There is no in-between. Kepler discovered that the majority of exoplanets are larger than Earth but smaller than Neptune, a variety unseen in our solar system. Astronomers are still puzzling out how hot Jupiters managed to move so close to their suns without falling in. But Kepler found that exoplanets can orbit two, three, or even four stars with relative ease. Keplerb was a particularly exciting discovery for Star Wars fans, as its solar system architecture mimics Tatooine, the home world of Luke Skywalker.
Unlike the fictional planet, Keplerb is frigid, inhospitable, and approximately the size of Saturn. Keplerb is one of only about 20 known circumbinary planets. Kepler revealed that planets that orbit a single star in a binary, triple, or quadruple star system are much more common.
But what if there were even more nearby stars? The Sun was born possibly in a dense grouping of stars that has since drifted apart but may once have contained dozens or hundreds of stars. Could our solar system have formed if the Sun had remained trapped in that kind of an environment?
The unprecedentedly large number of exoplanets with precisely measured sizes and temperatures enabled studies of planetary demographics for the first time. Kepler said yes. During its primary mission, Kepler discovered two mini-Neptune planets, Keplerb and Keplerb , orbiting different stars in a distant and crowded star cluster. That star, K , is the first multiplanet system known to survive in a dense stellar environment, and it could help astronomers understand the birth our solar system.
It found them by the thousands. A recent study showed that planets smaller than Neptune fall into two distinct and separate categories, like two branches of a family tree.
The branches were already familiar to astronomers—rocky super-Earths and gaseous mini-Neptunes—but astronomers now know that the categories represent a more fundamental planet property. Scientists are still working out what guides a planet-to-be down one path or the other.
The thousands of exoplanet measurements from Kepler also let astronomers explore relationships between different properties of the planets—such as size, mass, composition, and star type—that theoretical models could not yet predict. In addition, analysis of Kepler planets and their stars has shown that rocky planets are twice as likely and gas giants are 9 times more likely to form around stars abundant in elements heavier than helium.
Our solar system has a neat configuration: All the planets orbit in a mostly flat plane and move in the same direction that the Sun rotates in orbits that are only slightly skewed from circular. Kepler saw that exoplanetary orbits are not always so tidy. Some exoplanets, like Keplerb , a hot Jupiter around a star hotter than the Sun, orbit on highly elliptical orbits. Another exoplanet, Keplerb , orbits its star from pole to pole rather than parallel to the equator, which hints that it may have interacted with another, unseen planet sometime in its past.
Keplerb also orbits a G-star class sun like our sun, but the exoplanet's star is a little bit smaller and colder. Investigators praised the find as helping to fufill Kepler's mission of finding another Earth. The area around a star in which water can be liquid rather than ice is known as the habitable zone.
Sometimes called the " Goldilocks zone ," it's just right — not too hot so the water doesn't evaporate and not too cold so it won't freeze. A Kepler team member also suggested that the planet, at more than double Earth's size, may not be able to host life on its surface. Instead, it could have an environment that is closer to Neptune: rocky core, large ocean.
However, the habitability of Keplerb is not necessarily a sure thing. It is only listed in an "optimstic sample" of potentially habitable planets at The Habitable Exoplanets Catalog a project of the Planetary Habitability Laboratory of the University of Puerto Rico at Arecibo.
The fact it has been found so soon is certainly a slice of good fortune. Despite all the fanfare, Keplerb is certainly nothing like Earth.
Keplerb, it turns out, is around 2. Indeed, if the atmosphere of the planet is sufficiently dense, and rich in greenhouse gasses, it might well be more like Venus than the Earth, with a surface far too warm to house liquid water. But the detection of the first Kepler planet to lie comfortably within the theoretical habitable zone of its host star is still very exciting. Kepler has been carrying out observations for long enough now that at least some potentially-habitable worlds will have transited their host stars the minimum of three times required for firm detection — and the longer the satellite goes on observing, the more transits by such planets will be observed.
The star field that Kepler observes in the constellations Cygnus and Lyra can only be seen from ground-based observatories in spring through early fall. The data from these other observations help determine which candidates can be validated as planets. Keplerb is located light-years away. While the planet is larger than Earth, its orbit of days around a sun-like star resembles that of our world. The planet's host star belongs to the same class as our sun, called G-type, although it is slightly smaller and cooler.
Of the 54 habitable zone planet candidates reported in February , Keplerb is the first to be confirmed. This milestone will be published in The Astrophysical Journal. The Kepler team is hosting its inaugural science conference at Ames Dec.
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