Astronomers find evidence for a second supermoon beyond our solar system
An exomoon signal found in archival data hints at the possibility of more discoveries to come

Date:
January 13, 2022
Source:
Columbia University
Summary:
In a new study in Nature Astronomy, researchers report a second,
super- sized moon orbiting a Jupiter-sized planet beyond our solar
system. If confirmed, the sighting could mean that exomoons are
as common in the universe as exoplanets, and that big or small,
such moons are a feature of planetary systems.



FULL STORY ========================================================================== Astronomers have reported a second, super-sized moon orbiting a
Jupiter-sized planet beyond our solar system. If confirmed, the sighting
could mean that exomoons are as common in the universe as exoplanets, and
that big or small, such moons are a feature of planetary systems. But it
could be a long wait. The first-ever sighting of an exomoon four years
ago is still awaiting confirmation, and verification of this newest
candidate could be as equally long and contentious.


==========================================================================
The discovery, published in Nature Astronomy, was led by David Kipping
and his Cool Worlds Lab at Columbia University, which reported the first exomoon candidate in 2017.

"Astronomers have found more than 10,000 exoplanet candidates so far,
but exomoons are far more challenging," said Kipping, who has spent the
last decade hunting for exomoons. "They are terra incognita." The team
spotted the giant exomoon candidate orbiting the planet Kepler 1708b,
a world 5,500 light-years from Earth in the direction of the Cygna and
Lyra constellations. This new candidate is about a third smaller than
the Neptune- sized moon that Kipping and his colleagues earlier found
orbiting a similar Jupiter-sized planet, Kepler 1625b.

Both supermoon candidates are likely made of gas that has piled up under
the gravitational pull caused by their enormous size, said Kipping. If
one astronomer's hypothesis is correct, the moons may have even started
life as planets, only to be pulled into the orbit of an even bigger
planet like Kepler 1625b or 1708b.

Both moons are located far from their host star, where there's less
gravity to tug at planets and strip off their moons. In fact, the
researchers sought out cold, giant gas planets on wide orbits in their
search for exomoons precisely because the analog in our own solar system, Jupiter and Saturn, have more than a hundred moons between them.



==========================================================================
If other moons are out there, they will likely be less monstrous, but also harder to spot, said Kipping. "The first detections in any survey will generally be the weirdos," he said. "The big ones that are simply easiest
to detect with our limited sensitivity." Exomoons fascinate astronomers
for the same reasons that exoplanets do. They have the potential to
reveal how and where life may have emerged in the universe. They are
also curiosities in their own right, and astronomers want to know how
these exomoons form, if they can sustain life, and what role, if any,
they play in making their host planets habitable.

In the current study, the researchers looked at the sample of the
coldest gas giant planets captured by NASA's planet-hunting spacecraft,
Kepler. After scanning 70 planets in depth, they found just one candidate
-- Kepler 1708b - - with a moon-like signal. "It's a stubborn signal,"
said Kipping. "We threw the kitchen sink at this thing but it just
won't go away." Observations from other space telescopes, like Hubble,
will be needed to verify the discovery, a process that could take
years. Four years later, Kipping's first exomoon discovery continues
to be hotly debated. In a recent paper, he and his colleagues showed
how one group of skeptics may have missed Kepler 1625b's moon in their calculations. Meanwhile, Kipping and colleagues continue to investigate
other lines of evidence.

Eric Agol, an astronomy professor at University of Washington, said he's doubtful that this latest signal will turn out to be real. "It might
just be a fluctuation in the data, either due to the star or instrumental noise," he said.



========================================================================== Others sounded more optimistic. "This is science at its best," said
Michael Hippke, an independent astronomer in Germany. "We find an
intriguing object, make a prediction, and either confirm the exomoon
candidate or rule it out with future observations." "I am very excited to
see a second exomoon candidate, although it is unfortunate that only two transits have been observed," he added. "More data would be very cool." Spotting a moon or even a planet hundreds to thousands of light-years
from Earth is anything but straightforward. Moons and planets can only be observed indirectly as they pass in front of their host stars, causing
the star's light to intermittently dim. Catching one of these fleeting
transit signals with a telescope is tricky, and so is interpreting the light-curve data. Moons are even harder to detect because they're smaller
and block less light.

But the search is worth it, said Kipping, as he recalled how the
existence of exoplanets was greeted with the same skepticism as exomoons
are today. "Those planets are alien compared to our home system," he
said. "But they have revolutionized our understanding of how planetary
systems form." Other authors are: Steve Bryson, NASA Ames Research
Center; Chris Burke, MIT; Jessie Christiansen and Kevin Hardegree-Ullman, Caltech; Billy Quarles, Valdosta State University; Brad Hansen, University
of California, Los Angeles; Judit Szulagyi, ETH Zurich; and Alex Teachey, Columbia.

========================================================================== Story Source: Materials provided by Columbia_University. Original written
by Kim Martineau.

Note: Content may be edited for style and length.


========================================================================== Related Multimedia:
*
YouTube_video:_We_Discovered_a_New_Exomoon_Candidate!_A_Survey_of_70_Cool
Gas_Giants_(Cool_Worlds) ========================================================================== Journal Reference:
1. Kipping, D., Bryson, S., Burke, C. et al. An exomoon survey of
70 cool
giant exoplanets and the new candidate Kepler-1708 b-i. Nat Astron,
2022 DOI: 10.1038/s41550-021-01539-1 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/01/220113111402.htm
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