HUMANS & SOCIETY
Early treks in the
Humans got to South America
in at least 3 waves, DNA hints
Scientists seek planetary graveyards
Other stars’ Oort clouds may be visible in universe’s first light
B Y TINA HESMAN SAE Y
Two new genetic studies give a more
detailed and complicated picture of
the peopling of the Americas than ever
People from North America moved
into South America in at least three
migration waves, researchers report
in the Nov. 15 Cell. The first migrants,
who reached South America by at least
11,000 years ago, were genetically related
to a toddler who lived in Montana about
12,600 years ago (SN: 3/22/14, p. 6).
Known as Anzick- 1, the child’s skeleton
was found with artifacts from the Clovis
people, who researchers used to think
were the first people in the Americas,
although that idea has fallen out of favor.
Scientists also previously thought the
Clovis were the only ancient migrants
to South America.
But analysis of DNA from 49 ancient
people suggests that a second wave of
settlers replaced the Clovis group in
South America about 9,000 years ago.
And a third group related to ancient
people from California’s Channel
Islands spread over the central Andes
about 4,200 years ago, geneticist Nathan
Nakatsuka of Harvard University and
People who settled the Americas were
also much more genetically diverse than
previously thought. At least one group of
ancient Amazonians shared DNA with
modern indigenous Australians, a different group of researchers reports online
November 8 in Science.
Genetically related but distinct
groups of people came into the Americas
and spread quickly and unevenly, says
Eske Willerslev, a geneticist at the
Natural History Museum of Denmark
in Copenhagen and a coauthor of the
study in Science. “People were spreading
like a fire across the landscape and very
BY LISA GROSSMAN
A thick sphere of icy debris known as
the Oort cloud shrouds the solar system.
Other star systems may harbor similar
icy reservoirs, and those clouds may
be visible in the universe’s oldest light,
Astronomer Eric Baxter of the
University of Pennsylvania and colleagues looked for evidence of such
exo–Oort clouds in maps of the cosmic
microwave background, the cool cosmic
glow of the first light released after the
Big Bang, about 13. 8 billion years ago.
No exo–Oort clouds have been spotted
yet, but the technique looks promising, the team reports in the November
Astronomical Journal. Finding exo–Oort
clouds could help shed light on how
other solar systems — and perhaps even
our own — formed and evolved.
The Oort cloud is thought to be a
planetary graveyard stretching between
about 1,000 and 100,000 times as far
from the sun as Earth. Scientists think
this reservoir of billions or trillions of icy
objects formed early in the solar system’s
history, when violent movements of the
nascent giant planets tossed smaller
objects outward. Every so often, one
of those frozen planetary fossils dives
back in toward the sun and is visible as a
comet (SN: 11/16/13, p. 14).
But observing the Oort cloud directly
from within it is difficult. Despite a lot
of circumstantial evidence, no one has
actually seen the Oort cloud.
Baxter and colleagues thought exo–
Oort clouds might be easier to spot.
Objects in an exo–Oort cloud wouldn’t
reflect enough starlight to be seen
directly, but they would absorb starlight
and radiate it back out into space as heat.
For the sun’s Oort cloud, that heat sig-
nal would be smeared evenly across the
entire sky from Earth’s perspective. But
an exo–Oort cloud’s warmth would be
limited to a tiny region around its star.
Baxter’s group calculated that the tem-
perature of an exo– Oort cloud should be
about –265° Celsius, or 10 kelvins. That’s
right in range for experiments that detect
the cosmic microwave background, or
CMB, which is about 3 kelvins.
The team used data from the CMB-
mapping Planck satellite to search for
areas across the sky with the right tem-
perature (SN Online: 7/24/18). Then the
researchers compared the results with
the Gaia space telescope’s ultraprecise
stellar map to see if those regions sur-
rounded stars (SN: 5/26/18, p. 5).
Although the astronomers found
some intriguing signals around several
bright, nearby stars, it wasn’t enough
to declare victory. Other ongoing CMB
experiments with higher resolution, like
those with the South Pole Telescope and
the Atacama Cosmology Telescope in the
Chilean Andes, could confirm if those
hints of exo–Oort clouds are real.
“It’s a super clever observational idea,”
says astronomer Nicolas Cowan of McGill
University in Montreal. Cowan has suggested that the CMB could also be used to
search for a hypothetical planet known as
Planet Nine in the sun’s Oort cloud. “The
very coolest thing would be if we could get
measurements of the exo–Oort clouds
and find planets in those systems.” s
Objects in an exo–Oort cloud wouldn’t and find planets in those systems.” s
This map of the cosmic
taken by the Planck
satellite may hide signs
of exo–Oort clouds,