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.

Battered Tharsis Tholus Volcano On Mars

ScienceDaily (Nov. 8, 2011) — The latest image released from Mars Express reveals a large extinct volcano that has been battered and deformed over the aeons.

Tharsis Tholus Volcano - Mars

By Earthly standards, Tharsis Tholus is a giant, towering 8 km above the surrounding terrain, with a base stretching over 155 x 125 km. Yet on Mars, it is just an average-sized volcano. What marks it out as unusual is its battered condition.

Shown in images taken by the HRSC high-resolution stereo camera on the European Space Agency’s Mars Express spacecraft, the volcanic edifice has been marked by dramatic events.

At least two large sections have collapsed around its eastern and western flanks during its four-billion-year history and these catastrophes are now visible as scarps up to several kilometres high.

The main feature of Tharsis Tholus is, however, the caldera in its centre.

It has an almost circular outline, about 32 x 34 km, and is ringed by faults that have allowed the caldera floor to subside by as much as 2.7 km.

It is thought that the volcano emptied its magma chamber during eruptions and, as the lava ran out onto the surface, the chamber roof was no longer able to support its own weight.

So, the volcano collapsed, forming the large caldera.

November is a busy month for Mars exploration: Russia and NASA both plan launches this month.

Russia’s Phobos-Soil (formerly known as Phobos-Grunt) is designed to land on Phobos, the larger of Mars’ two moons, to collect samples, and return them to Earth in 2014. It also carries the first Chinese spacecraft to Mars, Yinghuo-1.

Mars Express HRSC digital elevation models of Phobos were used by Russian scientists to assess the mission’s potential landing sites and ESA is also providing telecommunications support for both Phobos-Soil and Yinghuo-1.

In return, the European scientific community will have access to data obtained by both spacecraft.

NASA’s mission is the Mars Science Laboratory, a large rover known as Curiosity, with experiments designed to detect organic molecules — past or present — on the Red Planet.

Also worth noting is the simulated Mars mission, Mars500, which ended on Friday when the hatch was opened for the first time since June 2010. For 520 days, the international crew had been working in a simulated spacecraft in Moscow.

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