Trapped between two jet streams, the Great Red Spot
is an anticyclone swirling around a center of high atmospheric pressure
that makes it rotate in the opposite sense of hurricanes on Earth.Credits: NASA
The largest and most powerful hurricanes ever recorded on Earth
spanned over 1,000 miles across with winds gusting up to around 200 mph.
That’s wide enough to stretch across nearly all U.S. states east of
Texas. But even that kind of storm is dwarfed by the Great Red Spot, a
gigantic storm in Jupiter. There, gigantic means twice as wide as Earth.
With tumultuous winds peaking at about 400 mph, the Great Red Spot
has been swirling wildly over Jupiter’s skies for the past 150
years—maybe even much longer than that. While people saw a big spot in
Jupiter as early as they started stargazing through telescopes in the
1600s, it is still unclear whether they were looking at a different
storm. Today, scientists know the Great Red Spot is there and it’s been
there for a while, but they still struggle to learn what causes its
swirl of reddish hues.
Understanding the Great Red Spot is not easy, and it’s mostly
Jupiter’s fault. A planet a thousand times as big as Earth, Jupiter
consists mostly of gas. A liquid ocean of hydrogen surrounds its core,
and the atmosphere consists mostly of hydrogen and helium. That
translates into no solid ground like we have on Earth to weaken storms.
Also, Jupiter’s clouds obstruct clear observations of its lower
atmosphere. While some studies of Jupiter have investigated areas in its
lower atmosphere, orbiting probes and telescopes studying the Great Red
Spot can only see clouds scattered high in the atmosphere.
Amy Simon, an expert in planetary atmospheres at NASA’s Goddard Space
Flight Center in Greenbelt, Maryland, said learning more about Jupiter
and its Great Red Spot could help scientists understand Earth’s weather
system better. Jupiter’s weather functions under the same physics as
Earth, she said, just millions of miles farther from the sun. Simon also
said Jupiter studies could improve our understandings of worlds beyond
our solar system. “If you just look at reflected light from an
extrasolar planet, you’re not going to be able to tell what it’s made
of,” Simon said. “Looking at as many possible different cases in our own
solar system could enable us to then apply that knowledge to extrasolar
planets.”
Studies predict Jupiter’s upper atmosphere has clouds consisting of
ammonia, ammonium hydrosulfide, and water. Still, scientists don’t know
exactly how or even whether these chemicals react to give colors like
those in the Great Red Spot. Plus, these compounds make up only a small
part of the atmosphere. “We’re talking about something that only makes
up a really tiny portion of the atmosphere,” Simon said. “That’s what
makes it so hard to figure out exactly what makes the colors that we
see.”
Like Simon, other scientists at Goddard work to shed light on the
Great Red Spot’s mystery. Goddard scientists Mark Loeffler and Reggie
Hudson have been performing laboratory studies to investigate whether
cosmic rays, one type of radiation that strikes Jupiter’s clouds, can
chemically alter ammonium hydrosulfide to produce new compounds that
could explain the spot’s color.
Ammonium hydrosulfide is unstable under Earth’s atmospheric
conditions, so Loeffler makes his own batch by heating hydrogen sulfide
and ammonia together. He then blasts them with charged particles,
similar to the cosmic rays impacting Jupiter’s clouds. “Our first step
is to try to identify what forms when ammonium hydrosulfide is
irradiated,” Loeffler said. “We have recently finished identifying
these new products, and now we are trying to correlate what we have
learned with the colors in Jupiter. ”
Other experts agree with the leading theory that deep under Jupiter’s
clouds, a colorless ammonium hydrosulfide layer could be reacting with
cosmic rays or UV radiation from the sun. But Simon said many chemicals
turn red under different situations. “That’s the problem,” she said. “Is
it turning the right color red?”
Under the right conditions, ammonium
hydrosulfide might be.
With the Great Red Spot and other reddish parts of Jupiter, coloring
may result from multiple factors, as opposed to just ammonium
hydrosulfide. “Ideally, what you’d want is a mixture with the right
components of everything that you see in Jupiter’s atmosphere at the
right temperature, and then irradiate it at the right levels,” Simon
said. Ultimately, Simon and Loeffler said solving the Great Red Spot’s
mystery will take more experiments combining chemicals under the right
temperatures, light exposures and radiation doses. “What we are trying
to do is design lab experiments more realistic to Jupiter’s atmosphere,”
Simon said.
Funded by NASA’s Planetary Atmospheres and Outer Planets programs,
Loeffler, Simon and Hudson’s research is scheduled to appear in the
journal Icarus later this year. New Mexico State University astronomer Nancy Chanover also takes part in their studies.
For facts and figures on Jupiter, visit: http://solarsystem.nasa.gov/planets/profile.cfm?Object=Jupiter
Roberto Molar Candanosa
NASA's Goddard Space Flight Center in Greenbelt, Maryland
Source: NASA/Jupiter
