Mars ... The Red Planet

Introduction to Mars

Well, here we are at the planet Mars. This is perhaps the most interesting planet, at least from a historical and science fiction standpoint. Television, movies, and countless books describe Martians and invaders from the Red Planet. While it will be fun to take a look at some of the lore about this planet, it is also important to give the truth. Mars is called the "red planet" because it appears dark red in the sky. While it is smaller than Earth or Venus, it rotated fast enough to moderate temepratures, and with an Earth-like tilt, Mars experiences seasons just as we do. What distinguished this planet from the others, besides the red color, are polar caps of ice and occasional dust storms that can enshroud the planet. The surface is marked by the solar system's largest mountains, and deepest, widest, and longest canyon. All kinds of excitement has abounded since the 1996 announcement of possible fossil life forms in a piece of rock blasted off the surface of Mars by a meteor impact and eventually landing on the Earth. As well, the study of Mars will reveal it to be a "Bermuda Triangle" of the Solar System since so many American and Russian satellites have broken either en route to Mars or after they arrived. Mars 1, Zond 2, Mars 2, Mars 3, Phobos 1 and Phobos 2 were all lost by the Soviets en route to Mars or shortly after touching down on the surface of Mars. Similarly, the U.S. lost Mariner 3, Mariner 8 and the Mars Observer.

Mars Exploration Rovers

But, on January 4, 2004, at 10:35 PM CST, engineers at the JPL received a signal that the latest Mars rover "Spirit" has successfully landed in the Gulev Crater on Mars. The signal was the lost temporarily, but at 10:51 the first photograph from "Spirit" came onto the computer screens at the JPL amid wild celebrations. What made this landing so significant was that the British and Japanese had both lost Mars spacecraft during the previous two months. There was nervousness on the part of the JPL team, for another failure such as the Mars Observer could have plunged NASA to the bottom of the money list on Capital Hill in Washington. To learn more about this mission, click on JPL to connect directly to the JPL website, or go to the Mars Exploration Rovers website.

Here are a few pictures of the "Spirit" rover, seen in a labeled image below, folowed by the celebration at the JPL upon its successful landing on the lower left image, and the first high resolution color image of its surroundings on the lower right.


Planetary Data

Mass (kg), and mass relative to Earth

6.419x1023 kg = .1074 earths

Equatorial diameter (km)


Mean density (gm/cm3)


Acceleration of gravity (m/s2)


Velocity of escape (km/s)


Period of rotation

24.6229 hours

Period of revolution

1.8809 years

Aphelion (AU)


Aphelion (km)


Perihelion (AU)


Perihelion (km)


Mean orbital distance from the sun (AU)


Mean orbital distance from the sun (km)


Orbital velocity (km/s)






Inclination to the ecliptic

1.850 degrees

Inclination of the equator to the orbit

25.19 degrees

Number of natural satellites


Names of natural satellites

Phobos, Deimos


More Information on the Planet Mars from the Nine Planets Website

Much of the information below is direct from the Nine Planets Website. Some material has been altered by me for this course, while other items and comments are directly copied. I hope to maintain a continuous update of this material to keep up with the findings from space satellites and telescopes.

In an extremely exciting news bulletin, it appears that there may be liquid water on Mars after all!

summary from NASA - Water on Mars?

The research was published in an on-line edition of Science magazine, arguably the most authorative science journal in the world. While I greet the article with great anticipation, we all should excercise healthy skepticism over the next few weeks to months as other geologists look at the evidence and evaluate new data from the Mars Global Surveyor.

Mars is the fourth planet from the Sun and the seventh largest:
orbit: 227,940,000 km (1.52 AU) from Sun
diameter: 6,794 km
mass: 6.4219x1023 kg
Mars (Greek: Ares) is the god of War. The planet probably got this name due to its red color; Mars is 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.
Mars has been known since prehistoric times. It is still a favorite of science fiction writers as the most 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.

The first spacecraft to visit Mars was Mariner 4 in 1965. Several others followed including Mars 2, the first spacecraft to land on Mars and the two Viking landers in 1976. Ending a long 20 year hiatus, Mars Pathfinder landed successfully on Mars on 1997 July 4. Wasn't that the same day the movie "Independence Day" was released? Hmmmmm? Aliens at Area 51?

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. While the average temperature on Mars is about 218 K (-55 C, -67 F), Martian surface temperatures range widely from as little as 140 K (-133 C, -207 F) at the winter pole to almost 300 K (27 C, 80 F) on the day side during summer.

Though Mars is much smaller than Earth, its surface area is about the same as the land surface area of Earth.

Except for Earth, Mars has the most highly varied and interesting terrain of any of the terrestrial planets, some of it quite spectacular:
- Olympus Mons: the largest mountain in the Solar System rising 24 km (78,000 ft.) above the surrounding plain. Its base is more than 500 km in diameter and is rimmed by a cliff 6 km (20,000 ft) high.







- 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.
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). Mars Global Surveyor has produced a nice 3D map of Mars that clearly shows these features.

The image to your left just shows that there is some humor in nature, for if you look closely at the large crater, you will find the unmistakable "smiley face," and astronomers have named this crater feature after the famous symbol :)






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 formerly molten rocky mantle somewhat denser than the Earth's and a thin crust. Data from Mars Global Surveyor indicates that Mars' crust is about 80 km thick in the southern hemisphere but only about 35 km thick in the north. 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).





Of critical relevance is the appearnce that Mars is geologically dead and with a "frozen" core. The word "frozen" here is used to describe a substance that has turned from liquid to solid. With no internal molten core, Mars does not generate a magnetic field. Without a magnetic field, Mars is unable to "protect" itself from harmful incoming radiation from space. Cosmic rays from deep space and gamma rays from the Sun strike the planet directly and "cleanse" the planet of any opportunity for life to continue without shielding. I am in an ongoing process of trying to discuss the value of magnetic fields on planets as a requirement of life. Please move to a reprinted article from the PNAS about the magnetic field of Mars.

Like Mercury and the Moon, Mars appears to lack active plate tectonics at present; there is no evidence of recent horizontal 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. There is no evidence of current volcanic activity, however. But there is new evidence from Mars Global Surveyor that Mars may have had tectonic activity in its early history, making comparisons to Earth all the more interesting!

There is very clear evidence of erosion in many places on Mars including large floods and small river systems. At some time in the past there was clearly some sort of fluid on the surface. Liquid water is the obvious fluid but other possibilities exist. There may have been large lakes or even oceans; the evidence for which was strenghtened by some very nice images of layered terrain taken by Mars Global Surveyor. But it seems that this occurred only briefly and very long ago; the age of the erosion channels is estimated at about nearly 4 billion years. (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.)



Early in its history, Mars was much more like Earth. As with Earth almost all of its carbon dioxide was used up to form carbonate rocks. But lacking the Earth's plate tectonics, Mars is unable to recycle any of this carbon dioxide back into its atmosphere and so cannot sustain a significant greenhouse effect. The surface of Mars is therefore much colder than the Earth would be at that distance from the Sun.

Mars has a very thin atmosphere composed mostly of the tiny amount of remaining carbon dioxide (95.3%) 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.








In spite of its tenuous nature, the atmosphere is thick enough to support very strong winds and vast dust storms that on occasion engulf the entire planet for months. To your left is an image of a dust storm that was brewing in the spring of 2002. A comparison to an Earth dust storm is shown so you can see how similar the events are for both planets. I have heard it said that the wind velocity during these storms is sufficient to scour the skin of a human completely away ... much like a sand-blasting would do to the paint on a house. Mars' thin atmosphere produces a greenhouse effect but it is only enough to raise the surface temperature by 5 degrees (K); much less than what we see on Venus and Earth. In fact, heat escapes so quickly from the surface that your head might feel 10-20 C cooler than your feet on a sunny day.





This recent image from the Mars Global Surveyor shows sand dune formations on Mars, that appear exactly as sand dunes appear on the Earth's Sahara desert. I left the image size larger because I just thought it looked so cool!














Mars Avalanche ... caught in action by the Mars Reconnaissance Orbiter. The pictures were released Mar 3, 2008

Click on the multiple-image set to see the photo at full resolution.

There are three suggested activities that will enable you to better understand Mars better, and these are all drawn from the USGS

Mars Topography

Mars Geology

Comparing Olympus Mons to Earth Mountains

I have added a page of pictures and links to even more images of Mars. To get there and see lots of really cool images, click on Mars Images. You just HAVE to go to this page because the pictures are amazing. However, be mindful that you may become overly awed and gleek on your computer screen. Keep the ooohs and aaahs with your lips pursed to save your delicate machinery.


To continue your learning about Mars, go now to Mars2 for the rest of the story on the Red Planet.

You could go back to one of the Inner Planets (Mercury, Venus, Earth), or return to Introduction to the Inner Rocky Worlds, or the Planet Introduction, or the Syllabus, but why would you want to stop learning now. Go forward to Mars2.


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