NASA / Ames / JPL-Caltech

This artist's concept depicts Kepler-62f, a planet 1.4 times the size of Earth that circles in the habitable zone of its host star. The small shining object at right is Kepler-62e, another potentially habitable world in the five-planet system.

By Clara Moskowitz
Space.com

Astronomers are closer than ever to finding a true alien Earth, though the process may be slowed by budget cuts, scientists told members of Congress late last week.

Officials from NASA, the National Science Foundation and the SETI (Search for Extraterrestrial Intelligence) Institute gave testimony to the House Science, Space and Technology Committee on Thursday about the state of exoplanet research, saying researchers were closing in on planets around other stars that are the same size and distance from their suns as Earth.

"Within the next few years, we will have the privilege of answering this age-old question: In the universe, is there anywhere else like home?" said Laurance Doyle, principal investigator for the Center for the Study of Life in the Universe at the SETI Institute. [6 Ways to Discover Alien Planets]

Astronomers have already found more than 800 planets orbiting distant stars. Most of them are large gas giants or worlds a bit bigger than ours called Super Earths. A few, though, are small enough to be rocky, and some are almost Earth-like. Within the coming months and years, scientists hope to find a terrestrial planet that could host liquid water.

"The next step for detecting life in the universe will be most likely biomarkers," Doyle said, referring to elements such as oxygen detected in the atmospheres of alien planets that might indicate the presence of living organisms on its surface. "Oxygen is indicative of plant life, possibly animal life, and maybe even intelligent life. It could be that the first detection of extraterrestrial life may be forests."

Yet observing biomarkers probably requires newer, larger telescopes than those currently available — a daunting prospect, given dwindling federal budgets for science.

"There's no question the budget environment has caused us to make some tough choices," John Grunsfeld, associate administrator of NASA's Science Mission Directorate, told members of Congress. "We're very fortunate that we have high-value observatories on orbit. One of the things we have to prioritize is, what are we going to keep operating on orbit?"

Older telescopes may have to be shut down due to a lack of funds, and the development of newer tools may be delayed, he said. For example, because of budget cuts, NASA has had to push back the start of the new Transiting Exoplanet Survey Satellite, also known as TESS, by about six months.

The National Science Foundation (NSF), which funds ground-based telescopes, faces similar difficulties.

"Some of the new observatories are more expensive to operate than the older observatories we used to have," said James Ulvestad, director of NSF's Division of Astronomical Sciences. "In order to operate those new tools, what sometimes has to give in the short term is the research grants to individual investigators."

For example, he said, the NSF has invested significantly in the new ALMA telescope in Chile(ALMA stands for Atacama Large Millimeter/submillimeter Array), which is a joint project among North America, Europe and Asia. Yet the NSF's budget woes mean it might not have enough money to give adequate grants to U.S. researchers applying for telescope time at ALMA.

"If we're not able to fund out investigators to do the research, some of the best exoplanet science done with that telescope might be done by our international partners, and not by our own investigators," Ulvestad said.

Many members of Congress expressed excitement for alien-planet research, and sympathy for the fiscal challenges the science agencies faced.

"Until the American people can help us address the entire piece of the federal spending pie, people who depend on discretionary spending are going to continually feel pinched, which is problematic," said Research Subcommittee Chairman Larry Bucshon, R-Ind. He asked the scientists how to communicate the value of their research to his constituents. "What can I tell people why what you're doing is important to the American people?"

"Investments in NASA, the NSF, in basic research, is really the investment in our future, and it's not an abstract thing," Grunsfeld, a former astronaut, responded. Money spent developing high-tech instruments for NASA telescopes, for example, stimulates the industrial innovations that are at the core of our country's prosperity, he said. "If we start cutting back on the basic research, on trying to solve very hard problems … we'll just start losing ground on the kinds of innovations that drive our economy."

Follow Clara Moskowitz on Twitter and Google+. Follow us @Spacedotcom, Facebook and Google+. Original article on Space.com.

• 9 Exoplanets That Could Host Alien Life
• The Search For Another Earth | Video
• The Strangest Alien Planets (Gallery)

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David A. Aguilar (CfA)

A planetary nebula surrounds a white dwarf star with a hypothetical habitable planet in orbit.

By Irene Klotz
Discovery

Earth-sized planets that host life should be far easier to find around parent stars that are white dwarfs, the ultimate incarnations of stars like the sun, a new study shows.

Alien worlds could circle dying white dwarf stars, this NBCNews.com report explains.

White dwarfs are the dense stellar cores that remain after a sunlike star runs out of fuel and goes through its expanding, red giant phase, a process that will consume its inner planets. In our solar system, for example, Mercury, Venus and possibly Earth will be destroyed when the sun evolves into a red giant some 4.5 billion years from now.

But the system won't necessarily be doomed.

PICTURES: Exquisite Exoplanetary Art

Outer planets may migrate inward, closer to the star, and new worlds may form. Not all will be in stable orbits, but an Earth-sized world located about 1 million miles away from a host white dwarf star would have a temperature roughly the same as Earth’s. At that distance, the planet could have liquid water on its surface, a condition believed to be necessary for life.

Scientists are developing techniques to scan the atmospheres of planets beyond the solar system for oxygen and other chemical signs of life. It's a laborious and time-consuming process to separating out light passing through a planet’s atmosphere from all the background starlight.

But Earth-sized planets circling white dwarf stars, which are themselves about as big as Earth, make for much bigger needles in extrasolar planet haystacks.

ANALYSIS: Could Dead Stars Support Life? 

Avi Loeb, a theorist at the Harvard-Smithsonian Center for Astrophysics, figures the upcoming James Webb Space Telescope, a successor to the Hubble observatory, would need only about five hours of observing time to look for biomarkers in the atmosphere of a planet circling in a white dwarf’s habitable zone.

“Usually the background star is so much brighter, it’s so much bigger than the planet that absorption (of light) due to the atmosphere is a very small signal that you have to fish out of the much more prominent emission from the background star,” Loeb told Discovery News.

“In the case of the white dwarf, it’s sort of the best of all circumstances, where the object that is blocking the star is of the same size as the star itself. That offers the best prospect for detecting the absorption due to the atmosphere, relative to the background light,” he said.

Like NASA’s planet-hunting Kepler Space Telescope, the technique would only work for white dwarf systems that are aligned relative to the observatory’s line of sight so that orbiting planets pass in front of, or transit, their parent stars.

While the star is eclipsed, some light will pass through the planet’s atmosphere -- if it has one -- and leave telltale chemical fingerprints that can be detected by instruments in a telescope.

“If we happen to be situated so that we can see an eclipse, then the planet would block a substantial fraction of the light from the white dwarf. Then we can basically use the light that is passing through the atmosphere to figure out what the atmosphere is made of,” Loeb said.

VIDEOS: Aliens and Other Space Mysteries

Of key interest would be detections of oxygen, which on Earth is a clear sign of life from photosynthesis by plants.

“The only reason we have oxygen in the atmosphere right now is because of life,” Loeb said. “If you remove life from Earth, then within 1 million years or so, the oxygen will be completely depleted. It will make all kinds of molecules of oxidized metals, for example, and it will be consumed from the atmosphere.”

Scans of exoplanets’ atmospheres also could find water vapor and other potential biomarkers.

While there is not yet any direct evidence of planets circling white dwarfs, astronomers believe they exist. Previous studies have shown that as many as 30 percent of white dwarf stars have heavy elements on their surfaces, presumably from rocky bodies that broke up relatively soon after the white dwarf formed.

PICTURES: Exquisite Exoplanetary Art

A planet could find a stable orbit in white dwarfs’ habitable zone, one that would have it circle its parent star in just 10 hours.

“I’m not saying that we definitely know that such planets are there, but it’s quite plausible that the system after a while cleans itself up and for over a billion years or more, it may have stable Earth-mass planets,” Loeb said.

“It sounds like a reasonable extrapolation for what we’ve seen,” added astronomer Marc Kuchner, with the Exoplanets and Stellar Astrophysics Laboratory at NASA’s Goddard Space Flight Center in Greenbelt, Md.

“There’s no reason to think you wouldn’t find one now and then," Kuchner told Discovery News.

The research will be published in an upcoming edition of the Monthly Notices of the Royal Astronomical Society and is available online via the arXiv preprint service.

Karen Teramura (With Adaptation, Artist's impression by Karen Teramura (UH Institute for Astronomy), background photo by Wei-Hao

The widest binaries and triple systems have very elongated orbits, so the stars spend most of their time far apart. But once in every orbital revolution they are at their closest approach.

By Mike Wall, SPACE.com

Alien planets born in widely separated two-star systems face a grave danger of being booted into interstellar space, a new study suggests.

Exoplanets circling a star with a far-flung stellar companion — worlds that are part of "wide binary" systems — are susceptible to violent and dramatic orbital disruptions, including outright ejection, the study found.

Such effects are generally limited to sprawling planetary systems with at least one distantly orbiting world, while more compact systems are relatively immune. This finding, which observational evidence supports, should help astronomers better understand the structure and evolution of alien solar systems across the galaxy, researchers said.

"The fact that planets observed within wide binaries tend to have more eccentric (or 'excited') orbits than those around isolated stars tells us that wide binaries do often disrupt planetary systems," lead author Nathan Kaib, of Northwestern University and the University of Toronto, told SPACE.com via email. [ The Strangest Alien Planets (Gallery) ]

"Thus, we believe most planetary systems are extended, with outer planets orbiting at tens of AU from their host stars," Kaib added. (One AU, or astronomical unit, equals the distance from Earth to the sun — about 93 million miles.)

The study was published Jan. 6 in the journal Nature and will be presented by Kaib at the 221st meeting of the American Astronomical Society in Long Beach, Calif., on Jan. 7.

Shifting stellar orbits
Two-star systems occur commonly throughout our galaxy; indeed, astronomers think the Milky Way harbors about as many binary systems as single stars. Recently, astronomers have begun discovering planets in binary systems, some of them "Tatooine" worlds with two suns in their skies, like Luke Skywalker's home planent in the "Star Wars" films.

Many double-star systems throughout the galaxy are wide binaries, in which 1,000 AU or more separate the stellar companions on average.

The distance between stars in a wide binary often changes dramatically over time, however, since their orbits around a common center of mass can be far from circular.

"The stellar orbits of wide binaries are very sensitive to disturbances from other passing stars as well as the tidal field of the   Milky Way," Kaib said in a statement. "This causes their stellar orbits to constantly change their eccentricity, their degree of circularity. If a wide binary lasts long enough, it eventually will find itself with a very high orbital eccentricity at some point in its life.”

Eccentric orbits bring the two stars quite close together from time to time, even if the wide binary has a large average separation distance. And these close encounters can wreak havoc on planetary systems, the researchers found after performing about 3,000 computer simulations. 

In one set of runs, for example, the team added a wide-binary companion to our own solar system. In nearly half of the simulations, at least one giant planet — Jupiter, Saturn, Uranus or Neptune — got booted out into space.

Signficant orbital disruption generally takes hundreds of millions or billions of years to manifest, Kaib and his colleagues calculated.

"Consequently, planets in these systems initially form and evolve as if they orbited an isolated star," Kaib said. "It is only much later that they begin to feel the effects of their companion star, which often times leads to disruption of the planetary system."

Shedding light on extrasolar systems
Such destabilization, which is more dramatic in wide binaries than in more tightly orbiting two-star systems, does not always take the form of planetary ejection. Often, exoplanets just get tugged from their orginal, near-circular orbits into more eccentric ones, the simulations showed.

The researchers also looked at orbital eccentricities of actual exoplanets. The team found that planets in wide binaries have more eccentric orbits than worlds that circle single stars, suggesting the computer models are on the money.

"The eccentric planetary orbits seen in these systems are essentially scars from past disruptions caused by the companion star," co-author Sean Raymond, of the University of Bordeaux and the National Center for Scientific Research in France, said in a statement.

The team's computer simulations further suggest that these disruptions generally happen only in planetary systems that extend at least 10 AU or so from the host star.

Taken together, the observational and modeling results imply that many extrasolar systems harbor distantly orbiting worlds, though such planets are tough for astronomers to detect at the moment, researchers said.

"Given that most planet-detection campaigns cannot detect planets beyond 5-10 AU from their host stars, our results provide new clues about the characteristics of planetary systems in a regime that is poorly constrained by current observations," Kaib told SPACE.com. "We believe that planets orbiting at distances of 10 AU or further from their host stars are common."

Follow SPACE.com senior writer Mike Wall on Twitter @michaeldwall or SPACE.com@Spacedotcom. We're also on Facebook and Google+.

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