The Real Reason US and China Rovers Can't Find Life on Mars [Reading Science]

NASA's Curiosity rover exploring Mars. Photo by NASA.

[Asia Economy Reporter Kim Bong-su] Recently, rovers from the United States and China have been actively working on Mars to verify the existence of life forms. They have recently found evidence of ancient seas and flooding events. However, so far, they have only confirmed 'circumstantial' evidence and have not secured decisive proof. Even if the samples they collected are retrieved and brought back to Earth for analysis, it is expected to be difficult to find evidence of life. Why is that? The answer lies in cosmic radiation and the 'excavator.'

◇ Cosmic Rays Destroy Evidence of Life

According to NASA on the 1st, a research team at NASA's Goddard Space Flight Center recently simulated an environment similar to the surface of Mars and concluded that cosmic radiation breaks down amino acids present in Martian soil much faster and deeper than expected. The team published a paper on this topic in the international journal "Astrobiology" on June 24.

NASA has been striving to confirm the existence of ancient life forms by collecting rock and soil samples through rovers such as Perseverance, which landed on Mars in February last year. The most desired substance to confirm is amino acids. Although amino acids can be produced by natural chemical reactions, they are components of proteins that make up life forms on Earth. The problem is that, unlike Earth, which is protected by an atmosphere, high-energy cosmic rays pouring onto the Martian surface break down substances like amino acids. Cosmic rays, mostly composed of protons and helium ions, are generated by stellar explosions such as the sun and penetrate solid rocks and all materials, ionizing and destroying all substances, including organic molecules like amino acids.

The research team concluded that the current depth to which rovers on Mars can extend their arms to collect samples is only about 2 inches (approximately 5 cm), and even if amino acids exist at that depth, cosmic rays would penetrate and decompose them within 20 million years. This period is extremely short compared to the estimated billions of years since life might have existed on Mars. Therefore, for Mars rovers to 'luckily' find evidence of life, they must find and collect materials from micro-craters or ejecta less than 10 million years old. The team also confirmed that the presence of water and perchlorates accelerates the decomposition of amino acids by cosmic rays. Consequently, they concluded that to find amino acids as evidence of ancient life on Mars, excavation of at least 2 meters or more would be necessary. In fact, scientists, including NASA, have anticipated this and are trying to send rovers capable of drilling deeper than 2 meters to Mars. The ExoMars mission, which the European Space Agency (ESA) had been pursuing with Russia but recently parted ways, is precisely such a mission.

Conceptual diagram of Mars excavation. Image source=NASA

◇ Digging on Other Planets Is More Difficult Than Expected

Even if the ExoMars mission is executed and a rover equipped with a 2-meter drill arrives, its success is uncertain. Digging on a planet other than Earth is an extremely challenging task. A representative example is NASA's failure last January. NASA planned to study the internal structure of Mars' crust by drilling at least 3 to 5 meters using a digging device called the "mole" aboard the Mars lander InSight. The mole was a pile driver, or a drill, made of a titanium tube 40 cm long and 2.7 cm in diameter. It worked by inserting the tube into the soil surface and tapping an internal hammer to gradually dig deeper. However, after starting hammering on February 29, 2019, the mole advanced only 30 cm in the first month and then stopped moving. The German Aerospace Center (DLR), which developed the equipment, made every effort for a year and a half but finally gave up on January 9 last year after 500 hammering attempts. Possible causes include soil being too soft or clumpy, or hitting hard rock, but no one knows the exact reason yet.

The Curiosity rover, which landed on Mars in 2012, faced similar difficulties. Even with the use of a nuclear power source much stronger than solar panels, it drilled at about 20 locations but only reached a depth of 6.4 cm. Using large drills like those on Earth might have been different, but the enormous cost and energy consumption make it impossible.

Human digging efforts have been no easier. During the Apollo 15, 16, and 17 lunar missions in the early 1970s, astronauts used 3-meter-long drills but faced hardships. Although the surface had fine soil, the subsurface was very hard. Apollo 15 drilled for three days but only managed to reach 1.6 meters. Apollo 16 could not perform drilling due to equipment failure. The last Apollo 17 astronauts succeeded in drilling up to 2.92 meters and installing a heat flow sensor. Additionally, the Soviet Luna 24 mission (1976) and China's Chang'e 5 mission (2020) drilled 2-meter holes to collect lunar rock samples during unmanned missions.