A moist explanation for Saturn’s Great
White Spots

NATURE GEOSCIENCE

Geoscience
Embargo

London: Monday 13 April 2015 16:00 (BST)

New York: Monday 13 April 2015 11:00 (EDT)

Tokyo: Tuesday 14 April 2015 00:00 (JST)

Sydney: Tuesday 14 April 2015 01:00 (AEST)
The occurrence of giant storms on Saturn, every 20 to 30 years, may be caused by moisture in
the planet’s atmosphere, which suppresses storm formation for long periods of time, according to
a study published online in Nature Geoscience. The research suggests that after a number of
years a massive storm is generated.
Six planet-encircling storms called Great White Spots have been observed on Saturn over the
past 140 years, alternating between the equator and mid-latitudes. The most recent Great White
Spot, the giant eye of which was similar in size to the Earth, erupted in 2010 and encircled the
planet in six months.
Cheng Li and colleagues theorized that moisture in Saturn’s atmosphere suppresses stormgenerating circulation for decades. This is because water molecules are relatively heavy
compared with the hydrogen and helium that dominate Saturn’s atmosphere, and thus prevent
warm air from rising and forming thunderstorms. The authors suggest that the resulting cooling of
the upper atmosphere will eventually override the suppressed circulation, causing warm moist air
to rapidly rise and trigger a giant thunderstorm.
Using numerical modelling, the authors showed that this mechanism matches spacecraft
observations of the 2010 Great White Spot. They also propose that the absence of planetencircling storms on Jupiter could be explained by the prediction that Jupiter’s atmosphere
contains less water vapour than Saturn’s atmosphere.
Article and author details
1. Moist convection in hydrogen atmospheres and the frequency
of Saturn's giant storms
Corresponding Author
Cheng Li
California Institute of Technology, Pasadena, California, United States
Email: cli@gps.caltech.edu, Tel: +1 626 395 6960
DOI
10.1038/ngeo2405
Online paper*
http://nature.com/articles/doi:10.1038/ngeo2405
* Please link to the article in online versions of your report (the URL will go live after the embargo ends).
Geographical listings of authors

United States