China's Zhurong rover on Mars
China's Zhurong rover on Mars, 11 June 2021

Currently, there is quite a bit of life on Mars – of the robotic kind. Two rovers are trundling across the ochre dust and a tiny helicopter is periodically hovering in the ultra-thin air. One of the rovers is from China. This is noteworthy because Mars is notoriously hard to reach, with around 60 per cent of spacecraft not fulfilling their entire mission. So far, China is the only country to succeed with both an orbiter and a rover on its first mission to the Red Planet.

The first truly successful spacecraft was Nasa’s Mariner 9, which in 1971 arrived during a planet-wide dust storm. As the dust settled, it revealed mega-volcanoes, fields of shifting sand dunes and canyons whose tributaries – bigger than the Grand Canyon – had almost certainly been gouged by water. Mars today is inhospitable. Its surface, beneath a carbon dioxide atmosphere a hundredth the thickness of the Earth’s, is raked by a deadly solar radiation and, on a hot summer’s day, barely reaches the freezing point of water. Elton John was not wrong when he sang: “Mars ain’t no place to raise your kids.”

Missions since Mariner 9 have revealed that Mars, in its first half billion years, was a very different place from today, with oceans and rivers, rain and snow. In fact, it would have been a Garden of Eden while Earth, still hot from the fires of its birth, was a molten hell. This has given rise to the suspicion that life got started on Mars first, before being transported to Earth inside a rock catapulted into space when an asteroid slammed into the surface. If this is the case, it is easy to find a Martian: look in a mirror.

Why exactly Mars dried out about 3.8 billion years ago is not known. But the transition from a wet to a desiccated world was seen by Nasa’s Curiosity – a rover about the size of a small car, which landed in 2012 – as it climbed a five-kilometre-high mound. Mount Sharp, as it is known, stands in the middle of the 154-kilometre-diameter Gale Crater, which in the ancient past was filled with water. That water lapped against the slopes of Mount Sharp, depositing sediment in stratified layers, which Curiosity’s scientists could read like a book.

All the ingredients necessary for life have now been found on Mars: water in the form of ice, organic molecules and energy, in the form of volcanism. However, the current missions are looking principally for evidence of ancient life. Nasa’s Perseverance, a souped-up version of the Curiosity rover, landed on 18 February 2021 carrying the 1.8 kilogram Ingenuity drone. When, on 19 April, it climbed to three metres and hovered for 90 seconds, it was the first flight of a helicopter on another world.

Perseverance is exploring the 45-kilometre-diameter Jezero Crater, which was once filled with a lake, fed through by a river delta. It is looking for the “biosignatures” of life, making it the first mission since Nasa’s Viking 1 and Viking 2 in 1976 to expressly look for Martian biology. Perseverance will also collect about 30 rock samples, inserting them in a canister to be picked up by a future mission to Mars and carried back to Earth. The rocks will then be analysed with sophisticated laboratory equipment which cannot be transported to Mars.

China’s Zhurong rover is exploring an area several hundred kilometres away from Perseverance. It was carried by the Tianwen-1 spacecraft and deposited on the Martian surface on 15 May. Among other things, Zhurong is using ground-penetrating radar to search for pockets of water.

The most exciting possibility, of course, is not that life merely existed in the distant past on Mars but that it survives there today. Once upon a time, the Red Planet was considered far too harsh a place for life. However, everything was changed by a series of unexpected discoveries beginning in the 1970s. Life was not only found in the Antarctic, but it was thriving in total darkness – both in solid rock, kilometres beneath the surface, and in boiling water around “hydrothermal vents”, kilometres down on the sea floor. If such organisms, known as “extremophiles”, could survive such harsh terrestrial conditions, argued scientists, then why not Martian ones?

It is a race against time to find life on present-day Mars. There is talk of human missions to the planet in the 2030s and such missions could easily contaminate the Martian environment with terrestrial organisms. If this happens, we will lose forever something beyond price: the chance to discover and study a unique and totally alien biology.

This article is from the New Humanist autumn 2021 edition. Subscribe today.