Our region of the Milky Way is dominated by red dwarf stars, but if you look up at the night sky you’ll not see any of them.
Smaller than our Sun, not one single red dwarf star is visible to the naked eye, not even the next star along, Proxima Centauri, which is just 4.24 light-years distant. Yet, being the most common and the longest-lasting stars of all, they dominate planet-hunting.
In fact, most of the Earth-sized exoplanets found in the habitable zones of stars orbit red dwarf stars, which are dim and emit infrared radiation rather than visible light.
Despite the fact that life may have had longer to evolve around red dwarf stars, they have a tendency to flare often, with high-energy bursts of radiation presumed to make life on any surrounding planets unlikely.
What if we could find an Earth-like planet around a Sun-like star? Isn’t that the real prize among exoplanet-hunters?
Today the Max Planck Institute for Solar System Research (MPS) in Göttingen is reporting that a project it led has found just that; an Earth-like, probably rocky planet called KOI-456.04 that orbits a star called Kepler-160.
This promising star system is 3,000 light-years from the solar system.
This is how similar KOI-456.04 is to Earth:
- A year on KOI-456.04 is 378 days.
- It receives about 93 percent of the sunlight received on Earth.
- Its surface temperature would be +5º Celsius, on average—about 10º Celsius lower than the Earth’s mean global temperature—if it has an Earth-like atmosphere.
- It’s in its star’s “habitable zone” where liquid water could exist on its surface.
In fact, the only major difference between KOI-456.04 and Earth is that the exoplanet is almost twice the size of Earth. “It’s relatively large compared to many other planets that are considered potentially habitable,” said Dr. René Heller, MPS scientist and lead author of the new study. “But it’s the combination of this less-than-double the size of the Earth planet and its solar-type host star that make it so special and familiar.”
However, what’s key here is the star itself. In terms of its own physical properties, Kepler-160 is a virtual mirror image of our Sun;
- Kepler-160’s radius is a tenth bigger than the Sun.
- Its surface temperature of 5,200º Celsius is just 300ºC cooler than the Sun.
- It’s got a very similar luminosity.
- It bathes KOI-456.04 in much the same kind of daylight as we receive on Earth.
In short, Kepler-160 is an astrophysical portrayal of our own parent star, says the MPS. “The full picture of habitability involves a look at the qualities of the star too”, said Heller.
Astronomers already knew that Kepler-160 hosts two other exoplanets—Kepler-160 b and Kepler-160 c—both of which are much larger than Earth and orbit closer to the star.
KOI-456.04 was found because it transited its host star, causing that star’s brightness to drop slightly.
However, it could, admit the astronomers, be a statistical fluke, or a systematic measurement error instead of a genuine planet.
The team gives KOI-456.04 an 85% chance of being an actual planet, and given that obtaining formal planetary status requires 99% certainty, this Earth-like planet around a Sun-like star will need more robust evidence before it officially exists.
“For now, KOI-456.04 remains a good candidate,” said Heller.
Cue the PLAnetary Transits and Oscillations of stars (PLATO) space telescope that the European Space Agency (ESA) will launch in 2026. PLATO’s mission will be to discover Earth-sized planets around Sun-like stars.
If PLATO is pointed in the right direction then KOI-456.04 might just get a life of its own.
Wishing you clear skies and wide eyes.
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