Sky & Telescope - December 2020 - 9

SOLAR SYSTEM

Early Mars Was Wet -
But Not Warm
ACCORDING TO NEW RESEARCH,

early Mars was wet but rarely warm.
Ancient Mars might have had ice
sheets advancing and retreating across
its surface, says lead researcher Anna
Grau Galofre (Arizona State University). She and colleagues report in the
August 3rd Nature Geoscience that rivers,
which cut channels across the Martian
surface long ago, mostly flowed underneath these glaciers.
Before now, scientists have largely
thought that these channel networks
were carved by water flowing on the
surface between 3.5 billion and 3.9 billion years ago. But three-dimensional
climate models have been unable to
reproduce the "wet and warm" Mars
required for this to happen.
Grau Galofre and her team examined subglacial channels on Devon
Island, a harsh, uninhabited place in
the Canadian Arctic Archipelago that
has served previously as a Mars analog.
The researchers developed metrics to
classify four possible origins for the
valley networks: surface rivers, glacial

meltwater, subglacial
flows, and seeping
flows from groundwater sources. Then they
applied these metrics
to trace the origins of
more than 10,000 Martian valleys making up
66 valley networks.
Of these networks,
22 showed the hallmarks of fluid erosion
under the pressure of
thick glacial ice sheets.
Another 9 networks
exhibited features associated with
retreating ice sheets. Seventeen valley
networks looked like surface flows: 14
that were cut by open rivers and three
formed from groundwater sapping. The
model couldn't pin down the origins of
the remaining 18 networks.
An icy Mars need not be lifeless,
Grau Galofre says. She points out
that a subglacial environment would
hover around the freezing point for an
extended time, which would protect any
life from dramatic temperature variations as well as intense solar radiation.
Jeffrey Kargel (Planetary Science
Institute), who was not involved in

S Subglacial channels carved on Devon Island,
shown here, share features with many Martian
valley networks.

the study, praises the team for a "great
quantitative analytical approach."
However, Victor Baker (University of
Arizona), who was also not involved in
the study, points out that other phenomena on Mars dating back to the
same time period are consistent with
warm conditions.
NASA's Perseverance rover, now on
its way to Mars, will hopefully cast
more light on how warm Mars was in
its early days.
■ JEFF HECHT

SUN

Radioactive Aluminum Sheds Light on Young Solar System

DE VON ISL A ND: A . G R AU G A LOFRE / A RIZON A STATE
UNIV ERSIT Y; R A DIOACTIV E A LU MINU M: N ASA / JPL- CA LTECH

ASTRONOMERS THOUGHT alumi-

num-26, a short-lived radioactive
isotope that flooded the early solar
system, could only be made in supernovae or around giant stars. Now, research
shows that Sun-like stars could produce
it themselves, right after they're born.
Calcium-aluminum-rich inclusions
(CAIs), tiny white specks found in larger
meteorites, were one of the first solids
to condense in the protostellar disk of
dust and gas around the still-forming
Sun. Studies of CAIs have shown that
the early solar system was awash in
aluminum-26, a quickly decaying
radioactive isotope that only forms in
extreme environments. Researchers
had suggested that the isotope might
have blown into the solar system from

a nearby supernova or via winds from
extremely massive stars. Either scenario
would make our Sun's birthplace busy.
New research points to a simpler
explanation: The Sun itself might
have helped produce aluminum-26.
Brandt Gaches (University of Cologne,
Germany) and colleagues developed
computer simulations, published in the
July 20th Astrophysical Journal, which
demonstrate that the young Sun would
have sent more than enough energetic
protons into the protostellar disk, where
they would have collided with existing
elements to make aluminum-26.
Gaches and his team propose that
production peaks as the protostar's
growth begins to slow and planets start
forming. For the solar system, this cor-

S Artist's illustration of the young solar system

responds to about 4.6 billion years ago,
when meteorites' CAIs formed.
Even if young stars' cosmic rays
made aluminum-26, though, that
doesn't explain the presence of other
short-lived radionuclides; only supernovae can produce iron-60, for example.
However, while nearby supernovae are
still needed to explain some features of
our solar system, the new findings relax
constraints on those scenarios.
■ JAVIER BARBUZANO
sk yandtelescope.org * DECEMBER 2 02 0

9


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Sky & Telescope - December 2020

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