In 2015, NASA announced the
discovery of water flowing down the sides of craters on Mars. NASA calls them
Reoccurring Slope Lineae, RSL for short. This seemed to answer the question of
whether liquid water currently existed on Mars. And since liquid water is
believed to be a prime requirement for life, the discovery also reinvigorated
the discussion of life, even if only microscopic, on the red planet. You can
see a NASA video montage of some RSLs at https://youtu.be/H44-XrGH5IQ.
Reoccurring Slope Lineae on Mars, credit NASA
In 2017, some researchers published
papers suggesting RSLs were not from water but consisted of sand sliding down
the slopes, driven by carbon dioxide that sublimated from dry ice just below
the surface. Carbon dioxide, being a relatively heavy gas, flows downhill and
carries sand grains with it. The researchers suggested that the sand just below
the surface might be darker, having not been bleached by UV radiation from the
sun.
The consensus of scientific
opinion, however, rested with water flow, but many wondered if water just below
the surface of the cold planet could never melt. Recently, Essam Heggy, a
research scientist at the University of Southern California and NASA's Jet Propulsion
Laboratory, and Abotalib Z. Abotalib, a postdoctoral research associate at USC,
suggested that the flows are triggered not by near-surface water but rather
from deep below the surface. "We propose an alternative hypothesis, that
they originate from a deep, pressurized groundwater source, which comes to the
surface, moving upward along ground cracks," said Hegggy.
They compared Martian geological features
to similar ones on Earth and determined that heat flow in the Martian
subsurface was similar to that in desert regions here on Earth. This research,
the two concluded, indicates that RSL water is probably coming from deeply
buried, briny aquifers.
This even explains the seasonal
aspect of the flows. "The system shuts down during winter seasons, when
the ascending near-surface water freezes within fault pathways, and resumes
during summer seasons when brine temperatures rise above the freezing
point," the researchers wrote.
The new study says nothing about
the existence of life on Mars, but it will surely strengthen arguments for at
least microbial Martians living below the surface.
On the first Tuesday of each month, I write an
astronomy-related column piece for the Oklahoman newspaper. On the following
day, I post that same column to my blog page.
This is reprinted by permission form the Oklahoman and www.newsok.com.
