Nov. 30, 2010 at 9:59 PM ET
Temperature readings from the Cassini orbiter support the view that warmth is welling up through cracks in the icy surface of Enceladus, one of Saturn's most intriguing moons.
The readings were taken by the 6.4-ton spacecraft's infrared spectrometer and high-resolution camera during an August flyby, and discussed today in a series of news releases and advisories. In an e-mailed alert, Cassini imaging team leader Carolyn Porco said a "phenomenal amount of heat is emerging" through the south polar fractures known as tiger stripes.
The hot spots might not sound all that hot: The warmest areas registered surface temperatures of 120 degrees below zero Fahrenheit, or 190 Kelvin. But Porco said that's staggeringly higher than the coldest temperatures in the south polar terrain, which dip as low as 365 degrees below zero F (52 Kelvin). She called particular attention to a warm fissure known as Damascus Sulcus.
The readings indicate that the relatively warm material cools off quickly as you look farther away from Damascus' central trench. The heat also varies dramatically within just a few miles running along the trench. An associate on the imaging team, Cornell University's Paul Helfenstein, was quoted as saying that the warm section of Damascus Sulcus "is among the most structurally complex and tectonically dynamic of the tiger stripes."
So what's behind the heating? Porco said it's "undoubtedly the result of the tidal flexing of Enceladus brought about by its orbital resonance with Dione," another one of Saturn's more than 60 moons. "However, details of this heating process are still unclear and are being studied at this very moment," she added.
The temperature-coded picture of the Alexandria and Cairo fissures reveals another intriguing feature: an isolated warm spot toward upper left, just beyond the fissures' "split ends."
"The ends of the tiger stripes may be the places where the activity is just getting started, or is winding down, so the complex patterns of heat we see there may give us clues to the life cycle of tiger stripes," said John Spencer, a Cassini team member based at the Southwest Research Institute in Boulder, Colo.
Previous observations from Cassini have confirmed that geysers of water ice are welling up from the tiger stripes. The latest views add to the evidence suggesting that water or slush is pushing up through the fissures. And if there's a hidden ocean of water beneath the surface ice, could there be life as well?
A definitive answer to that question will have to be left to follow-up space missions. The August flyby served as Cassini's last chance to observe the active south polar region in sunlight. NASA says it was also Cassini's last chance to do remote thermal sensing at Enceladus until 2015. "The geometry of the many flybys between now and 2015 will not allow Cassini to do thermal scans like theses, because the spacecraft will be too close to scan the surface and will not view the south pole," NASA said in today's advisory.
A particularly close flyby took place today, when Cassini came within 30 miles (48 kilometers) of Enceladus' surface. Images from that flyby should be coming down over the next few days.
Enceladus isn't the only Saturnian moon in Cassini's spotlight: Today the spacecraft's science team also released images of Tethys, another moon that was observed during an August flyby. Just last week, Rhea and its thin, oxygen-rich atmosphere were in the news. And over the past couple of days, Cassini has gotten some good looks at Hyperion, a moon that's 165 miles wide (266 kilometers wide) and shaped like a potato.
For much, much more about the recent revelations, check out NASA's Cassini mission webpage as well as the online home for Cassini's imaging team. And be sure to check out our "Best of Cassini" slideshow.