Io, the third-largest of Jupiter’s
moons, is caught in a pressurized, explosive dance.
Orbiting near Ganymede and Europa, two of
the other largest Jovian moons, and the planet itself, Io’s mineral composition
is constantly pulled and pushed by gravity, creating frictional heat deep
inside the moon. This makes it extremely volcanically active — there are
hundreds of volcanoes and extensive networks of lava flows marking Io’s
surface.
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“It’s being squeezed like an anger ball,”
said Jeff Morgenthaler, an astrophysicist at the Planetary Science Institute.
Despite a number of close-flying
spacecrafts over the past few decades — including the Voyager 1 and Galileo
missions — as well as constant observation from Earth, there are lasting
mysteries about the kind of volcanic activity on Io and how the moon’s fiery
energy interacts with Jupiter and other nearby bodies.
Last year, Morgenthaler, who studies gases
Io emits and the cloud these gases create around Jupiter, picked up signs that
a different kind of eruption — a more powerful or more persistent one — was
occurring.
“It’s an exciting observation,” said Ashley
Davies, a planetary scientist and volcanologist at NASA’s Jet Propulsion
Laboratory who was not involved in Morgenthaler’s study. “It’s showing that Io
is certainly one of the most energetic bodies in the solar system, and you have
no idea how it’s going to appear when you turn your telescope on it.”
The observation could help to guide future
study of Io, including preparations for NASA’s Juno space probe, which has been
orbiting Jupiter since 2016 and is scheduled to fly only a couple hundred miles
from the Jovian moon this December.
Hot and coldBecause Io is far from the sun and has a
very thin atmosphere, its surface, on average, sits at around minus 130 degrees
Celsius, and it is coated in a frosty layer of sulfuric compounds. Volcanic
eruptions there, which come in many different forms and intensities, can reach
temperatures up to 1,370 degrees Celsius.
There are lasting mysteries about the kind of volcanic activity on Io and how the moon’s fiery energy interacts with Jupiter and other nearby bodies
When super hot meets super cold, molecules
like sulfur dioxide and sodium can be shot into space. Some of the most
explosive eruptions come from fissures in the surface and throw fountains of
lava nearly a kilometer into space. The charged molecules create what is known
as a “plasma torus” in Io’s wake: a doughnut-shaped cloud of ionized gas that
collects in Jupiter’s magnetic field.
It is possible to look directly at Io’s
volcanic hot spots with infrared telescopes. However, since 2017, Morgenthaler
has taken a different approach, focusing on the moon’s plasma torus through the
Planetary Science Institute’s Io Input/Output observatory (IoIO), in Arizona.
Instead of using infrared light, Morgenthaler uses IoIO to block light from
Jupiter and measure the gas around it.
Reading the eruptionsDavies said that while infrared telescopes
can tell us where volcanoes are erupting on Io and how powerful they may be,
studying the plasma torus can tell us when an eruption is chemically rich —
signaling that it may be more powerful, more persistent, or just more peculiar.
One eruption could push more ionized gas into the torus. Another could send out
a lot of neutral gas. “It doesn’t happen every time, and it’s an interesting
link,” Davies said.
Io,
a moon of Jupiter, captured by the Juno spacecraft as it flew by on July 5,
2022.
Each year Morgenthaler has monitored
volcanic activity through IoIO, he has noticed some kind of increased
concentration, or brightening, of gases in the plasma torus. These changes
correlate with volcanic outbursts, the intensities of which can be measured by
the levels of sodium emitted from the moon. But, from September through
December 2022, after a large volcanic outburst, he noticed that the torus
contained much less sulfur dioxide than the size of the eruption would suggest.
The torus was not as bright as it should have been.
This could mean that the eruption had a
different chemical composition from the others, or that different kinds of
minerals had been disturbed. It would be like Mount St. Helens, a steep
stratovolcano that can erupt explosively, sending dirt, rock, and sodium into
the atmosphere, erupting on Earth, rather than Mauna Loa, a gently-sloped
shield volcano that erupts with liquid lava flows. Or it could mean that the
torus was rapidly diffusing in response to the intense eruption.
Studying the plasma torus can tell us when an eruption is chemically rich — signaling that it may be more powerful, more persistent, or just more peculiar
More than anything, Morgenthaler said, it
is a call for more research.
“I’m just raising the flag, and saying,
‘This has happened,’ ” Morgenthaler said after announcing the observation this
month.
What is next in Io observation?Studying the anomaly might draw out, in
better detail, the different kinds of volcanoes on Io, as well as the
interactions between the plasma torus and other massive moons around Jupiter.
However, much more data will have to be gathered to put all the pieces
together, including from other powerful telescopes on Earth, like the James
Webb Space Telescope, as well as from the Juno space probe.
For the moment, to study gases from Io,
Morgenthaler said that his method, which is cheap and could be adapted by small
research organizations and even some backyard astronomers, is often
underutilized. But his work may open the door for similar and widespread
research that could provide data to help understand the Jovian system.
Davies said that this kind of piecemeal
research is integral to understanding Io. “You can think of it like looking at
different parts of an elephant,” he said.
The fact that Morgenthaler’s most recent
observation was made with largely accessible instruments opens the possibility
of more studies, similar and different, in kind. “The more monitoring we can
get, the better it will be,” Davies said.
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