Marsthe red planet

Highlights
Mars once had liquid water on its surface and could have supported life.
Scientists are uncovering how Mars transformed into the colddry desert world it is today.
We explore Mars to understand the planet's history and look for evidence of past or even present life.

Mars facts
Surface temperature: -153°C (-243°F) to 20°C (70°F)
Average distance from Sun: 228 million kilometers (142 million miles)or 1.5 times farther from the Sun than Earth
Diameter: 6,780 kilometers (4,212 miles)Earth is 1.9 times larger
Volume: 163 billion km³ (39 billion mi³)Mars could fit inside Earth a little over 6 times
Gravity: 3.73 m/s²or 38% that of Earth’s
Solar day: 25 Earth hours
Solar year: 687 Earth days
Atmosphere: 95% carbon dioxide2.6% nitrogen1.9% argon0.5% other gases

Is there life on Mars?

This question has intrigued humans for centuries. Early telescope observations in the 18th and 19th centuries seemed to show a planet not all that different from Earthwith ice capsseasonsand features that were mistaken for seas and artificial canals. A few scientists even thought that Mars was inhabited by intelligent life.

We now know that Mars is very cold and drywith no breathable atmosphere and no global magnetic field to protect it from the Sun's radiation. But Mars wasn't always that way. Space missions have shown us that the planet once had liquid water on its surface and could have been hospitable to life as we know it. Todaythere may still be life beneath the Martian surfacewith access to water and protection from radiation and extreme temperatures.

Scientists have discovered that Mars was habitable to life as we know it for at least some periods of time around 3 or 4 billion years ago. But we don't know whether the planet was warm and wet long enough for life to ariseor mostly cold and dry with only brief intervals that could have supported life.

How did Mars go from a potential life-supporting oasis to a colddry desert? Does life still flourish underground? The answers to these questions will teach us more about where we come from and whether we are alone in the cosmos.

Mars with Olympus Mons This image of Mars captured by the United Arab Emirates' Hope Probe shows Olympus Monsthe solar system's largest volcano.Image: Emirates Mars Mission/EXI via The National

Spotting Mars at night

Mars can be seen from Earth with the naked eye. As the fourth planet from the Sunit is one of the closest worlds to Earth and one of the brightest planets in the Solar System. Venus and Jupiter are typically the only planets brighter than Mars in the night sky.

You can spot the planet Mars by its distinctive red color. Some ancient peoples associated this color with blood and named Mars after their god of war. Todaywe use the name of the Roman god of war to describe Mars itselfbut the Greek names of two figures related to MarsPhobos and Deimosto describe the planet’s two moons.

How we explore Mars

Humans have sent more spacecraft to Mars than any other planet beyond Earth. Todaythere are several missions operating on or around the planet.

The United States and the Soviet Union both began trying to send robotic probes to Mars in the 1960s. Each country failed at first. Thenin 1965NASA achieved a milestone when its Mariner 4 spacecraft became the first to successfully fly by Mars. The probe revealed a barren landscapebut later Mariner missions refined that picture. NASA’s Mariner 9for examplespotted Mars in the throes of a giant dust storm that covered almost the entire planet. After the dust storm clearedMariner 9 discovered Valles Marineristhe largest canyon in the Solar System. The eventual discovery of other dry canyonsdeltaslakebedsand river valleys would go on to suggest that liquid water once flowed on the Martian surface.

Mars or Earth? This imagecropped from a 116-frame panorama captured by NASA's Curiosity rover in January 2020shows Mount Sharp on Mars. The scene looks remarkably similar to the landscape found in some parts of the southwestern United States.Image: NASA/JPL-Caltech/MSSS

The NASA Viking landers of the mid-1970s — the first spacecraft to land on Mars successfully — tested the Martian soil to look for possible signs of life. The results showed no clear evidence of living microorganisms in the soil near the landing sites. What exactly these experiments revealed remains a source of debate to this day.

To help determine whether life once existed on Mars — and possibly still exists underground today — NASA initiated the Mars Exploration Program in the mid-1990s. In 2000the program adopted a goal to "follow the water." Since liquid water is essential to life on Earththe search for life on Mars shifted to focus more on looking in places where this key ingredient exists or used to exist.

Much of what we know about water on Mars comes from orbiters like the European Space Agency’s (ESA’s) Mars Express or NASA’s Mars Reconnaissance Orbiter. These spacecraft have studied the Martian atmospheremapped its geologic featuresand determined the composition of its surface. Data from Mars Express led to the discovery of water ice underneath Mars’ polar ice cap in the southern hemisphere. Together with the northern ice cap and ice scattered elsewhere on the surfacethere may be enough ice frozen on and beneath the Martian surface to cover the planet with a layer of ocean more than 20 meters (about 66 feet) deep.

Although much can be learned from Mars orbiterssome detailed observations can only be done on the surface. At firstMars landers were stationary and only analyzed the location where they touched down. Thenbeginning with the rover Sojourner — which The Planetary Society helped name — NASA developed a series of spacecraft able to travel widely and build a more complete picture of Mars’ past and present. After Sojourner,the SpiritOpportunity Curiosityand Perseverance rovers have all helped advance our understanding of the red planet. With its Tianwen-1 mission in 2021China became the second country to successfully deploy a rover on Mars.

Curiosity self-portraitsol 1065 Curiosity acquired this self-portrait with the Mars Hand Lens Imager (MAHLI) on sol 1065celebrating the third anniversary of the mission on Mars.Image: NASA / JPL-Caltech / MSSS / Damia Bouic

Future missions to Mars

The next rover set to arrive on Mars is the European Space Agency’s Rosalind Franklin rover. Currently scheduled to launch in 2028this mission will drill deep into the Martian soil to look for signs of life.

After Rosalind Franklinthe next phase of Mars exploration may involve returning surface samples back to Earth. Although rovers are highly capable mobile science labsthere are certain experiments that only facilities back on Earth are able to do. Retrieving just a few small samples would allow researchers to better understand the history of Marsits waterand whether the planet may have supported life.

The groundwork for sample return is already underway. NASA's Perseverance rover began collecting soil and rock samples in 2021storing them in small tubes and depositing them on the surface for future pickup. The NASA-ESA joint Mars Sample Return mission was slated to bring back these samples to Earth in 2030but that is now in flux.

By thenJapan’s MMX mission will have already collected samples of Mars' moon Phobos. Its goal will be to investigate how the moons of Mars formed and what the inner Solar System used to be like. To grab its samplesMMX will use a derivative of PlanetVaca technology that The Planetary Society helped support in development and testing.

Opportunity’s long and winding roadMay 2018 The gold line on the image on the left shows Opportunity's route from the Eagle Crater landing site to Cape Tribulationwhich is north of her current location in Perseverance Valley. The base image for the map is a mosaic of images taken by the Context Camera onboard the MRO. Larry Crumplerof the New Mexico Museum of Natural History and Scienceprovided the route add-ons. Right graphic shows the rover’s movements up to Sol 5068 (Apr. 262018) and her approximate location. Phil Stookeauthor of The International Atlas of Mars Exploration Volumes 1 and 2(Cambridge University Press)of the University of Western OntarioCanadadocumented this graphic with sol and site annotations. The base image was taken by the HiRISE camera also onboard MRO.Image: (left) NASA / JPL-Caltech / MSSS / L. Crumpler; (right) UA / P. Stooke

Sending humans to Mars would also provide a powerful way to explore and study the planet. A person in a spacesuit would be able to movecollect samplesand make decisions much more quickly than a robot controlled from Earthwhere the average round-trip time to send and receive rover signals is 25 minutes. One major step toward human exploration of Mars would be simply placing astronauts in orbitwhere they could control rovers on the surface in real-time. Though there are currently no NASA missions slated to put humans on or around Marssome private corporationslike Elon Musk’s SpaceXhave that as their goal.

Exploring Mars responsibly

If we send humans to the surface of Mars, we must do so responsibly. To avoid harming any existing ecosystems or any features of the planet with important scientific or cultural valuehumanity must commit to abiding by certain guidelines. The Planetary Society advocates for scientifically motivated planetary protection policieslike those described by The National Academies of SciencesEngineeringand Medicinethat balance responsibility with the desire to explore.