The sky — astronomy

Mars: The Red Planet

Mars is the fourth planet from the Sun, and it looks red because its surface dust is rich in iron oxides, essentially rust. It appears brightest from Earth around opposition, which comes roughly every 26 months. The latest was in January 2025, and the next is due in February 2027.

Mars is the fourth planet from the Sun and one of the easiest planets to recognise in the night sky: to the naked eye it is a bright point with a distinct orange-red tint. It is a rocky, Earth-like (terrestrial) planet about half the diameter of Earth, with surface gravity roughly 38% of ours.

Why Mars is red

The colour comes from the surface. Martian dust and rocks contain a lot of iron oxide, which is essentially rust. According to NASA, winds lift fine dust into the air, which is why the Martian daytime sky has a butterscotch, reddish-brown hue. Not everything is red: there are dark basaltic regions, and rock beneath the dust is often darker and greyer. This is the origin of the nickname the Red Planet.

Surface, water and atmosphere

Mars has dramatic terrain. It is home to Olympus Mons, the largest known volcano in the Solar System at about 22 km high, and to Valles Marineris, a canyon system roughly 4,000 km long. Its poles are capped with frozen water and carbon dioxide.

The atmosphere is very thin and mostly carbon dioxide. Surface pressure is below 1% of Earth’s, and the average temperature is around −60 °C, swinging widely between day and night and across seasons. The axis tilt is about 25°, similar to Earth’s, so Mars has seasons, although they are longer: a Martian year lasts about 687 Earth days, and a Martian day (a sol) is about 24 hours 39 minutes. See also Earth for comparison.

Liquid water is not stable on the surface today, but orbiters and rovers have found evidence of ancient rivers, lakes and deltas. Today water is found as ice at the poles and underground. Whether life ever existed on Mars is still an open scientific question: no confirmed evidence of life has been found, and current missions are looking for signs of past habitability.

Mars has two small, irregularly shaped moons, Phobos and Deimos.

Opposition: when Mars is brightest

Opposition happens when Earth passes between the Sun and Mars. Mars then lies opposite the Sun in the sky, rises at sunset and is visible all night. Because Earth travels on an inner, faster orbit, it catches up with Mars about every 26 months (roughly 780 days).

Not all oppositions are equal. Mars has a noticeably elliptical orbit, so the distance at opposition ranges from about 56 to about 100 million kilometres. At the closest oppositions Mars reaches a magnitude of about −2.9, outshining every star; among the planets only Venus is consistently brighter, while Jupiter is comparable. The most recent opposition was in January 2025 and the next is expected in February 2027.

For viewing, pick a dark site away from lights (see how to watch the sky and light pollution). Mars does not twinkle like stars; it shines with a steadier orange light. Through a telescope near a good opposition you can pick out the polar cap and darker surface markings.

The retrograde loop of Mars

Around opposition, Mars appears to drift backwards against the background stars for a while before resuming its usual eastward motion. This is an optical effect, not a real reversal: as Earth overtakes slower Mars, our line of sight shifts, much like passing another car on a motorway. This apparent retrograde motion lasts about two to three months and repeats about every 26 months. The mechanics are explained in the article on retrograde motion. How astrological tradition interprets this period is covered separately in Mars retrograde and Mars in astrology; that is a cultural tradition distinct from astronomy (see astronomy vs astrology). Mars can also appear alongside other planets, as in a planet parade.

Missions to Mars

Mars is the most explored planet after Earth. The first successful flyby was NASA’s Mariner 4 in 1965. Viking 1 and Viking 2 landed in 1976 and were the first long-lived American landers. Sojourner (1997) was the first rover on Mars. Spirit and Opportunity (2004) found mineral traces of ancient water. Curiosity (2012) explores Gale Crater, and Perseverance (2021) works in Jezero Crater, collecting samples intended for return to Earth in the future. It arrived with the small helicopter Ingenuity, the first powered flight on another planet; its mission ended in 2024.

The European Space Agency (ESA) has studied Mars with the Mars Express orbiter since 2003 and the ExoMars Trace Gas Orbiter since 2016, which analyses trace gases in the atmosphere. China has also succeeded with Tianwen-1 and its Zhurong rover (2021). Data from all these missions keep refining the picture of the planet’s history.

Interest in Mars is both scientific and cultural: from naked-eye watching to sophisticated robots on its surface, it remains a bridge between humanity’s ancient curiosity about the sky and modern discovery.

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