NASA is about to launch InSight: a new R10 billion ($850-million) Mars lander that will probe the red planet's secrets like never before.
InSight is slated to lift off on Saturday, which is one day after International Space Day, on May 4. But it's just one of dozens of robotic and satellite missions that humanity has rocketed to Mars over the decades.
These spacecraft have beamed back dazzling photos, inspired sci-fi movies like "The Martian", and even helped give Elon Musk, the founder of SpaceX, the idea to colonize the red planet with the Big Falcon Rocket.
While scientists readily admit they have much to learn about Mars, including the planet's internal structure (a mystery InSight will try to solve), what we have found out so far is incredible.
Here are 13 fascinating facts about Mars and our robotic exploration of the red planet.
The red planet doesn't have plate tectonics, which is what causes most quakes on Earth. But rising plumes of magma could trigger Mars quakes, as could meteorite impacts and the contraction of the world due to cooling. InSight will listen for them with its seismometer.
Mars has almost as much surface as Earth has land — but that doesn’t account for the 71% of Earth that’s covered in water.
The average surface temperature on Mars is -62.7 C (-81°F), 58.8 C (138 degrees) colder than on Earth.
The Martian atmosphere is 61 times thinner than Earth’s, and it consists almost entirely of carbon dioxide, which makes up just 0.04% of Earth’s atmosphere.
Valles Marineris is nearly five times deeper, about four times longer, and 20 times wider than the Grand Canyon.
Mars once had oceans, but adding them up would give you just 1.5% of all water on Earth.
If aliens existed on Mars, they might have lived in oasis-like pools. These pools would have been habitable for life, just as they are on Earth.
Martian oceans also had tsunamis like those on Earth. The tallest may have reached as high as 400 feet, just slightly shorter than the London Eye.
Like Earth, Mars has ice caps at its poles. The northern cap is up to 2 miles deep, is a mix of water and carbon dioxide, and covers an area half the size of South Africa.
Olympus Mons is more than twice as high as Hawaii's Mauna Loa.
Missions to Mars have become much rarer — after 23 launches in the 1960s and 1970s, we’ve launched just 10 in the new millennium (so far).
Getting to Mars is hard: About a third of the missions launched have failed.
On Earth, sunsets are a brilliant mix of reds, pinks, oranges, yellows, and other colors. But on Mars they're blue. The reason: Air is about 1/100th as dense on the surface of Mars than it is on our planet. This refracts white sunlight less, leading to fewer colors (primarily blues).