Today astronomers are kicking off a worldwide marathon to look for messages from any alien civilizations that might inhabit nearby stars.

Astronomers are aiming radio and optical telescopes at selected targets in the chance a "Hello, how are you?" message comes our way. The hypothesized radio or laser pulse messages would have to have been transmitted Earthward within a radius of 100 light-years. Participating countries included Australia, Japan, Korea, Italy, the Netherlands, France, Argentina, and the United States.

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This survey is being done in commemoration of the first SETI (Search for Extraterrestrial Intelligence) experiment, Project Ozma, which was launched in April 1960 by radio astronomer Frank Drake. He named it after the princess Ozma in the L. Frank Baum series: "The Land of Oz."

Shin-ya Narusawa of Nishi-Harima Astronomical Observatory in Japan launched the commemorative Project Dorothy, named after the Oz heroine memorialized by actress Judy Garland in the 1939 film musical production of Baum's "The Wizard of Oz."

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The SETI Institute will observe five target stars using the new Allen Telescope Array (ATA), located in northern California. The ATA will examine these stars between 1:00 a.m. and 5:00 a.m. Pacific Daylight Time, on November 6.

Any chance for success? Let’s take a look at the ATA's target stars from nearest to farthest:

Epsilon Eridani

One of Project Ozma’s very first targets, this orange dwarf star lies just 11 light-years away. It has two belts of rocky and icy debris. A Jupiter-size planet has been confirmed Inside the innermost belt. The gas giant world is in a very elliptical orbit that shuttles it from a distance just beyond that of Mars' orbit to closer than Venus’ orbit is to the sun. And, this carries the planet inside the star's habitable zone briefly once every 12 years. Any accompanying moons would alternately bake and freeze over the roller-coaster orbit. The star is estimated to be only 600 million years old. That’s way too young for the evolution of technological intelligent life as we know it.

Tau Ceti

At 12 light years away, Tau Ceti is a sun-like star encircled by a thick dust disk similar to our Kuiper belt that lies beyond Neptune. The star’s habitable zone is at about the distance Venus is from our sun. This was another Ozma target, but no planets have been discovered to date. Depending on the dynamics of any existing gas giant planets in the system, the thick disk might bombard any Earth-like world with cometary debris. This might disrupt biological evolution with a successive chain of mass extinctions. If intelligent life arose it would have to advance quickly to achieve the space technology needed for avoiding its own destruction by comet showers.

HD 69830

This orange dwarf star is 41 light-years away in the constellation of Puppis. It has a large asteroid belt, first discovered by NASA’s Spitzer Space Telescope in 2005. The belt is kept gravitationally corralled by three Neptune sized plants. One of these worlds lies in the star’s habitable zone. It could conceivably have a Titan-like moon that would be a home for life.

55 Cancri

At a distance of 41 light years, I’d buy a one-way ticket to this binary star system. The primary star 55 Cancri A is a solar-type star. Best of all, it’s the age or our sun and has a full-blown planetary system and Kuiper belt outer rim. The red dwarf companion star is 100 billion miles away, too far to disrupt a planetary system.

To date five know planets orbit the star within the radius of Jupiter’s orbit. A hot Jupiter and super-Earth mass planet orbit very close to the star. A nearly Saturn-mass planet lies within the star’s habitable zone. This would be a sweet spot to go looking for large habitable moons capable of possessing an atmosphere.

And there is room for yet undetected terrestrial mass planets near the habitable zone. I was so intrigued by this star I had my colleague, space artist Lynette Cook, do an illustration (above) for our 2005 book Infinite Worlds. 55 Cancri will be a likely target for an interstellar probe in the coming centuries.

Eta Arietis

Located 98 light-years away this seething star is eight-times more luminous than the sun. Its rapidly migrating habitable zone would sweep outward past the distance Jupiter is from our sun. No planets have been found here, yet. With a projected lifetime of roughly 2 billion years, this star is too short-lived for biological evolution as we know it. (Earth did not evolve multicelled organisms until nearly 4 billion years after its formation.)

So is anyone sending us an interstellar "tweet" from any of these stars? I’d place my money on 55 Cancri. Any civilization here would be intrigued to explore their planetary system. They would be enticed to send a probe to the dim red dwarf companion to explore any planets. Viewed from the surface of a planet in the 55 Cancri system our sun would be a bright white star near the burning blue-white star Sirius. It would no doubt get the attention of Cancri sky watchers. But would they be at a technological intersection in time where they are signaling us now? Just wait.

Image credit: AKA, SAO, NASA

Artwork copyright: Lynette Cook