NASA’s Hubble Space Telescope
and the ground-based Gemini Observatory in Hawaii have teamed up with the Juno
spacecraft to probe the mightiest storms in the solar system, taking place more
than 500 million miles away on the giant planet Jupiter.
A team of
researchers led by Michael Wong at the University of California, Berkeley, and
including Amy Simon of NASA’s Goddard Space Flight Center in Greenbelt,
Maryland, and Imke de Pater also of UC Berkeley, are combining multiwavelength
observations from Hubble and Gemini with close-up views from Juno’s orbit about
the monster planet, gaining new insights into turbulent weather on this distant
world.
“We want to know
how Jupiter’s atmosphere works,” said Wong. This is where the teamwork of Juno,
Hubble and Gemini comes into play.
Radio ‘Light Show’
Jupiter’s
constant storms are gigantic compared to those on Earth, with thunderheads
reaching 40 miles from base to top — five times taller than typical
thunderheads on Earth — and powerful lightning flashes up to three times more
energetic than Earth’s largest “superbolts.”
Like lightning
on Earth, Jupiter’s lightning bolts act like radio transmitters, sending out
radio waves as well as visible light when they flash across the sky.
Every 53 days,
Juno races low over the storm systems detecting radio signals known as
“sferics” and “whistlers,” which can then be used to map lightning even on the
day side of the planet or from deep clouds where flashes are not otherwise
visible.
Coinciding with
each pass, Hubble and Gemini watch from afar, capturing high-resolution global
views of the planet that are key to interpreting Juno’s close-up observations.
“Juno’s microwave radiometer probes deep into the planet’s atmosphere by
detecting high-frequency radio waves that can penetrate through the thick cloud
layers. The data from Hubble and Gemini can tell us how thick the clouds are
and how deep we are seeing into the clouds,” Simon explained.
By mapping
lightning flashes detected by Juno onto optical images captured of the planet
by Hubble and thermal infrared images captured at the same time by Gemini, the
research team has been able to show that lightning outbreaks are associated
with a three-way combination of cloud structures: deep clouds made of water,
large convective towers caused by upwelling of moist air — essentially Jovian
thunderheads — and clear regions presumably caused by downwelling of drier air
outside the convective towers.
The Hubble data
show the height of the thick clouds in the convective towers, as well as the
depth of deep water clouds. The Gemini data clearly reveal the clearings in the
high-level clouds where it is possible to get a glimpse down to the deep water
clouds.
Wong thinks that
lightning is common in a type of turbulent area known as folded filamentary
regions, which suggests that moist convection is occurring in them. “These
cyclonic vortices could be internal energy smokestacks, helping release
internal energy through convection,” he said. “It doesn’t happen everywhere,
but something about these cyclones seems to facilitate convection.”
The ability to
correlate lightning with deep water clouds also gives researchers another tool
for estimating the amount of water in Jupiter’s atmosphere, which is important
for understanding how Jupiter and the other gas and ice giants formed, and
therefore how the solar system as a whole formed.
While much has
been gleaned about Jupiter from previous space missions, many of the details —
including how much water is in the deep atmosphere, exactly how heat flows from
the interior and what causes certain colors and patterns in the clouds — remain
a mystery. The combined result provides insight into the dynamics and
three-dimensional structure of the atmosphere.
Seeing a ‘Jack-O-Lantern’ Red Spot
With Hubble and
Gemini observing Jupiter more frequently during the Juno mission, scientists
are also able to study short-term changes and short-lived features like those
in the Great Red Spot.
Images from Juno
as well as previous missions to Jupiter revealed dark features within the Great
Red Spot that appear, disappear and change shape over time. It was not clear
from individual images whether these are caused by some mysterious dark-colored
material within the high cloud layer, or if they are instead holes in the high
clouds — windows into a deeper, darker layer below.
Now, with the
ability to compare visible-light images from Hubble with thermal infrared
images from Gemini captured within hours of each other, it is possible to
answer the question. Regions that are dark in visible light are very bright in
infrared, indicating that they are, in fact, holes in the cloud layer. In
cloud-free regions, heat from Jupiter’s interior that is emitted in the form of
infrared light — otherwise blocked by high-level clouds — is free to escape
into space and therefore appears bright in Gemini images.
“It’s kind of
like a jack-o-lantern,” said Wong. “You see bright infrared light coming from
cloud-free areas, but where there are clouds, it’s really dark in the
infrared.”
Hubble and Gemini as Jovian Weather
Trackers
The regular imaging
of Jupiter by Hubble and Gemini in support of the Juno mission is proving
valuable in studies of many other weather phenomena as well, including changes
in wind patterns, characteristics of atmospheric waves and the circulation of
various gases in the atmosphere.
Hubble and
Gemini can monitor the planet as a whole, providing real-time base maps in
multiple wavelengths for reference for Juno’s measurements in the same way that
Earth-observing weather satellites provide context for NOAA’s high-flying Hurricane
Hunters.
“Because we now
routinely have these high-resolution views from a couple of different
observatories and wavelengths, we are learning so much more about Jupiter’s
weather,” explained Simon. “This is our equivalent of a weather satellite. We can
finally start looking at weather cycles.”
Because the
Hubble and Gemini observations are so important for interpreting Juno data,
Wong and his colleagues Simon and de Pater are making all of the processed data
easily accessible to other researchers through the Mikulski Archives for Space
Telescopes (MAST) at the Space Telescope Science Institute in Baltimore,
Maryland.
“What’s
important is that we’ve managed to collect this huge data set that supports the
Juno mission. There are so many applications of the data set that we may not
even anticipate. So, we’re going to enable other people to do science without
that barrier of having to figure out on their own how to process the data,”
Wong said.
The results were published in April 2020 in The Astrophysical Journal Supplement Series.
Journal article: https://iopscience.iop.org/article/10.3847/1538-4365/ab775f
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