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These alien planets may be more habitable for life than our own Earth

An artist's depiction of a rocky, Earth-size exoplanet.
An artist's depiction of a rocky, Earth-size exoplanet.
(Image: © NASA Ames/SETI Institute/JPL-Caltech)

On Earth, there is life virtually everywhere there is liquid water. As such, the hunt for extraterrestrial life has focused on so-called habitable or "Goldilocks" zones — areas around stars temperate enough for planets to possess liquid water on their surfaces. 

Since Earth is the only inhabited world known, this planet is usually the focus of studies on habitability. However, scientists have reasoned that worlds other than Earth-like ones could offer conditions suitable for life to emerge and evolve. Such worlds might even prove "super-habitable," or have better chances at hosting life than Earth.

"We are so over-focused on finding a mirror image of Earth that we may overlook a planet that is even more well-suited for life," study lead author Dirk Schulze-Makuch, an astrobiologist at Washington State University in Pullman and the Technical University of Berlin, told Space.com.

Related: 10 exoplanets that could host alien life

Potential havens for life

To search for potentially super-habitable exoplanets, researchers investigated the Kepler Object of Interest Exoplanet Archive, focusing on 4,500 planetary systems that likely possessed rocky planets within their stars' habitable zones.

In addition to looking at planetary systems with yellow dwarf stars like our sun, the scientists also looked at orange dwarf stars, which are somewhat cooler, dimmer and less massive than our sun. Whereas our sun has a lifetime estimated at less than 10 billion years, orange dwarfs have lifetimes of 20 billion to 70 billion years. Since complex life took about 3.5 billion years to appear on Earth, the longer lifetimes of orange dwarfs could give planets within their habitable zones more time to develop life and accrue biodiversity. Orange dwarfs are also about 50% more frequent than yellow dwarfs in the Milky Way.

"Our sun is actually not the best kind of star for hosting a planet with lots of life on it," Schulze-Makuch said.

An older planet might give life more time to evolve. Earth is about 4.5 billion years old, so the researchers speculated the sweet spot for life is a planet that is between 5 billion to 8 billion years old.

The size and mass of a planet can also influence how well it can support life. A planet that is 10% wider than Earth would have more habitable land. One that is about 1.5 times Earth's mass would be expected to retain its interior heat longer, which in turn would help keep its core molten and its protective magnetic fields active. A heavier planet would also have stronger gravity to help retain its atmosphere over a longer span of time.

Worlds that are slightly warmer than Earth by about 8 degrees Fahrenheit (5 degrees Celsius) might be super-habitable, since they could have larger tropical zones that could be more benign for more biodiversity. However, warmer planets might also need more moisture, since greater heat could expand deserts.

In addition, planets with the same amount of land area as Earth but broken up into smaller continents might be more habitable. When it comes to continents that are too large (such as Earth's past continent Gondwana about 500 million years ago), their centers are far from oceans, often rendering the interiors of large continents vast, inhospitable deserts. Moreover, Earth’s shallow waters have a greater biodiversity than its deep oceans, so planets with shallower waters may be super-habitable.

Super-habitable haul

All in all, the scientists identified 24 potentially super-habitable planets. None of them met all the criteria the researchers drew up for super-habitable planets, but one did meet at least two — KOI 5715.01, a planet about 5.5 billion years old and 1.8 to 2.4 times Earth's diameter orbiting an orange dwarf about 2,965 light-years away. It might have an average surface temperature about 4.3 degrees F (2.4 degrees C) cooler than Earth, but if it has more greenhouse gases than Earth to trap heat, it might be super-habitable, they said.

Schulze-Makuch's favorite potentially super-habitable world from these 24 was KOI 5554.01, a world about 6.5 billion years old 0.72 to 1.29 times Earth's diameter orbiting a yellow dwarf about 700 light-years from Earth. 

"I really liked the average surface temperature — about 27 degrees C [80 degrees F]," Schulze-Makuch said. "And it's probably about Earth's size, and a little bit older than Earth."

All 24 of these potentially super-habitable planets are more than 100 light-years from Earth. This makes them too far for NASA's Transiting Exoplanet Survey Satellite (TESS) spacecraft to capture high-quality images from to learn more about them. 

Still, Schulze-Makuch noted that future spacecraft, such as NASA's James Webb Space Telescope, NASA's LUVIOR space observatory and the European Space Agency's PLATO space telescope, could shed light on these worlds.

"We caution that while we search for super-habitable planets, that doesn't mean that they necessarily contain life," Schulze-Makuch said. "A planet can be habitable or super-habitable but uninhabited."

The scientists detailed their findings online Sept. 18 in the journal Astrobiology.

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  • rod
    This is a very interesting exoplanet study report. The paper says "Although an exact count of these potentially superhabitable planets is impossible given the uncertainties in our mostly qualitative model and given the uncertainties in the observed parameters, Fig. 2 shows that there are indeed at least about two dozen possible candidates for a superhabitable planet. We caution that we do not have any observational signatures of life from any of these planets. In fact, only Kepler 1126 b (KOI 2162) and Kepler-69c (KOI 172.02) are statistically validated planets (Morton et al., 2016). The other objects are unconfirmed Kepler Objects of Interest (KOIs), some of which may turn out to be astrophysical false positives.", In Search for a Planet Better than Earth: Top Contenders for a Superhabitable World, https://www.liebertpub.com/doi/10.1089/ast.2019.2161, "Abstract..."

    I checked for exoplanet masses 1.1 to 1.5 earth masses using MS SQL query and found 9 confirmed, most are 5 to 23 day orbital periods and the list includes TRAPPIST-c and g exoplanets, http://exoplanet.eu/catalog/
    Reply
  • rocketman6799
    These planets are so far away that the on your journey to them you just might see another space ship pass you up because of improved propulsion advancement.
    That risk is as great a risk on how to survive the journey and living on these "Goldilocks Planets".

    The vast distances of space is further proof that earth is a penal colony akin to what Alcatraz was and the history of Australia.
    Look how violent and distructive our society is. Would you want this mindset out exploring space, trashing every planet they visit, rape it of it's natural resources then move on to the next one?
    Reply
  • Wolfshadw
    rocketman6799 said:
    The vast distances of space is further proof that earth is a penal colony akin to what Alcatraz was and the history of Australia.

    Whether we like to admit it or not, the human race, as a whole, is more akin to a virus that multiplies, consumes and spreads until there is nothing left. For the time being, we are quarantined on this planet and it is my fervent hope (not that I'll live to see it) that we either die out here on a dead Earth or that we (the race) evolve to a less destructive organism long before we move beyond the reach of our star.

    -Wolf sends
    Reply
  • Wolfshadw
    rod said:
    I checked for exoplanet masses 1.1 to 1.5 earth masses using MS SQL query and found 9 confirmed, most are 5 to 23 day orbital periods and the list includes TRAPPIST-c and g exoplanets

    Can you modify your query to include the type of star? 1.1 to 1.5 Earth masses is fine, but if it's orbit is 5 to 23 days around a yellow dwarf like our star, that doesn't bode well, one would think.

    -Wolf sends
    Reply
  • rocketman6799
    Wolfshadw said:
    Whether we like to admit it or not, the human race, as a whole, is more akin to a virus that multiplies, consumes and spreads until there is nothing left. For the time being, we are quarantined on this planet and it is my fervent hope (not that I'll live to see it) that we either die out here on a dead Earth or that we (the race) evolve to a less destructive organism long before we move beyond the reach of our star.

    -Wolf sends

    Yes pretty much what was said in one of the movies in the Matrix.
    Reply
  • rod
    Wolfshadw said:
    Can you modify your query to include the type of star? 1.1 to 1.5 Earth masses is fine, but if it's orbit is 5 to 23 days around a yellow dwarf like our star, that doesn't bode well, one would think.

    -Wolf sends
    Wolfshadow, you can run a query at the site too.
    mass:mjup > 0.0034 and mass:mjup < 0.005 will execute the query in the filter field. The star types are listed. TRAPPIST system is 0.08 solar mass red dwarf, other stars smaller too like 0.5 solar mass, one is larger in mass than our Sun, etc.

    http://exoplanet.eu/catalog/
    Reply
  • MS Geneva
    I also wonder how important the presence of a magnetic field is to sustain life. Its the magnetic field after all that protects earth from a lot of dangerous cosmic radiation out there. Can they detect magnetic fields for these habitable planets?
    Reply
  • rod
    I have not read reports of magnetic fields documented on exoplanets but some are looking for them.
    'A New Method for Detecting Magnetic Fields in Exoplanets', https://ui.adsabs.harvard.edu/abs/2020AAS...23532107O/abstract, January 2020.

    We have a new report today about habitable Earth and magnetic field, the Moon is used too. 'Life on earth: Why we may have the moon's now defunct magnetic field to thank for it', https://phys.org/news/2020-10-life-earth-moon-defunct-magnetic.html
    Reply
  • Cosmo47
    rod said:
    This is a very interesting exoplanet study report. The paper says "Although an exact count of these potentially superhabitable planets is impossible given the uncertainties in our mostly qualitative model and given the uncertainties in the observed parameters, Fig. 2 shows that there are indeed at least about two dozen possible candidates for a superhabitable planet. We caution that we do not have any observational signatures of life from any of these planets. In fact, only Kepler 1126 b (KOI 2162) and Kepler-69c (KOI 172.02) are statistically validated planets (Morton et al., 2016). The other objects are unconfirmed Kepler Objects of Interest (KOIs), some of which may turn out to be astrophysical false positives.", In Search for a Planet Better than Earth: Top Contenders for a Superhabitable World, https://www.liebertpub.com/doi/10.1089/ast.2019.2161, "Abstract..."

    I checked for exoplanet masses 1.1 to 1.5 earth masses using MS SQL query and found 9 confirmed, most are 5 to 23 day orbital periods and the list includes TRAPPIST-c and g exoplanets, http://exoplanet.eu/catalog/

    I use the Exoplanet phone app database. Can you help me find KOI 5715.01 and KOI 5554.01 in there? I did a search and came up empty. Many thanks.
    Reply
  • rod
    Cosmo47, good question. I checked quickly using MS BING, KOI 5715.01. It is listed as a candidate exoplanet so at the moment, not confirmed, https://exoplanetarchive.ipac.caltech.edu/cgi-bin/DisplayOverview/nph-DisplayOverview?objname=KOI-5715.01&type=KEPLER_CANDIDATE
    When it comes to exoplanet databases, I use these two sites as my SOR or System of Record :)

    https://exoplanetarchive.ipac.caltech.edu/index.htmlhttp://exoplanet.eu/catalog/
    Reply