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Eight New Planets Found in “Goldilocks” Zone

By Christine Pulliam

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. (Image by David A. Aguilar)

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. (Image by David A. Aguilar)

Astronomers announced today that they have found eight new planets in the “Goldilocks” zone of their stars, orbiting at a distance where liquid water can exist on the planet’s surface. This doubles the number of small planets (less than twice the diameter of Earth) believed to be in the habitable zone of their parent stars. Among these eight, the team identified two that are the most similar to Earth of any known exoplanets to date.

“Most of these planets have a good chance of being rocky, like Earth,” says lead author Guillermo Torres of the Harvard-Smithsonian Center for Astrophysics (CfA).

These findings were announced today in a press conference at a meeting of the American Astronomical Society.

The two most Earth-like planets of the group are Kepler-438b and Kepler-442b. Both orbit red dwarf stars that are smaller and cooler than our Sun. Kepler-438b circles its star every 35 days, while Kepler-442b completes one orbit every 112 days.

With a diameter just 12 percent bigger than Earth, Kepler-438b has a 70-percent chance of being rocky, according to the team’s calculations. Kepler-442b is about one-third larger than Earth, but still has a 60-percent chance of being rocky.

To be in the habitable zone, an exoplanet must receive about as much sunlight as Earth. Too much, and any water would boil away as steam. Too little, and water will freeze solid.

“For our calculations we chose to adopt the broadest possible limits that can plausibly lead to suitable conditions for life,” says Torres.

Kepler-438b receives about 40 percent more light than Earth. (In comparison, Venus gets twice as much solar radiation as Earth.) As a result, the team calculates it has a 70 percent likelihood of being in the habitable zone of its star.

Kepler-442b get about two-thirds as much light as Earth. The scientists give it a 97 percent chance of being in the habitable zone.

“We don’t know for sure whether any of the planets in our sample are truly habitable,” explains second author David Kipping of the CfA. “All we can say is that they’re promising candidates.”

Prior to this, the two most Earth-like planets known were Kepler-186f, which is 1.1 times the size of Earth and receives 32 percent as much light, and Kepler-62f, which is 1.4 times the size of Earth and gets 41 percent as much light.

The team studied planetary candidates first identified by NASA’s Kepler mission. All of the planets were too small to confirm by measuring their masses. Instead, the team validated them by using a computer program called BLENDER to determine that they are statistically likely to be planets. BLENDER was developed by Torres and colleague Francois Fressin, and runs on the Pleaides supercomputer at NASA Ames. This is the same method that has been used previously to validate some of Kepler’s most iconic finds, including the first two Earth-size planets around a Sun-like star and the first exoplanet smaller than Mercury.

After the BLENDER analysis, the team spent another year gathering follow-up observations in the form of high-resolution spectroscopy, adaptive optics imaging, and speckle interferometry to thoroughly characterize the systems.

Those follow-up observations also revealed that four of the newly validated planets are in multiple-star systems. However, the companion stars are distant and don’t significantly influence the planets.

As with many Kepler discoveries, the newly found planets are distant enough to make additional observations challenging. Kepler-438b is located 470 light-years from Earth while the more distant Kepler-442b is 1,100 light-years away.

The paper reporting these results has been accepted for publication in The Astrophysical Journal and is available online.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.


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  • Over the last few decades, powerful new ground and space-based observatories have completely changed previous understanding of the outer Solar System.

  • Wolverine

    We need to study the stars but forget about the fantasy of traveling to a new earth! Deal with the one we have and seek better cooperation among its inhabitants…..we have no other alternative.

  • CharlieSeattle

    ahhh, but to get there.

    • catalinda8

      I know, it would be torturous to know there’s life on another planet, but we can’t get to them, and they can’t get to us… Although maybe it would finally kickstart the space program into high gear again. (And that “life” better not just be bacteria or something boring like that, I just have to add…)

      • CharlieSeattle

        Given the distances, seeding distant planets or even the Andromeda Galaxy with a massive shotgun blasts of trillions of earth borne life forms like amino acids, lichen and bacteria encased in ice may be the best we can ever do.

        Andromeda and the Milky Way will merge in about 4 billion years. So, send our fastest spacecraft, plant the seeds and let them grow.

        Resisting Radiation – By Leslie Mullen – Mar 20, 2006

        astrobio. net/topic/origins/extreme-life/resisting-radiation/

        …the only organisms known to survive space exposure – at least in the short term – are bacteria and lichen. Bacteria need some shielding so they won’t get fried by the UV, but lichen have enough biomass to act as a protective spacesuit.

        But even with a good barrier in place, sometimes radiation damage does occur. The lichen and bacteria hibernate while in space – they do not grow, reproduce, or engage in any of their normal living functions. Upon return to Earth, they exit this dormant state and, if there was damage inflicted, proteins in the cell work to piece together DNA strands that were broken apart by radiation.

        • catalinda8

          Well, I was thinking more about life that might have evolved on that planet (or those planets) just as life evolved on Earth – unless I’m misreading your post? I don’t know if I really want to wait 4 billion years for things to finally get close enough to hop over to… I mean, I keep myself in shape, but by then, I’m not sure I’ll be spry enough to go planet hopping. 😉

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