THE surface of Venus, which is often
considered dead and inactive, is
covered in weird lines that suggest
some kind of active erosion.
These lines, called tesserae, cover
about 7 per cent of the planet. They
were spotted by Russian Venera
orbiters in the early 1980s and are
characterised by long, parallel lines
on hills and mountains that look like
the ground has folded over itself.
Paul Byrne at North Carolina
State University and his colleagues
examined the few radar images we
have of Venus’s surface to try to
figure out what these tesserae are.
They noticed that the lines tend to
curve along features on the ground,
similar to a topographical map,
rather than simply cutting across.“If you imagine getting a phone
book and then you take a chainsaw
and carve topography into it, when
you look down on that book that
you’ve now butchered, you see
this complicated curving pattern of
those sheets of paper,” says Byrne.
That is similar to the pattern of the
tesserae, and indicates that they are
made of some sort of layered rock.
Byrne and his colleagues suspect
that some of these layers may be
sheets of lava folded into stacks.
Regardless of whether it is a stack
of lava or simply sedimentary rock,
they found that something must
be wearing down the surface to
expose the sides of the layers.
“For us to see these lines in
this curving pattern, there must be
erosion,” says Byrne, who was due
to present the work at the cancelled
Lunar and Planetary Science
Conference in Texas. “In the last
few hundred million years, there
has been wind planing off sediment
and carving these weirdo terrains.” ❚12 | New Scientist | 28 March 2020News
“There has been wind
planing off sediment
and carving these
weirdo terrains”
Solar systemLeah CraneStrange lines on
Venus’s surface may
be stacks of lavaAT THE summit of Llullaillaco,
a volcano in the Andes that
rises 6739 metres above sea
level, lives a mouse.
Not just any mouse – it is the
highest dwelling mammal in
the world – and how it survives
in an environment so hostile
that it has been compared to
Mars has left scientists baffled.
Life isn’t easy at the top of
Llullaillaco, which is on the
border of Chile and Argentina.
The average temperature is -15°C
and the air pressure is so low
that there is less than half as
much oxygen in each lungful
of air as at sea level.
Humans can’t survive
for long at the peak. In 1999,
archaeologists uncovered the
frozen and perfectly preserved
mummies of three Inca children
who had been drugged and
left to die on the summit
500 years ago, as part of a ritual
sacrifice. But the yellow-rumped
leaf-eared mouse (Phyllotis
xanthopygus) apparently
thrives there.
Mountaineers have reported
seeing mice near the top of
Llullaillaco, so last month an
international team of biologists
journeyed to the Andes to
investigate. The team, led by
Jay Storz at the University of
Nebraska and Guillermo D’Elíaat the Austral University of
Chile, spent weeks studying
mice at a range of elevations
before Storz and a colleague
journeyed to the peak of
Llullaillaco, where they
spotted and trapped a mouse
(bioRxiv, doi.org/dp5d).
The altitude meant the
researchers struggled to get
enough oxygen. “I felt like I was
staggering around up there,”
says Storz. “But the mouse
didn’t seem too impaired.”
What makes the fact that
mice are so active on the
volcano’s peak even more
astonishing is that they are
so small. “They lose heat so
much more easily becausethey have a higher surface-area-
to-volume ratio,” says Graham
Scott at McMaster University
in Canada. “They’re having to
generate lots of body heat to
keep warm, but they’re doing
it even though there is very
little oxygen available.”
This suggests the mice must
have a voracious appetite to
gain the energy they need to
survive. That puzzles biologistsbecause there are no green
plants growing anywhere near
the summit, making exactly
what the mice eat a mystery.
“The summit is more than
2000 metres above the limits
of green plants,” says Storz.
He thinks the mice might
survive at least in part on
insects, but more clues will
come in the months ahead
when the researchers analyse
the mouse’s gut contents.
Astrobiologists have
previously drawn parallels
between the conditions on
Llullaillaco and those on other
worlds including Mars in
terms of temperature, aridity
and exposure to ultraviolet
light. “It’s not the moon, but
Llullaillaco is definitely not a
place productive enough and
hospitable enough that we
would expect a mammal to
live there,” says Scott.
Some birds can briefly survive
at even greater altitudes: geese
migrating over the Himalayas
reportedly reach heights above
7200 metres, says Grant
McClelland, also at McMaster
University. But the mice on
Llullaillaco may spend their
entire lives above 6700 metres.
“It certainly changes our idea
of the limits of where mammals
can live,” he says. ❚This mouse
somehow lives
on Llullaillaco (left),
an Andean volcanoZoologyColin BarrasGE
RARDPRINS/GETT
Y^ IMAGES
;^ RIGHT:^ MAR
CIAL^ QUIROGA-CARMONA6739m
The height above sea level
of the summit of LlullaillacoThe world’s highest-
living mammal