The U.S. Postal Service has selected two images by the University of Arizona’s Erich Karkoschka for a special stamp edition highlighting the beauty of our solar system.
When Karkoschka, a senior staff scientist in the UA’s Lunar and Planetary Laboratory, persuaded NASA to point the Hubble Space Telescope at Jupiter and Uranus to gather clues about the atmospheres of the two giant gas planets, he had no idea that his images might end up years later in mailboxes across the nation and possibly the world.
On March 28, 2004, three of Jupiter’s largest moons — Io, Ganymede and Callisto — came together in a rare alignment, casting their shadows onto the Earth-facing side of the planet to form a triple eclipse.
Karkoschka had been waiting for this moment and he was ready. NASA had granted him 40 minutes — the viewing time offered by Hubble orbiting Earth once — to observe how the three moons danced around their host planet.
“Having three shadows and two moons transiting the disk of Jupiter at the same time is very rare,” Karkoschka said. “It hadn’t happened for 60 years when I made the proposal to use Hubble to observe this event.”
Hubble took that image with its “infrared eyes,” a camera developed by a team of UA astronomers and engineers, using three different optical filters. Because human eyes can’t see infrared light, those wavelengths are translated into false-color renditions of blue, green and red.
Most images of Uranus, like those taken by the Voyager 2 space probe during its flyby in 1986, revealed a hazy, pale blue disk that looked rather bland and not too exciting, said Karkoschka, who took his image of Uranus in 2003, this time using Hubble’s Advanced Camera for Surveys.
Because his image combined three filters, he was able to get a more colorful and revealing rendition of features in Uranus’ atmosphere, such as three bright red glowing clouds in the planet’s northern hemisphere.
Together with his equally colorful image of Jupiter, Karkoschka’s Uranus picture features in a special edition of stamps, “Views of Our Planets,” which the U.S. Postal Service officially will release on Tuesday at the World Stamp Show, the world’s largest philatelic event, held in the U.S. only once every decade.
Karkoschka has been researching the altitudes and structure of clouds on the giant gas planets. Once he had images taken over several years, he could see how the clouds and their altitudes changed.
Jupiter’s clouds consist mainly of ammonia crystals, while similar features spotted on Uranus are made up of frozen methane. Because it takes Uranus more than 84 Earth years to complete a trip around the Sun, studying seasonal changes takes generations of researchers.
Scientists are still a long way away from understanding the causes of those changes.
“The northern hemisphere of Uranus appears to be much more active now than the southern hemisphere,” Karkoschka said. “We don’t know why. If we wait for another 40 years for the season to change, and if then only the southern hemisphere is active, we know it’s a seasonal effect. But if the activity is still only in the northern hemisphere, then we’ll know there really is some intrinsic asymmetry at work.”
