Ammonia sparks unexpected, exotic lightning on Jupiter

Date:
August 5, 2020
Source:
Cornell University
Summary:
NASA's Juno spacecraft -- orbiting and closely observing the planet
Jupiter -- has unexpectedly discovered lightning in the planet's
upper atmosphere, according to a multi-institutional study.



FULL STORY ========================================================================== NASA's Juno spacecraft -- orbiting and closely observing the planet
Jupiter - - has unexpectedly discovered lightning in the planet's upper atmosphere, according to a multi-institutional study led by the NASA/Jet Propulsion Laboratory (JPL), which includes two Cornell University
researchers.


==========================================================================
The work was published Aug. 5 in the journal Nature.

Jupiter's gaseous atmosphere seems placid from a distance, but up close
the clouds roil in a turbulent, chemically dynamic realm. As scientists
have probed the opaque surface with Juno's sensitive instrumentation,
they've learned that Jupiter's lightning occurs not only deep within the
water clouds but also in shallow atmospheric regions (at high altitudes
with lower pressure) that feature clouds of ammonia mixed with water.

"On the night side of Jupiter, you see fairly frequent flashes -- as if
you were above an active thunderstorm on Earth," said Jonathan I. Lunine,
the David C. Duncan Professor in the Physical Sciences and chair of the Department of Astronomy in the College of Arts and Sciences at Cornell University. "You get these tall columns and anvils of clouds, and the
lightning is going continuously. We can get some pretty substantial
lightning here on Earth, and the same is true for Jupiter." The research, "Small Lightning Flashes From Shallow Electrical Storms on Jupiter,"
was directed by Heidi N. Becker, the Radiation Monitoring Investigation
lead of NASA's Juno mission. Lunine and doctoral candidate Youry Aglyamov
were the two Cornell co-authors in the study.

Previous missions to Jupiter -- such as Voyager 1, Galileo and New
Horizons - - had all observed lightning. But thanks to Juno's Stellar
Reference Unit, a camera designed to detect dim sources of light, the spacecraft's close observational distance and instrument sensitivity
enabled lightning detection at a higher resolution than previously
possible.



========================================================================== Ammonia is the key. While there is water and other chemical elements such
as molecular hydrogen and helium in Jupiter's clouds, ammonia is the "antifreeze" that keeps water in those upper atmospheric clouds from
freezing entirely.

Lunine notes Aglyamov's ongoing dissertation work focuses on how lightning
is generated under these conditions. The collision of the falling droplets
of mixed ammonia and water with suspended water-ice particles constitutes
a way to separate charge and produce cloud electrification -- resulting
in lightning storms in the upper atmosphere.

"The shallow lightning really points to the role of ammonia, and
Youry's models are starting to confirm this," Lunine said. "This would
be unlike any process that occurs on Earth." Jupiter's wild gaseous
world fascinates Aglyamov.

"Giant planets in general are a fundamentally different kind of world from Earth and other terrestrial planets," he said. "There are hydrogen seas transitioning gradually into skies stacked with cloud decks, weather
systems the size of the Earth and who-knows-what in the interior."
The discovery of shallow lightning on Jupiter shifts our understanding
of the planet, Aglyamov said.

"Shallow lightning hadn't really been expected and indicates that there's
an unexpected process causing it," he said. "It's one more way in which
Juno's observations show a much more complex atmosphere of Jupiter than
had been predicted. We know enough now to ask the right questions about processes going on there, but as Juno shows, we're in a stage where
every answer also tends to multiply the questions."

========================================================================== Story Source: Materials provided by Cornell_University. Original written
by Blaine Friedlander. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Heidi N. Becker, James W. Alexander, Sushil K. Atreya, Scott
J. Bolton,
Martin J. Brennan, Shannon T. Brown, Alexandre Guillaume, Tristan
Guillot, Andrew P. Ingersoll, Steven M. Levin, Jonathan I. Lunine,
Yury S. Aglyamov, Paul G. Steffes. Small lightning flashes from
shallow electrical storms on Jupiter. Nature, 2020; 584 (7819):
55 DOI: 10.1038/ s41586-020-2532-1 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200805160926.htm

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