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Category Archives: exoplanet

Researchers find a planet they can’t see

A new planet was detected via its gravitational influence on a hot Jupiter-class planet.
NASA

The Kepler mission has only been taking data for two years. In that time, its rate of discovery has been staggering: over 2,300 planet candidates, with another 61 confirmed planets. Those numbers are even more impressive if you consider that Kepler can only detect planets around a small fraction of the stars that it's observing.

Kepler works by watching for the shadow cast when a planet passes between its host star and the Earth. That means the plane of a planet's orbit has to be aligned so that it passes between us and the star. If the orbital plane is tilted, we won't be able to detect it with this method.

But now, researchers have demonstrated that it's possible to spot a few objects that Kepler can't otherwise see directly. While searching for hints of moons orbiting exoplanets, they found that one of the planets spotted by Kepler was being tugged around by another planet—one that orbited in a slightly different plane, and was otherwise undetectable using this method.


Researchers find a planet they can’t see

A new planet was detected via its gravitational influence on a hot Jupiter-class planet.
NASA

The Kepler mission has only been taking data for two years. In that time, its rate of discovery has been staggering: over 2,300 planet candidates, with another 61 confirmed planets. Those numbers are even more impressive if you consider that Kepler can only detect planets around a small fraction of the stars that it's observing.

Kepler works by watching for the shadow cast when a planet passes between its host star and the Earth. That means the plane of a planet's orbit has to be aligned so that it passes between us and the star. If the orbital plane is tilted, we won't be able to detect it with this method.

But now, researchers have demonstrated that it's possible to spot a few objects that Kepler can't otherwise see directly. While searching for hints of moons orbiting exoplanets, they found that one of the planets spotted by Kepler was being tugged around by another planet—one that orbited in a slightly different plane, and was otherwise undetectable using this method.

Read more on Ars Technica…


Tatooine-like planets may be common

Exoplanets—planets in star systems other than our own—have been found in orbit around single stars, with a lone exception: Kepler-16b is circumbinary, having two host stars in close orbit. Now, researchers working with data from the Kepler space-based observatory have identified two more promising exoplanet candidates orbiting binary stars, known as Kepler-34b and Kepler-35b. While the planets most likely are gas giants, the host stars in Kepler-34b are more Sun-like than the Kepler-16 system. These observations indicate that giant exoplanets orbiting two stars may be fairly common, occurring in perhaps one percent of close binaries.

In some ways, our Sun is unusual: stars with similar masses are more commonly found in binary systems. Lower-mass stars are more often found on their own and, since they are also less luminous than the Sun, it has been easier for astronomers to detect planets orbiting them. Finding circumbinary planets is plagued by two major difficulties: both the gravitational pull by the exoplanet and the amount of light it blocks if it passes between us and its hosts are tiny in comparison with the effect the two stars have on each other.

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Remains of gas giants, swallowed by red giant star, now orbit as small planets

There may come a day when exoplanet discoveries start to bore me, but we're not there yet. A day after the Kepler team announced the identification of Earth-sized planets orbiting a distant star, they're back with the description of a truly bizarre planetary system. In its past, KIC 05807616 expanded out to red giant size, swallowing two gas giants in the process. The cores of these planets continued to orbit, reemerging once the star shrunk again. Meanwhile, their impact on the star may have caused it to become an unusually hot form of dwarf star.

The star in question, KIC 05807616, has a rather interesting description: "a seemingly isolated pulsating hot B subdwarf." These have a somewhat unusual history. Normally, stars near the mass of our sun expand out as red giants, but then contract as they switch from fusing hydrogen to fusing the helium that has built up at their cores. Hot B dwarfs occur when something happens during the red giant phase that removes all the star's hydrogen, leaving nothing but a helium fusing core behind. KIC 05807616 has been in this stage for less than 20 million years, and in addition to its high temperatures, undergoes regular fluctuations, hence the "pulsating" part of that description.

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Kepler team spots Earth-sized planets orbiting sun-like star

Just two weeks after the confirmation of a planet that's within the habitable zone of a distant star, the Kepler team is back with the discovery of two Earth-sized planets orbiting in what is now a five-planet system (three other planets orbiting the star, Kepler-20, had been spotted earlier). Although these planets are much too hot to support liquid water, one of them (Kepler-20e) is the smallest exoplanet yet detected.

Kepler-20 was already a busy star system, with three small planets orbiting close in to the star: Kepler-20b is about twice the size of Earth and orbits once every 3.7 days; Kepler-20c is three times Earth's radius and orbits every 11 days; and Kepler-20d is 2.75 Earth radii with an orbit of 77.6 days. If that seems somewhat tightly packed, the new finds actually jam a couple more planets within the orbit of Kepler-20d. Kepler-20e has an orbit of six days, while Kepler-20f takes 19.6 days to orbit its host star.

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Sun-like star hosts Kepler’s first confirmed habitable zone planet

This week, NASA is playing host to a conference dedicated to the results pouring in from Kepler, its first dedicated planet-hunting probe. The space-based telescope spots planets as they pass in front of their host star and temporarily reduce the amount of light from the star that reaches Kepler's sensors; ground based observatories are then used to confirm these planetary candidates. Right now, that confirmation process is turning out to be the big hold-up, as Kepler has identified over 2,300 planet candidates, of which only 28 have been confirmed. But NASA has announced that one of the confirmed planets sits in the habitable zone of a sun-like star.

The initial period of planet spotting was heavily biased towards heavy, Jupiter-sized planets, which were the easiest things to spot. Kepler has completely changed that; the vast majority of the planet candidates are either Super-Earths or Neptune-sized, and just over 200 candidates are roughly the size of our own planet. Forty-eight of these candidates lie in the habitable zone of their stars, where liquid water on the surface is a possibility; 10 of those are roughly Earth-sized. That's actually a small drop from previous counts, as NASA has added consideration of atmospheric warming driven by greenhouse gasses when calculating whether liquid water is likely to be present.

Attention was then focused on the Kepler-22 system, where there was a planet candidate, Kepler-22b, that orbits on the inner edge of the habitable zone. If it were in our solar system, Kepler-22b would orbit somewhere between Venus and the Earth; its orbits take 290 days.

Follow-up observations with the Spitzer space telescope have now confirmed the presence of Kepler-22b, making it the first confirmation of a habitable zone planet by the program. Right now, all we can say about the planet is that it has a radius that's about 2.4 times that of Earth's. Since we don't know its mass, we can't calculate its density, and thus its most likely composition. And, since it's 600 light years away, it will be hard to get a much better look any time soon.

The vast backlog of planet candidates indicates that we'll probably be sorting through Kepler data for years. But the other habitable zone candidates are likely to be high priorities for follow-up observations, so there's a good chance we'll be hearing more about those sooner rather than later.

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