Mars too small for extraterrestrial life with fate decided from beginning

Many scientists believe that Mars once had lakes, and even oceans, on its surface before changes in its atmosphere led to the surface water freezing, or dissipating into space.

It’s the theoretical existence of these primordial oceans that leads exobiologists to hope that some kind of microscopic lifeforms could still be clinging to life in the frozen Martian soil.

But new evidence has emerged to suggest that the Red Planet may never have had significant amounts of surface water, because it’s just too small.

Kun Wang, an assistant professor of earth and planetary sciences in Arts and Sciences at Washington University in St. Louis, says: “Mars’s fate was decided from the beginning.”

He believes that planets below a certain size can’t retain large amounts of water, and that Mars falls below the threshold.

He concedes that there was almost certainly some water on Mars, but just not as much as the optimists think.

“It’s indisputable that there used to be liquid water on the surface of Mars,” Professor Wang writes in a paper published this week in the Proceedings of the National Academy of Sciences, “but how much water in total Mars once had is hard to quantify through remote sensing and rover studies alone”.

“There are many models out there for the bulk water content of Mars. In some of them, early Mars was even wetter than the Earth. We don’t believe that was the case.”

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He says that when looking beyond the Solar System for the potential of liquid water – and thus the potential of life as we know it – we should be thinking about a lot more than just the "Goldilocks Zone" of distance from a parent star.

“The size of an exoplanet is one of the parameters that is easiest to determine,” he explained.

“Based on size and mass, we now know whether an exoplanet is a candidate for life, because a first-order determining factor for volatile retention is size.”

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Klaus Mezger, of the Centre for Space and Habitability at the University of Bern, in Switzerland worked with Wang on the research.

He said: "This study emphasises that there is a very limited size range for planets to have just enough but not too much water to develop a habitable surface environment.

“These results will guide astronomers in their search for habitable exoplanets in other solar systems.”

Most recent figures, compiled earlier this month, confirm the existence of 4,834 confirmed exoplanets in 3,572 star systems, with 795 systems having more than one planet.

A great many of these exoplanets are so-called "Super Earths" – rocky planets considerably larger than our own.

One of the most promising candidates for life is Planet K2-18 b, a Super Earth orbiting a red dwarf star that's roughly 110 light-years away in the constellation Leo.

"Given that the star is much cooler than the Sun, in the end, the planet is receiving similar radiation to the Earth," says Angelos Tsiaras, an astronomer at University College London.

"And based on calculations, the temperature of the planet is also similar to the temperature of the Earth.”

Scientists looking for extraterrestrial life are sure to find it one day, but they may have to look a lot further than Mars.

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