[Perseverance will use its instruments to look for signs of
ancient life in the delta and lake deposits in Jezero crater and will
hopefully allow us to finally answer the question of whether there was
ever life on Mars.] [[link removed]]

IS THERE LIFE ON MARS?  
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John Grant
February 25, 2021
Smithsonian Magazine
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_ Perseverance will use its instruments to look for signs of ancient
life in the delta and lake deposits in Jezero crater and will
hopefully allow us to finally answer the question of whether there was
ever life on Mars. _

Artist’s conception of the Perseverance rover sampling rocks on the
floor of Jezero crater, NASA

 

“Is there life on Mars?” is a question people have asked for more
than a century. But in order to finally get the answer, we have to
know what to look for and where to go on the planet to look for
evidence of past life. With the succesful landing of
the _Perseverance_ rover on Mars on February 18, 2021, we are
finally in a position to know where to go, what to look for, and
knowing whether there is, or ever was, life on the Red Planet.

Science fiction aside, we know that there were not ancient
civilizations or a population of little green people on Mars. So, what
sort of things do we need to look for to know whether there was ever
life on Mars? Fortunately, a robust Mars exploration program,
including orbiters, landers, and rovers, has enabled detailed mapping
of the planet and constrained important information about the
environment.

We now know that there were times in the ancient past on Mars when
conditions were wetter and at least a little warmer than the fairly
inhospitable conditions that are present today. And there were once
habitable environments that existed on the surface. For example,
the _Curiosity_ rover has shown that more than three billion years
ago, Gale crater was the location of a lake that held water likely
suitable for sustaining life. Armed with information about the
conditions and chemical environments on the surface,
the _Perseverance_ rover is outfitted with a science payload of
instruments finely tuned for extracting information related to any
biosignatures that might be present and signal the occurrence of life
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Panoramic view of the interior and rim of Gale crater. Image generated
from pictures captured by the Curiosity rover. (NASA/JPL-Caltech/MSSS)
(NASA/JPL-Caltech/MSSS)

But where should we go on Mars to maximize the chances of accessing
the rocks most likely to have held and preserve any evidence of past
life? To get at that answer, I co-led a series of workshops attended
by the Mars science community to consider various candidate landing
sites and help determine which one had the highest potential for
preserving evidence of past life. Using data from Mars orbiters
coupled with more detailed information from landers and rovers, we
started with around thirty candidate sites and narrowed the list over
the course of four workshops and five years. Some sites were clearly
less viable than others and were weeded out fairly quickly. But once
the discussion focused on a couple of different types of potentially
viable sites, the process became much tougher. In the end, the science
community felt—and the _Perseverance_ mission and NASA
agreed—that Jezero crater was the best place to look for evidence of
past life on Mars.

The landing site for the Perseverance rover is on the floor of Jezero
crater and will enable the rover to access and interrogate rocks
deposited some 3.5 billion years ago in an ancient lake and river
delta that are deemed as having a good chance of incorporating and
preserving ancient biosignatures. ((ESA/DLR/FU-Berlin))

What is so special about Jezero crater and where is it? Jezero crater
is ~30 miles (~49 km) across, was formed by the impact of a large
meteorite, and is located in the northern hemisphere of Mars (18.38°N
77.58°E) on the western margin of the ancient and much larger Isidis
impact basin. But what makes it special relates to events that
happened 3.5 billion years ago when water was more active on the
surface of Mars than it is today. Ancient rivers on the western side
of Jezero breached the crater rim and drained into the crater, forming
a river delta and filling the crater with a lake. From the study of
river deltas on the Earth, we know that they typically build outwards
into lakes as sediment carried by the associated river enters the
lake, slows down, and is deposited. As this process continues, the
delta builds out over the top of lake beds and can bury and preserve
delicate and subtle signatures of past life. These “biosignatures”
are what _Perseverance_ will be looking for when it lands on the
floor of the crater and explores the ancient lake beds and nearby
delta deposits.

_Perseverance_ will use its instruments to look for signs of ancient
life in the delta and lake deposits in Jezero crater and will
hopefully allow us to finally answer the question of whether there was
ever life on Mars. In addition, _Perseverance_ will begin the
process of collecting samples that could one day be returned to Earth.
The importance of sample return cannot be overstated. Whether or not
evidence of past life is found by _Perseverance’s_ instruments,
the legacy enabled by samples the rover collects will be the
“scientific gift that keeps on giving”. Once returned to Earth by
a future mission, these Mars samples can be subjected to more detailed
analysis by a much wider set of instruments than can be carried
by _Perseverance_. Moreover, sample archiving can preserve material
for future analysis here on Earth by new and/or more detailed
instruments that may not yet exist. So even if _Perseverance_ does
not find evidence of past life, it will collect samples that, once
returned to Earth, could provide new insight into the evolution of
Mars and whether there was ever life on the Red Planet.

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