Mars' landscape is presently being explored by robotic rovers. A rover's
job includes searching the globe for evidence of life. There may not be
anything to discover, but what if there is something there that the rovers
simply cannot "see"?
Today's
Nature Communications
publication of new study raises the possibility that the rovers' current
technology may not be adequate to discover signs of life.
As a microbiologist who studies harsh environments, I am acquainted with
the difficulties of looking for life in environments where it seems
virtually impossible.
Astrobiology is the study of the variety of life in places on Earth that
have physical or biological characteristics similar to areas that have
already been identified on Mars. These on-earth settings are referred to as
"Mars model" locations.
Detection limitations
The advanced instruments used by NASA's Curiosity and Perseverance rovers,
as well as some newer lab equipment planned for future analysis, were tested
in the Mars equivalent of the Atacama Desert by the new research, which was
directed by Armando Azua-Bustos at the Center for Astrobiology in
Madrid.
The testbed equipment on the rovers, which is used to analyze samples in
the field, was discovered to have a limited capacity to identify signs of
life that we might expect to find on the red planet, according to
Azua-Bustos and coworkers. They were able to identify the samples' inorganic
components, but they occasionally had trouble identifying organic
compounds.
The Dry Valleys and Windmill Islands in Antarctica are the icy, arid
regions that serve as my team's Mars model locations.
Despite intense constraints, life persists in both of these locations.
Given the hostile environment and dearth of microscopic life, finding signs
of life is difficult.
We must first establish the biochemical and physical limits of life that
can persist (and be found) in analogous "extreme" settings. Then, we must
create instruments to recognize the "biosignatures" of life. These consist
of molecular substances like proteins, lipids, and nucleic acids. Lastly, we
decide what level of sensitivity is required for instruments to find those
biosignatures on Mars and on Earth. This informs us of the detection's
boundaries.
locating a black microbiota
In my area of extreme microbiology, the preponderance of microscopic
organisms in a sample are considered "microbial dark matter" if they haven't
been isolated and/or characterized. We need to describe next-generation
sequencing in order to find them. Azua-Bustos' team goes one step further by
putting forth the idea of a "dark microbiome" that may hold relics of
vanished Earth species.
The Atacama Desert's martian-like hyper-arid soil samples were found to
contain a dark microbiome, as discovered by Azua-Bustos' team using advanced
laboratory methods. On Mars, though, the rovers' existing technology
wouldn't be able to find it.
We use extremely delicate laboratory techniques, such as gene sequencing
and microscopy analysis, to find microbial life in samples with so little
biomass. Although prototypes for in-field genome sequencing are being
created, they currently lack the precision required for low density
samples.
different laws for a different world
The hunt for life on other worlds also depends on our knowledge of the
prerequisites for life, the most basic of which are energy, carbon, and
liquid water.
The majority of living things on Earth use photosynthesis to convert
sunshine into energy. Water is necessary for this process, but it is
virtually nonexistent in desiccated, arid places like Antarctica, the
Atacama Desert, and, most likely, Mars. We believe that a procedure we
called "atmospheric chemosynthesis" might be addressing this issue.
In the chilly arid soils of Antarctica, my team made the initial discovery
of air chemosynthesis. Bacteria actually "live on thin air" in this
underappreciated biochemical process by ingesting minute amounts of hydrogen
and carbon monoxide gas from the environment.
In addition to the water produced as a byproduct of this process, we
believe that arid desert microbiomes may also depend on it for energy. One
of the most hopeful ecological models for the hunt for life on Mars can now
be found in ecosystems similar to those we've discovered in
Antarctica.
We now think that Mars' ice-cemented subsoil may contain the seeds of life.
In the University Valley of Antarctica, my team will explore this with help
from partners at NASA and the University of Pretoria by identifying the
environmental limits to energy, metabolic water, and carbon output via trace
gas consumption.
What we cannot identify, we cannot discover.
When building or improving future instrumentation to be used on missions to
search for life, our new understanding of target biosignatures and the
degree of sensitivity required to identify them will be crucial.
Future trips to Mars, such as the Icebreaker Life project scheduled for
2026, have the objective of looking for signs of life. A Mars Sample Return
mission would be given top priority if the Icebreaker Life finds evidence of
life in ice-cemented ground that is comparable to dry permafrost in
Antarctica.
It is dangerous to send samples back to Earth for scientific examination.
Challenges can include contamination, maintaining low temps during transit,
and the need for specialized quarantine labs to analyze samples without
destroying them, as we discovered with our Antarctic soil samples.
However, as Asua-Bustos proposes, the only certain way to find out if there
is life now or ever was may be to transport samples to Earth for in-depth
lab analyses.
