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This artist's conception shows an extremely volcanic moon orbiting a gas giant planet in another star system. New research suggests that astronomers using the James Webb Space Telescope could potentially detect volcanic activity on a distant Earth-sized planet by measuring volcanic gases in its atmosphere. Credit: Wade Henning
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Volcanoes display the awesome power of nature like few other
events. Earlier this year, ash from an Icelandic volcano disrupted air travel
throughout much of northern Europe. Yet this
recent eruption pales next to the fury of Jupiter's moon Io, the most volcanic
body in our solar system.
Now that
astronomers are finding rocky worlds orbiting distant stars, they're asking the
next logical questions: Do any of those worlds have volcanoes? And if so, could
we detect them? Work by theorists at the Harvard-Smithsonian Center
for Astrophysics suggests that the answer to the latter is a qualified
"Yes."
"You
would need something truly earthshaking, an eruption that dumped a lot of gases
into the atmosphere," said Smithsonian astronomer Lisa Kaltenegger. "Using
the James Webb Space Telescope, we could spot an eruption 10 to 100 times the
size of Pinatubo for the closest stars," she added.
Astronomers
are decades away from being able to image the surface of an alien world, or
exoplanet. However, in a few cases they have been able to detect exoplanet
atmospheres for gas giants known as "hot Jupiters." An eruption sends
out fumes and various gases, so volcanic activity on a rocky exoplanet might
leave a telltale atmospheric signature.
To examine
which volcanic gases might be detectable, Kaltenegger and her Harvard
colleagues, Wade Henning and Dimitar Sasselov, developed a model for eruptions
on an Earth-like exoplanet based on the present-day Earth. They found that
sulfur dioxide from a very large, explosive eruption is potentially measurable
because a lot is produced and it is slow to wash out of the air.
"Our
first sniffs of volcanoes from an alien Earth might be pretty rank!"
Kaltenegger said. "Seeing a volcanic eruption on an exoplanet will show us
similarities or differences among rocky worlds."
The 1991
eruption of Mount Pinatubo in the Philippines spewed about 17 million
tons of sulfur dioxide into the stratosphere. The largest volcanic eruption in recorded history, the 1815
Tambora event, was about 10 times more powerful.
Such gigantic
eruptions are infrequent, so astronomers would have to monitor many Earth-sized
planets for years to catch one in the act. However, if alien worlds are more
volcanically active than Earth, success might be more likely.
"A
Tambora-sized eruption doesn't happen often here, but could be more common on a
younger planet, or a strongly tidally active planet - analogous to Io,"
said Henning. "Once you detected one eruption, you could keep watch for
further ones, to learn if frequent eruptions are common on other planets."
To look for
volcanic sulfur dioxide, astronomers would rely on a technique known as the
secondary eclipse, which requires the exoplanet to cross behind its star as
seen from Earth. By collecting light from the star and planet, then subtracting
the light from the star (while the planet is hidden), astronomers are left with
the signal from the planet alone. They can search that signal for signs of
particular chemical molecules.
Due to its
proximity, a hypothetical Earth or super-Earth orbiting Alpha Centauri would
offer a best-case scenario for a sun-like star. A super-Earth orbiting a
smaller host star close to our own Sun would show the biggest signal. But any
Earth-like planet less than 30 light-years away could show faint signs of
volcanism when studied with the James Webb Space Telescope.
This research will be published in The
Astrophysical Journal. Headquartered in Cambridge,
Mass., the Harvard-Smithsonian Center
for Astrophysics (CfA) is a joint collaboration between the Smithsonian
Astrophysical Observatory and the Harvard College Observatory. CfA scientists,
organized into six research divisions, study the origin, evolution and ultimate
fate of the universe.
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