Friday, December 31, 2010

Imaging Extrasolar Planets

While astronomers have identified over 500 planets around other stars, they're all too small and distant to fill even a single pixel in our most powerful telescopes. That's why science must rely on art to help us imagine these strange new worlds. From Spitzer Space Telescope.

While astronomers have identified over 500 planets around other stars, they're all too small and distant to fill even a single pixel in our most powerful telescopes. That's why science must rely on art to help us imagine these strange new worlds.

Even without pictures of these exoplanets, astronomers have learned many things that can be illustrated in artwork. For instance, measurements of the temperatures of many "Hot Jupiters," massive worlds orbiting very close to their stars, hint that their atmospheres may be as dark as soot, glowing only from their own heat.

While "Hot Jupiters" would be relatively dark in visible light, compared to their stars, their brightness is proportionally much greater in the infrared. Illustrating this dramatic contrast change helps explain why the infrared eye of NASA's Spitzer Space Telescope plays a key role in studying exoplanets.

As our understanding evolves, so must the artwork. Astronomers found a blazing hot spot on the exoplanet Upsilon Andromedae b that at first, appeared to face towards its star. More data has revealed that the hottest area is actually strangely rotated almost 90 degrees away, near the day/night terminator.

WASP 12b is as hot as the filament in a light bulb, and would be blazing bright to our eyes. Most interestingly, if it proves to have a strongly elliptical orbit, as first thought, calculations show it would be shedding some of its outer atmosphere into a gassy disk around its star.

Computer simulations of HD 80606 b, constrained by global infrared measurements, are helping astronomers to better understand the details of how its atmosphere circulates. These computations can feed back into the artwork helping us produce more plausible illustrations.

The closest known exoplanet is 10 light years away in the Epsilon Eridani system. Excess infrared light found here by Spitzer has led astronomers to conclude it also has two asteroid belts, hinting at the possibility of other small, rocky worlds.

Perhaps the strangest known planetary system orbits the pulsar PSR B1257+12, the neutron star remnant of a supernova. Astronomers have detected three planets that either survived the explosion, or formed afterwards in this region filled with spinning magnetic fields and hostile radiation.

Until the day we can explore other star systems as thoroughly as our own, exoplanet art inspired by the real science will help fill in the gaps in our imagination.

Tuesday, December 14, 2010

Ice Volcano on Titan

NASA's Cassini spacecraft has found possible ice volcanoes on Saturn's moon Titan that are similar in shape to those on Earth that spew molten rock.

Topography and surface composition data have enabled scientists to make the best case yet in the outer solar system for an Earth-like volcano landform that erupts in ice. The results were presented today at the American Geophysical Union meeting in San Francisco.

"When we look at our new 3-D map of Sotra Facula on Titan, we are struck by its resemblance to volcanoes like Mt. Etna in Italy, Laki in Iceland and even some small volcanic cones and flows near my hometown of Flagstaff," said Randolph Kirk, who led the 3-D mapping work, and is a Cassini radar team member and geophysicist at the U.S. Geological Survey (USGS) Astrogeology Science Center in Flagstaff, Ariz.

Scientists have been debating for years whether ice volcanoes, also called cryovolcanoes, exist on ice-rich moons, and if they do, what their characteristics are. The working definition assumes some kind of subterranean geological activity warms the cold environment enough to melt part of the satellite's interior and sends slushy ice or other materials through an opening in the surface. Volcanoes on Jupiter's moon Io and Earth spew silicate lava.

Some cryovolcanoes bear little resemblance to terrestrial volcanoes, such as the tiger stripes at Saturn's moon Enceladus, where long fissures spray jets of water and icy particles that leave little trace on the surface. At other sites, eruption of denser materials might build up volcanic peaks or finger-like flows. But when such flows were spotted on Titan in the past, theories explained them as non-volcanic processes, such as rivers depositing sediment. At Sotra, however, cryovolcanism is the best explanation for two peaks more than 1,000 meters (3,000 feet) high with deep volcanic craters and finger-like flows.

"This is the very best evidence, by far, for volcanic topography anywhere documented on an icy satellite," said Jeffrey Kargel, a planetary scientist at the University of Arizona, Tucson. "It's possible the mountains are tectonic in origin, but the interpretation of cryovolcano is a much simpler, more consistent explanation."

Kirk and colleagues analyzed new Cassini radar images. His USGS group created the topographic map and 3-D flyover images of Sotra Facula. Data from Cassini's visual and infrared mapping spectrometer revealed the lobed flows had a composition different from the surrounding surface. Scientists have no evidence of current activity at Sotra, but they plan to monitor the area.

"Cryovolcanoes help explain the geological forces sculpting some of these exotic places in our solar system," said Linda Spilker, Cassini project scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "At Titan, for instance, they explain how methane can be continually replenished in the atmosphere when the sun is constantly breaking that molecule down."