Researchers from the Warsaw University of Technology and the US National Aeronautics and Space Administration (NASA) calculated the minimum temperatures needed for a tree to survive on the Martian surface.
Their simulations showed that conditions would first become suitable in Hellas, one of the largest impact basins in the solar system.
The study was published in the scientific journal PLoS One. The team used the Siberian pine as its model. The high-altitude conifer is particularly resistant to cold.
For such a tree to grow, its growing season would need to last at least 110 Martian days.
During that period, the minimum temperature could not fall below minus 6 degrees Celsius, while the average daily temperature would have to exceed 6 degrees. The maximum temperature could not remain above 40 degrees for extended periods.
The researchers divided the Martian surface into 4,002 sections. Their model considered local topography, seasonal changes in sunlight, atmospheric pressure and heat transfers between the atmosphere and the ground.
They then simulated the effects of raising atmospheric pressure and artificially strengthening the greenhouse effect.
This process is part of the hypothetical concept of terraforming, meaning the large-scale alteration of a planet to make its environment more suitable for Earth-based life.
Scientists had expected the first suitable area to appear near the Martian equator, where sunlight is strongest. The model instead pointed to the Hellas Basin in the planet’s southern hemisphere.
"Most researchers believed that this location would be somewhere in the equatorial zone of Mars," study co-author Robert Olszewski of the Warsaw University of Technology said.
"Our model shows that it would be the enormous Hellas crater," he added.
The basin lies several kilometers below the average level of the Martian surface. Its low elevation gives it higher atmospheric pressure than the surrounding highlands.
The southern hemisphere also experiences an unusually warm summer when Mars is closest to the sun. Together, the higher pressure and warmer summers could create the first suitable temperature window for trees.
The study found that additional warming would initially make larger areas of Mars suitable for plant growth. Beyond a certain point, however, parts of the southern hemisphere would become too hot during summer.
Present-day Mars remains far outside the conditions required for complex terrestrial life. Its average surface temperature is about minus 60 degrees Celsius, and its atmosphere is roughly 100 times thinner than Earth’s. It consists mainly of carbon dioxide.
Olszewski said artificial greenhouse warming could theoretically raise the Martian temperature by about 60 degrees. This could melt water ice and frozen carbon dioxide, releasing more gas into the atmosphere and increasing its density.
Such a process would take hundreds of years. Even then, the atmosphere would not be breathable for humans.
Mars also lacks a global magnetic field to protect its atmosphere from charged particles emitted by the sun. A warmer and denser atmosphere would therefore continue escaping into space.
The researchers stressed that their study examined temperature rather than the full biological requirements for a tree. Water, oxygen, soil nutrients, microorganisms and protection from ultraviolet and cosmic radiation would also be necessary.
Olszewski said the simulations were conceptual and warned against altering Mars before scientists had established whether the planet contained, or once contained, native life.
"Before we begin physically transforming this planet, we should first make sure that no forms of even primitive life exist there," he said.
The research also involved scientists from NASA’s Ames Research Center, the University of Basel in Switzerland and San José State University in the United States.
(rt/gs)
Source: PAP