Meet Earth’s closest known exo-relative, Kepler 78b. First discovered earlier this year, scientists today confirmed that it’s like Earth in more ways than one—Kepler 78b is rocky, about the same size, and about the same density. Where other exoplanets have been nothing like our home planet, this one comes remarkably close, at least in physical properties.
Astrophysicists first spotted the body by observing the flickering of its sun through the powerful optics of the Kepler satellite. That gave them an idea of the size of the exoplanet, but no clue as to its density. To find that out, they tracked the subtle wobble of the sun as 78b orbited. Their observations confirmed the planet’s nearly Earth-like density, hinting at a rocky or iron composition. Both results were reported today in the journal Nature.
There have been exoplanet discoveries before, but scientists are particularly excited about this one. Here’s Michael Lemonick, reporting for Time:
What makes this find truly compelling, however, is the very fact that there is not just one paper, but two. And that second one, based on independent observations from a European team, reaches exactly the same conclusion. “When results agree like this,” says Howard, “that’s really the gold standard.”
Kepler 78b may resemble Earth in many ways, it’s far different in others. The planet is searingly close to its sun, making its surface temperature as hot as 8,500˚ F. That proximity also makes its orbital period incredibly brief—the exoplanet orbits its sun in just 8.5 hours. So in about one Earth-day’s time, Kepler 78b has completed three of its years.
Kepler, the telescope that discovered the exoplanet, won’t be spotting any more new exoplanets, though. Two of its four reaction wheels have failed, making it too unstable to observe the flickers and wobbles of distant stars that are telltale signs of exoplanets. In the meantime, scientists still have reams of Kepler data to sift through, so there may be a discovery or two waiting to be uncovered. But if there isn’t, in 2017, the Transitioning Exoplanet Survey Satellite, known as TESS, takes to the skies, which could be sensitive enough to find an planetary relative that’s even more similar than Kepler 78b.