Sky & Telescope - May 2021 - 57

Pro-Am Conjunction by Diana Hannikainen

Exoplanet Watch
Have a hankering to contribute to a NASA project? With the
right equipment you can, right from your own backyard.
xoplanets are one of the hottest
topics in professional astronomy
today. Less than three decades after
scientists discovered the ﬁrst worlds
around other stars, we know of more
than 4,300 planets outside the solar
system. Another couple thousand candidates await conﬁrmation.
The Transiting Exoplanet Survey Satellite (TESS; a NASA-MIT collaboration)
is actively adding to that tally. Astronomers predict that once they've ﬁnished
digging through TESS's ﬁrst two years
of data, they'll identify about 10,000
new exoplanets via the transit method,
which measures the minuscule change
in the brightness of a star as a planet
traverses its disk. Thus far, astronomers
have used this method to ﬁnd about
three-quarters of all known exoplanets.
Not only does it tell us something about
the planet's size relative to its host star,
it also provides a means for disentangling the chemical composition of the
planet's atmosphere (see page 34).
The Hubble Space Telescope is already
looking for - and ﬁnding - signatures
of water in exoplanets' atmospheres.
Several ventures in the planning, among
them the James Webb Space Telescope
(scheduled for launch in October) and
the European Space Agency's Ariel mission (launch in 2029), will also be on

the prowl, snifﬁng for exoplanets' chemical ﬁngerprints. But to be able to do
this, we need to catch the exact moment
that a planet crosses its star's face.
That is challenging. Astronomers
have to " keep the transit times 'fresh'
to enable the efﬁcient use of large
telescope time, " Robert Zellem (Jet
Propulsion Laboratory) told participants
during the virtual winter meeting of the
AAS. " If your transit-timing uncertainty
is on the order of 15 minutes, that's an
extra 15 minutes you need to build into
your observing scenario and your overhead. And that's effectively 15 minutes
that's potentially wasted on just waiting
for that transit to occur - or even completely missing the transit event. "
Enter Exoplanet Watch. Led by Zellem, this NASA project aims to accurately identify the mid-transit times of
exoplanets - with amateur help. Debuting this June, Exoplanet Watch (https://
is.gd/exo_watch) is calling on amateurs
to routinely observe carefully selected
transiting exoplanets so as to keep their
mid-transit times and orbital periods
precise. Even telescopes as small as 6
inches in aperture are capable of detecting a 1-2% transit depth event in the
light curve of an 11th-magnitude star.
The project lists high-priority targets,
but observers can point their telescopes

Brightness

S&T, SOURCE: N ASA / ESA / Z. LE V Y / STSCI

Wavelength

at any known exoplanet. Once you've
collected the data with your astronomical camera, you must reduce them.
Exoplanet Watch's in-house data reduction software, EXOTIC, is a good place
to start, as is the American Association
of Variable Star Observers' package,
AstroImageJ.
Once your data are spick-and-span,
you'll upload them to the AAVSO's
Exoplanet Database, established in 2018
to provide a long-term repository that
professional astronomers can pull from
to supplement their own data, explains
Dennis Conti, chair of AAVSO's exoplanet section (https://is.gd/exo_aavso).
" Since even these observations need a
repository in order to discern long-term
trends, AAVSO's Exoplanet Database
was fortunately there to ﬁll the need. "
The project's data will be immediately made public. Exoplanet Watch
staff will " scrape " the AAVSO database
daily, process and ﬁt all the data, and
publish them also on their own website. And voilà - your data will be ripe
for the picking. Zellem stresses that
amateurs who contribute to published
results will have coauthor status on all
journal papers.
And who knows - maybe while gathering the all-important transit-timing
data, you might even discover an exoplanet of your own. Zellem concludes,
" Small telescopes really do have the
opportunity to have a high impact on
measuring these exoplanet transits. " Go
on, get your scope out, and start looking.
Observing Editor DIANA HANNIKAINEN
can't get over how much we learn from
watching worlds pass in front of stars.

When starlight passes through
the atmosphere of a transiting
exoplanet en route to us, astronomers can use it to decipher
the chemical composition of the
atmosphere. But to do this efﬁciently, we need to know exactly
when the exoplanet transits in
front of its host star.

s k y a n d t e l e s c o p e . o r g * M AY 2 0 2 1

https://www.is.gd/exo_aavso https://www.is.gd/exo_watch https://www.is.gd/exo_watch http://www.skyandtelescope.org

Sky & Telescope - May 2021

Table of Contents for the Digital Edition of Sky & Telescope - May 2021