ATOM & COSMOS
Fading star still baffles astronomers
Slow dimming, sharp drops in light cannot yet be explained
EARTH & ENVIRONMENT
Age of Americas’
Latest analysis dates land
bridge to 3 million years ago
BY CHRISTOPHER CROCKET T
A star that made headlines for its bizarre
behavior has got one more mystery for
astronomers to ponder.
Tabby’s star, also known as KIC
8462852, has been inexplicably flickering and fading. The Kepler Space Telescope has caught two dramatic drops
in light — by up to 22 percent — spaced
about two years apart. Photographs
from other telescopes dating back to
1890 showed that the star also faded by
about 20 percent over much of the last
century. Explanations for the behavior
range from mundane comet swarms to
fantastical alien engineering projects.
A new analysis of data from Kepler,
NASA’s premier planet hunter, shows that
Tabby’s star steadily darkened throughout the telescope’s primary four-year mission from 2009 to 2013. That’s in addition
to the abrupt flickers already seen during
the same time period. Over the first 1,100
BY THOMAS SUMNER
A debate over when the gap between
North and South America closed has
opened a rift in the scientific community.
Analyzing data from rocks, fossils and
genetic studies, researchers have assem-
bled a defense of the conventional view
that the Isthmus of Panama formed
about 3 million years ago. The work
rebuts papers published last year that
concluded that the continental connec-
tion began millions of years earlier (SN:
5/2/15, p. 10). The authors of the new
paper, published August 17 in Science
Advances, caution against the “uncritical
acceptance” of the older formation date.
days, the star dimmed by nearly 1 percent.
The light dropped another 2. 5 percent
over the next six months before leveling
off during the mission’s final 200 days.
Astronomers Benjamin Montet of
Caltech and Josh Simon of the Obser-
vatories of the Carnegie Institution of
Washington in Pasadena, Calif., report
the findings online August 4 at arXiv.org.
The slow fading hadn’t been noticed
“Those of us who are advocating the
traditional view are in danger of being
seen as old fuddy-duddy conservatives,”
says molecular evolutionist Harilaos
Lessios of the Smithsonian Tropical
Research Institute in Panama City. “But
sometimes the traditional view is the
The American continents drifted apart
after the breakup of the Pangaea super-
continent some 200 million years ago.
Eventually, the landmasses slid back
together. As they reconnected, a volca-
nic mound on the Caribbean tectonic
plate collided with South America and
rose above the ocean, closing a seaway
between the Pacific and Atlantic oceans.
Aaron O’Dea, a paleontologist at the
Smithsonian institute, Lessios and colleagues revisited several lines of evidence
to date the seaway closure. Fossils reveal
that land animals began migrating more
frequently between the Americas about
2. 7 million years ago, possible evidence of
before because Kepler data are pro-
cessed to remove long-term trends that
might confuse planet-finding algorithms.
Montet and Simon analyzed images that
are typically used only to calibrate data.
“Their analysis is very thorough,”
says Tabetha Boyajian, an astronomer
at Louisiana State University in Baton
Rouge who in 2015 reported the two precipitous drops in light (and for whom the
star is nicknamed).
But the work doesn’t yet explain the
star’s erratic behavior.
An object moving in front of the
star and blocking light is the favored
a new land route, O’Dea’s team concludes.
Critics counter that those migrations
were driven by climate and ecosystem
changes that allowed animals to migrate.
In the ocean, the closed seaway divided
populations of marine organisms such
as sand dollars. Over time, these populations’ genetic makeups diverged. Based
on the degree of genetic change between
groups, O’Dea’s team estimates that the
seaway closed about 3 million years ago.
Christine Bacon, an evolutionary biologist at the University of Gothenburg in
Sweden, and colleagues analyzed similar evidence last year but came to a different conclusion. The seaway closed
between 23 million and 7 million years
ago, Bacon’s team estimated in the
Proceedings of the National Academy of
Sciences. That study assumed a different
rate of genetic divergence and looked at
more species, Bacon says.
Rocks also trace the isthmus’s rise. Last
year, geologists described volcanically
During the first four
years of the Kepler
Space Telescope mission,
the brightness of Tabby’s
star faded. A gradual
dimming in the first
1,100 days was followed
by a relatively steep
six-month decline that
then leveled off. Around
days 800 and 1,550, the
brightness also plum-
meted and rebounded by
roughly 20 percent. Days observing Tabby’s star
0 200 400 600 800 1,000 1,200 1,400 1,600
Kepler telescope’s recorded dimming of Tabby’s star