Mars: Facts about the Red Planet, its moons, and possibilities for life

Mars is smaller than Earth. It has a diameter of roughly 4,222 miles (6,794 km) — about half Earth's diameter, according to the European Space Agency (ESA).

The Red Planet is rocky, much like Earth. The inside structure of Mars is also similar to Earth's, NASA rovers have revealed. Mars' outer crust is 6 to 30 miles (10 to 50 km) thick and is composed mainly of iron, magnesium, aluminum, calcium and potassium, according to NASA. Below that is a rocky mantle that's 770 to 1,170 miles (1,240 to 1,880 km) thick, which surrounds a dense core that's made of iron, nickel and sulfur and has a radius of 930 to 1,300 miles (1,500 to 2,100 km).

Mars has two small, potato-shaped moons, called Phobos and Deimos. These moons are named for two sons of the Greek god of war, Ares, which the Romans called Mars. The names Phobos and Deimos mean "fear" and "panic."

The innermost moon, Phobos, has lots of craters and is roughly 13.8 miles (22.2 km) in diameter. In about 50 million years, it is expected to break up or crash into Mars.

Deimos orbits 2.5 times farther from Mars than Phobos does and is half the size — about 7.8 miles (12.6 km) across. Both moons are made mostly from rock and iron and may have once been asteroids that got captured by Mars' gravitational pull.

NASA scientists think life may have once been plentiful on Mars, as there is a lot of evidence that the planet used to be much warmer and wetter billions of years ago. Whether there is anything alive today on Mars is not known.

However, scientists can make some educated guesses about the kind of life that might be there or might have lived there in the past. If there is life on Mars today, it is probably microscopic — teeny-tiny organisms living beneath the Martian soil.

NASA's Perseverance rover has spent years drilling into Martian rocks to collect samples, in hopes that scientists can one day test them for signs of life. Scientists are working on plans to bring those samples back to Earth.

Although Mars is a dry planet today, lots of evidence suggests there were once oceans and rivers all over Mars. Lines carved into rocks show where water once flowed, and there may have even been sandy beaches like we have on Earth today. However, sometime in the past 2 billion years or so, Mars' water dried up.

Some satellites have found signs of water in the form of frost at the top of Mars' tallest volcanoes and in buried frozen lakes deep below the planet's surface. But for now, no liquid water has been spotted on the Red Planet.

Humans have never been to Mars, but we've been studying it for hundreds of years — starting with British astronomer William Herschel, who watched the Red Planet through an early telescope in the late 1700s.

The first spacecraft to successfully reach Mars was NASA's Mariner 4 probe, in July 1965. Flying without any humans aboard, the probe soared past Mars and sent back photos of the planet's surface, according to NASA.

In 1971, NASA's Mariner 9 became the first mission to successfully orbit Mars. The Viking 1 and 2 landers were the first human-made objects to make it to the Red Planet's surface and survive for more than a few minutes, when they touched down in 1976, according to The Planetary Society. From the surface, they took photos and conducted the first search for life on the planet.

The current group of robots on Mars includes NASA's Curiosity and Perseverance rovers, both of which have made incredible scientific discoveries. Perseverance carried Ingenuity, the first helicopter to fly on Mars, which took many incredible images before several of its rotor blades broke during a rough landing in 2024. China's Zhurong rover successfully landed on Mars in 2021, and it has sent back beautiful pictures, and even sounds from the surface.

Many other missions, both past and present, have revealed amazing insights about the planet's history, and future planned missions should help continue this progress. NASA aims to send humans to explore the Red Planet in the 2030s, though there is no specific plan to do so yet.