Eight Likely Habitable Exoplanets Discovered

By Liz Kruesi | January 6, 2015 12:14 pm

This artist’s conception depicts an Earth-like planet orbiting an evolved star that has formed a stunning “planetary nebula.” Credit: David A. Aguilar (CfA)

The search for a planet like our own Earth just got one step closer to the ultimate goal. Astronomers have confirmed three more exoplanets orbiting their stars in the habitable zone — where the temperature is just right for liquid water to exist on a planet’s surface. They also added five worlds that are likely in their stars’ habitable zones.

This new crop of planets nearly doubles the number of worlds up to twice Earth’s size in habitable zones. And it includes two of the most Earth-like planets yet discovered.

Confirming Distant Worlds

The observations came from the Kepler telescope, which stared at the same patch of sky for four years between 2009 and 2013. Specifically, Kepler was tracking tiny drops in light as planets crossed in front of their stars.

While Kepler has found 1,004 confirmed exoplanets and another 4,175 possible worlds, it also sees objects that turn out to be false-positives — such as distant background stars that are eclipsed by other stars. To verify that Kepler’s possible planets are actually there, astronomers then have to further observe the objects with ground-based telescopes and run advanced computer simulations.

Guillermo Torres of the Harvard-Smithsonian Center for Astrophysics and colleagues used both of these methods to verify the eight new worlds and analyze three previously confirmed ones. The new planets all orbit stars smaller and cooler than the Sun and therefore have habitable zones that lie closer to their star. Five are smaller than two times Earth’s width, which means they’re much more likely to be rocky instead of gaseous.

Earth Cousins

The scientists found that two of these newly verified exoplanets look especially Earth-like – in fact, argue the scientists, the most similar ones found to date.

The first, known as Kepler-438b, is only slightly larger than Earth but orbits much more closely to its sun, which it circles in just 35 days. That means it receives about 40 percent more light than Earth. Light is important as a factor in habitability: Too much, and water would boil away; too little, and water will freeze. The researchers also believe, from their computer simulations, that Kepler-438b has a 70 percent chance of being a rocky world, like Mars, Earth, Venus, and Mercury are.

A slightly larger exoplanet, Kepler-442b, clocks in at about 1.34 times our planet’s width. It has a 112-day year and receives about two-thirds as much light as Earth. The researchers believe this world is also likely rocky. And they give it pretty strong chances of being habitable: According to their calculations, its 97 percent certain that it has the physical conditions to allow liquid water.

Looking Forward

“Growing this sample really helps us to make a more accurate estimate of the frequency of small habitable zone planets in the galaxy,” said SETI Institute’s Douglas Caldwell, who presented the information at the American Astronomical Society meeting today. “We’re not only closing in on an Earth twin, we’re better understanding the diversity in this special neighborhood.”

While these planets are promising candidates for harboring life, said co-author David Kipping of Harvard in a statement, “We don’t know for sure whether any of the planets in our sample are truly habitable.” Still, doubling the number of Earth-sized rocky worlds that might harbor surface water is a great start to finding those truly habitable planets.


CATEGORIZED UNDER: Space & Physics, top posts
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  • zlop

    Habitable planet range is much greater. Even in intergalactic space,
    on a planet without a star, a warm surface could exist.

    • ziff

      Warmed by what? Everything radiates energy which causes them to cool. So without something else to warm them up, any such planet would cool to incredibly cold temperatures.

      • zlop

        “Warmed by what?”

        The Cosmic Microwave Background interacts with an atmosphere. From that temperature, lapses down to warmer below. He3 has half an atmosphere pressure, at the CMB temperature.

        • ziff

          The CMB temperature is about 2.7 K, barely above absolute zero. And since radiant flux is proportional to T^4, its impact would be a million billion times less than what our sun delivers to Earth.
          Consider the outer planets of our solar system. If those planets are too cold to support us *with* the help of the Sun and CMB, why would you expect the CMB alone be sufficent?
          If you have a scientific paper that says otherwise, please source it as i’d love to read it. But i don’t buy that CMB has any chance of warming a rogue planet to anything remotely close to Earth temperatures.

          • zlop

            “why would you expect the CMB alone be sufficient?”

            Radiation absorbed by the atmosphere, from the CMB = radiated from the atmosphere, to the CMB.

            Below the zone of radiation exchange, temperature is increased, magnified, per adiabatic lapse.

          • ziff

            “Radiation absorbed by the atmosphere, from the CMB = radiated from the atmosphere, to the CMB”

            If this is true, then you have a perfect blackbody and your planet’s temperature goes to 2.7 K.

            You can’t create energy. If everything that is absorbed is then emitted, there is no excess energy to do anything.

          • zlop

            “You can’t create energy”
            Energy is not created. Energy is conserved.
            Consider energy of a molecule, in the Earth’s atmosphere
            Potential + Kinetic — mgh+(7/2)kT
            Near the surface, all kinetic (warmer)
            High up, Colder.

          • ziff

            “Near the surface, all kinetic (warmer)
            High up, Colder.”

            Actually, that’s only true in the Tropopause. After about 10-15km up, atmospheric temperatures increase.

            But that’s not the point. In the case of Earth, the energy comes from the sun. But your rogue planet has no sun. You said: “Radiation absorbed by the atmosphere, from the CMB = radiated from the atmosphere, to the CMB”

            So the only source of energy is the CMB, and you just said that all that energy is re-radiated back to space. So where’s the extra energy to heat the surface?

            As i said, if you’ve got a source, please post it.

          • zlop

            “So where’s the extra energy to heat the surface?”

            You have a mental block, which cannot be resolved by appeal to authority.

            There is no extra energy, temperature is increased by gravitational force. Look up adiabatic atmosphere — lapse = -g/Cp

          • Curious

            I wish I could join in, but there would be no way to keep up with the two of you. I can’t imagine what you do for fun….

          • zlop

            Look up adiabatic atmosphere, to explain why, the top of the mountain is cold.

            Additionally, the Ocean is slightly warmer, at the bottom, because of gravitational lapse.

            Fluids convect up, when the temperature rises above the adiabatic lapse.

          • ziff

            I think the block is with you. The issue is not the adiabatic lapse rate (you’ve only quoted the simplest, dry, anyways). You’ve not explained your mechanism of action at all.

            The issue is you have no where near the energy to heat your atmosphere to Earth-like levels. To achieve equilibrium, the input must equal the output. A planet at Earth temperatures (~280K) will radiate *far* more energy back to space than the CMB can provide.

            Read up on blackbody behavior and radiation. The CMB has a temperature of less than 3K. That means a radiance upon the planet of of ~1.46 W/m^2sr. But an Earth-like planet has a temperature of 280K, and so will radiate ~110 W/m^2sr. So this planet would radiate 76 million times more energy than it receives. To counter this, your CMB-atmosphere interaction would have to produce 76 million times more energy than the CMB is inputting itself. Do you think that is possible?

            And if you do think that the CMB-atmopshere interaction can result in that much energy, explain why Neptune and Uranus (which have 20% and 15% Helium) are so cold.

          • zlop

            “The issue is you have no where near the energy to heat your atmosphere to Earth-like levels”
               Energy is concentrated by gravity.

            “This value equates to an “effective radiating temperature” of 300K (27°C). This is nothing like the surface of Venus.”

            “explain why Neptune and Uranus (which have 20% and 15% Helium) are so cold.”
               Top, effective radiating zone is cold.
            “Is It Raining Diamonds On Uranus and Neptune – SpaceDaily”

          • zlop

            Tgb of Venus is 248.2°K
            Tgb of Earth and Moon is 154.3°K

            So, intergalactic planet, Tgb = 2.72°K, would still be warmer below.

          • ziff

            “So, intergalactic planet, Tgb = 2.72°K, would still be warmer below.”
            Whether it’s warmer at the surface compared to the upper atmosphere is irrelevant. The point is it won’t be nearly warm enough to be habitable.

            A habitable planet needs to be ~280K. All matter radiates energy. And all that energy ultimately gets lost to space, no matter the mechanism. So to maintain a temperature of 280K, you need to have an equivalent amount of energy input. The CMB is no where close to having sufficient radiant flux to do this. Your rogue planet would cool to just a few degrees about absolute 0.

            “You are onto something. There is a net gain of energy above the Troposphere and a net loss of energy below the Stratosphere.”
            Actually, no. You are confusing temperature and energy- they are not the same thing.

          • zlop

            “Whether it’s warmer at the surface compared to the upper atmosphere is irrelevant.”
              I looked at Helium and Hydrogen phase diagrams. They would be liquid, at high temperature and high pressure. Solid surface would be too hot.

            “The point is it won’t be nearly warm enough to be habitable.”
               Hot enough for Aliens swimming in high pressure, liquid Helium and Hydrogen?

            “Actually, no. You are confusing temperature and energy- they are not the same thing.”
               Although colder, Stratosphere has more energy/molecule. When air, from the Stratosphere, falls into the Antarctic Vortex, energy is added to the Troposphere, and temperature rises.

  • stevlich

    But how can they find out if life exists in the habitable zone? They’re never going to have space telescopes that can see an object the size of a basketball on the surface. It’s going to be speculation forever with never any proof of alien life.

    • ziff

      It’s a difficult challenge, but you’d not necessarily have to see an individual critter to confirm life. You could possibly tell by analyzing spectrum of the planet’s atmosphere and identifying complex compounds. Or if intelligent, maybe they’re sending radio waves just as we Earthlings do (see SETI).

      • zlop

        Solar system sized phased arrays are possible, using orbiting satellites.
        What resolution?

      • Eric Lipps

        You don’t even have to find “complex compounds.” If you find a large percentage of free oxygen, that practically guarantees there’s life, since even on Earth, left to itself oxygen will simply combine with other elements to form CO2, silicate minerals and so on. There’s oxygen in our air only because living things (plants) break down carbon dioxide and are in turn sustained by animals reversing the process. (The reason this cycle didn’t keep oxygen from accumulating in the first place is that plants reached land many millions of years before animals did, so the CO2-to-oxygen side had a head start.)

  • zlop

    Looking at an Alien at Alpha Centauri, using a Solar System size radio telescope at 100 GHZ (battlefield radar frequency)

    distance to Alpha 4.35*9.461 * 10^15 meters
    λ = 0.003 meters (100 GHZ)
    distance to Pluto 5.9*10^12 meters
    r/( 4.358*9.461 * 10^15) =1.22* 0.003/(2* 5.9*10^12)
    Resolution is 12.8 meters, cannot see the Alien


    Near infrared λ = 10^-6 meters
    r/( 4.358*9.461 * 10^15) =1.22* (10^-6)/(2* 5.9*10^12)
    r = 0.00426 meters or 4 millimeters.

  • Ratatoskr

    You don’t need to find life in a distant solar system. We will probably find life soon outside of Earth in our own solar system.
    Understand what life IS, or simply what the building blocks are.

    With those findings we can conclude that life exists everywhere in the Universe.
    Our planet is not unique. Humans have a tendency to always think we are so special and unique, even on our own planet.

    • Charity5712

      I’m stunned
      that people
      able to
      in 1 month
      on the computer
      . look at more info

      • 19don36

        And how is that relevant to this discussion? If what you are peddling does that much damage to your brain, I would suggest staying very far away!

  • http://www.johnclarkprose.com johnclark1

    What a great argument for the existence of a God. Whoever or whatever he she or it is, was smart enough to keep all forms of life well apart, with no chance of communicating star to star and galaxy to galaxy. We are all within one extraordinary universe, an experiment which will blow up in a few billion years. And then what, a recycle?

    • zlop

      Bull CH4 — Universe has a tendency towards development, enabled by, Second Law Violation. The God was not so dumb, as to have to continually fine tune and send lightning bolts to impress blasphemers.

      • Buddy199

        The second law indicates that the universe undergoes constant entropy.

        • zlop

          “The second law indicates that the
          universe undergoes constant entropy.”?

          Second Law is just a fantasy, relying on a proof,
          that assumes, homogeneous, direction independent
          random velocity. Due to forces, motion is not
          direction independent, objects are not homogeneous.

          Entropy is a local approximation, similar to
          plane survey, on a curved Earth.

  • Smile it is almost Friday!

    I think this is facinating. I am collecting data for my science fiction novel. I want it to me at least a little beliveable. A little science in my fiction is a good thing.



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About Liz Kruesi

Liz Kruesi is a science writer specializing in everything astronomical. She studied physics and astrophysics in college and graduate school, before leaving behind mathematical equations to instead focus on the words that tell the stories of the universe.


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