NASA's Kepler planet-hunting probe has identified two potentially habitable planets only a little bigger than Earth, circling a star that's 1,200 light-years away. The planets could conceivably be covered by a global ocean, and they may well lead the growing list of alien worlds that can host life as we know it.

"These two planets are our best candidates for planets that might be habitable," said Bill Borucki, a space scientist at NASA's Ames Research Center who is the principal investigator for the $600 million Kepler mission.

The two habitable-zone planets, Kepler-62e and Kepler-62f, are part of a five-planet system that lies in the constellation Lyra, within a patch of sky that's been monitored by the Kepler space telescope over the past four years. The Kepler-62 parent star is about two-thirds the size of our own sun and about a fifth as bright.  Three of the star's confirmed planets circle the star in orbits so close that they'd be too hot for life. But the e and f planets are considered to lie in a zone where liquid water could exist, a ring of space that's defined as the habitable zone.

Water worlds?
Two members of the Kepler science team say their modeling suggests the two planets could be "water worlds" — with no land in sight.

"These planets are unlike anything in our solar system. They have endless oceans," Lisa Kaltenegger, an astronomer at the Max Planck Institute for Astronomy and the Harvard-Smithsonian Center for Astrophysics, said in a news release. "There may be life there, but could it be technology-based like ours?"

The report on the Kepler-62 system was published online on Thursday by the journal Science, and was the focus of a NASA news conference timed to coincide with publication. The water-world analysis, authored by Kaltenegger and Harvard's Dimitar Sasselov and Sarah Rugheimer, is contained in a separate paper that has been accepted for publication in The Astrophysical Journal.

The characterization of the two planets' habitability is based on an analysis of their size, plus what's known about the parent star. The Kepler data can show how wide a planet is, and how quickly it makes its orbit, by analyzing the telltale dips in light as the planet passes over its parent star. But Kepler can't make direct observations of a planet's mass. So, in Kepler-62's case, scientists had to make educated guesses about the planets' mass, composition and whether they had atmospheres.

Kepler-62e is 1.6 times as wide as Earth and orbits its star every 122.4 Earth days. Kepler-62f is 1.4 times Earth's width, with an orbital period of 267.3 Earth days. "It's highly likely they're rocky planets," Borucki told NBC News. "They might be water worlds, but they are so different, we just don't know."

David A. Aguilar / CfA

This artist's conception shows Kepler-62f as an ice-covered world, and Kepler-62e as an Earthlike planet with dense clouds. Other planets follow closer-in orbits and are not considered habitable.

NASA Ames / JPL-Caltech

The diagram compares the planets of the inner solar system to Kepler-62, a five-planet system about 1,200 light-years from Earth in the constellation Lyra. The five planets of Kepler-62 orbit a star classified as a K2 dwarf, measuring two-thirds the size of the sun and one-fifth as bright.

What would life be like?
Astrobiologists say the fact that the planets are bigger than Earth wouldn't be an obstacle for life. In fact, some experts argue that a super-Earth is more likely to have life than an Earth-sized planet. "If you and I walked on it, our weight would double," Borucki said. "But my weight has doubled since I was a teenager ... so we could do it."

If the planets had atmospheres like Earth's, Kepler-62e's surface temperature would be 86 degrees Fahrenheit (30 degrees Celsius), while Kepler-62f's temperature would be 19 degrees below zero F (-28 degrees C), Borucki said. "You'd see the sun being substantially larger than our sun, because it's so much closer," he said. "But it'd be darker, like walking around on a cloudy day."

In their research paper, Kaltenegger and Sasselov assume that Kepler-62e has a slightly cloudier atmosphere than Earth's, and that Kepler-62f has a thick carbon-dioxide atmosphere with a strong greenhouse effect. Without a thick atmosphere, Kepler-62f could get chillier than Mars. It might even look more like a Europa-style iceball than a Kevin Costner-style water world.

"Kepler-62e probably has a very cloudy sky, and is warm and humid all the way to the polar regions," Sasselov said. "Kepler-62f would be cooler, but still potentially life-friendly. The good news is, the two would exhibit distinctly different colors and make our search for signatures of life easier on such planets in the near future."

Habitable worlds ahead
Kepler-62e and Kepler-62f aren't the first habitable-zone planets to be identified by the Kepler team, and they won't be the last. A year and a half ago, Kepler-22b came to light as the mission's first potentially habitable planet. It's 2.4 times wider than Earth, which puts it halfway between our planet and Neptune on the size scale. Kepler-47c, unveiled last year, is also a habitable-zone planet — but it's 4.6 times wider than Earth, which makes it Neptune-sized.

This January, the science team discussed the habitability of another candidate planet, then known as KOI 172.02. The existence of that world has now been confirmed under the name Kepler-69c, with a size that's 1.7 times Earth's width. "Today we can announce that this is a bona fide planet," Thomas Barclay, an astronomer at Ames Research Center, said during Thursday's news conference. 

Three months ago, Kepler-69c was hailed as potentially the most Earthlike world detected beyond our solar system, but now researchers say Kepler-62e and Kepler-62f could be stronger contenders.

There will be more contenders ahead: Borucki said about four dozen of the more than 2,700 candidate planets being tracked by Kepler lie within their stars' habitable zones, and it takes about a year to confirm each candidate's existence through detailed analysis. "We really wish we were faster," he told NBC News. "I really wish we could knock off one a week."

Boruckin and his colleagues are poring through the oceans of observations coming in from the Kepler telescope, and although the spacecraft has had its problems, he's hoping that the flood of data will continue for years to come.

"When you're born a scientist, they leave out the gene for saying, 'We have enough data,'" Borucki joked.

More about the planet hunt:

• Alien Earths in our backyard?
• 17 billion hot Earths in our galaxy
• NBC News on planets | Cosmic Log on Kepler

Borucki, Kaltenegger, Sasselov and Barclay are among 64 authors of the Science paper, "Kepler-62: A Five-Planet System with Planets of 1.4 and 1.6 Earth Radii in the Habitable Zone." Barclay and Borucki are among 31 authors of "A Super-Earth-Sized Planet Orbiting in or near the Habitable Zone around Sun-like Star," published in The Astrophysical Journal. Kaltenegger, Sasselov and Rugheimer are the authors of "Water Planets in the Habitable Zone: Atmospheric Chemistry, Observable Features, and the Case of Kepler-62e and -62f."

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

NASA / JPL-Caltech / MSSS

This graphic shows the relative sizes of Earth, Mars and Europa, an icy moon of Jupiter.

A British astrobiology conference has revived a years-old debate over the best place to look for life elsewhere in the solar system: Mars, or the moons of Jupiter and Saturn?

"For reasons I don't really understand, the wider solar system and the potential for life there has not been high priority," The Telegraph quoted Robert Pappalardo, a senior research scientist at NASA's Jet Propulsion Laboratory, as saying on BBC Radio 4.

Pappalardo's remarks were occasioned by this week's astrobiology conference at the UK Center for Astrobiology in Edinburgh, Scotland. The center recently established the International Subsurface Astrobiology Laboratory, or ISAL, half a mile (1 kilometer) beneath the surface in Yorkshire's Boulby mine. Biologists will use that facility to see how organisms hold up in extreme environments, learn about life's chemical signatures, and test instruments that could look for those signatures on other worlds.

Someday, one of the worlds may well be Europa, an icy moon of Jupiter. With a diameter of 1,945 miles (3,130 kilometers), Europa is just slightly smaller than Earth's moon, and yet it is thought to contain more water than Earth's oceans beneath a miles-deep layer of ice. Researchers recently suggested that hydrogen peroxide in the ice could serve as an energy supply for simple forms of life in the ocean hidden below.

Europa is the focus of Pappalardo's research, and for months he has been urging NASA to support a $2 billion mission to study Europa at close range. However, proposals for NASA missions to Europa have been losing out, in part because of the cost of missions to Mars. Last week's federal budget proposal for the next fiscal year provides no funding for a Europa mission, but it does fund Mars missions such as Maven (launching this year), InSight (launching in 2016) and a new science rover (launching in 2020).

Kevin Hand (JPL-Caltech) / Jack Cook (WHOI) / Howard Perlman (USGS)

If Europa's ocean is 100 kilometers (62 miles) deep, and all that water were gathered into a ball, it would have a radius of 877 kilometers (545 miles). This graphic compares that hypothetical ball of Europan water to the size of the Jovian moon itself, as well as all the water on planet Earth. Europa is thought to have two to three times the volume of water in Earth's oceans.

At February's annual meeting of the American Association for the Advancement of Science, Pappalardo worried that NASA's study of the outer solar system would go "radio-dark" in 2017, when the Cassini mission to Saturn and the Juno mission to Jupiter are both due to end. He continued that theme in this week's BBC interview.

"I worry that if Europa exploration is delayed, but then finally it happens some day, we might look back and say 'Why didn't we do that sooner?' Imagine 50 years from now, we get a lander there and find signs of life. All this time we'll have been looking in the wrong place," he was quoted as saying.

Europa isn't the only moon that intrigues astrobiologists: In the Jovian system, Callisto and Ganymede also have icy shells and may hold hidden oceans. Meanwhile, Cassini has repeatedly observed geysers of water ice rising from the surface of the Saturnian moon Enceladus — suggesting that liquid water and perhaps life may lie beneath the surface. Saturn's largest moon, Titan, has a thick atmosphere and seas of hydrocarbon that some scientists think could harbor a totally alien kind of life.

As for Mars, astrobiologists say hints of life could well lurk beneath the surface. To some extent, the Red Planet has been winning out over Europa and Enceladus because it's easier to get to. Moreover, NASA's vision calls for sending astronauts to Mars and its moons in the 2030s. NASA's robotic missions serve as precursors for those human voyages, as well as steps in a long-term program to learn about life in the universe.

Europa's fans can take heart in the fact that the European Space Agency is planning its own mission to Jupiter's moons: The Jupiter Icy Moons Explorer, or JUICE, is due for launch in 2022 and arrival at the Jovian system in 2030. There's also talk of a sample return mission that would target Enceladus' geysers, and a proposal to drop a boat onto Titan's seas.

So what if all of these worlds — Mars and Europa, Callisto and Ganymede, Titan and Enceladus — turn out to be lifeless? Charles Cockell, who heads the UK Center for Astrobiology, addressed that scenario in an interview with the BBC.

"A lot of people think astrobiology is some sort of hunt for life, and if we don't find life, it will be a big disappointment," Cockell said. "But in fact, that's not the case. The discovery of many lifeless planets across the universe, the discovery that the Earth might be unique as a place for life, would be an astonishing discovery in itself. It would be a very lonely discovery, but it would be an astonishing discovery."

More about the search for life:

• Which alien worlds are most livable?
• Maybe we are alone, after all 
• Cosmic Log archive on astrobiology

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

WISSARD Project via Antarctic Sun

A laptop screen shows a video view of the borehole drilled through Antarctica's ice down to Lake Whillans.

The first signs of potentially exotic life have been spotted in a sample of water drawn from Antarctica's hidden Lake Whillans, a half-mile beneath the surface, according to reports from the scene.

The telltale green glow of cells stained with a DNA-sensitive dye could be seen when water from the lake was put under the microscope on Monday, Discover Magazine's Crux blog reported. "It was the first evidence of life in an Antarctic subglacial lake," science journalist Douglas Fox reported for The Crux. Fox is an embedded journalist reporting from Lake Whillans under the auspices of a National Science Foundation program.

The U.S. scientists in charge of the project to drill into Lake Whillans — known as the Whillans Ice Stream Subglacial Access Research Drilling, or WISSARD — will be more circumspect: They'll have to demonstrate that the green-glowing cells are truly alive and capable of growing in culture. They'll also conduct tests to make sure that the microbes are indigenous to the lake, rather than the result of contamination from the drilling operation.

Last year, Russian scientists analyzed water from Lake Vostok, an even deeper and bigger subglacial lake beneath Antarctica's Vostok Station, but the only microbes they found in the sample were surface-dwelling species that may have come from contaminated drilling chemicals rather than the lake itself.

During the current Antarctic research season, the Russians resumed their drilling at Vostok. They said earlier this month that they had reached transparent lake ice at a depth of 3.4 kilometers (2.1 miles). Since then, they've reported retrieving "fresh frozen" ice cores from slightly deeper levels.

The Russian and U.S. teams are drilling into the lakes in hopes of finding evidence of life forms that could have been living in the dark for thousands of years, or even millions of years. Theoretically, such organisms could live off the minerals in deep-buried rock, plus oxygen dissolved in the lake water.

The Whillans Ice Stream is a glacial river that pushes ice from the West Antarctic Ice Sheet into the Ross Ice Shelf. Lake Whillans lies about 800 meters (0.5 miles) beneath the ice, less than 400 miles (640 kilometers) from the South Pole. Just this past weekend, the WISSARD team reported that their borehole connected with the lake after several days of drilling. 

Fox quoted scientists as saying that Lake Whillans is just 5 to 6 feet (1.5 to 2 meters) deep, as opposed to the 20 to 30 feet (6 to 9 meters) that was expected. The first water samples that were brought up contained the ancient fossils of dead diatoms — tiny marine creatures that are thought to have been pushed down into the lake from West Antarctica.

The study of Lake Whillans and other subglacial lakes should shed light on Antarctica's climate history, as well as the long-term interaction between the continent's ice and the water and rocks that lie beneath. The discovery of novel life forms could open up an entirely new frontier for biologists. And even if the organisms found in the lakes aren't all that unusual, the drilling operations could set the stage for future missions to the ice-covered moons of Jupiter and Saturn, where similarly challenging conditions for subsurface life are thought to exist.

More about the mysteries beneath the ice:

• Saturnian moon Enceladus eyed for sample return mission
• Underground ocean goes deep on Jovian moon Europa
• Mission to drill into Antarctica's Lake Ellsworth suspended

For more about the WISSARD project at Lake Whillans, check out this report from The Antarctic Sun.

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

WISSARD Project

The WISSARD camp spreads out on the bleak Antarctic landscape, about 800 meters (2,625 feet) above a subglacial body of water known as Lake Whillans.

U.S. scientists successfully drilled into Lake Whillans, a subglacial expanse of water hidden deep beneath the Antarctic ice sheet, they reported on Sunday.

About a month ago, a similar British attempt to reach subglacial Lake Ellsworth had failed. Drilling operations for the WISSARD project (Whillans Ice Stream Subglacial Access Research Drilling), which is funded by the U.S. National Science Foundation's Office of Polar Programs, started on Jan. 21.

Over the next couple of days, equipment will be lowered down the 2,625-foot-deep (800-meter-deep) hole to carry out measurements and to obtain water samples for further study onboard container-based scientific laboratories on the surface. As of Sunday, the WISSARD team said they may have penetrated the lake surface.

"Sensors on the hot water drill show a water pressure change, indicating that the borehole has connected with the lake," they write on the WISSARD blog. "Verification awaits visual images from a down-borehole camera this evening. We are excited about the latest developments at the lake!" [See Photos of Subglacial Lake Whillans Drilling Site]

The bottom of the world
On Dec. 9, I visited the WISSARD test site on the Ross Ice Shelf, just off the coast of the Antarctic continent and close to McMurdo Station, as a selected member of the NSF Antarctic media visitation program. The test site resembled a small factory, with generators, water tanks, labs, workshops, data centers and, of course, the actual drilling platform — all mounted on giant skis. In the background were the tractors that would pull the whole installation to Lake Whillans, across hundreds of miles of solid ice.

"This is a first go," said Ross Powell of the University of Northern Illinois, one of WISSARD's 13 principal investigators. "Next year we hope to return to drill more holes."

Frank Rack, a geologic oceanographer of the University of Nebraska who leads the WISSARD drill team, explained how a powerful jet of pressurized hot water is used to melt a hole in the ice. 

"Our hot water drill is state-of-the-art," Rack said. Part of the system, including two 225-kilowatt generators and the power distribution modules, had previously been used to drill the holes for the IceCube Neutrino Observatory at the South Pole. The technique is simple in principle, but prone to unexpected problems. "My biggest worry is that something might get stuck," Powell said. With the successful completion of the actual drilling at Lake Whillans, this worry has now been laid to rest.

Preventing contamination
A big concern for the WISSARD team has been to prevent contamination of samples from the subglacial lake with microbes. After all, an important goal of the project is studying the lake's ecosystem, if it exists at all. Even at 195 degrees Fahrenheit (90 degrees Celsius) — the temperature the pressurized water for drilling is heated to — water contains a lot of spore-forming bacteria. That’s why the drilling hose is fed through a collar of ultraviolet lamps: The energetic radiation kills 99.9 percent of all microorganisms. 

In contrast, the Russian team that drilled into subglacial Lake Vostok last year used kerosene to lubricate the borehole — a technique significantly less clean than hot-water drilling.

Microbiologist Jill Mikucki of the University of Tennessee is pretty sure there might be life under the ice: microorganisms that are able to thrive in the cold, dark, isolated subglacial lakes. She doesn't expect to encounter larger organisms, because there's so little energy available at 2,625 feet (800 meters) below the icecap, but "microbes are everywhere," Mikucki said. "There's even potential to find new species."

Subglacial microbes could accelerate weathering of rocks, Mikucki explained, releasing silicon and iron that finds its way into the ocean and serves as nutrients for other life forms. "I want to find out how they help to run the planet," she said. [Antarctica Album: Stunning Photos of IceBridge Mission]

Hidden plumbing
Meanwhile, geologists and glaciologists are eager to learn more about water transport and ice dynamics beneath the frozen Antarctic surface. Lake Whillans lies beneath a 66-foot-wide (20-meter-wide) ice stream that moves about a meter per day, as opposed to something like a meter per year for the surrounding icecap. Little is known about the possible relation between ice streams on the surface and subglacial river systems, which have only been discovered — and charted through radar — over the past couple of decades.

"Lake Whillans is just one of a few hundred interconnected lakes," said Powell, "and radar observations have revealed that it fills and drains in a five- to 10-year cycle. We want to find out what causes these cycles. And knowing more about ice dynamics is important to better understand the effects global warming might have on the Antarctic continent. Thanks to WISSARD, we will be able for the first time to use real field data as input in our glacialogical models."

Even the 66-foot-deep (80-meter-deep) test drill through the Ross Ice Shelf, completed in mid-December, was of interest to scientists. An earlier program called ANDRILL (for Antarctic Drilling project), also led by Rack, encountered some unusual life forms beneath the ice, including giant anemones and previously unknown organisms looking like floating spring rolls.

"Pretty surprising," Rack said. "I have a museum guy doing the taxonomy right now, and we are writing it up for Science magazine. At the WISSARD test site we could find similar — or very different — organisms. We'll have to see.” Results from the test drilling have not yet been released. [Life on Ice: Gallery of Cold-Loving Creatures]

Robotic submersible
Planetary scientist Britney Schmidt of the University of Texas at Austin has deployed a small, tethered robotic submersible through the test borehole. Known as SCINI (Submersible Capable of under Ice Navigation and Imaging), it is outfitted with a lamp and a camera. "It looks for everything under the ice," Schmidt told me at her temporary office at McMurdo Station. "There's no reason that I could think of why we would not find interesting organisms."

In the future, Schmidt hopes to use similar techniques to search for life in the subglacial ocean of Europa, one of the four large satellites of Jupiter. "I'm not 100 percent sure that there is life on Europa," she said, "but if it’s not there, I'd like to learn why it isn't there." Again, the SCINI results from the test site are not yet published, but it's clear that projects like WISSARD are already firing the imagination of planetary scientists and astrobiologists.

It will be a while before scientists succeed in drilling through the polar ice of Mars, or through the icy crust of Europa, but the success at Lake Whillans gives them a taste of things to come. Meanwhile, WISSARD will provide geochemists and microbiologists alike with a unique picture of an integrated subglacial ecosystem.

"Other systems are much easier to study," said Mikucki, "but from Antarctica we only have limited samples so far. Since 10 percent of the Earth's land surface is covered with ice, we really need more data to understand our planet. Antarctica is an important piece of the puzzle."

Follow LiveScience on Twitter @livescience. We're also on Facebook and Google+.

• Extreme Antarctica: Amazing Photos of Lake Ellsworth
• Antarctica: 100 Years of Exploration (Infographic)
• Creatures of the Frozen Deep: Antarctica's Sea Life

© 2012 LiveScience.com. All rights reserved.

AP file

Russian researchers at the Vostok station in Antarctica pose for a picture after reaching Lake Vostok in February 2012. Scientists hold a sign reading "05.02.12, Vostok station, boreshaft 5gr, lake at depth 3769.3 metres." The researchers now report that they have brought up fresh samples from the borehole.

Russian researchers say they have brought up fresh samples of clear ice from Antarctica's Lake Vostok, a huge reservoir of freshwater more than 2 miles (3.2 kilometers) beneath the surface.

Lake Vostok could contain water and perhaps living organisms that have been sitting undisturbed in the deep dark for up to 20 million years. The drilling operation also could set a precedent for far more ambitious efforts to find life beneath the ice of the Jovian moon Europa or the Saturnian moon Enceladus.

Because of the potential for contamination, scientists have been taking extreme care at Lake Vostok, which is situated 800 miles (1,300 kilometers) from the South Pole in East Antarctica. A year ago, the Russian drilling team reached the lake and brought up water samples. Some of the water was even served to Vladimir Putin, who was then Russia's prime minister and is now the country's president. But it wasn't clear whether those samples were actually from the lake or from the glacier above the lake, the Russian news service RIA Novosti reported.

This year's drilling operation is aimed at bringing up samples that can be linked more definitively to the lake itself.

"The first core of transparent lake ice, 2 meters long, was obtained on Jan. 10 at a depth of 3,406 meters," Russia's Arctic and Antarctic Research Institute said in a statement. "Inside it was a vertical channel filled with white bubble-rich ice."

The institute said that drilling operations would be extended another 24 meters with the existing cables, and that new cables were being delivered to the Vostok research station. The core samples were to be subjected to chemical and biological analysis.

Lake Vostok is about 160 miles (250 kilometers) long and 30 miles (50 kilometers) wide, making it the largest of Antarctica's nearly 400 subglacial lakes. Last year's drilling operation drew up samples from a depth of 12,366 feet (2.34 miles, or 3,769 meters). In October, Russian team members reported finding no native life within those samples. They said the only microbes they detected were traced to contaminants from the drilling oil.

The lake could serve as a laboratory for studying what Antarctica's climate and ecosystem was like millions of years ago. It may contain creatures unlike any that exist today. And as ambitious as all that sounds, the Vostok operation is seen as a mere warmup for future sampling missions to Europa, Enceladus and perhaps other icy moons in the solar system.

Planetary scientists see ample evidence that liquid water exists on those worlds, miles beneath the icy surface, and astrobiologists have theorized that internal heat may provide enough energy for organisms living within those hidden oceans.

Correction for 1:30 p.m. ET Jan. 14: I initially described Vostok station as 800 miles east of the South Pole, but that's not quite right: All directions from the South Pole are north, as commenters have pointed out. There is an "east" and "west" to the continent, and Vostok happens to be in East Antarctica. I've changed the reference to the location accordingly.

More about the mysteries beneath the ice:

• Saturn moon eyed for sample return mission
• Satellite shows Russia's 'moon shot' ice station
• Mission to drill into Antarctica's Lake Ellsworth suspended

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.