D8 Y THE NEW YORK TIMES, TUESDAY, JULY 28, 2020
In the winter of 2004, Sarah
Stewart Johnson, then a grad-
uate student at the Massachu-
setts Institute of Technology,
was on a field trip in the desert
east of California’s Sierra Nevada. While
learning to map geological terrains, she fell
prey to an adolescent thrill. Boulders were
perched on ledges; when nobody was
watching, she would strain and push one
over the edge just to watch it roll hundreds
of feet, crash and break apart.
“It was just the power of it,” she said re-
cently in an interview. “It would just echo up
through that emptiness. The dust would
come up and the boulder would clang into
the rocks as it barreled down.”
The anecdote is one of many that Dr.
Johnson, 41, relates in her first book, “The
Sirens of Mars: Searching for Life on An-
other World,” which was published this
month. Part history, part science lesson and
part memoir, the book is full of inside stories
about the quest to find life, or something, on
Mars, a planet we have been invading ever
since the space age began.
When I read that rock-rolling passage I
felt a shock of recognition, having had simi-
lar escapades with my friends in the Cas-
cade Mountains of Washington as a young-
ster. But it was more than just rock-rollingwe shared; it was the endless allure of
Mars, that beacon of otherness looming red
in the sky.
Interest in the red planet is again reach-
ing a peak, with the launch of three robot
missions to Mars, including NASA’s Perse-
verance rover, which will collect rock and
dirt samples to be sent back to Earth. The
planet itself is growing brighter in the sky
as it edges closer in its orbit, bringing with it
renewed questions about possible extrater-
restrial life.
“Mars has been our mirror, our foil, a tell-
tale reflection of what has been deepest in
our hearts,” Dr. Johnson writes in the book’s
foreword. “We have seen in Mars a utopia. A
wilderness. A sanctuary. An oracle. With so
few landmarks, guideposts, or constraints,
all is possible; without data that could be
used to cabin our inquiry or limit our imagi-
nation, Mars has been a blank canvas. And
tenderly, our human seeking has rushed to
fill it.”
The book is also a coming-of-age story for
Dr. Johnson and a new generation of plan-
etary explorers. In the next half-century,
their machines are likely to determine
whether anything like life as we know it re-
sides elsewhere in the solar system.
At Georgetown, Dr. Johnson runs her
own lab, which studies old rocks for signs of
ancient exotic life of the sort that might be
found on Mars or another extreme world.
The lab’s website is festooned with pic-
tures of her and colleagues combing the
rocks and sands in Antarctica, Australia
and the Atacama Desert in Chile, for signs
of ancient life. She is also a visiting scientist
at NASA’s Goddard Space Flight Center,
where she is part of a team working with
Curiosity, NASA’s older rover now climbing
a mountain in a crater on Mars. And she
hopes one day to be analyzing rocks re-
turned from Mars in her lab.
Reached over Zoom in Kentucky, where
she was visiting family, Dr. Johnson radiat-
ed an easy, unflappable manner. She re-
sponded to questions with a wide smile, as if
the light had just broken on her face, and a
drawn-out “Yeah” as she mulled her an-
swers.
In “Sirens of Mars,” Dr. Johnson chroni-
cles the personalities, the surprises, the
dashed expectations and the claims —
made and abandoned — of the discovery of
life on Mars. It’s also a personal chronicle;
the due date for her first pregnancy, in Au-
gust 2012, coincided with the landing of the
Curiosity rover on Mars, temporarily de-
railing her chances of participating in what
was the biggest Mars mission yet. She
watched her colleagues at the Jet Propul-
sion Laboratory on television, saddened
that Mars might be slipping away.
“Opportunities only come around so of-
ten,” she writes. “The planets aligned and
then swung apart.”
She had not set out to make herself a
character in the book, she said. The project
began with the habit of writing down poign-
ant and evocative things that would never
make it into scientific journals, and grew
from there.
“I guess at some point it just felt like Mars
deserved a different kind of treatment,” she
said. “You know, something that will cap-
ture a lot of the mystery and the wonder of
the whole endeavor, the whole search forlife.”
“The more we study the science, the more
the beauty and profundity of it strikes you,”
she continued. “And it does make you re-
flect on your own life and existence and geo-
logic time scales, and what it’s like to be so
small in a vast universe.”
Dr. Johnson grew up in Lexington, Ky.,
watching “Cosmos” with her father, a lab
technician who was a geology and astron-
omy enthusiast. Her mother had been a
teacher but stopped when her older sister,
Emily, was born with Down syndrome. Dr.
Johnson recalls her father dragging her and
Emily to look at exposed strata in road cuts.
“There was a point I remember when I
was young where I just felt like, ‘Oh, this is
so nerdy,’ ” Dr. Johnson recalled.
Science fiction was not on her radar, de-
spite the similarity of her book’s title to
“The Sirens of Titan,” Kurt Vonnegut’s cos-
mic novel. “Little Kentucky girls, in my gen-
eration, liked the ‘Babysitter’s Club’ and
‘Sweet Valley High’ books,” she said.
She thought she might become a math-
ematician, but as an undergrad at Washing-
ton University in St. Louis she fell under the
spell and mentorship of Raymond Arvid-
son, a planetary geologist. All those things
she thought were nerdy became fascinating
again. “It’s what I was really gravitating to-
ward,” she said.
She found her calling when she discov-
ered a tiny fern underneath a rock on the
barren slopes of Mauna Kea during a geol-
ogy field trip.
“I suddenly saw something I might haunt
the stratosphere for, something for which
I’d fall into the sea,” she writes. “Not fame or
glory or a sense of adventure, but a chance
to discover the smallest breath in the deep-
est night and, in so doing, vanquish the void
that lurked between human existence and
all else in the cosmos.”
From there she skyrocketed through aca-
demia: first to M.I.T., where she earned a
Ph.D. in planetary science in 2008 under
Maria Zuber, a planetary geologist and
Mars mapper and now the institute’s vice
president for research; then to Harvard, as
a junior fellow in the Society of Fellows.
Along the way there was what she called
a “gap year” — a Rhodes scholarship,
studying philosophy at Oxford — and, later,
a stint as a White House fellow. She consid-
ered applying to be an astronaut, but in the
end she decided that robot probes could
take her further than the space shuttle, and
more safely.
Dr. Zuber called herself “blessed” to have
had Dr. Johnson as a Ph.D. student. One re-
search project involved collecting samples
of simple primitive life-forms. The work
sent Dr. Johnson to Denmark to help har-
vest DNA from Arctic ice cores, then on to
the Siberian tundra, where she found bacte-
ria that were still alive after a half-million
years of dormancy, providing the oldest
known viable DNA at the time. The result-
ing paper was one of the highest cited in the
Proceedings of the National Academy of
Sciences in 2007.
“That’s the way Sarah is,” Dr. Zuber said
in an email. “She would look like she was
bouncing around trying to zero in on some-
thing useful, and then she would do some-
thing absolutely brilliant.”
Dr. Johnson’s family came to Cambridgeto see her defend her Ph.D. dissertation.
Emily, her sister, was a fan of Miley Cyrus,
so when Dr. Johnson gave a public lecture
she added a picture of the singer to her most
important slides.
“Sprinkled throughout the talk there
would be a little Miley Cyrus in the corner
saying ‘Whoa!’ or ‘Cosmic!’ and her sister
would perk up and clap,” Dr. Zuber said. “It
just shows you the kind of thoughtful person
Sarah is and her extraordinary ability to
communicate at all levels.”
From Harvard, Dr. Johnson went to
Georgetown with an unusual joint appoint-
ment in biology and the program in science,
technology and international affairs.
The work happily takes her to extreme
corners of the world — deserts in Chile, Aus-
tralia, Iceland and Antarctica — in search of
improbable forms of life that have survived
the kinds of circumstances that prevail on
Mars and elsewhere out there. “Fieldwork
is always tremendously exciting,” she said.
“I mean, just to be at the edge of the world;
it really does feel sometimes like you’re on
another planet.”
She is now the mother of two children,
ages 5 and 7, but that has not slowed her. She
recalled strapping her son’s booster seat
into the back of a four-wheel drive vehicle in
Iceland, and taking the whole family on a
fieldwork trip in Australia when her daugh-
ter was only a couple of months old and still
breastfeeding. “We also met up with col-
leagues,” she said. “They were almost all
women, so that was great.”
Her proxy rockhound, the robot Perse-
verance, is now about to be launched to-
ward Mars as the flagship of this year’s
flotilla. If it lands safely this winter, its mis-
sion is to procure Martian rocks and store
them for return to Earth later this decade.
Dr. Johnson hopes that her lab will be
among those given samples to scour for evi-
dence of ancient life.
In a warm review of “Sirens of Mars,” The
Wall Street Journal described the book as
“an elegy” and the search for life on the Red
Planet as “a cycle of diminishing returns.”
But Dr. Johnson, declaring herself an opti-
mist, pushed back against the implication
that the hunt was naïve or in vain.
Anyone with the attitude that Martian life
is a lost cause “is just not really understand-
ing the science,” she said. “We’re looking for
something small, like looking for microbes,
you know. We’re not looking for little green
men. But I don’t see that as any less extraor-
dinary to find, even if it’s small.”
On Earth, she noted, a vast amount of the
planet’s biomass resides underground.
“We’ve barely scratched the surface of
Mars,” she said.
Still, as a result of our explorations, the
planet has become a real place. “And now
we almost have, like, an actual mirror. We
could look back from the surface of Mars
and we can actually see ourselves, we can
take pictures of our planet.”
Before the space age, Mars was an empty
vessel; it could be almost anything, Dr.
Johnson said: “And in some ways like the
exoplanets are sort of like that now, you
know? Yeah. You can know just enough
about them that they could really hold any-
thing. You can find another Earth.”
For an optimist it will always be a big and
fertile universe.Utopia, Wilderness, Sanctuary:
The Allure of the Red Planet
In a new book, the planetary scientist Sarah Stewart Johnson recalls how the many possibilities
that surround Mars drew her to study it. By DENNIS OVERBYE
Sarah Stewart Johnson,
a professor of planetary
science at Georgetown
University, has worked
on NASA’s Spirit,
Opportunity and
Curiosity rovers.
‘Mars has been
our mirror, our
foil, a telltale
reflection of
what has been
deepest in our
hearts.’
SARAH STEWART JOHNSON
GEORGETOWN
MORGAN HORNSBY FOR THE NEW YORK TIMESMars is the darling of many
planetary scientists, who contin-
ue to visit it through increasingly
advanced robotic explorers. But
don’t forget that our planetary
neighbor is adorned with two
moons: puny Phobos, a lumpy
mass 17 miles across; and dimin-
utive Deimos, just nine miles
long. Their names in ancient
Greek may mean “fear” and
“dread’, but the aesthetics of
these Lilliputian space potatoes
inspire anything but.
They don’t look anywhere near
as interesting as the volcanic or
icy-ocean moons of Jupiter and
Saturn, nor is their desolation as
extreme or diverse as Earth’s
moon. But that hasn’t stopped
generations of scientists from
being eager to get a closer look
at the ramshackle duo.
The Soviet Union and, later,
Russia have tried three times to
reach Phobos, but software
errors and launch disasters have
doomed every attempt. Scien-
tists in the United States have
tried and, so far, failed to con-
vince the powers-that-be at
NASA that a mission to the two
moons will be worthwhile. The
next great hope is Japan, which
is aiming to launch a heist mis-
sion to Phobos in 2024 that will
try to steal some of its rocks.
What’s all the fuss about? For
many, the desire to visit Phobos
and Deimos was galvanized by
their deeply mysterious nature.
“They’re super weird, confusing
and interesting,” said Abigail
Fraeman, a planetary scientist
studying Mars, Phobos and
Deimos at NASA’s Jet Propulsion
Laboratory.
We don’t know where the
moons came from because they
look like asteroids foreign to the
red planet but behave like by-
products of Mars’ early, impact-
laden history. And if that Japa-
nese mission manages to grab
some samples and decode the
chemistry of the mangled moons,
we might be able to discover
their origins. In doing so, we
won’t just gain a better under-
standing of Mars’ ancient past.
We will also be able to peer back
in time to the chaos that shaped
the early solar system.
Much of what we know about
Phobos and Deimos comes from
serendipitous observations.
Rovers on the surface as well as
mechanical eyes orbiting Mars
are sometimes in the right place
to angle their cameras and snap
shots of the two moons. Phobos,
being larger and closer to Mars,
can be seen in greater detail: a
misshapen mess scarred by a
large crater and multiple grooves
that look like they were made by
a cosmic cat’s claws.
Remote observations of theirsurfaces haven’t revealed any
standout mineral features or
textures that could definitively
detail the moons’ overall compo-
sitions and, ultimately, their
origins, said Laura Kerber, the
Mars Odyssey spacecraft’s depu-
ty project scientist at NASA’s Jet
Propulsion Laboratory.
“They check all of the boxes
that are consistent with them
being these captured asteroids,”
said Dr. Fraeman — rubbly
patchworks that drifted too close
to Mars long ago and became
trapped in the planet’s orbit.
But both moons orbit the
equator in a neat-and-tidy circu-
lar fashion, which suggests they
coalesced from a disk of debris
that danced around a young
Mars. It’s difficult to capture an
asteroid and have it “wind up in
this beautiful, symmetric, circu-
lar orbit,” said Jeffrey Plaut, the
project scientist for the Mars
Odyssey mission.
Mars, having a tenth of Earth’smass, has a relatively weak
gravitational pull, so it seems
improbable that it would be able
to capture asteroids zipping by,
said Tomohiro Usui, a robotic
planetary exploration expert at
the Japan Aerospace Exploration
Agency. But if they formed from
a debris disk launched up from
Mars after a colossal impact,
Deimos should be orbiting closer
to Mars than it is today.Reconciling their appearances
with their orbits is difficult.
“They just shouldn’t exist,” Dr.
Fraeman said. “They don’t make
any sense.”
Cast as siblings, both moons
may not even have the same
origin story.
In fewer than 100 million
years, said Matija Cuk, a re-
search scientist at the SETI
Institute in Mountain View, Calif.,
Phobos will get so close to Mars
that its gravity will tear themoon apart, transforming into a
beautiful system of rings.
It won’t be the first time, some
scientists say. Recent calcula-
tions suggest that Phobos was
once 20 times more massive. But,
as one hypothesis goes, it drifted
toward Mars and shattered into
ring material, much of it raining
onto Mars. The remaining ring
material clumped together into a
new, smaller Phobos. This cycle
has repeated several times over
billions of years.
Although made of ancient
matter, the Phobos we see today
may have been assembled just
200 million years ago. If it were
confirmed that Phobos is a hap-
hazardly clumped-together mass,
it would be a revelation, suggest-
ing planets with rings are the
norm for our solar system.
Tiny Deimos, on the other
hand, may have remained intact
for 3.5 billion years. It is on track
to eventually escape Mars en-
tirely, Dr. Usui said, to wander
elsewhere in the void.
NASA’s Perseverance rover,
launching Thursday, is the first
stage of a protracted series of
missions to bring pristine sam-
ples of Mars back to Earth for
study. Mars’s atmosphere, an-
cient volcanism and flowing
water has eroded away many of
the planet’s earliest rocks. But if
Phobos is made of Martian flot-
sam from a massive impact
shortly after the planet’s birth,
then the moon has retained theearliest memories of Mars.
“Many theories suggest the
terrestrial planets, including the
Earth, formed dry, and water
was delivered by icy meteorites
that were scattered inward,” Dr.
Usui said. “If the moons are
captured asteroids, they are
evidence of this process in action
and their composition shows
what materials were delivered to
the early Earth.”
Meteors crashing into Mars
could have coated Phobos in a
fine layer of Martian dust
sourced from all over the planet.
This matter may be both very
young and extremely old, and
grabbing some of it will help
scientists unpack “how Mars
may have progressed from a
habitable world to an uninhabit-
able one,” Dr. Usui said.
With one successful asteroid
sample-return mission under its
belt and another speeding back
to Earth, the Japanese space
agency has a “fairly good track
record” at snatching up space
rocks, Dr. Fraeman said. Hopes
are understandably high for
Japan’s Martian Moons eXplora-
tion, or MMX mission, which will
arrive at Mars in 2025.
Should it be successful, these
huge questions may finally have
clear answers. We will come to
see not just Mars, but also Earth,
in a new light.
“To me, that’s really cool,” Dr.
Fraeman said.SPACE POTATOES
The Fascinating
And ‘Super Weird’
Moons of Mars
By ROBIN GEORGE ANDREWS
Phobos, the larger of Mars’s two moons.A 2009 color-enhanced view of Deimos.NASA/JPL-CALTECH/UNIVERSITY OF ARIZONANASA/JPL-CALTECH/UNIVERSITY OF ARIZONA