In the last 14 years, astronomers have identified more than 4,000 planets orbiting far-away solar systems, but none seems to come close to KOI-467.04. Don’t be fooled by its unceremonious designation, for this is a rare astronomical gem.
According to a new study led by researchers at the Max Planck Institute for Solar System Research in Göttingen, Germany, KOI-467.04 is less than twice the size of Earth and orbits a star that is almost like a twin to our Sun. What’s more, the exoplanet orbits its star at a distance similar to that between Earth and the Sun, suggesting that its surface temperature is conducive to life.
In other words, the scientists may have found a twin solar system — all that astronomers have been wishing for since the first exoplanet was discovered in 1992.
Billions of planets, but there’s only one place like home… or is there?
There are billions — perhaps trillions — of stars in the Milky Way galaxy alone and, on average, each of those stars has at least one planet orbiting them
“We are seeing just how diverse planets are. Planets are more common than they were thought to be before the first exoplanets were found. The number of planets in our galaxy is at least as large as the number of stars. But while planets and planetary systems are so diverse, planets like Earth may be very, very rare,” Dr. Jack Lissauer, a scientist at the NASA Ames Research Center and co-investigator of the Kepler mission, told me last year at a conference in Budapest.
The vast majority of exoplanets identified by astronomers in the past are the size of gas giants like Neptune or Jupiter and orbit their parent stars much too close for life to stand a chance.
Occasionally, astronomers will come across exoplanets that are Earth-sized and potentially rocky, but these planets either orbit too close or too far away from the star. On the extremely rare occasion that scientists discover an Earth-sized rocky exoplanet orbiting in the Goldilocks Zone — or habitable zone, where the distance from the parent star is just right for liquid water to form.
But even then, things are typically far from perfect. Almost all exoplanets less than twice the size of Earth found thus far orbit around a red dwarf, which present their own set of limitations.
Red dwarfs are by far the most common types of stars in the Universe. They’re small, dim, and relatively cool, and also have a long lifetime.
Yet, although life on an exoplanet orbiting a red dwarf would have twice as much time than that on Earth to evolve, it would have to overcome other important challenges.
One has to do with radiation. While the surface temperature might be just right for liquid water to form, exoplanets orbiting red dwarfs are mostly hit by infrared rather than visible light.
If that wasn’t enough, red dwarfs also regularly spew powerful solar flares that can fry nearby planets. What’s more, because red dwarfs are so faint, exoplanets hoping to harbor life need to orbit so close to the parent stars that they get deformed by the stellar gravity. This can result in tidal heating that can trigger global volcanism and turn the promising exoplanet into a hellish world.
So, it’s not just a question of exoplanet quality, stellar quality is vital too. Now, an international team of researchers think they’ve found one that checks all the boxes.
Mirror Earth and Sun
The Earth-like planet candidate that orbits a sun-like star is located over 3,000 light-years away, in the Kepler-170 system.
It was first identified in 2009 and since 2014, astronomers have found that it hosts two exoplanets, known as Kepler-160b and Kepler-160c, which are both much bigger than Earth and in relatively close orbits around their stars. Nothing to warrant particular attention so far.
But then the researchers combed the archival Kepler data of Kepler-160 hoping to perhaps find other planets using a novel method developed by Michael Hippke and René Heller, both from Max Planck. Their investigation was prompted by evidence that Kepler-160c’s orbit was perturbed — something was out there.
This is when they found another two planets, among them the exciting KOI-456.04.
“Our analysis suggests that Kepler-160 is orbited not by two but by a total of four planets,” Heller said in a statement.
“The planetary signal is so faint that it’s almost entirely hidden in the noise of the data. Our new search mask is slightly better in separating a true exoplanetary signal from the noise in the critical cases,” Heller adds.
According to Heller and colleagues, KOI-456.04 has a radius of 1.9 Earth radii (almost twice as large as Earth) and orbits its parent star every 378 days — that’s mighty close to Earth’s 365 days (or 366 days during a leap year).
As for the star, the astronomers estimate that its radius is 1.1 that of the Sun, with a surface temperature of around 5,200 degrees Celsius, just 300 degrees shy of that of the sun. Its luminosity is also sun-like.
Given this information, the researchers believe that KOI-456.04 might have an average surface temperature of around 5 degrees Celsius, as long as it has an atmosphere that can support at least a mild Earth-like greenhouse gas effect.
“KOI-456.01 is relatively large compared to many other planets that are considered potentially habitable. 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,” Heller
Don’t get too excited, though. As a caveat, the researchers claim that they cannot entirely rule out KOI-456.01 as a statistical fluke. According to the study published in the journal Astronomy & Astrophysics, the odds of KOI-456.04 being a real planet and not some statistical aberration is 85%. Formal planetary status requires a 99% degree of confidence.
All hope is not lost, though. Astronomers will have a good chance to confirm their findings once ESA’s PLATO space mission launches in 2026. Plato will specialize in the examination of rocky exoplanets orbiting in habitable zones around Sun-like stars, particularly focusing on the potential for these planets to hold liquid water. Fingers crossed.
