Planets of Ancient Red Dwarf Stars –“At SETI’s ‘Magic Frequencies’ of Advanced Civilizations”

 

 

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The SETI Institute is putting old wine in a new bottle, repackaging a decade-old suggestion that planetary systems orbiting red dwarfs — dim, long-lived stars that are on average billions of years older than our sun — are worth investigating for signs of advanced extraterrestrial life. The star that’s closest to our sun, Proxima Centauri, is a red dwarf. A variety of observing efforts, including Cornell's Pale Red Dot initiative, are looking for habitable planets around Proxima Centauri (shown above).


“Red dwarfs – the dim bulbs of the cosmos – have received scant attention by SETI scientists in the past,” SETI Institute engineer Jon Richard said today in a news release announcing the initiative. “That’s because researchers made the seemingly reasonable assumption that other intelligent species would be on planets orbiting stars similar to the sun.”

 

“This may be one instance in which older is better,” said astronomer Seth Shostak of California-based SETI, a private, non-profit organization which stands for Search for Extraterrestrial Intelligence. “Older solar systems have had more time to produce intelligent species.” A super-Earth known as Kapteyn b that orbits an 11.5 billion-year-old red dwarf, for example, makes the star and the planet 2.5 times older than Earth.]

The two-year project involves picking from a list of about 70,000 red dwarfs and scanning 20,000 of the nearest ones, along with the cosmic bodies that circle them using the SETI Institute’s Allen Telescope Array in the High Sierras of northern California, a group of 42 antennas that can observe three stars simultaneously.

“We’ll scrutinize targeted systems over several frequency bands between 1 and 10 GHz,” said SETI scientist Gerry Harp. “Roughly half of those bands will be at so-called ‘magic frequencies’ — places on the radio dial that are directly related to basic mathematical constants. It’s reasonable to speculate that extraterrestrials trying to attract attention might generate signals at such special frequencies.”

For a long time, scientists ruled out searching around red dwarfs because habitable zones around the stars are small, and planets orbiting them would be so close that one side would be constantly facing the star, making one side of the planet very hot and the other quite cold and dark.

But more recently, scientists have learned that heat could be transported from the light side of the planet to the darker side, and that much of the surface could be amenable to life.

“In addition, exoplanet data have suggested that somewhere between one sixth and one half of red dwarf stars have planets in their habitable zones, a percentage comparable to, and possibly greater than, for Sun-like stars,” said the statement.

The brightest of Red Dwarfs are a tenth as luminous as the sun, and some are just 0.01 percent as bright, but account for three-quarters of all stars, with 6 percent or more of all red dwarfs having potentially habitable, Earth-sized planets.

 

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The predominant stars in globular clusters of the Milky Way are faint, long-lived red dwarfs. Any potentially habitable planets they host would orbit nearby and be relatively safe from stellar interactions. "A globular cluster might be the first place in which intelligent life is identified in our galaxy," says Rosanne DiStefano of the Harvard-Smithsonian Center for Astrophysics (CfA). Globular star clusters are extraordinary in almost every way. Globular clusters, which are found in the halo of a galaxy, contain considerably more stars than the less dense galactic, or open clusters, which are found in the disk. They're densely packed, holding a million stars in a ball only about 100 light-years across on average. They're old, dating back almost to the birth of the Milky Way. And according to new research, they also could be extraordinarily good places to look for space-faring civilizations.

"Once planets form, they can survive for long periods of time, even longer than the current age of the universe," explains DiStefano, who presented this research today in a press conference at a meeting of the American Astronomical Society.

So if habitable planets can form in globular clusters and survive for billions of years, what are the consequences for life should it evolve? Life would have ample time to become increasingly complex, and even potentially develop intelligence.

Such a civilization would enjoy a very different environment than our own. The nearest star to our solar system is four light-years, or 24 trillion miles, away. In contrast, the nearest star within a globular cluster could be about 20 times closer – just one trillion miles away. This would make interstellar communication and exploration significantly easier.

"We call it the 'globular cluster opportunity,'" says DiStefano. "Sending a broadcast between the stars wouldn't take any longer than a letter from the U.S. to Europe in the 18th century. Interstellar travel would take less time too. The Voyager probes are 100 billion miles from Earth, or one-tenth as far as it would take to reach the closest star if we lived in a globular cluster. That means sending an interstellar probe is something a civilization at our technological level could do in a globular cluster," she adds.

The closest globular cluster to Earth is still several thousand light-years away, making it difficult to find planets, particularly in a cluster's crowded core. But it could be possible to detect transiting planets on the outskirts of globular clusters. Astronomers might even spot free-floating planets through gravitational lensing, in which the planet's gravity magnifies light from a background star.

A more intriguing idea might be to target globular clusters with SETI search methods, looking for radio or laser broadcasts. The concept has a long history: In 1974 astronomer Frank Drake used the Arecibo radio telescope to broadcast the first deliberate message from Earth to outer space. It was directed at the globular cluster Messier 13 (M13) shown at the top of the page.

The Daily Galaxy via SETI Institute, AFP, Harvard-Smithsonian Center for Astrophysics

Image credits: CfA, NASA, ESA and K. Luhman (Penn State University), and wikipedia/commons

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