S
ARA SEAGER points to a notch in
the graph on her computer screen.
Like an icicle clinging to the edge
of a rooftop, it hangs downward, recording
a temporary dip in the brightness of a
nearby star.
“This one looks pretty,” remarks the
Canadian-born astronomer as she flips
through sample data at the TESS Payload
Operations Center in Cambridge, Massa-
chusetts. It’s the kind of signal Seager and
her colleagues are interested in when they
hunt for exoplanets—worlds belonging to
solar systems beyond our own.
TESS is the Transiting Exoplanet Survey
Satellite, an Earth-orbiting planet finder de-
veloped at the Massachusetts Institute of
Technology and launched by NASA on
April 18, 2018. Seager, who is deputy direc-
tor of the TESS science team, is taking me
on a tour of the mission’s data pipeline—the
stream of observations from which poten-tial discoveries are flagged and checked be-
fore being sent out to the astronomical com -
munity for confirmation and follow-up.
The goal of the mission—and Seager
herself—is to reveal a diverse population
of exoplanets comparable in size to Earth
and located less than 200 light-years away.
These planets will almost certainly pre -
occupy researchers for decades into the
future because they’re close enough to be
scrutinized by a coming generation of giant
telescopes and astronomical spacecraft.
Mission team member David Charbon-
neau, an astronomer at Harvard University,
comments: “Basically, we’re meeting our
neighbours for the first time.”
Now into the second half of its initial
sweep, TESS has already identified some300 candidate planets—more than two
dozen of them confirmed.SYSTEMATIC SEARCH
Anyone preparing to glimpse November’s
transit of Mercury (see page 23) will recog-
nize the principle underlying how TESS
operates. Just as Mercury can be seen in
silhouette when it lines up exactly between
Earth and the Sun, exoplanets with favour -
ably oriented orbits can be detected cutting
across their stars.
However, while we can resolve Mercury
as a black dot against the brilliant solar
disc, a transiting exoplanet is too distant to
spot directly. Instead, TESS measures the
subtle change in a star’s brightness that
occurs when a minute portion of its lightDIM SUNAbove: TESS is primarily designed to search for nearby Earth-sized planets orbiting close
to stars cooler and redder than our Sun. Small, close-in specimens are well suited to follow-up obser-
vations that can determine whether any of them has an atmosphere. ILLUSTRATION COURTESY ESO/M. KORNMESSERDOORSTEP
A new NASA mission called TESS scans nearby stars
for transiting Earth-sized worlds by IVAN SEMENIUKON
THE
8 SKYNEWS •NOVEMBER/DECEMBER 2019