 1900 | 1750 |
| Geometric albedo | 0.06 | 0.07 |
| Visual magnitude V(1,0) | +11.8 | +12.89 |
Phobos
Phobos ("FOH bus") is the larger and innermost of Mars' two moons. Phobos
is closer to its primary than
orbit: 9378 km from the center of Mars
In Greek mythology, Phobos is one of the sons of Ares (Mars) and
Aphrodite (Venus). "phobos" is Greek for
Discovered 1877 August 12 by Hall; photographed by Marriner 9 in 1971,
Viking 1 in 1977, and Phobos in
Phobos orbits Mars below the synchronous orbit radius. Thus it rises in
the west, moves very rapidly across
And Phobos is doomed: because its orbit is below synchronous altitude
tidal forces are lowering its orbit
Phobos and Deimos may be composed of carbon-rich rock like C-type
asteroids. But their densities are so
The Soviet spacecraft Phobos 2 detected a faint but steady outgassing
from Phobos. Unfortunately, Phobos
The most prominent feature on Phobos is the large crater named Stickney,
the maiden name of Hall's wife
Phobos and Deimos are widely believed to be captured asteroids. There is
some speculation that they
Deimos
orbit: 23,459 km from Mars
In Greek mythology, Deimos is one of the sons of Ares (Mars) and Aphrodite
(Venus); "deimos" is Greek for
Discovered 1877 August 10 by Hall, photographed by Viking 1 in 1977.
Deimos and Phobos are probably asteroids perturbed by Jupiter into orbits
that allowed them to be
any other moon in the solar system, less than
6000 km above the surface of Mars. It is also one of the
smallest
moons in the solar system.
diameter: 22.2 km (27 x 21.6 x 18.8)
mass: 1.08e16 kg
"fear" (the root of "phobia").
1988.
the sky and sets in the east, usually twice
a day. It is so close to the surface that it cannot be seen
above the
horizon from all points on the surface of Mars.
(current rate: about 1.8 meters per century).
In about 50 million years it will either crash onto the surface
of
Mars or (more likely) break up into a ring. (This is the opposite
effect to that operating to raise the orbit of the
Moon.)
low that they cannot be pure rock. They are
more likely composed of a mixture of rock and ice. Both are
heavily
cratered.
2 died before it could determine the nature
of the material; water is the best bet.
(above). Like Mimas' crater Herschel (on a
smaller scale) the impact that created Stickney must have almost
shattered Phobos. The grooves and streaks on the surface were probably
also caused by the Stickney
impact.
originated in the outer solar system rather than
in the main asteroid belt. Phobos and Deimos may someday
be useful as "space stations" from which to
study Mars or as intermediate stops to and
from the Martian
surface; especially if the presence of ice is confirmed.
Deimos ("DEE mos") is the smaller and outermost of Mars' two moons. It
is the smallest known moon in the
solar system.
diameter: 12.6 km (15 x 12.2 x 11)
mass: 1.8e15 kg
"panic".
Deimos and Phobos are composed of carbon-rich rock like C-type asteroids
and ice. Both are heavily
cratered.
captured by Mars.
Sun
Venus
Mars
Saturn
Neptune