Introduction
When E.T. phoned home, where did he call? If it was a local connection, Mars was the likeliest place. Although the chances are slim, scientists hold out the possibility that Martians of some sort existed – and may yet exist – on the Red Planet, pictured here. Orbiters and rovers sent to investigate have found evidence of a watery past and hints of organic compounds, key ingredients for life. Some have even suggested the probes themselves accidentally killed alien microbes. Nevertheless, the search continues. NASA’s Phoenix Mars Lander is touching down near Mars' north pole on May 25 to study the history of water ice and look for organic compounds. As tantalizing as the prospect of life on Mars is, the Red Planet isn’t the only place where alien organisms may lurk. The universe contains septillions of stars (a septillion is 1 followed by 24 zeros), and scientists suspect any number of them could harbor planets and moons with the right ingredients for life. Click on the \"Next\" arrow above to learn about seven more relatively nearby targets where scientists believe they could find E.T.
Newsvine: Where do you think E.T. calls home?
-- John Roach, msnbc.com contributor
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In Europa’s depths?
Jupiter's moon Europa has long been considered a top priority to prospect for extraterrestrial life. The satellite, pictured here, is covered in a layer of white and brown-tinged water ice. Beneath it, scientists speculate, is a liquid ocean. And where there is water, there might be life. In addition, scientists believe tidal friction between the moon and Jupiter prevents the water from freezing and perhaps accounts for the moon's highly fractured and uneven surface. Cuts to NASA's budget, however, have put proposals to explore Europa on the back burner. If E.T. lurks beneath the ice, it'll remain hidden from human eyes at least a while longer.";
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Geysers of ice
In 2006, scientists identified cold, icy geysers spewing from Saturn's moon, Enceladus – a phenomenon that put it toward the top of the list of places to look for extraterrestrial life in our solar system. Scientists said the geysers are likely fueled by liquid reservoirs located just tens of yards beneath the surface. The Cassini space probe currently zipping around Saturn and its moons also has detected organic material signatures such as methane, carbon dioxide and propane on Enceladus. Water and organics are considered key ingredients for life. Scientists speculate the third ingredient, an energy source, may come from hydrothermal vents at the bottom of moon's subsurface ocean. The blue stripes in this enhanced image of Enceladus are thought to be the cracks from which the ice geysers spew forth. ";
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The next stars over
To find E.T. beyond our own solar system, astronomers may need to look no further than the Alpha Centauri star system, just 4 light-years away. Computer models suggest that planets could form in the so-called ”habitable zone” around the second-closest in the trio of stars, Alpha Centauri B. A star’s habitable zone is the area where the temperature is just right for liquid water – and perhaps life – to exist. Astronomers said Alpha Centauri B contains plenty of heavy materials to make planets, and because the star is part of a trio, the formation of Jupiter-mass gas giants would be suppressed. Terrestrial planet formation is more likely. About five years of observation with a ground-based telescope could help astronomers determine if such planets exist. The Alpha Centauri system, pictured here, is located high in the Southern Hemisphere sky.";
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Inside a dusty disk?
Epsilon Eridani, a star somewhat cooler and smaller than our sun and located about 10.5 light years away, is known to host at least one Jupiter-sized planet, depicted here. More planets may yet be forming from a disk of dust and gas circling the star. Astronomer Frank Drake, famous for the first SETI searches, listened for radio transmissions from planets around the star in 1960. He heard none, but astronomers have not given up hope of finding aliens there. The star ranks high on the list of targets for NASA's Terrestrial Planet Finder mission, which has been postponed indefinitely due to budget woes.";
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Leading star
Epsilon Indi A, a star located about 11.8 light years from Earth, leads a list compiled by astronomers at the Carnegie Institution in Washington of nearby stars likely to have planets that could support life. The star is about a quarter smaller and slightly cooler than our sun. It was recently found to host a pair of tightly orbiting brown dwarfs, as shown in this artist's rendering. Astronomers hope to look for potential alien harbors someday with NASA's Terrestrial Planet Finder mission.";
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Not quite right?
Last April, astronomers cheered the announcement of the first planet outside our solar system that orbited its host star in the “Goldilocks zone” – a region not too hot or too cold, but just right for liquid water to exist. Liquid water is considered a key ingredient for life. Subsequent computer models suggested that the planet, called Gliese 581c, would probably be hit by runaway global warming, making things too hot for life. The same greenhouse effect, however, could make the planet's sibling, Gliese 581d, just right for liquid water and perhaps life. It orbits at a slightly farther distance from the host star, about 20.5 light-years from Earth. Astronomers are calling for more research, including a fleshing-out of the idea of the Goldilocks zone. In this artist's rendering, Gliese 581c is in the foreground.
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Sweet spot
E.T. scouts have long gazed at a star and planetary system 41 light-years from Earth, called 55 Cancri, with high hopes that a planet lies in the system’s “habitable zone,” a sweet spot where the temperature is just right for liquid water – and perhaps life – to exist. That planet's discovery was announced last November, pushing the anticipation up a notch. In this artist's rendering, the planet looms in the foreground. It is the fifth in the system discovered to date. The planet is a gas giant about half the size of Saturn and thus is unlikely to teem with aliens itself. But it could have a rocky moon with a watery surface. Or a more Earthlike planet may yet exist in the habitable gap between the new planet and another gas giant closer to the star.
Newsvine: Where do you think E.T. calls home?
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