How Habitable Was Early Mars?
It’s a serene image: A river flowing into an
expansive lake that fills a crater basin.
Waves lapping at the shoreline; sediment
piling into a delta. A lake bed caked with
clay.
This is the type of aquatic environment
that might support life, and it was once a
familiar sight on Mars.
“The evidence for the lakes and rivers is
incontrovertible,” said Ken Farley, a
project scientist on Perseverance and a
geochemist at the California Institute of
Technology.
Although Mars was once a wet planet,
there is substantial debate about the ori-
gins, extent and life span of its long-lost
bodies of water.
For instance, early Mars might have
been warmed by the gassy belches of ac-
tive volcanoes, which thickened its atmos-
phere and caused Martian permafrost to
melt. Cataclysmic asteroid impacts might
have also unleashed 900-foot mega-
tsunamis that flooded the planet’s terrain.
There’s even disputed evidence that an
ocean once covered its northern lowlands.
“Was it weird, short, transient events,
or was there an ocean?” Dr. Farley said. “I
would say there’s no consensus. There’s a
lot of ideas out there, and we really need a
lot more data to sort it out.”
One major question concerns the lon-
gevity of Mars’s liquid water. Nobody
knows how much time is required for life
to emerge on a planet, including on Earth.
But the odds of life forming get better the
longer that stable bodies of water persist.
During Curiosity’s eight-year journey
across Gale Crater, an ancient lake bed,
the rover discovered sediments that sug-
gest water was present for at least a few
million years. Curiosity also detected or-
ganic compounds, key ingredients for life
as we know it.
“What we’ve learned from Curiosity
suggests that Mars was habitable,” said
Dawn Sumner, a planetary geologist at the
University of California, Davis, and a
member of the Curiosity science team.
Of course, “habitable” does not neces-
sarily mean “inhabited.” The surface of
Mars is exposed to damaging solar and
cosmic radiation, which could have re-
duced the odds of complex, multicellular
life ever forming.
“If life did exist on Mars, there would be
a strong evolutionary force toward being
resistant to radiation,” Dr. Sumner said.
There are microbial extremophiles on
Earth that can endure intense radiation,
often healing their own DNA on the fly.
So it’s not far-fetched to imagine that
there might be Martian microbes that
could tolerate an onslaught of radiation.
Plus, they may have been able to retreat
underground if conditions became partic-
ularly hostile at the surface.
“The big lesson about life, from the rev-
olution of being able to use DNA, is life is
able to go everywhere,” Dr. Farley said. “It
is amazing. It will fill every niche it can get
itself into, and it will do it in a relatively
short period of time.”Why Did Mars Become Less Habitable?
The bygone oases of Mars are now mi-
rages of a distant past, and modern Mars
is a dried-up husk.Earth, in contrast, has been habitable to
microbes for most of its life span and has
positively burst at the seams with bio-
diversity for eons. Why did these sibling
worlds experience such different out-
comes?
As baby planets, Mars and Earth were
each swaddled in two protective blankets:
a relatively thick atmosphere and a strong
magnetic field. Earth has held on to both
comforts. Mars has neither.
Mars mysteriously lost its magnetic
mojo billions of years ago. With no mag-
netic sheath to protect it from solar wind,
the Martian atmosphere was stripped
away over time, though it still maintains a
thin shell of its past skies.
These changes have left Mars relatively
inert for billions of years, while Earth re-
invents itself through tectonic activity, at-
mospheric shifts and the ingenuity of life.
This is great news for Earthlings, as we
need those processes to survive. Yet the
sheer deadness of Mars over the past few
billion years could make it easier to recon-
struct its early history.
“Life has been so successful on Earth
that it’s hard to trace back its origin,” Dr.
Sumner said. “On Earth, everything is
covered with organic matter from modern
life.”
“One of the really cool and exciting
things about Mars is that, because it does-
n’t have plate tectonics, large parts of its
surface have these super-old rocks,” she
continued.
“It’s a good place to go to try to under-
stand what an early planet would be like.”Could Mars Host Life Now?
Robot explorers on Mars have turned up
countless insights about the red planet,
but they have never found clear-cut signs
of creatures currently residing there. Life,
at least as we know it on Earth, simply
does not seem probable on the Martian
surface.
“If there’s any life on Mars now, it needs
at least some liquid water,” Dr. Sumner
said. “The surface of Mars now is very dry.
Just incredibly dry. If there’s life on Mars
now, it would be in the deep subsurface.”
There’s some evidence that liquid water
is locked away in subterranean reser-
voirs, so perhaps there are sunless
ecosystems lurking there. If these hab-
itats exist, they are beyond the direct
reach of our rovers and landers.
Recent detections of methane and other
gases in what’s left of Mars’ atmosphere
are “a tantalizing potential signature,” Dr.
Farley said, bolstering speculation about
subterranean Martians.
Many microbes on Earth produce meth-
ane, so it is possible that whiffs of the gas
on Mars could be traced to alien life-forms
deep underground.
Curiosity, which is equipped with a
methane-sensitive spectrometer, has
compounded the mystery by recording
weird spikes of the gas at the Martian sur-
face that remain unexplained.
Unfortunately, the satellites orbiting
the red planet have not been able to pro-
vide backup for these readings, and thenew NASA and Chinese rovers on the red
planet may not be able to solve the puzzle.
Methane can also be created by a wide
range of natural processes that have noth-
ing to do with life. Some experts, like Dr.
Sumner, say that the presence of the gas
on Mars is “not a surprise” because it has
all the geological processes it needs to
produce the gas without life.
The discovery of life on Mars, either in
the form of ancient fossils or subterranean
reservoirs, would be one of the most mo-
mentous breakthroughs in human history.
At last, we would have another example
of a living planet, even if it flourished only
in the past, implying that, at the very
least, life can strike twice in the universe.
But even if we never find Martians,
“Mars is a place we can go to answer some
of the questions about life on Earth,” Dr.
Sumner said. The red planet remains an
eerie time capsule of the era when life first
sprouted on our own world, and the direc-
tion it could have gone had all the factors
that made our world possible not turned
out just the right way.Do You Like Mysteries?
You’ve Chosen the Right Planet
Asking three important questions, and theorizing about possible answers, as NASA prepares to
launch its latest rover, Perseverance, on a seven-month journey to Mars.
Mars is the most explored planet in the solar system other than Earth. With
all of our robotic visitors there, we’ve discovered that it is a world far too
dry, cold and irradiated to support the scheming humanoids or tentacled
invaders once imagined by science fiction. ¶But our trips to Mars have
opened a window into the deep past of the red planet, when conditions were far more
conducive to life. ¶This summer, NASA will launch its latest rover, Perseverance, on a
seventh-month journey to Mars. Like its predecessor, Curiosity, Perseverance will touch
down in the remains of an ancient Martian lake bed. What it finds there — along with
missions launched by China and the United Arab Emirates — could help us Earthlings
understand what Mars was like as a young planet some four billion years ago, and
whether life ever blossomed on its surface.By BECKY FERREIRA‘If there’s life on
Mars now, itwould be in the
deep subsurface.’
DAWN SUMNER
UNIVERSITY OF
CALIFORNIA, DAVISILLUSTRATIONS BY MIGUEL PORLANTHE NEW YORK TIMES, TUESDAY, JULY 28, 2020 Y D7
When NASA’s Perseverance rover
arrives on Mars, mission manag-
ers will be watching, helpless to
do anything. The $2.4 billion
spacecraft will hit the top of the
Martian atmosphere at more than
12,000 miles per hour and then
come to a complete stop seven
minutes later.
That the one-ton rover will end
up on Mars on the afternoon of
Feb. 18 is nearly certain (presum-
ing it is able to launch before the
middle of August, when the planet
moves too far away from Earth).
The spacecraft navigators will
have put the robotic explorer on a
collision course with the planet.
The only question is whether
Perseverance will be on the
ground in one piece, or smashed
to bits.
Spacecraft from Europe and the
Soviet Union have made it all the
way to the red planet, only to end
up as expensive scorch marks on
its dusty surface. But NASA has a
good track record on Mars. It is
the only space agency to pull off a
successful mission on the surface
of the red planet.
Perseverance is largely the
same design as the Curiosity
rover, which set down in 2012, and
will have the same convoluted but
tried-and-true “sky crane” land-
ing choreography.
“When people look at it, it looks
crazy,” Adam Steltzner, a NASA
engineer, said in a video that
NASA produced leading up to
Curiosity’s landing that described
the components: heat shield,
parachute, rocket engines and
finally a hovering crane that
lowered the rover to the surface.
“That’s a very natural thing,”
Dr. Stelzner said. “Sometimes
when we look at it, it looks crazy.
It is the result of reasoned, engi-
neering thought. But it still looks
crazy.”
While everything worked, the
engineers got a chance to take a
look at what could be improved
this time around.
“We don’t usually get a chance
to kind of redo or fix the mistakes
we made last time,” Allen Chen,
who leads the Perseverance
entry, descent and landing team
for NASA’s Jet Propulsion Lab-
oratory, said in an interview.
For example, Curiosity actually
landed too slowly, hitting the
ground at 1.4 miles per hour in-
stead of the 1.7 miles per hour
that had been expected. That, by
itself, was not a problem. A softer
landing is gentler on the space-
craft.
But the engineers wanted to
understand what had happened in
order to make sure that the next
landing — that of Perseverance —did not come down faster than
intended.
It turns out that their calcula-
tion of the gravity of Mars was
slightly wrong. In areas of the
planet that possess less mass —
like the 96-mile-wide crater that
Curiosity landed in — the pull of
gravity is a bit weaker.
“We didn’t have sufficient
fidelity in our gravity modeling to
understand that the gravity there
was actually different than else-
where on the planet,” Mr. Chen
said. “So that was one thing that
we fixed.”
Another component that was
tweaked was the parachute that is
unfurled when the spacecraft is
hurling down at supersonic
speeds.
A parachute failure in a proto-
type test of a future Mars landing
system led Mr. Chen’s team to
make sure they had not just got-
ten lucky with Curiosity. “That
gave us pause,” he said.
The engineers are now confi-
dent of Perseverance’s parachute
after supersonic tests of a
strengthened design.
One major addition to Persever-
ance is what NASA calls “terrain-
relative navigation.” A camera onthe spacecraft will take pictures
of the landscape and match them
with its stored maps. It would
then steer to what looks like the
safest landing spot it can. “I don’t
need the whole place to be flat
and boring,” Mr. Chen said. “I just
need parts of it that I can reach to
be flat and boring.”
Without this system, there
would be more than a one-in-five
chance that Perseverance would
end up somewhere unfortunate —
damaged by a boulder, tipped
over on a steep slope or sur-
rounded by sand traps. That
would be an unacceptably high
risk for such a high-profile, ex-
pensive mission.
If it works, the same technol-
ogy will be used when NASA
sends a mission to pick up the
rock samples that Perseverance
will be collecting, part of the
so-called Mars sample return.
That spacecraft will carry enough
fuel to avoid obstacles and fly to a
specific location, landing within
tens of yards of the target.
Still, next Feb. 18, the control
room at the Jet Propulsion Lab-
oratory is expected to be full of
nervous engineers watching the
telemetry coming back from
Perseverance. That data will take
minutes to travel millions of miles
— far too far and too slow for
anyone at NASA to make last-
second corrections.
“Mars is not for the faint of
heart,” Mr. Chen said.PERSEVERANCE ROVER
Ideal Landing
Would Be
‘Flat, Boring’
By KENNETH CHANG
NASA/JPL-CALTECHLeft, a rendering of NASA’s
Curiosity rover landing on
Mars. Below, the type of
parachute designed to help
the rover Perseverance land
safely on the planet next year.NASA/JPL-CALTECH/AMES