Could One of These Worlds Be E.T.’s Home?


by Gregory Mone
04.05.2012

Of the more than 700 planets discovered outside our solar system, none yet fit the description alien hunters dream about: an Earth-like planet in an Earth-like orbit around a sunlike star. But some scientists want to broaden the parameters of their search. In November a team led by Washington State University astrobiologist Dirk Schulze-Makuch devised the Planetary Habitability Index, or PHI, a scoring system for distant worlds that measures their suitability for any kind of life, not merely life as we know it. “We can’t go after only the Earth model of life,” he says. “You really want to be open-minded.”

Courtesy Habitability Laboratory at UPR Arecibo; Courtesy NASA (3)

Under Schulze-Makuch’s criteria, a faraway world racks up points if it has a solid surface and an atmosphere, which act together to support chemical reactions and deflect damaging radiation. Liquid water is not a prerequisite for a high score: A planet with liquids on the surface receives more points than a dry world, but the presence of water confers no additional advantage. “If you didn’t know that water worked on Earth,” Schulze-Makuch says, “you might think methanol would work much better for life.”

The PHI scores of bodies within the solar system reflect Schulze-Makuch’s hypothesis that the most Earth-like places are not necessarily the friendliest for life. Earth gets a near-perfect score of 0.96 on the 0 to 1 scale (it just has less available energy now than it did when life originated 4 billion years ago). But second place goes to Saturn’s moon Titan (0.64), which hosts vast lakes of liquid hydrocarbons but has surface temperatures of –300 degrees Fahrenheit. Mars, the target of more than a dozen robotic missions to hunt for signs of microbial life, comes in third at 0.59.

None of the planets yet found outside our solar system score particularly well. Gliese 581d, a rocky world nestling a cool, dim star, nets a rating of 0.43. Kepler-22b, the most Earth-like planet NASA’s Kepler space telescope has found so far, gets a similar score. However, Schulze-Makuch emphasizes that the numbers are subject to change. Astronomers have been able to determine the surface and atmospheric composition of only a few exoplanets, so for most planets the data are incomplete. Future telescopes that are powerful enough to probe these worlds, such as NASA’s proposed Terrestrial Planet Finder, should make the PHI much more useful.

Stunning vortex appears on Saturn’s moon, puzzles scientists

By Mike Wehner, Tecca

NASA’s Cassini orbiter has already taken some stunning photos of Saturn and its moons, but the latest snapshot from the multi-billion-dollar mission might be its most impressive yet. After swinging down to the southern hemisphere of Titan — Saturn’s largest moon — the high-powered orbiter captured images of a massive vortex forming at its pole, and scientists can only guess as to why it’s suddenly appeared.

The massive collection of swirling gas has gathered at Titan’s south pole, which measures approximately 3,200 miles across. The whirlwind has never before been spotted, and it remains unclear how long it has been forming. Cassini — which first arrived near Saturn in 2004 (and shot the stunning images below) — had been orbiting the moon too far north to have captured it, until now.

Photo of Titan against backdrop of Saturn

Prior to this discovery, the probe spotted images of a large “hood” on Titan’s north pole, which researchers believe is the result of cell convection — a process where dense air sinks towards the surface, pushing air at its edges upwards to create clouds. As Titan’s seasons change, scientists believe that the same mechanism may be at work at the moon’s southern pole, but they can’t be sure.

Cassini photo of Saturn

A single year on Titan lasts approximately 30 Earth years, making the study of each season a lengthy endeavor. The planet is composed of rock, water ice, and methane, making for some weather formations not typically seen here on Earth. The gigantic, swirling anomaly — which is spinning at four times the speed of the rest of the moon — appears to be yet another interesting characteristic of Saturn’s most interesting satellite.

High-contrast photo of Saturn from Cassini probe