Sky & Telescope - July 2023 - 57

Pro-Am Conjunction by Diana Hannikainen
Explore
Exorings
The hunt for rings around
other planets is on.
W
e know that rings encircle the
giant planets in our solar system
- Jupiter, Saturn, Uranus, and Neptune
all orbit the Sun accompanied by an
entourage of rings. We also know of
more than 5,000 confirmed exoplanets
today, many of which are giants. It follows
that they'd have rings, too.
But exoplanets are many light-years
away and hard to find in their own
right. If they're so tough to spot, how
can we go about finding their rings?
Matthew Kenworthy (Leiden University)
is taking a unique approach to this
task. And he has called upon the amateur
community to help him out.
Big, big rings. While examining
archival data of the young star
J1407 (short for 1SWASP J140747.93394542.6),
Erik Mamajek (University
of Rochester) and his graduate student
at the time, Mark Pecaut, noticed that
it exhibited a series of complex eclipses
over a period of about two months. Kenworthy's
subsequent analysis showed
that not only was the star's dimming
likely due to an unseen substellar companion
- dubbed J1407b - passing in
front of the star from our perspective,
but the model that most satisfactorily fit
the data pointed to a ringed exoplanet.
Further analysis revealed that the ring
system is huge, with some 30 rings
spanning around 120 million kilometers
in diameter. That's about the size of
Venus's orbit around the Sun.
We can't see exorings directly, but
instead light from the star acts like a
backlighting flashlight. If we can detect
this starlight, then we can measure the
distribution of material around the
companion, which could tell us how
much gas and dust there is and whether
pSUPER SATURN Saturn's rings are very close in to the planet, within its Roche radius. But the
Hill sphere is where the gravitational influence of a planet is stronger than that of its star (and is much
bigger than the Roche radius). Material in the Hill sphere of a young planetary system is a vast structure,
such as that of J1407b (above), which is some 200 times more extensive than Saturn's rings. If
Saturn had such rings, it would appear as large as about 10 full Moons! (See S&T: Sept. 2020, p. 34.)
there are clear clumps or gaps that
might be caused by moons.
Finding suitable candidates for
further study, though, proved challenging.
But one day a friend of Kenworthy's
tagged him on, of all things, an ASAS-SN
Twitter post. The All-Sky Automated
Survey for Supernovae automatically
surveys the entire sky every night down
to about magnitude 18. As its name
implies, it's mainly primed to search
for new supernovae and other transient
events. But the event Kenworthy's friend
had pointed him to was no supernova: A
star, named J0600 for short, had started
exhibiting complex eclipses.
Amateurs help out. The stars that
Kenworthy is after are very similar to
our Sun. They're on the main sequence
and are " quiet and boring for a few years
until they undergo these weird dimming
episodes, " he says. Professional telescopes'
finite time is largely dedicated to
observing the faintest objects in the sky
- it's tough to get them to consistently
observe these targets. And so for his
objects of interest, which are well within
reach of amateur scopes at around
magnitude 12 or so, Kenworthy turned
to the American Association of Variable
Star Observers, with its cohorts of willing
and capable astronomers armed with
hefty backyard scopes.
The support of the AAVSO is crucial:
The data are not only immediately
available, but the different wavelengths
tell us the nature of the material passing
between us and the star. If more
blue light is blocked than red, we know
there's dust. Once this information is in
hand, coupled with detections of weird
eclipses, Kenworthy turns to the big
professional telescopes for targeted data.
He's currently writing a paper on J0600
- and among the coauthors are several
AAVSO observers.
Kenworthy notes that spitting out
weird light curves is not ASAS-SN's
primary goal (remember, it's supernovae
they're after). " But to me it's gold
dust, " he says. " Because they're willing
to share their data, it's opening up a
brand-new subfield. We couldn't have
done this 10 years ago. " The combination
of the internet (including social
media), able amateurs, and the surge in
citizen science is enabling this fun and
curious new science.
If you're interested in looking for
exorings, keep an eye on https://is.gd/
aavso_campaigns. And, if you happen
to spot unusual flickering, make sure
you let Kenworthy and his team know.
¢ Observing Editor DIANA HANNIKAINEN
is fascinated by planets' Hill spheres.
sk yand tele scope .o r g * JULY 2023 57
RON MILLER / NASA

https://www.is.gd/aavso_campaigns https://www.is.gd/aavso_campaigns http://skyandtelescope.org

Sky & Telescope - July 2023

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