This artist’s concept depicts a potential volcanic
moon between the exoplanet WASP-49 b, left, and its parent star. New evidence
indicating that a massive sodium cloud observed near WASP-49 b is produced by
neither the planet nor the star has prompted researchers to ask if its origin
could be an exomoon.
NASA/JPL-Caltech
The existence of a moon located outside our solar system has never been
confirmed but a new NASA-led study may provide indirect evidence for one.
New research done at NASA’s Jet
Propulsion Laboratory reveals potential signs of a rocky, volcanic moon
orbiting an exoplanet 635 light-years from Earth. The biggest clue is a sodium
cloud that the findings suggest is close to but slightly out of sync with
the exoplanet, a Saturn-size gas giant named WASP-49 b, although
additional research is needed to confirm the cloud’s behavior. Within our solar
system, gas emissions from Jupiter’s volcanic moon Io create a similar phenomenon.
Although no exomoons (moons of
planets outside our solar system) have been confirmed, multiple candidates have been identified. It’s likely these planetary companions have
gone undetected because they are too small and dim for current telescopes to
detect.
The sodium cloud around WASP-49 b was first detected in 2017, catching the attention of Apurva Oza, formerly a postdoctoral researcher at NASA’s Jet Propulsion Laboratory and now a staff scientist at Caltech, which manages JPL. Oza has spent years investigating how exomoons might be detected via their volcanic activity. For example, Io, the most volcanic body in our solar system, constantly spews sulfur dioxide, sodium, potassium, and other gases that can form vast clouds around Jupiter up to 1,000 times the giant planet’s radius. It’s possible that astronomers looking at another star system could detect a gas cloud like Io’s even if the moon itself were too small to see.
Exomoons — moons around planets outside our solar
system — are most likely too small to observe directly with current technology.
In this video, learn how scientists tracked the motion of a sodium cloud 635
light-years away and found that it could be created by volcanos on a potential
exomoon. NASA/JPL-Caltech
Both WASP-49 b and its star are
composed mostly of hydrogen and helium, with trace amounts of sodium. Neither
contains enough sodium to account for the cloud, which appears to be coming
from a source that is producing roughly 220,000 pounds (100,000 kilograms) of
sodium per second. Even if the star or planet could produce that much sodium,
it’s unclear what mechanism could eject it into space.
Could the source be a volcanic
exomoon? Oza and his colleagues set out to try to answer that question. The
work immediately proved challenging because from such a great distance, the
star, planet, and cloud often overlap and occupy the same tiny, faraway point
in space. So the team had to watch the system over time.
A Cloud on the
Move
As detailed in a new study published in the Astrophysical Journal Letters, they found several pieces of evidence that suggest the cloud is created by a separate body orbiting the planet, though additional research is needed to confirm the cloud’s behavior. For example, twice their observations indicated the cloud suddenly increased in size, as if being refueled, when it was not next to the planet.
New NASA-led research suggests a sodium cloud seen
around the exoplanet WASP-49 b might be created by a volcanic moon, which is
depicted in this artist’s concept. Jupiter’s fiery moon Io produces a similar
cloud.
NASA/JPL-Caltech
They also observed the cloud moving faster than the planet in a way that
would seem impossible unless it was being generated by another body moving
independent of, and faster, than the planet.
“We think this is a really critical
piece of evidence,” said Oza. “The cloud is moving in the opposite direction
that physics tells us it should be going if it were part of the planet’s
atmosphere.”
While these observations have
intrigued the research team, they say they would need to observe the system for
longer to be sure of the cloud’s orbit and structure.
A Chance of
Volcanic Clouds
For part of their sleuthing, the
researchers used the European Southern Observatory’s Very Large Telescope in
Chile. Oza’s co-author Julia Seidel, a research fellow at the observatory,
established that the cloud is located high above the planet’s atmosphere, much
like the cloud of gas Io produces around Jupiter.
They also used a computer model to
illustrate the exomoon scenario and compare it to the data. The exoplanet
WASP-49 b orbits the star every 2.8 days with clocklike regularity, but the
cloud appeared and disappeared behind the star or behind the planet at
seemingly irregular intervals. Using their model, Oza and team showed that a
moon with an eight-hour orbit around the planet could explain the cloud’s
motion and activity, including the way it sometimes seemed to move in front of
the planet and did not seem to be associated with a particular region of the
planet.
“The evidence is very compelling
that something other than the planet and star are producing this cloud,” said
Rosaly Lopes, a planetary geologist at JPL who co-authored the study with Oza.
“Detecting an exomoon would be quite extraordinary, and because of Io, we know
that a volcanic exomoon is possible.”
A Violent End
On Earth, volcanoes are driven by
heat in its core left over from the planet’s formation. Io’s volcanoes, on the
other hand, are driven by Jupiter’s gravity, which squeezes the moon as it gets
closer to the planet then reduces its “grip” as the moon moves away. This
flexing heats the small moon’s interior, leading to a process called tidal
volcanism.
If WASP-49 b has a moon similar in
size to Earth’s, Oza and team estimate that the rapid loss of mass combined
with the squeezing from the planet’s gravity will eventually cause it to
disintegrate.
“If there really is a moon there, it will have a very destructive ending,” said Oza.
By: Jet Propulsion
Laboratory
Source: Does Distant Planet Host Volcanic Moon Like Jupiter’s Io? - NASA
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