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'Orange dwarfs' may be the best stars to study in search for life

An infographic compares the potential of red dwarfs (M), orange dwarfs (K) and sun-like stars (G) as potential hosts for life.
An infographic compares the potential of red dwarfs (M), orange dwarfs (K) and sun-like stars (G) as potential hosts for life.
(Image: © NASA, ESA and Z. Levy (STScI))

Move over, red dwarfs. Emerging research shows that another star type could be more friendly to life.

Building on nearly 30 years of exoplanet discoveries and studies, some researchers now suggest that orange dwarfs, not the more commonly discussed red dwarfs, could be the best stars to host life. These stars are more stable than their redder counterparts; they burn for billions of years and are less likely to send out damaging X-ray and ultraviolet radiation.

There are other arguments in favor of looking for life around orange dwarfs, too, the scientists behind a new study said during a presentation on Jan. 7 at the 235th meeting of the American Astronomical Society in Honolulu. For example, even though we're used to living with a larger sun, orange dwarfs are three times more abundant than stars of our type, the researchers said. More abundant stars means more chances at life.

Related: The Biggest Alien Planet Discoveries of 2019

Luckily for scientists, orange dwarfs (also known as K stars) represent relatively easy targets for finding planets. The light of such stars is slightly dimmer than our own star, making planets more easily visible as they cross the star's face. And the mass of an orange dwarf is a little smaller than that of a star like our sun, making for a bigger gravitational wobble in the star as it gets tugged on by an orbiting planet.

Orange dwarfs are also remarkably long-lived compared with our sun, allowing more time for complex life to potentially arise on their planets. Our sun is roughly halfway through its 10-billion-year estimated life span, and the star is expected to grow so large that it will make Earth uninhabitable in only 1 billion or 2 billion years. By contrast, orange dwarfs remain more stable and can last for between 15 billion and 45 billion years.

"The K stars, especially the warmer ones, have the best of all worlds," Edward Guinan, an astronomer at Villanova University in Pennsylvania, said in a NASA statement. "If you are looking for planets with habitability, the abundance of K stars pump up your chances of finding life."

Related: How to Tell Star Types Apart (Infographic)

Guinan and fellow Villanova astronomer Scott Engle are co-leading a program called "GoldiloKs," which is generating data about K-type stars as well as stars like our sun, which are called G stars. Working with undergraduate students, the scientists seek to learn more about K and G stars: how old they are, how fast they rotate, and how much X-ray and ultraviolet radiation they emit.

The researchers are also scrutinizing planets that are potentially habitable and that orbit nearby orange dwarfs, like Kepler-442, Tau Ceti and Epsilon Eridani. Scientists usually define "habitability" as referring to rocky worlds orbiting at a distance from a star that permits water to exist on the planetary surface. If the planet is too close to the star, the water may evaporate, and if the world is too far, that water may freeze into ice. (Planetary habitability can also be defined in metrics such as exposure to radiation, which GoldiloKs is trying to take into account, too.)

GoldiloKs researchers are pulling data from several telescopes to inform the research, including NASA's Hubble Space Telescope, NASA's Chandra X-ray Observatory and the European Space Agency's XMM-Newton satellite. Powerful future observatories, such as NASA's James Webb Space Telescope, which is expected to launch in 2021, could also study these worlds, the researchers said.

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  • rod
    Admin said:
    Move over, red dwarfs. Emerging research shows that another star type could be more friendly to life.

    'Orange dwarfs' may be the best stars to study in search for life : Read more

    Spectral class K stars are more abundant than stars like our Sun (G class) as the report notes. Many however, are about 0.8 solar mass and about 0.85 solar radii, they emit about 40% of the Sun's energy window in the orange spectrum region or 600 to 650 nm wavelengths. Many of the K stars surface temperatures <= 5000 K and rotate more rapidly than the Sun, some 3-4 km/s or more. Presently, this site shows 4168 confirmed exoplanets, The Extrasolar Planets Encyclopaedia

    415 are listed as exoplanets around class K type stars. 573 exoplanets are listed as orbiting class G host stars. All of these confirmed exoplanets around K and G type stars, show a wide variety of eccentricity and orbital period in days along with a wide range of semi-major axis distances from their parent stars in their elliptical orbits.
    Reply
  • voidpotentialenergy
    I still think red dwarfs are still the best bet to find life, just a numbers game.
    Trouble is we are looking for the wrong thing.
    Looking for an earthlike world around a red dwarf when we should be looking for a earthlike world going around a neptune sized world going around a red dwarf.
    Tidal locking of earth would make it a nasty place going around a red dwarf of even quiet type.

    Probably 1/2 of red dwarfs are pretty nasty flare monsters though so only 1/2 might be safe.
    They seem to settle down with age though.
    Then again what is 5 or 10 billion years of nasty flare monsters in a life of 1-2 trillion years.
    Reply
  • rosa u podne
    voidpotentialenergy said:
    Then again what is 5 or 10 billion years of nasty flare monsters in a life of 1-2 trillion years.
    I see two problems for the current search for habitable planets around red dwarfs:

    1. In the few first billion years, earth-sized planets in a habitable zone could probably lose its atmosphere due to star flares.

    2. The universe is around 13 billion years old. Nearby stars are all a few billion years old. Right now, there might not be many earth-like planets around calm nearby red dwarfs.
    voidpotentialenergy said:
    Looking for an earthlike world around a red dwarf when we should be looking for a earthlike world going around a neptune sized world going around a red dwarf.
    In case the magnetic field of a parent planet is strong and wide enough to protect an earth-sized moon, the moon could be habitable.
    Reply
  • rod
    I expanded my MS SQL query on the exoplanet site and looked for all exoplanets confirmed around stars between 0.7 and 0.85 solar masses, common for most spectral class K, main sequence stars. 602 exoplanets reported for duty in the MS SQL query. The average mass is 4.96 Jupiter masses. Using the query and looking for exoplanets reported orbiting host stars in the mass range 0.2 through 0.6 solar masses (spectral class M, red dwarf stars), 330 exoplanets are confirmed. Average mass 6.7 Jupiter masses. Presently none are confirmed as earth-like or habitable exoplanets.
    Reply
  • voidpotentialenergy
    rosa u podne said:
    I see two problems for the current search for habitable planets around red dwarfs:

    1. In the few first billion years, earth-sized planets in a habitable zone could probably lose its atmosphere due to star flares.

    2. The universe is around 13 billion years old. Nearby stars are all a few billion years old. Right now, there might not be many earth-like planets around calm nearby red dwarfs.

    In case the magnetic field of a parent planet is strong and wide enough to protect an earth-sized moon, the moon could be habitable.
    I agree it's early days for red dwarfs.
    I think for red dwarfs we need to be a moon.
    Breaks tidal locking and offers protection.

    Same percentage game works for all stars though as a moon of a large planet.
    If we are looking for more than algae then the stability and safety of being a moon is attractive.

    Our earth without a moon is a wobble beast so advanced life would find the climate changes very difficult.
    Earth would probably experience long ice ages.

    Earth/ moon setup= oddity
    Big planet/moon setup= many

    Finding earth like planets in the right spot, few , finding them with a decent moon very few of them.
    Finding large planets in the right spot, lots, with moons nearly all,
    With an earthlike moon, few.
    Reply
  • rosa u podne
    rod said:
    I expanded my MS SQL query on the exoplanet site and looked for all exoplanets confirmed around stars between 0.7 and 0.85 solar masses, common for most spectral class K, main sequence stars. 602 exoplanets reported for duty in the MS SQL query. The average mass is 4.96 Jupiter masses. Using the query and looking for exoplanets reported orbiting host stars in the mass range 0.2 through 0.6 solar masses (spectral class M, red dwarf stars), 330 exoplanets are confirmed. Average mass 6.7 Jupiter masses. Presently none are confirmed as earth-like or habitable exoplanets.
    What exoplanet site are you writing about? I am quite an expert in MSSQL. I'd like to have access to that site.
    Reply
  • rod
    rosa u podne said:
    What exoplanet site are you writing about? I am quite an expert in MSSQL. I'd like to have access to that site.

    rosa u podne, here is the site, The Extrasolar Planets Encyclopaedia, presently there are 4169 exoplanets listed as confirmed. You can click on All Catalogs, and dowload a copy. I use .csv format and import into Excel, ACCESS DB. From there I run charts and MS SQL queries. I find this much more helpful to compare with different, popular science site reports on exoplanets, and use real data :)
    Reply