What Uranus Cloud Tops Have in Common With Rotten Eggs

Even
after decades of observations and a visit by NASA’s
Voyager 2 spacecraft,
Uranus held on to one critical secret —
the composition of its clouds. Now,
one of the key components
of the planet’s clouds has finally been verified.

A
global research team that includes Glenn Orton of NASA’s Jet
Propulsion
Laboratory in Pasadena, California, has
spectroscopically dissected the
infrared light from Uranus
captured by the 26.25-foot (8-meter) Gemini North
telescope on
Hawaii’s Mauna Kea. They found hydrogen sulfide, the odiferous
gas
that most people avoid, in Uranus’ cloud tops. The
long-sought evidence was
published in the April 23rd issue of
the journal Nature Astronomy.

The
detection of hydrogen sulfide high in Uranus’ cloud deck
(and presumably
Neptune’s) is a striking difference from the
gas giant planets located closer
to the Sun — Jupiter and
Saturn — where ammonia is observed above the clouds,
but no
hydrogen sulfide. These differences in atmospheric composition
shed
light on questions about the planets’ formation and
history.

“We’ve
strongly suspected that hydrogen sulfide gas was
influencing the millimeter and
radio spectrum of Uranus for
some time, but we were unable to attribute the
absorption
needed to identify it positively. Now, that part of the puzzle
is
falling into place as well,” Orton said.

The
Gemini data, obtained with the Near-Infrared
Integral
Field Spectrometer (NIFS), sampled reflected sunlight from a
region immediately above the main visible cloud layer in
Uranus’ atmosphere.

“While
the lines we were trying to detect were just barely
there, we were able to
detect them unambiguously thanks to the
sensitivity of NIFS on Gemini, combined
with the exquisite
conditions on Mauna Kea,” said lead author Patrick Irwin of
the University of Oxford, U.K.

No worries, though, that the odor of hydrogen sulfide would
overtake human senses. According to Irwin, “Suffocation and
exposure in the negative 200
degrees Celsius [392 degrees
Fahrenheit] atmosphere made of mostly hydrogen,
helium and
methane would take its toll long before the smell.”

Read
more on the news of Uranus’ atmosphere from Gemini
Observatory here.

Caltech
in Pasadena, California, manages JPL for NASA.

News Media Contact

Gretchen McCartney
Jet Propulsion Laboratory, Pasadena, Calif.
818-393-6215
Gretchen.p.mccartney@jpl.nasa.gov

JoAnna Wendel
NASA Headquarters, Washington
202-358-1003
joanna.r.wendel@nasa.gov

Peter Michaud
Gemini Observatory, Hilo, Hawaii
808-974-2510
pmichaud@gemini.edu

2018-079