The
planet Mars, like Earth, has clouds in its atmosphere and a deposit of ice at
its north pole. But unlike Earth, Mars has no liquid water on its surface. The
rustlike color of Mars comes from the large amount of iron in the planet's soil.
Image credit: NASA/JPL/Malin Space Science Systems
Mars is one of the brightest
objects in the night sky. It has been known since ancient times. The planet is
named for the Roman God of War. It has two moons, Phobos (fear) and Deimos
(panic). The moons get their scary names from the horses that pulled the chariot
of the Greek god Ares.
Mars is the fourth planet from
the Sun. It is sometimes called the 'Red Planet' because of its red soil. The
soil on Mars is red because it contains iron oxide (rust).
The red planet Mars has inspired
wild flights of imagination over the centuries, as well as intense scientific
interest. Whether fancied to be the source of hostile invaders of Earth, the
home of a dying civilization, or a rough-and-tumble mining colony of the future,
Mars provides fertile ground for science fiction writers, based on seeds planted
by centuries of scientific observations.
We know that Mars is a small
rocky body once thought to be very Earth-like. Like the other
"terrestrial" planets - Mercury, Venus, and Earth - its surface has
been changed by volcanism, impacts from other bodies, movements of its crust,
and atmospheric effects such as dust storms. It has polar ice caps that grow and
recede with the change of seasons; areas of layered soils near the Martian poles
suggest that the planet's climate has changed more than once, perhaps caused by
a regular change in the planet's orbit. Martian tectonism - the formation and
change of a planet's crust - differs from Earth's. Where Earth tectonics involve
sliding plates that grind against each other or spread apart in the seafloors,
Martian tectonics seem to be vertical, with hot lava pushing upwards through the
crust to the surface. Periodically, great dust storms engulf the entire planet.
The effects of these storms are dramatic, including giant dunes, wind streaks,
and wind-carved features.
Scientists believe that 3.5
billion years ago, Mars experienced the largest known floods in the solar
system. This water may even have pooled into lakes or shallow oceans. But where
did the ancient flood water come from, how long did it last, and where did it
go?
In May 2002, scientists announced
the discovery of a key piece in the puzzle: the Mars Odyssey spacecraft had
detected large quantities of water ice close to the surface - enough to fill
Lake Michigan twice over. The ice is mixed into the soil only a meter (about 3
feet) below the surface of a wide area near the Martian south pole.
Many questions remain. At
present, Mars is too cold and its atmosphere is too thin to allow liquid water
to exist at the surface for long. More water exists frozen in the polar ice
caps, and enough water exists to form ice clouds, but the quantity of water
required to carve Mars' great channels and flood plains is not evident on - or
near - the surface today. Images from NASA's Mars Global Surveyor spacecraft
suggest that underground reserves of water may break through the surface as
springs. The answers may lie deep beneath Mars' red soil.
Unraveling the story of water on
Mars is important to unlocking its past climate history, which will help us
understand the evolution of all planets, including our own. Water is also
believed to be a central ingredient for the initiation of life; the evidence of
past or present water on Mars is expected to hold clues about past or present
life on Mars, as well as the potential for life elsewhere in the universe. And,
before humans can safely go to Mars, we need to know much more about the
planet's environment, including the availability of resources such as water.
Mars has some remarkable geological characteristics, including the largest
volcanic mountain in the solar system, Olympus Mons (27 km high and 600 km
across); volcanoes in the northern Tharsis region that are so huge they deform
the planet's roundness; and a gigantic equatorial rift valley, the Valles
Marineris. This canyon system stretches a distance equivalent to the distance
from New York to Los Angeles; Arizona's Grand Canyon could easily fit into one
of the side canyons of this great chasm.
Mars has two small moons: Phobos
and Deimos. Phobos (fear) and Deimos (panic) were named after the horses that
pulled the chariot of the Greek war god Ares, the counterpart to the Roman war
god Mars. Both Phobos and Deimos were discovered in 1877 by American astronomer
Asaph Hall. The moons appear to have surface materials similar to many asteroids
in the outer asteroid belt, which leads most scientists to believe that Phobos
and Deimos are captured asteroids.
Quick Facts about
Phobos and Deimos
Phobos
Deimos
Mean
distance from Mars (km)
9377
23436
Orbital
period (Mars days)
0.31891
1.26244
Major
axis (km)
26
16
Minor
axis (km)
18
10
Mass (x
1015 kg)
10.8
1.8
Mean
density (kg/m3)
1900
1750
Mars Exploration
Rovers
Opportunity &
Spirit
NASA's twin robot geologists, the
Mars Exploration Rovers, launched toward Mars on June 10 and July 7, 2003, in
search of answers about the history of water on Mars. They landed on Mars
January 3 and January 24 2004 . The Mars Exploration Rover mission is part of
NASA's Mars Exploration Program, a long-term effort of robotic exploration of
the red planet.
A
Postcard From Opportunity
Views
from the jagged-edged Victoria Crater on Mars, taken by NASA's Opportunity rover
NASA
JPL VIdeo
First
image from Spirit posted on NASA/JPL website
A
Postcard From Spirit
NASA's
Spirit rover sends a stunning panorama from Gusev Crater, Mars
NASA
JPL VIdeo
This
360-degree view, called the "McMurdo" panorama, comes from the
panoramic camera (Pancam) on NASA's Mars Exploration Rover Spirit. From April
through October 2006, Spirit has stayed on a small hill known as "Low
Ridge." There, the rover's solar panels are tilted toward the sun to
maintain enough solar power for Spirit to keep making scientific observations
throughout the winter on southern Mars. This view of the surroundings from
Spirit's "Winter Haven" is presented in approximately true color.
Mars: Facts &
Figures
Discovered By
Known by the Ancients
Date of Discovery
Unknown
Average Distance from the Sun
Metric: 227,936,640 km
English: 141,633,260
miles
Scientific Notation:
2.2793664 x 108 km (1.523662 A.U.)
By Comparison: 1.524 x
Earth
Perihelion (closest)
Metric: 206,600,000 km
English: 128,400,000
miles
Scientific Notation:
2.066 x 108 km (1.381 A.U.)
By Comparison: 1.404 x
Earth
Aphelion (farthest)
Metric: 249,200,000 km
English: 154,900,000
miles
Scientific Notation:
2.492 x 108 km (1.666 A.U.)
By Comparison: 1.638 x
Earth
Equatorial Radius
Metric: 3,397 km
English: 2,111 miles
Scientific Notation:
3.397 x 103 km
By Comparison: 0.5326 x
Earth
Equatorial Circumference
Metric: 21,344 km
English: 13,263 miles
Scientific Notation:
2.1344 x 104 km
Volume
Metric: 163,140,000,000
km3
Scientific Notation:
1.6314 X 1011 km3
By Comparison: 0.150 x
Earth
Mass
Metric:
641,850,000,000,000,000,000,000 kg
Scientific Notation:
6.4185 x 1023 kg
By Comparison: 0.10744 x
Earth
Density
Metric: 3.94 g/cm3
By Comparison: 0.714 x
Earth
Surface Area
Metric: 144,100,000 km2
English: 89,500,000
square miles
Scientific Notation:
1.441 x 108 km2
By Comparison: 0.282 x
Earth
Equatorial Surface Gravity
Metric: 3.693 m/s2
English: 12.116 ft/s2
By Comparison: If you
weigh 100 pounds on Earth, you would weigh 38 pounds
on Mars.
Escape Velocity
Metric: 18,072 km/h
English: 11,229 mph
Scientific Notation: 5.02
x 103 m/s
By Comparison: Escape
velocity of Earth is 25,022 mph.
Sidereal Rotation Period (Length
of Day)
1.026 Earth days
24.62 hours
By Comparison: Earth's
rotation period is 23.934 hours.
Sidereal Orbit Period (Length of
Year)
1.8807 Earth years
686.93 Earth days
Mean Orbit Velocity
Metric: 86,871 km/h
English: 53,979 mph
Scientific Notation:
24,130.9 m/s
By Comparison: 0.810 x
Earth
Orbital Eccentricity
.0934
By Comparison: 5.59 x
Earth
Orbital Inclination to Ecliptic
1.8 degrees
Equatorial Inclination to Orbit
25.19
Orbital Circumference
Metric: 1,366,900,000 km
English: 849,400,000
miles
Scientific Notation:
1.3669 x 109 km
By Comparison: 1.479 x
Earth
Minimum/Maximum Surface
Temperature
Metric: -87 to -5 °C
English: -125 to 23 °F
Scientific Notation: 186
to 268 K
Atmospheric Constituents
Carbon Dioxide, Nitrogen, Argon
Scientific Notation: CO2,
N2, Ar
By Comparison: CO2
is responsible for the Greenhouse Effect and is used
for carbonation in beverages.
N2 is 80% of Earth's air and is a crucial
element in DNA. Ar is used to make blue neon light
blubs.
Mars/Earth
Comparison
Bulk parameters
Mars Earth Ratio (Mars/Earth)
Mass (1024 kg) 0.64185 5.9736 0.107
Volume (1010 km3) 16.318 108.321 0.151
Equatorial radius (km) 3396.2 6378.1 0.532
Polar radius (km) 3376.2 6356.8 0.531
Volumetric mean radius (km) 3389.5 6371.0 0.532
Core radius (km) 1700 3485 0.488
Ellipticity (Flattening) 0.00648 0.00335 1.93
Mean density (kg/m3) 3933 5515 0.713
Surface gravity (m/s2) 3.71 9.80 0.379
Surface acceleration (m/s2) 3.69 9.78 0.377
Escape velocity (km/s) 5.03 11.19 0.450
GM (x 106 km3/s2) 0.04283 0.3986 0.107
Bond albedo 0.250 0.306 0.817
Visual geometric albedo 0.150 0.367 0.409
Visual magnitude V(1,0) -1.52 -3.86 -
Solar irradiance (W/m2) 589.2 1367.6 0.431
Black-body temperature (K) 210.1 254.3 0.826
Topographic range (km) 30 20 1.500
Moment of inertia (I/MR2) 0.366 0.3308 1.106
J2 (x 10-6) 1960.45 1082.63 1.811
Number of natural satellites 2 1
Planetary ring system No No
Orbital parameters
Mars Earth Ratio (Mars/Earth)
Semimajor axis (106 km) 227.92 149.60 1.524
Sidereal orbit period (days) 686.980 365.256 1.881
Tropical orbit period (days) 686.973 365.242 1.881
Perihelion (106 km) 206.62 147.09 1.405
Aphelion (106 km) 249.23 152.10 1.639
Synodic period (days) 779.94 - -
Mean orbital velocity (km/s) 24.13 29.78 0.810
Max. orbital velocity (km/s) 26.50 30.29 0.875
Min. orbital velocity (km/s) 21.97 29.29 0.750
Orbit inclination (deg) 1.850 0.000 -
Orbit eccentricity 0.0935 0.0167 5.599
Sidereal rotation period (hrs) 24.6229 23.9345 1.029
Length of day (hrs) 24.6597 24.0000 1.027
Obliquity to orbit (deg) 25.19 23.45 1.074
Mars Observational Parameters
Discoverer: Unknown
Discovery Date: Prehistoric
Distance from Earth
Minimum (106 km) 55.7
Maximum (106 km) 401.3
Apparent diameter from Earth
Maximum (seconds of arc) 25.1
Minimum (seconds of arc) 3.5
Mean values at opposition from Earth
Distance from Earth (106 km) 78.39
Apparent diameter (seconds of arc) 17.9
Apparent visual magnitude -2.0
Maximum apparent visual magnitude -2.91
Mars Mean Orbital Elements
(J2000)
Semimajor axis (AU) 1.52366231
Orbital eccentricity 0.09341233
Orbital inclination (deg) 1.85061
Longitude of ascending node (deg) 49.57854
Longitude of perihelion (deg) 336.04084
Mean Longitude (deg) 355.45332
North Pole of Rotation
Right Ascension: 317.681 - 0.106T
Declination : 52.887 - 0.061T
Reference Date : 12:00 UT 1 Jan 2000 (JD 2451545.0)
T = Julian centuries from reference date
Martian Atmosphere
Surface pressure: 6.36 mb at mean radius (variable from 4.0 to 8.7 mb depending on season)
[6.9 mb to 9 mb (Viking 1 Lander site)]
Surface density: ~0.020 kg/m3
Scale height: 11.1 km
Total mass of atmosphere: ~2.5 x 1016 kg
Average temperature: ~210 K (-63 C)
Diurnal temperature range: 184 K to 242 K (-89 to -31 C) (Viking 1 Lander site)
Wind speeds: 2-7 m/s (summer), 5-10 m/s (fall), 17-30 m/s (dust storm) (Viking Lander sites)
Mean molecular weight: 43.34 g/mole
Atmospheric composition (by volume):
Major : Carbon Dioxide (CO2) - 95.32% ; Nitrogen (N2) - 2.7%
Argon (Ar) - 1.6%; Oxygen (O2) - 0.13%; Carbon Monoxide (CO) - 0.08%
Minor (ppm): Water (H2O) - 210; Nitrogen Oxide (NO) - 100; Neon (Ne) - 2.5;
Hydrogen-Deuterium-Oxygen (HDO) - 0.85; Krypton (Kr) - 0.3;
Xenon (Xe) - 0.08
