Kepler Mission Hits 3,500 Candidates

The Kepler team has released its analysis of the mission’s first three years of observations. The haul includes 10 Earth-size (and probably rocky) exoplanets in their stars’ habitable zones, and the stats show such planets are common.

Kepler can now officially boast finding more than 3,500 extra-solar planet candidates. The announcement came this week when the Kepler team released their analysis of data from the first three years of observation, adding the third year to data from years one and two (previously released).

According to this new analysis, researchers estimate about 70% of stars are host to at least one planet, making planets a common cosmic occurrence. There are now 1,750 candidates that are super-Earth-size or smaller, and 1,788 are Neptune-size or larger. Only 167 of the 3,538 candidates are confirmed to be planets, but Kepler has a good track record: the vast majority of these are probably real.

In the first three years of Kepler data, more than 3,500 exoplanet candidates have been named. Since January's update, the number of candidates increased by 29 percent, now totaling 3,538. The largest increase of 78 percent was for the Earth-size category.
NASA
This plethora of information is in a public archive used not only by the Kepler team but also by others looking for planets, such as the crowdsourcing program Planet Hunters. From 2009 until its fateful failure earlier this year, the craft gathered observational information on 150,000 stars, yielding over 21 million light curves, the graphs that show how a star’s brightness changes with time. These light curves reveal the periodic dips caused by a transiting planet.

Since its beginning, the variety of Kepler’s discoveries (both confirmed and unconfirmed) has been astonishing. Some exoplanets have no equivalent in our own solar system. Kepler has found a world with the density of Styrofoam, worlds larger than Jupiter, and worlds around binary stars. There’s even a world with a size on par with Mercury which seems to be evaporating. These distant planets have orbital periods ranging from a few hours to many years.

The new analysis adds 838 planetary candidates to the existing Kepler catalog. Two dozen of these new candidates orbit in their parent star’s putative habitable zone — defined for simplicity’s sake as the region in space where there’s the right amount of starlight to create friendly temperatures on an Earth-like planet. Of those, 10 are less than double Earth’s size and possibly rocky in composition. With these additions, we now have a total of 674 Earth-size candidates.

The new work yields a 78% increase of Earth-size planet candidates compared with the team’s release from this past January, which only used observations from the first two years. Given the larger data set, researchers estimate that one in five Sun-like stars host at least one rocky planet orbiting in their habitable zone. That ratio is about the same as what some astronomers have calculated for the prevalence of rocky planets in orbits smaller than Mercury’s, as well as the prevalence of rocky planets around cool, small stars called M dwarfs.

An artist's rendering of the Kepler space telescope. After over four years of searching for transiting exoplanets and racking up about 3500 planetary candidates (with more to come), its intended operations are at an end.
NASA
When Kepler began, it was mostly detecting gas giants in tight orbits around their stars, simply because such planets are easiest to find. The reason for the recent increase in Earth-size candidates is due not only to having more observations in hand, but also to refinements in researchers’ vetting and analysis — in other words, researchers are getting better at detecting Earth-sized planets. For this reason, the team postulates that the final, fourth year of data (which is still unexplored) will be the most important in the search for small exoplanets.

While Kepler ended its fruitful planet-hunt in May 2013 when a second of the telescope’s four reaction wheels failed for good, all hope it not lost. The team is drafting plans for a new mission called K2, which would repurpose the space telescope in spite of its defects to continue the exoplanet hunt.

Since the problem is one of precision and stabilization, the plan is to point the telescope at the ecliptic, the plane drawn by Earth’s orbit. In this position, the pressure from solar radiation will act as a virtual third wheel, balancing out the remaining two reaction wheels to enable a pointing precision that (the team hopes) will be on par with what Kepler had in its full-functioning state. K2 would search for planets around smaller, cooler dwarf stars and in a range of stellar environments not in Kepler’s previous view, such as star clusters and nurseries. The team will submit their proposal in the next few months.

6 thoughts on “Kepler Mission Hits 3,500 Candidates

  1. Anthony Barreiro

    Using the solar wind to stabilize Kepler so it can continue to record light curves of stars along the ecliptic is a brilliant idea! I hope it works. This plan reminds me vaguely of Lord Rosse’s meridian telescope. It was huge, with a six-foot mirror and a 53-foot focal length. It could only observe objects when they were transiting the meridian, the line that runs from due north to due south in the sky. Despite this limitation, it was the biggest telescope in the world from 1845 until 1917, and it was used to make important discoveries, e.g. resolving individual stars in "spiral nebulae" that we now know as galaxies. Best wishes to the K2 team.

  2. Al

    I’ve been looking for this ever since Kepler launched! Look along the ecliptic! It’s where Earths shadow will project among the nearest stars… it would be interesting to study what adjustments could be made to see which stars would see our shadow, still. In the long run, should we assume any intelligent life with ~>600years of science could direct image anyway?

  3. Ed Marshall

    I read somewhere that the kepler spacecraft cost about $600 million-ish? Although the idea of K2 is indeed brilliant– and let’s do it– I’m all for NASA funding (oops, I said a bad phrase!) to maybe be increased just a little bit create a series of Kepler telescopes with funding spread out over the years. Let’s get a bunch of them up there looking all over the place!I was kind of hoping that Kepler’s "K2" mission would have been the spacecraft surviving long enough to pick out a new piece of sky to observe, but why do we have to stop at "Kepler 1"?

  4. Ed Marshall

    I read somewhere that the kepler spacecraft cost about $600 million-ish? Although the idea of K2 is indeed brilliant– and let’s do it– I’m all for NASA funding (oops, I said a bad phrase!) to maybe be increased just a little bit create a series of Kepler telescopes with funding spread out over the years. Let’s get a bunch of them up there looking all over the place!I was kind of hoping that Kepler’s "K2" mission would have been the spacecraft surviving long enough to pick out a new piece of sky to observe, but why do we have to stop at "Kepler 1"?

  5. Bruce Mayfield

    Imagine that, a guy named Marshall wanting more funding for NASA, who woulda thunk it? :) I wonder if Ed’s from Alabama. Nevertheless, at least one more mission like Kepler would be good, provided they improve the tracking redundancy. But exoplanet fans should also be looking forward to the massive data haul that should be coming from the Gaia probe. This is a ESA mission at a cost of $650 EUR (not US dollars) that should pin down the existence of planets of many nearby stars via stellar motion analysis. I keep looking for a story about this exciting mission here or in the print magazine, but haven’t seen one yet. (Editors, hint hint. ;)

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