Space & Innovation

Most 'Earth-Like' Alien World Discovered

About 500 light-years away in the constellation Cygnus lives a star, which, though smaller and redder than the sun, has a planet that may look awfully familiar.

About 500 light-years away in the constellation Cygnus lives a star, which, though smaller and redder than the sun, has a planet that may look awfully familiar.

With a diameter just 10 percent bigger than Earth's, the newly found world is the first of its size found basking in the benign temperature region around a parent star where water, if it exists, could pool in liquid form.

Scientists on the hunt for Earth's twin are focused on worlds that could support liquid surface water, which may be necessary to brew the chemistry of life.

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Statistically speaking, Earth-sized planets orbiting in stars' so-called habitable zones -- not too far away for water to freeze, not too close for it to vaporize -- should be common, recent studies show.

But observations are difficult to come by. NASA's Kepler space telescope spent four years staring at about 150,000 target stars looking for slight and repeated dips in their light caused by orbiting planets passing by, or transiting, relative to the telescope's line of sight.

A planet the size of Earth positioned about as far from a host, sun-like star and as far away as Earth orbits the sun would block just 80- to 100 photons of starlight out of every million -- and do so only once every 365 days, notes astronomer Thomas Barclay, with the Kepler science team at NASA's Ames Research Center in Moffett Field, Calif.

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An Earth-sized planet circling a smaller star is an easier target. The newly found world, designated Kepler-186f, obscures about 400 photons of starlight out of every million as it transits its parent star -- and repeats the cycle every 130 days.

"I wouldn't say this is the ‘bingo' planet, but this is really one of the major milestones on the road," Barclay told Discovery News. "This isn't an Earth twin, but perhaps it's an Earth cousin."

Scientists need at least three transits -- plus follow-up observations by ground-based telescopes -- before an extrasolar planet is confirmed. Since the first planet beyond the solar system was discovered in 1996, astronomers have added nearly 1,800 to the list.

"Kepler-186f is significant because it is the first exoplanet that is the same temperature and the same size (well, ALMOST!) as the Earth," David Charbonneau, with the Harvard-Smithsonian Center for Astrophysics, wrote in an email to Discovery News.

"Previously, the exoplanet most like Earth was Kepler-62f, but Kepler-186f is significantly smaller," Charbonneau added.

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"Now we can point to a star and say, ‘There lies an Earth-like planet,'" he said.

Scientists continue to analysis archived Kepler data in hopes of finding true Earth twins. The telescope currently is sidelined by a positioning system problem.

Meanwhile, the Kepler-186 star, which hosts at least four more planets in addition to the strategically positioned and outermost 186f, will become the focus of sister science project that scans the skies for non-naturally occurring radio transmissions in a quest to find technically advanced extraterrestrial life.

The research is published in this week's Science.

Artist's impression of the surface of the newly confirmed exoplanet Kepler-186f orbiting a sunlike star in its habitable zone.

Exquisite Exoplanetary Art

Sept. 19, 2011 --

They're alien worlds orbiting distant stars far out of reach of detailed imaging by even our most advanced telescopes. And yet, day after day, we see vivid imaginings of these extrasolar planets with the help of the most talented space artists. The definition of an extrasolar planet -- or "exoplanet" -- is simply a planetary body orbiting a star beyond our solar system, and nearly 700 of these extrasolar worlds have been discovered so far (plus hundreds more "candidate" worlds). With the help of NASA's Kepler space telescope, the ESO's High Accuracy Radial velocity Planet Searcher (HARPS), French COROT space telescope and various other advanced exoplanet-hunting observatories, we are getting very good at detecting these worlds, but to glean some of the detail, we depend on artist's interpretations of fuzzy astronomical images and spectral analyses. That's the way it will be until we build a vast telescope that can directly image an exoplanet's atmosphere or physically travel to an alien star system. So, with the flurry of recent exoplanet discoveries, Discovery News has collected a few of the dazzling pieces of art born from one of the most profound searches mankind has ever carried out: the search for alien worlds orbiting other stars; a journey that may ultimately turn up a true "Earth-like" world.

The Transit

As an exoplanet passes in front of its star as viewed from Earth, a very slight dip in starlight brightness is detected. Observatories such as NASA's Kepler space telescope use this "transit method" to great effect, constantly detecting new worlds.

Hot Jupiters

Some exoplanets orbit close to their parent stars. Due to their close proximity and generally large size, worlds known as "hot Jupiters" are easier to spot than their smaller, more distant-orbiting cousins.

Habitable Worlds

The primary thrust of exoplanet hunting is to find small, rocky worlds that orbit within their stars' "habitable zones." The habitable zone, also known as the "Goldilocks zone," is the region surrounding a star that is neither too hot nor too cold. At this sweet spot, liquid water may exist on the exoplanet's surface. Where there's water, there's the potential for life.

A Phantom

Usually, exoplanet hunters look for the slight dimming of a star or a star's "wobble" to detect the presence of an exoplanet. However, in the case of Kepler-19c, its presence has been detected by analyzing its gravitational pull on another exoplanet, Kepler-19b. Kepler-19c is therefore the Phantom Menace of the exoplanet world.

Keeping Warm

The habitable zone seems to be the pinnacle of extraterrestrial living. If you're an alien with similar needs to life on Earth, then you'll need liquid water. If your planet exists outside your star's habitable zone, well, you're in trouble. Either your world will be frozen like a block of ice, or boiling like a kettle. But say if your world had the ability to extend your star's habitable zone? There may be some atmospheric factors that might keep water in a comfy liquid state. Even better, if you like deserts, a dry world could even be oddly beneficial.

Crazy Aurorae

Planets with a global magnetic field, like Earth, have some dazzling interactions with the winds emanating from their stars. The high-energy particles bombard the planet's atmosphere after being channeled by the magnetism. A wonderful auroral lightshow ensues. But say if there's an exoplanet, with a magnetosphere, orbiting really close to its star? Well, stand back! The entire world would become engulfed in a dancing show, 100-1000 times brighter than anything we see on Earth.

The "Candidates"

"Candidate" exoplanets are often mentioned, especially when talking about detections by the Kepler space telescope. But what does this mean? As a world passes in front of its star, slightly dimming the starlight, this isn't considered a "confirmed" exoplanet detection. To make sure that signal is real, more orbital passes of the exoplanet need to be logged before a bona fide discovery can be announced. Until then, these preliminary detections are called exoplanet candidates.

Angry Suns, Naked Planets

Exoplanets come in all sizes and all states of chaos. Some might have wonky orbits, others might be getting naked. Other times, they're simply being ripped apart by X-rays blasted from their parent star. Bummer.

Super-Earths

Super-Earths get a lot of press. Mainly because "Earth" is mentioned. Sadly, most of these worlds are likely completely different to anything we'd call "Earth." And you can forget calling the vast majority of them "Earth-like." It's simply a size thing -- they're bigger than Earth, yet a lot smaller than Jupiter, hence their name, "super-Earth." Easy.

Let's Go!

For now, we have to make do with artist's renditions of exoplanets for us to visualize how they may look in their alien star systems. However, plans are afoot to send an unmanned probe to an interstellar destination. Although these plans may be several decades off, seeing close-up photographs of these truly alien worlds will be well worth the wait.