Journey Through the Solar System: Planet Mars

Mars globe
Mars is the closest Earth-like planet in the solar system, but with an atmosphere much thinner than Earth's and no water to be seen on its surface. NASA

Mars is a fascinating world that will very likely be the next place (after the Moon) that humans explore in person. Currently, planetary scientists are studying it with robotic probes such as the Curiosity rover, and a collection of orbiters, but eventually the first explorers will set foot there. Their early missions will be scientific expeditions aimed at understanding more about the planet.

Eventually, colonists will start long-term residencies there to study the planet further and exploit its resources. They may even start families on that distant world. Since Mars may become humanity's next home within a couple of decades, it's a good idea to know some important facts about the Red Planet.

Mars from Earth

Mars appears as a reddish-orange dot in the nighttime or early morning sky. Here is how a typical star chart program will show observers where it is. Carolyn Collins Petersen

Observers have watches Mars move across the backdrop of stars since the dawn of recorded time. They gave it many names, such as Aries, before settling on Mars, the Roman god of war. That name seems to resonate due to the red color of the planet. 

Through a good telescope, observers might be able to make out the Mars polar ice caps, and bright and dark markings on the surface. To search out the planet, use a good desktop planetarium program or digital astronomy app.  

Mars by the Numbers

Pictures of Mars - Mars Daily Global Image
Pictures of Mars - Mars Daily Global Image. Copyright 1995-2003, California Institute of Technology

Mars orbits the Sun at an average distance of 227 million kilometers. It takes 686.93 Earth days or 1.8807 Earth years to complete one orbit. 

The Red Planet (as it is often known) is definitely smaller than our world. It's about half the diameter of Earth and has a tenth of Earth's mass. Its gravity is about one third that of Earth's, and its density is about 30 percent less.

Conditions on Mars are not quite Earth-like. Temperatures are quite extreme, ranging between -225 and +60 degrees Fahrenheit, with an average of -67 degrees. The Red Planet has a very thin atmosphere made up mostly of carbon dioxide (95.3 percent) plus nitrogen (2.7 percent), argon (1.6 percent) and traces of oxygen (0.15 percent) and water (0.03 percent).

Also, water has been found to exist in liquid form on the planet. Water is an essential ingredient for life. Unfortunately, the Martian atmosphere is slowly leaking to space, a process that began billions of years ago.

Mars from the Inside

Pictures of Mars - Lander 2 Site
Pictures of Mars - Lander 2 Site. Copyright 1995-2003, California Institute of Technology

Inside Mars, its core is probably mostly iron, with small amounts of nickel. Spacecraft mapping of the Martian gravity field seems to indicate that its iron-rich core and mantle are a smaller portion of its volume than Earth's core is of our planet. Also, it has a much weaker magnetic field than Earth, which indicates a mostly solid, rather than the highly viscous liquid core inside Earth. 

Due to a lack of dynamic activity in the core, Mars does not have a planet-wide magnetic field. There are smaller fields scattered around the planet. Scientists aren't quite sure exactly how Mars lost its field, because it did have one in the past.

Mars from the Outside

Pictures of Mars - Western Tithonium Chasma - Ius Chasma
Pictures of Mars - Western Tithonium Chasma - Ius Chasma. Copyright 1995-2003, California Institute of Technology

Like the other "terrestrial" planets, Mercury, Venus, and Earth, the Martian surface has been changed by volcanism, impacts from other bodies, movements of its crust, and atmospheric effects such as dust storms. 

Judging by images sent back by spacecraft starting in the 1960s, and particularly from landers and mappers, Mars looks very familiar. It has mountains, craters, valleys, dune fields, and polar caps. 

Its surface includes the largest volcanic mountain in the solar system, Olympus Mons (27 km high and 600 km across), more volcanoes in the northern Tharsis region . That's actually a huge bulge that planetary scientists think it may have tipped the planet slightly. There's also a gigantic equatorial rift valley called the Valles Marineris. This canyon system stretches a distance equivalent to the width of North America. Arizona's Grand Canyon could easily fit into one of the side canyons of this great chasm.

The Tiny Moons of Mars

Phobos from 6,800 Kilometers
Phobos from 6,800 Kilometers. NASA/JPL-Caltech/University of Arizona

Phobos orbits Mars at a distance of 9,000 km. It is about 22 km across and was discovered by American astronomer Asaph Hall, Sr., in 1877, at the US Naval Observatory in Washington, DC.

Deimos is Mars's other moon, and it's about 12 km across.  It was also discovered by American astronomer Asaph Hall, Sr., in 1877, at the U.S. Naval Observatory in Washington, DC. Phobos and Deimos are Latin words meaning "fear" and "panic". 

Mars has been visited by spacecraft since the early 1960s.

Mars Global Surveyor Mission. NASA

Mars is currently the only planet in the solar system solely inhabited by robots. Dozens of missions have gone there either to orbit the planet or land on its surface. More than half have successfully sent back images and data. For example, in 2004, a pair of Mars Exploration Rovers called Spirit and Opportunity landed on Mars and started providing pictures and data. Spirit is defunct, but Opportunity continues to roll.

These probes revealed layered rocks, mountains, craters, and odd mineral deposits consistent with flowing water and dried-up lakes and oceans. The Mars Curiosity rover landed in 2012 and continues to provide "ground truth" data about the surface of the Red Planet. Many other missions have orbited the planet, and more are planned over the next decade. The most recent launch was ExoMars, from the European Space Agency. The Exomars orbiter arrived and deployed a lander, which crashed. The orbiter is still functioning and sending back data. Its prime mission is to search for signs of past life on the Red Planet.

One day, humans will walk on Mars.

NASA's new Crew Exploration Vehicle (CEV) with solar panels deployed, docked with a lunar lander.
NASA's new Crew Exploration Vehicle (CEV) with solar panels deployed, docked with a lunar lander in lunar orbit. NASA & John Frassanito and Associates

NASA currently is planning a return to the Moon and has long-range plans for trips to the Red Planet. Such a mission is not likely to "lift off" for at least a decade.  From Elon Musk's Mars ideas to NASA's long-term strategy for exploring the planet to China's interest in that distant world, it's pretty clear that people will be living and working on Mars before the middle of the century. The first generation of Marsnauts could well be in high school or college, or even beginning their careers in space-related industries.

Edited and updated by Carolyn Collins Petersen.

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Greene, Nick. "Journey Through the Solar System: Planet Mars." ThoughtCo, Jul. 31, 2021, Greene, Nick. (2021, July 31). Journey Through the Solar System: Planet Mars. Retrieved from Greene, Nick. "Journey Through the Solar System: Planet Mars." ThoughtCo. (accessed June 10, 2023).