Ross 128b: How Far Away Is Our Closest Potentially Habitable Exoplanet?

A little less than 11 light years from our solar system, in the constellation Virgo, lives a red dwarf star called Ross 128. But orbiting this faint solar neighbor is the closest potentially habitable Earth-like planet astronomers have ever detected, called Ross 128 b.

A little less than 11 light years from our solar system, in the constellation Virgo, lives a red dwarf star called Ross 128. There’s nothing inherently special about Ross 128; it’s a typical red dwarf star, one of the hundreds of billions throughout the Milky Way. But orbiting this faint solar neighbor is the closest potentially habitable Earth-like planet astronomers have ever detected, called Ross 128 b.

The nearest Earth-like exoplanet to us, Proxima b, orbits Proxima Centauri less than four light years away, but because of Proxima Centauri’s young age and frequent bursts of radiation, it is not believed to be habitable. Proxima Centauri is a red dwarf and is the Sun’s closest known stellar neighbor. Ross 128 is currently drifting toward our solar system, and in about 79,000 years, it will become our nearest celestial neighbor.

Humanity is living in the golden age of exoplanet discovery. Exoplanets are planets that orbit stars other than the Sun, and since 51 Pegasi B, the first exoplanet orbiting a Sun-like star was detected in 1995, astronomers have found thousands throughout the Milky Way.

“It’s not the only potentially habitable planet we’ve detected this year—just the closest one. It’s been a fantastic year for finding planets,” said Xavier Bonfils, leader of the Université Grenoble Alps team that made the discovery.

Indeed, it has been; 162 exoplanets were found in 2017 alone (so far), although none have yet been confirmed to be able to harbor life. The research is published in the Journal of Astronomy and Astrophysics.

Does Ross 128 harbor a habitable world? Maybe.

The exoplanet, which has been designated Ross 128 b, is 1.35 times the mass of the Earth and orbits its star at only 5 million kilometers, or 20 times closer than Earth is to the Sun. Ross 128 b’s proximity means it receives 1.38 times more energy from its star than Earth does from the Sun, even though Ross 128 is 280 times less luminous than the Sun. Red dwarf stars, like Ross 128, are much smaller and far less luminous than stars like the Sun.

These characteristics place the “habitable zone,” an orbital region where liquid water could exist on the surface of a planet, of Ross 128 much closer to the star than the Sun’s. According to Bonfils and his team, Ross 128 b likely lies in the “inner edge” of its star’s habitable zone. Ross 128 b whips around its star in just 9.9 days.

The age of the system is also promising for potential habitability of Ross 128 b; at nearly 7 billion years old, the planet’s rotation has had plenty of time to slow down and stabilize, making the prospect of habitability more promising. A slow, stable rotation means Ross 128 b could have a temperate climate and cyclical seasons, like Earth. Life on Earth appeared around 3.9 billion years ago, and Ross 128 b has had nearly twice the amount of time for life to potentially evolve. Given its age and the fact that Ross 128 is magnetically quiet and doesn’t erupt with frequent flares, Ross 128 b is an auspicious place to look for life.

Just because Ross 128 b is Earth-like, however, does not necessarily mean it is habitable. Venus and Mars are technically both Earth-like, due to their composition, mass, and distances from the Sun. Like Earth, both planets lie within the Sun’s habitable zone and have rocky surfaces. In fact, billions of years ago, Mars had liquid water flowing on its surface. Of course, today, Venus is a 900-degree Hell with a crushing atmosphere and sulfuric acid rain, and Mars is a cold, sterile desert. Determining the habitability of Ross 128 b and other exoplanets requires analyses of their atmospheres, which will be the mission of the James Webb Space Telescope once it launches into space in 2019. Webb will scan the infrared spectrum of exoplanets, enabling it to determine their atmospheric compositions.

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