Glossary term: Mars

Description: Mars is the fourth planet from the Sun in the Solar System. It is a rocky, terrestrial planet with a radius of a little under 3400 kilometers (km), just over one half of the Earth's radius. Mars has a very thin atmosphere, a large canyon system, and the tallest mountain in the Solar System: an extinct volcano called Olympus Mons. It is thought to have hosted liquid water earlier in its existence.

Its typical distance from the Sun is about 228 million km or 1.52 astronomical units (Earth–Sun distances). It takes 687 days to complete one orbit of the Sun. Mars has two small moons, Phobos and Deimos.

It is named after the Roman god of war. It is often called the "red planet" due to its reddish rusty color. Scientists have sent many landers to Mars over the years to study its composition and atmosphere.

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Term and definition status: This term and its definition have been approved by a research astronomer and a teacher

The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".

Related Media

The NASA Mars rover Curiosity stands on a hill on Mars.

Mars rover Curiosity

Caption: This self-portrait of NASA's Curiosity Mars rover shows the vehicle at the site from which it reached down to drill into a rock target called "Buckskin" on lower Mount Sharp. The selfie combines several component images taken by Curiosity's Mars Hand Lens Imager (MAHLI) on 5 August 2015, during the 1,065th Martian day, or sol, of the rover's work on Mars.
Credit: NASA/JPL-Caltech/MSSS credit link

License: PD Public Domain icons

The planet Mars with a rusty red surface, volcanoes, valleys, craters, ice clouds and a white polar cap


Caption: This image of the planet Mars taken by NASA's Mars Global Surveyor Orbiter in 1999 shows its dry surface. The picture features the most spectacular geological regions on Mars. Besides the deep Valles Marineris valley we see four volcanoes. While three of them form the Tharsis ridge, the Olympus Mons is largest volcano we have so far discovered in the Solar System. Ice clouds cover parts of the Martian surface.
Credit: NASA/JPL/MSSS credit link

License: PD Public Domain icons

The Milky Way over a cloudy landscape. A triangle of bright objects is visible on the left of the image.

Equatorial Milky Way

Caption: Honourable mention in the 2022 IAU OAE Astrophotography Contest, category Still images of celestial patterns: Equatorial Milky Way   Taken in Bromo-Tengger-Semeru National Park, Java Island, Indonesia, in March 2016, this image captures regions of the southern Milky Way and, at its left edge, the two planets Mars and Saturn. Mars appears orange and is similar in colour to the star Antares, whose Greek name — anti Ares — references this. Saturn is a little bit fainter than Mars, but clearly visible among the stars of Ophiuchus, above the Pipe Nebula and forming an isosceles triangle with Mars and Antares. Mars is on the top and Saturn is vertically below. Visible to the naked eye, both planets have significance in many cultures around the world. In Roman mythology Mars is the god of war and fertility, and Saturn the god of sowing and agriculture. Its Greek equivalent, the god Kronos, is also considered the regent of completion. Indigenous Australians, including the Kamilaroi and Wailan people, associate Saturn with “wunygal”, a small bird. Mars is called Iherm-penh (something burnt in flames) by the Anmatyerre people of the Central Desert, while the Kokatha people of the Western Desert associate Mars and the star Anatres with the red-tailed black cockatoo (Kogolongo). In the middle of this photograph, the most famous southern constellations are clearly recognisable: the Southern Cross (Crux), the pointer stars, Alpha and Beta Centauri, the dark Coalsack Nebula and the red Eta Carina Nebula, which is not visible to the unaided eye but is prominent in modern photographs. In the 19th century, the star eta Carinae had been the second-brightest star in the sky for some time, but since it varies irregularly, it has hardly been recognisable in recent decades, and its future visibility is unpredictable. Triangulum Australe is visible between the pointer stars and the Scorpion, and in the constellation of Centaurus, the bright globular star cluster Omega Centauri is clearly displayed. It was considered a “nebulous star” since antiquity and, thus, was listed in star catalogues for at least 2000 years. Only within the last century did astronomers discover that globular star clusters are in the halo of our galaxy and that this one consists of roughly 10 million stars. The dark regions in the Milky Way, which are cool, dense clouds of dust and gas, form the head and body of the Celestial Emu Tchingal. Together with the Southern Cross and the pointer stars, they appear in the Dreamtime stories of many Indigenous Australians. One story associated with the Djab Wurrung and the Jardwadjali people is part of a Dreamtime Story involving Tchingal, the Bram-bram-bult brothers (the pointer stars), their mother Druk (Delta Crux), and Bunya the hunter, who gets transformed into a possum (Gacrux, the red star at the top of the Southern Cross).
Credit: Giorgia Hofer/IAU OAE

License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons

A montage of images of Mars, seen here as a series of red dots in a squashed z-shaped pattern.

Retrograde Motion of Mars

Caption: This image captures the celestial waltz of Mars as it demonstrates its intriguing retrograde motion against the background of fixed stars. This event, when Mars appears to backtrack in its orbit, arises from the different speeds at which Earth and Mars orbit the Sun. Earth’s faster movement occasionally positions it ahead of Mars, creating the illusion of the Red Planet moving in reverse from our perspective. This retrograde motion occurs when Mars is on the other side of the sky from the Sun, when it is said to be in opposition. Following Mars from 14 August 2022 to 5 April 2023, this smartphone image stands as a testament to perseverance and precision in the tranquil setting of Bataan, Philippines. Enduring unpredictable weather and ever-shifting celestial alignments, the photographer meticulously captured each shot at regular intervals of five to eight days. The process involved aligning 35 distinct images of Mars, taken without any external lens or telescope, alongside a stacked background image composed of 54 frames lasting 15 seconds each, portraying the starry expanse. Fusing these images involved precisely aligning them and cropping Mars in order to centre its position, revealing its retrograde movement against the backdrop of stars. This intricate process, blending the images seamlessly into the background by masking, highlights the planet’s unique motion. In the lower right corner, the Pleiades star cluster is visible.
Credit: Rob Kerby Guevarra/IAU OAE (CC BY 4.0)

License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons

Related Activities

Children's Planetary Maps: Mars

Children's Planetary Maps: Mars

astroEDU educational activity (links to astroEDU website)
Description: Explore planet Mars, learning how to use planetary maps!

License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons

Tags: Maps , Planetary cartography
Age Ranges: 6-8 , 8-10 , 10-12 , 12-14
Education Level: Middle School , Primary , Secondary
Areas of Learning: Social Research
Costs: Free
Duration: 2 hours
Group Size: Group
Skills: Analysing and interpreting data , Asking questions , Constructing explanations

Driving on Mars

Driving on Mars

astroEDU educational activity (links to astroEDU website)
Description: An educational interdisciplinary game to drive a rover on Mars

License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons

Tags: Game , robot , robotics , simulation , telecommunications
Age Ranges: 14-16 , 16-19
Education Level: Middle School , Secondary
Areas of Learning: Guided-discovery learning
Costs: Low Cost
Duration: 2 hours
Group Size: Group
Skills: Communicating information , Developing and using models , Using mathematics and computational thinking