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AAS: 8 New Planets in Habitable Zone

One way to confirm the existence of a transiting planet is to run a radial velocity check to see if it shows up there as a gravitationally induced ‘wobble’ in the host star. But in many cases, the parent stars are too far away to allow accurate measurements of the planet’s mass. What Guillermo Torres (Harvard-Smithsonian Center for Astrophysics) did in the case of eight new candidates possibly in their stars’ habitable zones was to use BLENDER, a software program he and Francois Fressin developed that runs at NASA Ames on the Pleiades supercomputer.

A BLENDER analysis can determine whether candidates are statistically likely to be planets. Torres and Fressin have applied it before in the case of small worlds like Kepler 20e and Kepler 20f, important finds because both were exoplanets near the size of the Earth. Using the software allowed the researchers to create a range of false-positive scenarios to see which could reproduce the observed signal. A nearby binary star system, for example, could cause a dimming of the star’s light that might be mistaken for a planet. The Pleiades supercomputer allowed the team to work through almost a billion different scenarios, which in the case of Kepler 20e showed that it was 3,400 times more likely to be a planet than a false positive.

Applying the same techniques to the eight new planet candidates, Torres and team went on to spend a year doing follow-up work in adaptive optics imaging, high-resolution spectroscopy and speckle interferometry to characterize the new systems. We learn from all this that all eight of these worlds meet the team’s standards for verifiability. All orbit at a distance where liquid water could occur on their surfaces, while two are, as researchers told a meeting of the American Astronomical Society today, more similar to Earth than any exoplanets we’ve yet found.

The similarity in question refers to the size and composition of the two planets rather than other broad characteristics like the star they orbit. Unlike our G-class star, the primary star for Kepler-438b is a red dwarf, while Kepler-442b orbits a K-class star. Kepler-438b receives about 40 percent more light than Earth (Venus receives twice the solar flux of Earth), while Kepler 442b gets about two-thirds the light of Earth. The team gives the latter a 97 percent chance of being in the habitable zone, while the former’s chances are calculated at 70 percent.


Image: This artist’s conception depicts an Earth-like planet orbiting an evolved star that has formed a stunning “planetary nebula.” Earlier in its life, this planet may have been like one of the eight newly discovered worlds orbiting in the habitable zones of their stars. Credit: David A. Aguilar (CfA).

Kepler-438b, 470 light years from Earth, is in a 35-day orbit, while Kepler 442b (1100 light years away) completes an orbit around its star every 112 days. Four of the eight newly found planets are in multiple-star systems, although in each case, according to this CfA news release, the companion stars are far enough away not to exert a significant influence on the observed planets.

A key question is whether these really are rocky worlds — without a measurement of planetary mass, their composition is unknown. Torres and colleagues think that Kepler-438b, with a diameter about 12 percent larger than Earth, has a 70 percent chance of being rocky. Kepler 442b is about a third larger than Earth, but by the team’s reckoning has a 60 percent chance of being rocky. So these are intriguing possibilities, but it has to be said that habitability remains no more than an inference. “We don’t know for sure whether any of the planets in our sample are truly habitable,” says second author David Kipping (CfA). “All we can say is that they’re promising candidates.”


Comments on this entry are closed.

  • Andrew Palfreyman January 6, 2015, 16:07

    Can we take it that all analysis of all Kepler data to date is now complete? I know there was a significant backlog.

  • ljk January 6, 2015, 17:57

    Two New Exoplanet Findings Bring Us Closer to Discovering Other Earth-Like Worlds

    By Paul Scott Anderson

    When it comes to exoplanets, the most exciting for many people are of course the ones which may be the most Earth-like, since these are regarded as the most likely to possibly support some form of life. Now, two new findings announced today will help astronomers to find these worlds, and narrow down the best places to search for evidence of life in other Solar Systems.

    The new results, announced this morning at the annual meeting of the American Astronomical Society (AAS), focus on super-Earth and other potentially Earth-like exoplanets.

    In the first update, new theoretical models for super-Earth exoplanets were presented, which show that such planets should be able to maintain water oceans for billions of years in some cases.

    Full article here:


  • Daniel January 6, 2015, 19:10

    Andrew Palfreyman ask:

    “Can we take it that all analysis of all Kepler data to date is now complete?”

    This is what I find at space.com:

    “While K2 observations continue, Batalha and other Kepler scientists are still busy analyzing data from the prime mission. NASA wants this work done by September 2017, and the team should meet that deadline, Batalha said.

    “Sometime around September of 2016, we’ll probably have our final catalog,” she said. “And then between September and January [of 2017], we’ll be producing the products that will allow people to do the statistics with the catalog. And then we’ll kind of write up all of our documentation and final papers, and turn off the lights and go home sometime around the end of summer 2017.”


    I think still a long way to finish the Kepler/K2 Mission.

  • Joy January 7, 2015, 3:31

    Although it is a bit larger, I like Kepler 442b much more than the other. With a K primary, it would be less likely to be exposed to the notorious M star flares. Also Earth is arguably at the inner edge of Sol’s habitable zone. Less stellar flux than Earth is better than more. Perhaps with the wider orbit, Kepler 442b could have escaped tidal locking?

    In any case, these worlds are far too distant for study. Kepler was a great pathfinder experiment, and I look forward to the follow on TESS. But with a less than 1% chance that a stellar system will be edge on, the transit method of planet finding (largely a statistical exercise) will have run its course after TESS.

    Over 414 stellar objects (a few are white or brown dwarfs) are now known to be located within 10 parsecs of Sol. These are the ones we need to survey with direct imaging. Hopefully TESS results will finally succeed in renewing interest in funding a true planet finder. And please, with a better name than TPF, like the Giordano Bruno Space Telescope!

  • Ronald January 7, 2015, 6:34

    Slightly off-topic, but interesting news:
    Stars’ Spins Reveal Their Ages

    It is the already known gyrochronology by the also well-known astronomer Barnes (one of the founders of gyrochronology), but it seems that gyrochronology is getting mature now, well within 10% error margin.

    Separate post, Paul?

  • Paul Gilster January 7, 2015, 10:07

    Ronald, yes, it’s on my radar — maybe as early as tomorrow.

  • ljk January 19, 2015, 11:55

    Three nearly Earth-size planets found orbiting nearby star

    Jan 16, 2015

    NASA’s Kepler Space Telescope, despite being hobbled by the loss of critical guidance systems, has discovered a star with three planets only slightly larger than Earth. The outermost planet orbits in the “Goldilocks” zone, a region where surface temperatures could be moderate enough for liquid water and perhaps life, to exist.

    The star, EPIC 201367065, is a cool red M-dwarf about half the size and mass of our own sun. At a distance of 150 light years, the star ranks among the top 10 nearest stars known to have transiting planets. The star’s proximity means it’s bright enough for astronomers to study the planets’ atmospheres to determine whether they are like Earth’s atmosphere and possibly conducive to life.

    “A thin atmosphere made of nitrogen and oxygen has allowed life to thrive on Earth. But nature is full of surprises. Many exoplanets discovered by the Kepler mission are enveloped by thick, hydrogen-rich atmospheres that are probably incompatible with life as we know it,” said Ian Crossfield, the University of Arizona astronomer who led the study.

    A paper describing the find by astronomers at the University of Arizona, the University of California, Berkeley, the University of Hawaii, Manoa, and other institutions has been submitted to Astrophysical Journal and is freely available on the arXiv website.

    Full article here: