Saturn’s
90. dynamic aurorae
These images reveal the dynamic nature of Saturn’s aurorae. Viewing the planet’s southern polar region for several days,
Hubble snapped a series of photographs of the aurora dancing in the sky. The snapshots show that Saturn’s aurorae differ
in character from day to day, as they do on Earth, moving around on some days and remaining stationary on others. But
compared with Earth, where auroral storms develop in about 10 minutes and may last for a few hours, Saturn’s auroral
displays always appear bright and may last for several days.
The observations, made by Hubble and the Cassini spacecraft, while en route to the planet, suggest that Saturn’s auroral
storms are driven mainly by the pressure of the solar wind - a stream of charged particles from the Sun - rather than by the
Sun’s magnetic field.
The aurora’s strong brightening on Jan. 28, 2004 corresponds with the recent arrival of a large disturbance in the solar wind.
The image shows that when Saturn’s auroras become brighter (and thus more powerful), the ring of light encircling the pole
shrinks in diameter.
Seen from space, an aurora appears as a ring of glowing gases circling a planet’s polar region. Auroral displays are initiated
when charged particles in space collide with a planet’s magnetic field. The charged particles are accelerated to high
energies and stream into the upper atmosphere. Collisions with the gases in the planet’s atmosphere produce flashes of
glowing energy in the form of visible, ultraviolet, and infrared light.
Astronomers combined ultraviolet images of Saturn’s southern polar region with visible-light images of the planet and its rings
to make this picture. The auroral display appears blue because of the glow of ultraviolet light. In reality, the aurora would
appear red to an observer at Saturn because of the presence of glowing hydrogen in the atmosphere. On Earth, charged
particles from the Sun collide with nitrogen and oxygen in the upper atmosphere, creating auroral displays colored mostly
green and blue.
The ultraviolet images were taken on Jan. 24, 26, and 28, 2004 by Hubble’s Space Telescope Imaging Spectrograph. Erich
Karkoschka of the University of Arizona, USA used the telescope’s Advanced Camera for Surveys on March 22, 2004 to take
the visible-light images.
Credit: NASA, ESA, J. Clarke (Boston University, USA), and Z. Levay (STScI)
“Hubble has been a pivotal observatory in my work. One of my first
projects involved processing early images from before Hubble’s
corrective optics were installed, and I have been involved in
observing the outer planets ever since.
“Hubble images have been used in most of my scientific projects,
and have provided a long-term record of the atmospheres of
those planets. Given the very long orbits in the outer solar system,
having a record over decades is critical to understanding their
atmospheric processes.”
— Dr. Amy A. Simon
Senior Scientist for Planetary Atmospheres
NASA Goddard Space Flight Center
Greenbelt, Maryland