Astronomers Have Found the Star/Exoplanet Combo That’s the Best Twin to the Sun/Earth

At times, it seems like there’s an indundation of announcements featuring discoveries of “Earth-like” planets. And while those announcements are exciting, and scientifically noteworthy, there’s always a little question picking away at them: exactly how Earth-like are they, really?

After all, Earth is defined by its relationship with the Sun.

There’s no strict definition of the term “Earth-like.” It just means a world that’s similar in some respects.

But most of the time when the term Earth-like is used to describe an exoplanet, it refers to the size, and to the potential for liquid water to persist on the surface. The problem is, most worlds that are described as Earth-like—most exoplanets in fact—are orbiting red dwarf stars.

“The full picture of habitability, however, involves a look at the qualities of the star too.”

Dr. René Heller, Lead Author, Max Planck Institute for Solar System Research.

Red dwarf stars are very different from our Sun. They’re small, dim, and cool. They’re the smallest and coolest stars on the main sequence. The Sun, on the other hand, is large, luminous, and has a surface temperature of about 5700 K (5420 C) compared to a red dwarf’s surface temperature of about 2,000 K (1730 C).

So if an exoplanet described as Earth-like is orbiting a red dwarf star, how Earth-like can it really be? It’s more accurate to describe planet-star pairs as Earth-Sun-like, since the relationship between a planet and its star determines to much about the planet.

The author of a new study holds that view.

The study is titled “Transit least-squares survey. III. A 1.9 R? transit candidate in the habitable zone of Kepler-160 and a nontransiting planet characterized by transit-timing variations.” The lead author is Dr. René Heller from the Max Planck Institute for Solar System Research (MPS). The study is published in the journal Astronomy and Astrophysics.

When it comes to habitabiliy, and whether or not a planet is Earth-like, Heller says in a press release that “The full picture of habitability, however, involves a look at the qualities of the star too.”

The new paper revolves around Kepler-160, a main-sequence star very similar to the Sun. Kepler-160 is about 90% the mass of the Sun, about 1.12 the radius of the Sun, and has a surface temperature of about 5470 K (5200 C). That’s very similar to the Sun’s surface temperature, which is about 5770 K (5500 C).

Kepler 160 is about 3140 light years away, in the constellation Lyra.

This distant star also has two confirmed planets orbiting it, and astronomers have known about them for years. Those planets are named Kepler-160 b and Kepler-160 c, following exoplanet naming conventions. Both of those planets are considerably larger than Earth, and they orbit closely to the star. They’re far too hot for life as we know it to survive there.

But something’s happening with Kepler-160 c (K160c). It’s wobbling, and something small is tugging on it to cause these tiny orbital variations. Was there something hidden in the original Kepler data? Another small planet in orbit around K160?

That’s where Heller and his colleagues come in. They had already been successful combing through existing Kepler data and finding planets that were missed. In 2019, Keller and his colleagues, Michael Hippke and Kai Rodenbeck, published a paperpresenting the discovery of 17 new exoplanets hidden in the original Kepler data. And they were all in solar systems where planets had already been discovered.

Now it looks like they’ve done it again.

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