ADVANCES
16 Scientific American, February 2022BIOLOGYPolar Night Light
Even without the sun, Arctic crustaceans
follow a day-and-night rhythmDuring Arctic winter, the sun disappears below the
horizon for long weeks of “polar night.” But new
research shows that tiny crustaceans in the Arctic
Ocean somehow maintain their daily rhythms during
these extended periods of darkness.
Most living creatures use sunlight to time their bio-
logical processes and behaviors. This becomes a chal-
lenge when there is effectively no sunrise or sunset—
and even more so under the sea, where water dims
what little light there is. But small, shrimplike animals
known as Arctic krill, an important food source for
many aquatic species, have developed a crafty adapta-
tion to maintain their habits during the polar night.
Even underwater they can detect extremely subtle
changes in light from the sky as the sun shifts position
below the horizon, researchers report in PLOS Biology.
“Biological clocks are how our bodies anticipate
what’s going to happen next, like how we know to
start getting hun-
gry around lunch-
time,” says Univer-
sity of Delaware
marine biologist
Jonathan Cohen,
lead author on the
new study. Krill
behavior shows that the polar night has enough light
to keep this biological timer ticking in some creatures.
Cohen and his colleagues studied the krill species
Thysanoessa inermis in the laboratory and in its natural
Arctic Ocean habitats off the Svalbard archipelago.
They found not only that krill could detect minimal
shifts in very scant light but that the electrical activity
in their eyes heightened at night, suggesting increased
light sensitivity. Moreover, the crustaceans were using
the faint light variations to coordinate their move-
ments through the water column, gliding to the sur-
face to search for food in the darkest times and retreat-
ing to the depths during the “brighter” hours to evade
predators. So far scientists know of only a few other
animals, including flies and mice, that can tune biologi-
cal clocks with such low levels of light, Cohen says.
The researchers are still unsure why krill continue
swimming up and down during the very darkest
nights. “If there’s no light, there’s no primary pro-
duction and algal blooms—so there’s nothing for
them to eat,” says Emma Cavan, a marine biologist
at Imperial College London who was not involved in
the study. “So why are they moving to the surface?
It’s one of the big mysteries of vertical migrations.”
— Daniela Mocker and Nikk Ogasa
TECHLunar Shadowlands
New algorithm illuminates the moon’s murky polar regions
Certain areas near the moon’s poles linger perpetually in shadow, never
receiving direct sunlight. Recent studies suggest these so-called permanently
shadowed regions (PSRs) contain rich ice reservoirs that could reveal details
about the early solar system; they could also help future visitors make fuel and
other resources. But these areas are hard to photograph from satellites orbiting
the moon and thus are a challenge to study. The few photons PSRs do reflect
are often overwhelmed by staticlike camera noise and quantum effects.
Now researchers have produced a deep-learning algorithm to cut through
the interference and see these dark zones. “Our images enable scientists to
identify geologic features, such as craters and boulders... as small as three
meters across for the first time—a five- to 10-fold increase in resolution com-
pared to previous efforts,” says Valentin Bickel, a planetary scientist at the Max
Planck Institute of Solar System Research in Germany and lead author of a
Nature Communications study testing the new algorithm.
The researchers used more than 70,000 images of completely dark lunar
areas—with no light signal—paired with details about the camera’s temper-
ature and position in orbit to train their algorithm to recognize and filter out
camera noise. Next they tackled residual noise, such as quantum effects on
traveling photons; this algorithm stage learned from millions of sunlit lunar
photos, paired with simulated versions of the same images in shadow. Igna-
cio Lopez-Francos, a study co-author and engineer at the nasa Ames Re -
search Center, says using this simulated shadow was necessary because
sun lit PSR images do not exist. A similar technique is also used in low-light
digital camera photography.
“It’s an interesting application of machine-learning technology, and the noise
model seems realistic and useful for this real case,” says computer scientist
Chongyi Li, who uses similar strategies to enhance underwater images at Sin-
gapore’s Nanyang Technological University and was not involved in the study.
The researchers used their algorithm to analyze the size and distribution of
craters and boulders in several PSRs that might be explored by nasa’s Artemis
moon program. They also evaluated the likely origins of some boulders and
plotted a potential route for a rover through a PSR on the moon’s Leibnitz pla-
teau, avoiding obstacles and slopes steeper than 10 degrees.
“There’s a lot of interest in the poles—not just from the human exploration
standpoint but also the topography of the ground surface,” says University of
Texas at El Paso geologist Jose Hurtado, who was not involved in the study. Ice
might either be interspersed in the lunar soil or stored in more concentrated
layers, deforming the landscape, he says. “And so this kind of image processing
Jonathan Cohenoffers a way of testing some of those hypotheses.” — Connie ChangThe moon’s south pole hosts
regions in constant shadow.Arctic krill
NASA/JPL/USGS