Uranus and Neptune aren’t the identical egg-blue twins they appear to be in
natural color, according to NASA Hubble Space Telescope images released

Erich Karkoschka of the University of Arizona Lunar and Planetary Laboratory
used different color filters on Hubble’s Space Telescope Imaging
Spectrograph and the Advanced Camera for Surveys for the observations, taken
in August 2003.

Karkoschka used red, green, and blue light filters to show Uranus and
Neptune in their natural colors. He used other filters, including
near-infrared, for enhanced views. Enhanced views show that Uranus and
Neptune are two different worlds.

“I took extraordinary care that the natural-color images are very close to
what a human would see from a spacecraft near these planets,” he said. “The
enhanced-color images show how an instrument with different spectral
sensitivity than that of the human eye can change the view. There is more to
everything than what the eye can see.”

The new images show how Uranus’s rotational axis is tilted almost 90 degrees
to Neptune’s axis. The south poles of Uranus and Neptune are both tilted
slightly toward Earth. Uranus shows greater contrast between its
hemispheres, which may be caused by its extreme seasons.

Bands of clouds and haze are aligned parallel to the equator on both
planets. Colors in the bands show layers of clouds and haze at different
altitudes and thicknesses.

Some cloud features appear bright orange or red, a color caused by methane
absorption in the red part of the spectrum. Methane is the third most
plentiful gas in both planets’ atmospheres, second only to hydrogen and

Uranus’ faint rings and several of its satellites are visible in a wider
view of Uranus. These include Uranus’ bright moon Ariel and darker moons
Desdemona, Belinda, Portia, Cressida, and Puck.

Karkoschka has been studying the atmospheres of outer planets for 21 years,
first as a graduate student and since as a researcher with UA’s Lunar and
Planetary Laboratory. He has used the Hubble Space Telescope to take images
of Saturn and Titan, as well as Uranus and Neptune, to study the vertical
structure of their gases and aerosols. He made spectroscopy observations at
the European Southern Observatory in 1993 and 1995 for more such data.

Karkoschka is currently modeling Saturn’s atmosphere based on images of that
planet he took with the Hubble Space Telescope in March 2003. These images
are currently featured in the cover story of Arizona Alumnus, the winter
2004 issue.

The Space Telescope Science Institute (STScI), which released the Uranus and
Neptune images today, has electronic images files and more information
on-line at http://hubblesite.org/news/2004/05

The Space Telescope Science Institute (STScI) is operated by the Association
of Universities for Research in Astronomy, Inc. (AURA), for NASA, under
contract with the Goddard Space Flight Center, Greenbelt, MD. The Hubble
Space Telescope is a project of international cooperation between NASA and
the European Space Agency (ESA).

Related Web site