Kepler-62: A Star System With Two Earths?
Around 1,200 light-years from Earth, two potentially habitable Earth-sized worlds orbit a sun-like star.
About 1,200 light-years from Earth, five planets are circling around a sun-like star in the constellation Lyra, two of which are fortuitously positioned for water, if any exists, to remain liquid on their surfaces, a condition believed to be necessary for life.
The discovery, made by scientists using NASA's planet-hunting Kepler space telescope, is the strongest evidence yet for more than one Earth-sized planet existing in a star's so-called "habitable" zone.
"We're particularly delighted to find that there are two planets in the habitable zone," lead Kepler scientist William Borucki, with NASA's Ames Research Center in California, told Discovery News.
"It sort of doubles our chances of finding that Earth we'd all like to find. When you think about Earth and Mars, if Mars had been a bit larger, if Jupiter hadn't been so close, we'd again have two planets in the habitable zone and maybe we'd have a place to go," he said.
The newly found planets are the outermost pair circling a star known as Kepler-62.
The most distant planet, Kepler-62f, is about 1.4 times as big as Earth and orbits its parent star in 267 days.
"It was a surprise," University of Washington astronomer Eric Agol told Discovery News. "It was a fairly immediate realization that this planet was potentially suited to have liquid surface water."
The other planet, Kepler-62e, is 1.6 times Earth's size and circles its star in 122 days.
Whether either or both of Kepler-62's optimally positioned planets actually has water is beyond the technical capabilities of the Kepler and other telescopes. Kepler works by detecting the very slight dips in light coming from a star caused by a planet passing by, relative to the telescope's line of sight.
Sifting through the information is a painstaking and long process. Every download of data from Kepler includes about 18,000 events of potential interest to scientists.
"We have at any given time thousands of candidate planets," Borucki said. "You pick one, you spend a lot of time and a lot of ground-based telescope effort to make sure it couldn't be anything else. All the possibilities have to be eliminated."
Scientists are not yet finished with Kepler-62. The observatory hasn't been operating long enough to find and confirm the transits of any planets with longer orbital periods.
"I wouldn't at all be surprised if we find another one, or maybe two or three," Borucki said.
The Kepler team previously discovered a star with six planets in orbit, while a group of European researchers using a different telescope and technique, have found a seven-planet system.
Artist's impression of the five-planet Kepler-62 system, with two worlds in the habitable zone -- the distance from their star at which they receive enough light and warmth for liquid water to theoretically exist on their surfaces.
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.
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.
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.
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.
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.
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.
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.
"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 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.
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.