Hunt is on for another planet Earth

Villanova University astronomer Edward Guinan has had some adventures over the years, from scrounging for black-market cement to make Iran's first high-powered telescope to discovering the rings around Neptune at an observatory in New Zealand.

But none of this will compare, he said, to witnessing the discovery of the first Earth-like planet orbiting another star - a feat that a NASA satellite called Kepler could do within the coming weeks.

In the early 1990s, Guinan wrote a paper suggesting the planet-hunting method that Kepler is employing - looking for tiny eclipses as planets pass in front of their stars. Such eclipses, called transits, can show up as dips in a star's brightness.

More recently, he urged NASA to shift the focus of the project to include a number of stars much dimmer than our sun - red dwarfs. That's where he is betting the first Earths will be found.

"I never thought I'd live to see this," said Guinan, 67, who is optimistic about the project's success.

The space-based Kepler telescope was launched in March and has begun monitoring about 100,000 stars in a region about twice the size of the Big Dipper's scoop.

While Kepler was designed to concentrate on bright stars like the sun, it will now also look at 4,000 red dwarfs, said Jon Jenkins, a principal investigator on the project. It also will look at 40,000 so-called K stars, which Guinan calls orange dwarfs. They are brighter than red dwarfs but dimmer than our sun.

They are also great prospects for habitable planets, said Guinan.

These lesser stars are being included thanks to the influence of Guinan and Andrej Prsa, a Villanova post-doctoral researcher who developed an artificial intelligence system that is helping Kepler distinguish real planets from false alarms.

Planets are more than a billion times dimmer than the stars they orbit, which is why it's so hard to see them.

Even indirect methods are tricky. A transit of another Earth would dim a star such as the sun by less than a hundredth of one percent.

This is one reason Guinan is excited about red dwarfs, also called M dwarfs. They hold less than half the sun's mass and give off less than a tenth of its energy.

If an Earth-size planet passes in front of a red dwarf, it will cause a relatively big dip in the star's brightness compared with what Kepler would see if the same planet transited a bright star like the sun.

Another reason red dwarfs are so interesting is that they make up about 80 percent of the stars in the galaxy.

In the last two years, astronomers have begun to find some of the most Earth-like planets yet around red dwarfs - not quite Earths, but a class called "super Earths." Ranging from two to about 20 times the size of our planet, super Earths may be covered in ice, rock, or even oceans.

But could planets around such low-wattage stars sustain life? Guinan's calculations show it's possible.

For the last seven years, he's been exploring the life question, along with his colleague Scott Engle, as part of a program titled "Living With a Red Dwarf." This project encompasses not just theoretical work but a comprehensive study of red dwarfs using an automated "Four University" telescope in Arizona, as well as data from the Hubble Space Telescope and several NASA and European satellites that observe the sky in ultraviolet light and X-rays.

Guinan works with undergraduates as well as Engle, a Villanova graduate now officially with James Cook University in Australia.

Guinan presented the most recent fruits of the program last month at a meeting in Baltimore billed as "The Search for Life in the Universe."

He said his interest in astronomy grew from a childhood taste for science fiction. He built his first telescope at 10. "It was kind of a crappy telescope," he said, though he could observe the moon and see the rings around Saturn.

As a teenager, he was inspired by Sputnik to build his own rockets, launching them from Hog Island. He once attached a cockroach in an attempt to send a test animal into orbit.

As a graduate student, he traveled to New Zealand in 1967, hoping to observe a rare astronomical event in the southern sky - the passage of Neptune in front of a star.

His assignment was to more accurately calculate the planet's size by the way it blocked the starlight, but by a stroke of luck he became the first person to chart rings around Neptune, he said.

But his luck turned on his long route home, he said, when the charts he'd made of the data were stolen in the Soviet Union.

He still had some IBM data cards, he said, and made a tentative announcement at an astronomy meeting.

The rings were later confirmed when the Voyager spacecraft got a closer look.

Between 1975 and 1978, before the Iranian revolution, he took on the job of assembling a telescope and starting an astronomy program in Iran, partly because his archaeologist wife wanted to work there. He still goes back every year.

Before he focused on red dwarfs, he spent 25 years studying the sun and its effect on the planets. In a program called "The Sun in Time," he showed how the early sun spun faster than today and sent out more X-rays.

The sun is about halfway through its life. But the nuclear reactions that power it are speeding up and making the sun hotter. In a billion years, the sun could destroy life on Earth, Guinan said, turning our blue planet into another Venus.

In five billion more years, he said, it will swell into a red giant, engulfing the Earth, before burning out.

During the 1990s, as the first planets were detected around other stars, he shifted his focus to red dwarfs and their far different life-cycles.

Red dwarfs burn more slowly and could live for hundreds of billions of years. Since the universe is only 13.7 billion years old, said Guinan, we can't see any old red dwarfs. "They're all teenagers."

But early in life, they can still be unruly, blasting 1,000 times their normal ultraviolet radiation during a flare, he said.

This poses a problem for life, especially since planets would have to orbit extremely close to these dim stars - about a tenth the Earth's distance from the sun - to avoid perpetual freezing. Luckily, it appears red dwarfs settle down after a billion years.

Still, conditions on such a close-orbiting planet would be a little weird. The years would fly by every few Earth days, for example.

This is great from the perspective of the Kepler scientists seeking temperate planets, because the transits they seek would happen every few days.

But for life, there's another problem. Planets that close to their stars could stop rotating, thanks to friction created by the gravitational pull between planet and star.

This happened to the moon with respect to the Earth - we always see the same face.

But even that doesn't rule out life, said Guinan. If a planet has a thick enough atmosphere, pockets of warm air would rise and cool air would sink, creating circulation.

Living beings would probably thrive more on the dark side, since they could avoid flares with their UV and X-rays, he said. Or life might colonize areas of perpetual dusk or twilight.

Sometime in the far future, when all the material for making new stars runs out and all the faster-burning stars have died, our galaxy will be made of nothing but red dwarfs.

And eventually those, too, will die.

That still leaves plenty of time for the galaxy's inhabitants to find each other. For this small but inhabited planet, the Kepler mission represents a giant leap. So far, everything has gone as well as anyone could have dreamed, says Guinan.

On May 13, astronomers officially started their hunt for other Earths.