Kepler finds three smallest exoplanets so far

Artist's conception of the KOI-961 system. Credit: NASA/JPL-Caltech

The Kepler space telescope has been finding exoplanets by the thousands, and as the mission progresses, it has been able to detect smaller and smaller planets over time. Indeed, it was just recently announced, among other significant discoveries, that the smallest exoplanets have (again) been found.

These three planets all orbit one star, KOI-961, a red dwarf star only about one-sixth the diametre of our Sun. They all orbit very close to the star, taking less than two days to complete an orbit, and are only about 0.78, 0.73 and 0.57 times Earth’s radius. The smallest is actually close to the size of Mars!

According to Doug Hudgins, Kepler program scientist at NASA Headquarters in Washington, “Astronomers are just beginning to confirm thousands of planet candidates uncovered by Kepler so far. Finding one as small as Mars is amazing, and hints that there may be a bounty of rocky planets all around us.”

Size comparison of smallest known exoplanets to Earth and Mars. Credit: NASA/JPL-Caltech
Scale comparison of KOI-961 planets to Jupiter and its four largest moons. Credit: NASA/JPL-Caltech

The discovery was made by a team led by astronomers from the California Institute of Technology in Pasadena.

The easiest exoplanets to detect are larger gas giants, like Jupiter or Saturn, and planets with very tight orbits around their stars (and smaller, dimmer stars). As Kepler accumulates more data, it is able to detect both smaller planets like Earth or even smaller as in this case, and planets that orbit farther out from their stars.

“This is the tiniest solar system found so far,” said John Johnson, the principal investigator of the research from NASA’s Exoplanet Science Institute at the California Institute of Technology in Pasadena. “It’s actually more similar to Jupiter and its moons in scale than any other planetary system. The discovery is further proof of the diversity of planetary systems in our galaxy.”

Interestingly, the new planets were found by comparing KOI-961 to another very similar star, Barnard’s Star. This aided in determining the planets’ sizes.

Red dwarfs are the most common type of star in the galaxy, so discoveries such as this help to reinforce earlier conclusions that smaller rocky planets are common. If this one red dwarf star has at least three planets, than how many other red dwarfs do also?

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Saturn-like ring system discovered orbiting another star

Artist's conception of the Saturn-like ring system. Credit: Michael Osadciw/University of Rochester

For the first time, astronomers have found a ring system orbiting another star that seems to be similar to the rings of Saturn in our own solar system. It encircles a low-mass object which orbits the star, but it isn’t clear yet if that object is a planet, a very low-mass star or a brown dwarf star.

The scientists used data from the international SuperWASP (Wide Angle Search for Planets) and the All Sky Automated Survey (ASAS) project to study the light curves of young Sun-like stars in the Scorpius-Centaurus region of our galaxy.

This star, 1SWASP J140747.93-394542.6., is about 420 light-years away. It is similar in mass to the Sun, but is much younger, only about 16 million years old.

The ring appears to be a multi-ring system, with at least three or four rings and two or three gaps, another similarity to Saturn’s rings. These are much larger however; Saturn’s rings are a few hundred thousand kilometres across, while these ones are tens of millions of kilometres.

According to Eric Mamajek, Assistant Professor of Physics and Astronomy at the University of Rochester, “When I first saw the light curve, I knew we had found a very weird and unique object. After we ruled out the eclipse being due to a spherical star or a circumstellar disk passing in front of the star, I realized that the only plausible explanation was some sort of dust ring system orbiting a smaller companion—basically a ‘Saturn on steroids.’ We suspect this new star is being eclipsed by a low-mass object with an orbiting disk that has multiple thin rings of dust debris.”

He continued: “This marks the first time astronomers have detected an extrasolar ring system transiting a Sun-like star, and the first system of discrete, thin, dust rings detected around a very low-mass object outside of our solar system. But many questions remain about what exactly has been discovered.”

If the object is less than 13 MJ (Jupiter masses), it is most likely a planet. If however it is between 13 MJ and 75 MJ, than it is probably a brown dwarf star.

Mamajek says that more definite conclusions about these rings will take another couple of years or so of analysis. Finding other ones would of course also be helpful.

Saturn, with its majestic rings, is one of the most beautiful places in the solar system. Jupiter, Uranus and Neptune also all have rings, albeit not as striking as Saturn’s. As we continue to find exoplanets by the thousands, how many of those may also be graced by rings? There might be a wide variety of ringed planets out there, all beautifully unique.

The findings will be published in an upcoming issue of the Astronomical Journal.

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A Milky Way full of planets

Artist's illustration showing how common planets are in our galaxy. Credit: ESO/M. Kornmesser

The discovery of exoplanets, planets that orbit other stars, has continued to grow exponentially over the last few years. Twenty years ago, when the first ones were found, it was unknown how many may be out there. The first exoplanets were found orbiting a pulsar, the rapidly spinning remains of a dead star, which made them easier to spot than if they orbited a normal star. Were they a fluke or did they indicate that perhaps many stars might have planetary companions?

As it turns out, it is the latter; not only do many, if not most stars apparently have planetary systems, but by some calculations those planets may even outnumber the stars themselves in our galaxy…

new six-year study by an international team of astronomers has concluded that planets are the rule, rather than the exception, in our galaxy. The study was published in the January 12, 2012 issue of Nature.

The group has used a technique called gravitational microlensing, which can detect planets of various masses and farther distances from their star than some other methods. When looking at a star for possible planets, the researchers look at its gravitational field – if there are planets, that gravitational field, combined with the gravitational field of the planets, acts like a lens which magnifies the light of any background stars.

Microlensing, however, requires the rare chance alignment of a background and a lensing star. Finding the actual planet also requires an alignment of the planet’s orbit.

In the six-year survey, three exoplanets were found. That may not sound like very many, but it’s important. Because of the rare chance alignments needed, it means that the astronomers were either very lucky, like finding needles in a haystack, or planets are so abundant that finding them was almost guaranteed.

By comparing the results with previous planetary detections, it was determined that one in six of the stars examined has a planet similar in mass to Jupiter, about half have Neptune-mass planets and about two-thirds have super-Earths (rocky worlds that are larger than Earth but smaller than Neptune). It also suggests that the average number of planets around a star is greater than one.

According to Arnaud Cassan, lead author of the Nature paper, “We have searched for evidence for exoplanets in six years of microlensing observations. Remarkably, these data show that planets are more common than stars in our galaxy. We also found that lighter planets, such as super-Earths or cool Neptunes, must be more common than heavier ones.”

Considering these findings plus the incredible results so far from the Kepler space telescope mission and other ground-based telescopes, it would appear that indeed, the Milky Way is full of planets. Extrapolate that then to the billions of other galaxies and, well, you get the idea…

The paper is available here.

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Tatooine the sequel: Kepler finds two more exoplanets orbiting binary stars

Artist's conception of the Kepler-35 system. Credit: Lynette Cook / / Nature

For exoplanet fans, this week has been an exciting one, with some amazing new discoveries being announced at the American Astronomical Society meeting in Austin, Texas – our galaxy is brimming with planets, probably billions, and the smallest known planets have been found (again), with one about the size of Mars. But that’s not all; it was also announced that Kepler has found not one but two more planets orbiting binary stars!…

See Universe Today for the full article.

Analysis of the first Kepler SETI observations

Example of signals KOI 817 and KOI 812. Credit: The Search for Extra Terrestrial Intelligence at UC Berkeley

As the Kepler space telescope begins finding its first Earth-sized exoplanets, with the ultimate goal of finding ones that are actually Earth-like, it would seem natural that the SETI (Search for Extraterrestrial Intelligence) program would take a look at them as well, in the continuing search for alien radio signals. That is exactly what SETI scientists are doing, and they’ve started releasing some of their preliminary results

See Universe Today for the full article.