How Villanova scientists scoped out 'new' planet for water

A pair of Villanova University astronomers had spent years studying the radiation emitted by red dwarfs - a type of star that includes the sun's nearest neighbor, Proxima Centauri.

Then, two months ago, they were let in on a big secret.

After studying a pattern of "wobbles" in the light from Proxima Centauri, an international team of scientists concluded the phenomenon was caused by a previously unknown planet. Could the Villanova scientists help determine if water might exist on its surface?

Wednesday, they and their colleagues jolted the world of astronomy with the answer: "Maybe."

The presence of water in liquid form would mean the planet, dubbed Proxima b, could theoretically harbor some form of life.

In the next few years, sophisticated new telescopes are expected to shed more light on that question, said Villanova's Edward F. Guinan and Scott G. Engle. The telescopes will allow scientists to study the planet's atmosphere for signs of gases associated with life, such as water vapor and methane.

In the meantime, the findings announced Wednesday have given new life to that age-old question: Are we alone?

"It's a huge deal," said Engle, a research assistant professor of astrophysics and planetary science.

The discovery of the planet was reported in the journal Nature.

Two companion studies on the planet's habitability, including the one to which Guinan and Engle contributed, were posted online the same day at www.proximacentauri.info.

Those studies are still undergoing review before formal publication but so far have been well-received by others in the field.

The analysis done by Guinan, Engle, and their colleagues is solid, said Ravi Kopparapu, an astrophysicist at the NASA Goddard Space Flight Center in Greenbelt, Md.

"If I were in their place, I would do the same thing," Kopparapu said.

Broadly, the analysis involved two parts. First, the authors engaged in a kind of celestial thought experiment, running through all the factors that would have to line up in order for water to be delivered to the planet, presumably by ice-laden comets.

Then they determined the likelihood that the water is still there. The key to that question is radiation.

High-energy radiation from Proxima Centauri, in the ultraviolet and X-ray portions of the spectrum, would break up water molecules in the planet's atmosphere into hydrogen and oxygen, said Villanova's Engle.

The remnants of atmosphere could then be borne away by stellar winds. The star's radiation also would heat up the planet's surface, evaporating surface water.

The team calculated the amount of high-energy radiation that the planet currently receives, based on data from the Hubble Space Telescope, NASA's Chandra X-ray Observatory, and a European X-ray satellite.

But the amount of radiation emitted by a star varies throughout its lifetime, so the researchers looked at other red dwarf stars of varying ages to model what happened with Proxima Centauri during its 5 billion-year history.

Evidence indicates that the planet may have been near the boiling point of water early on but now may be cool enough for water to exist on its surface.

Taking all this into account, the scientists estimated that Proxima b, the "new" planet, could have lost an amount of water equal to the total in all Earth's oceans.

Depending on how much water the new planet had to begin with, some might still be present, said Guinan, a professor of astrophysics and planetary science at Villanova. That result was a surprise, he said.

"I thought at first glance that it couldn't have any water left because of how active the star was in the past," he said. "There is a pathway for this planet to have water and even a climate similar to Earth's."

A big unknown is whether the planet has a strong magnetic field, which would protect it from the star's high-energy radiation.

Even if the planet is habitable, it would be a long trip. Though Proxima Centauri is the nearest star to our own solar system, it is nearly 25 trillion miles away, a distance that would take half a century to travel, given current propulsion technology.

That has not stopped people in the astronomy world from aiming higher.

In April, months before news of the planet's discovery, Russian entrepreneur Yuri Milner announced a $100 million effort to develop an unmanned, light-propelled "nanocraft" that could reach Proxima Centauri in 20 years.

"It's not science fiction," Guinan said. "It's accessible."

tavril@phillynews.com

215-854-2430 @TomAvril1