New findings from NASA’s Juno probe orbiting Jupiter provide a fuller picture of how the planet’s distinctive and colorful atmospheric features offer clues about the unseen processes below its clouds. The results highlight the inner workings of the belts and zones of clouds encircling Jupiter, as well as its polar cyclones and even the Great Red Spot.
Researchers published several papers on Juno’s
atmospheric discoveries today in the journal Science and the Journal of
Geophysical Research: Planets. Additional papers appeared in two recent issues
of Geophysical Research Letters.
“These new observations from Juno open up a treasure
chest of new information about Jupiter’s enigmatic observable features,” said
Lori Glaze, director of NASA’s Planetary Science Division at the agency’s
headquarters in Washington. “Each paper sheds light on different aspects of the
planet’s atmospheric processes – a wonderful example of how our
internationally-diverse science teams strengthen understanding of our solar
system.”
Juno entered Jupiter’s orbit in 2016. During each of
the spacecraft’s 37 passes of the planet to date, a specialized suite of instruments has peered below its
turbulent cloud deck.
“Previously, Juno surprised us with hints that
phenomena in Jupiter’s atmosphere went deeper than expected,” said Scott
Bolton, principal investigator of Juno from the Southwest Research Institute in
San Antonio and lead author of the Journal Science paper on the depth of
Jupiter’s vortices. “Now, we’re starting to put all these individual pieces
together and getting our first real understanding of how Jupiter’s beautiful
and violent atmosphere works – in 3D.”
Juno’s microwave radiometer (MWR) allows mission scientists to peer beneath Jupiter’s cloud
tops and probe the structure of its numerous vortex storms. The most famous of
these storms is the iconic anticyclone known as the Great Red Spot. Wider than
Earth, this crimson vortex has intrigued scientists since its discovery almost
two centuries ago.
The new results show that the cyclones are warmer on
top, with lower atmospheric densities, while they are colder at the bottom, with
higher densities. Anticyclones, which rotate in the opposite direction, are
colder at the top but warmer at the bottom.
The findings also indicate these storms are far taller
than expected, with some extending 60 miles (100 kilometers) below the cloud tops
and others, including the Great Red Spot, extending over 200 miles (350
kilometers). This surprise discovery demonstrates that the vortices cover
regions beyond those where water condenses and clouds form, below the depth
where sunlight warms the atmosphere.
The height and size of the Great Red Spot means the
concentration of atmospheric mass within the storm potentially could be
detectable by instruments studying Jupiter’s gravity field. Two close Juno
flybys over Jupiter’s most famous spot provided the opportunity to search for
the storm’s gravity signature and complement the MWR results on its
depth.
With Juno traveling low over Jupiter’s cloud deck at
about 130,000 mph (209,000 kph) Juno scientists were able to measure velocity
changes as small 0.01 millimeter per second using a NASA’s Deep Space Network
tracking antenna, from a distance of more than 400 million miles (650 million
kilometers). This enabled the team to constrain the depth of the Great Red Spot
to about 300 miles (500 kilometers) below the cloud tops.
“The precision required to get the Great Red Spot’s
gravity during the July 2019 flyby is staggering,” said Marzia Parisi, a Juno
scientist from NASA’s Jet Propulsion Laboratory in Southern California and lead
author of a paper in the Journal Science on gravity overflights of the Great
Red Spot. “Being able to complement MWR’s finding on the depth gives us great
confidence that future gravity experiments at Jupiter will yield equally
intriguing results.”
Belts and Zones
In addition to cyclones and anticyclones, Jupiter is
known for its distinctive belts and zones – white and reddish bands of clouds
that wrap around the planet. Strong east-west winds moving in opposite
directions separate the bands. Juno previously discovered that these winds, or
jet streams, reach depths of about 2,000 miles (roughly 3,200 kilometers).
Researchers are still trying to solve the mystery of how the jet streams form.
Data collected by Juno’s MWR during multiple passes reveal one possible clue:
that the atmosphere’s ammonia gas travels up and down in remarkable alignment
with the observed jet streams.
“By following the ammonia, we found circulation cells
in both the north and south hemispheres that are similar in nature to ‘Ferrel
cells,’ which control much of our climate here on Earth”, said Keren Duer, a
graduate student from the Weizmann Institute of Science in Israel and lead
author of the Journal Science paper on Ferrel-like cells on Jupiter. “While
Earth has one Ferrel cell per hemisphere, Jupiter has eight – each at least 30
times larger.”
Juno’s MWR data also shows that the belts and zones
undergo a transition around 40 miles (65 kilometers) beneath Jupiter’s water
clouds. At shallow depths, Jupiter’s belts are brighter in microwave light than
the neighboring zones. But at deeper levels, below the water clouds, the
opposite is true – which reveals a similarity to our oceans.
“We are calling this level the ‘Jovicline’ in analogy
to a transitional layer seen in Earth’s oceans, known as the thermocline –
where seawater transitions sharply from being relative warm to relative cold,”
said Leigh Fletcher, a Juno participating scientist from the University of
Leicester in the United Kingdom and lead author of the paper in the Journal of
Geophysical Research: Planets highlighting Juno’s microwave observations of
Jupiter’s temperate belts and zones.
Polar Cyclones
Juno previously discovered polygonal arrangements of giant cyclonic storms at both of Jupiter’s poles – eight
arranged in an octagonal pattern in the north and five arranged in a pentagonal
pattern in the south. Now, five years later, mission scientists using
observations by the spacecraft’s Jovian Infrared Auroral Mapper (JIRAM) have
determined these atmospheric phenomena are extremely resilient, remaining in
the same location.
“Jupiter’s cyclones affect each other’s motion,
causing them to oscillate about an equilibrium position,” said Alessandro Mura,
a Juno co-investigator at the National Institute for Astrophysics in Rome and
lead author of a recent paper in Geophysical Research Letters on oscillations
and stability in Jupiter’s polar cyclones. “The behavior of these slow
oscillations suggests that they have deep roots.”
JIRAM data also indicates that, like hurricanes on
Earth, these cyclones want to move poleward, but cyclones located at the center
of each pole push them back. This balance explains where the cyclones reside
and the different numbers at each pole.
Image & info via APOD
Image credit: International Gemini
Observatory/NOIRLab/NSF/AURA/NASA/ESA, M.H. Wong and I. de Pater (UC Berkeley)
et al.
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