24 AUSTRALIAN SKY & TELESCOPE April 2018
THE EXOPLANETS NEXT DOORWHAT TESS MAY FIND: LEAH TISCIONE /S&T, SOURCE: TESS TEAM; OBSERVING SECTORS: LEAH TISCIONE /S&T, SECTORS SOURCE: C. BEALS / MIT, COVERAGE MAP SOURCE: D. DEMING / TESS TEAMcurve that indicate the signal could
be from a transiting planet, then
put those candidates at the top of
the TESS Object of Interest list,
which is sent out simultaneously
to the TESS team and to the wider
astronomical community. Making
all of the data public (with no
proprietary period) is one of the
unique features of TESS’s mission:
We aim to encourage the entire
community to participate in planet
finding and follow-up science.
Each TESS exoplanet candidate
won’t necessarily be a true planet.
The international TESS follow-up team will scrutinise
candidates using many ground-based observations to rule
out imposters. Then they’ll funnel the bona fide worlds to
astronomers working with the most precise radial-velocity
and photometric instruments on ground-based telescopes
so that they can measure the planets’ masses. Beyond the
50 small exoplanets TESS has promised to deliver, the team
anticipates finding thousands of planet candidates of all sizes
and around a variety of star types.
Once the transit signals are confirmed as planets and
have measured masses, members of the TESS Science Team
and other exoplanet astronomers around the globe will pick
the choicest transiting planets for follow-up observations, in
order to try to detect their atmospheric makeup. Although
we aim to investigate any planets of interest, we’re especially
keen to find small, rocky planets in the habitable zones of
red dwarf stars. These stars are abundant in the galaxy, andknowing the composition of their exoplanets’ atmospheres
might give us a good picture of conditions around the
most common stars across the Milky Way. I would imagine
that over the next decade, dozens of small exoplanets and
hundreds of larger planets will have their atmospheres
extensively studied.Database for discovery
TESS’s 27-day observing strategy will make it sensitive
to planets with orbital periods up to about 13 days long,
corresponding to the habitable zone of some small red dwarf
stars. However, the overlap at the ecliptic poles adds up to
more than 300 days, enabling us to discover worlds with
much longer orbits or habitable-zone planets around more
massive, Sun-like stars, especially if we stack the data.
The most exciting possibility, of course, is the discovery
of a transiting rocky exoplanet orbiting in an M dwarf star’sDetectionsEarths
<1.25
Earth
radiiGiants
>4
Earth
radiiExoplanets70
± 9
67
± 8250 410
443286k 190k 188k486
± 221111
± 12217k5103kStarsEclipsing
binariesFull-frame images
Target starsEclipsing
binaries
in a
triple
systemChance-
aligned
starsSuper-
Earths
1.25 – 2
Earth
radiiMini-
Neptunes
2 – 4
Earth
radii101102103104105106351 daysEcliptic
poleEcliptic poleEcliptic
latitude 6°JWST
continuous
viewing zone189 days108 days81 days54 days27 daysAB C96 °24 °ECLIPTICSOBSERVING SECTORS The combined field of view of TESS’s four cameras spans a long, 24°×96° strip of sky (A). Every 27 days, the spacecraft
will observe a different strip of sky (B), slicing it into 26 sectors (13 per hemisphere). These sectors overlap near the ecliptic pole (C). The dashed
black circle around the pole shows the region that the upcoming James Webb Space Telescope can observe uninterrupted.XWHAT TESS MAY FIND
Team members expect
TESS to detect roughly 70
Earth-size planets around
nearby stars and about
seven times as many
super-Earths. Full-frame
images will only enable
the discovery of deeper
transits (and, thus, larger
objects) because the stars
they include are fainter
than those in the high-
time-resolution ‘postage
stamp’ segments.