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Newfound Alien Star System Boasts 5, Maybe 7, Planets

About 127 light-years away there’s a star like our sun that hosts at least five planets, each roughly the same mass as Uranus or Neptune, astronomers announced today.
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A closeup of the sky around HD 10180

—Image courtesy ESO and Digitized Sky Survey 2. Acknowledgment: Davide De Martin

The planets were found via what’s called the radial velocity method, aka the Doppler wobble. This method of planet hunting looks for periodic shifts in starlight caused by the gravitational pull of orbiting worlds.

Using an instrument dubbed the HARPS spectrograph on a European Southern Observatory telescope in Chile, the team saw five strong wobbles corresponding to planets between 13 and 25 times Earth’s mass orbiting the star HD 10180.

For comparison, Uranus is roughly 14 times Earth’s mass, and Neptune is about 17 times Earth’s mass. By contrast, Saturn is 95 Earth masses, and Jupiter tips the scales at almost 318 Earth masses.

What’s more, there are hints that the planetary system also hosts a world roughly the mass of Saturn, with at least 65 Earth masses, and another more like Earth itself.

The Saturn-like world would be farther out, taking about 2,200 days to complete an orbit. The Earthlike planet, meanwhile, would be closer in than all the rest, and it would be the least massive exoplanet yet found, at just 1.4 Earth masses.

If confirmed, the two additions would make this planetary system the most like our own yet discovered, at least in terms of number and general layout.

But don’t bust out the interstellar Mayflower just yet.

The Earthlike world, if it’s there, would be incredibly close to its star—one year would last just 1.18 Earth days. At that distance, the rocky planet would be more like the hot, raging volcanic hell Corot-7b.

The system also seems to be missing a Jupiter-like gas giant planet, and all its Neptunes are huddled up fairly close to the star, with years ranging from about 6 to 600 days.

Scientifically, the find “highlights the fact that we are now entering a new era in exoplanet research: the study of complex planetary systems and not just of individual planets,” team leader Christophe Lovis said in a press release.

“Studies of planetary motions in the new system reveal complex gravitational interactions between the planets and give us insights into the long-term evolution of the system.”

Culturally, however, it’s likely the news is making waves because we’re constantly hoping we’ll find another version of home.
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—Image courtesy NASA Goddard Space Flight Center

Right now we have 480+ exoplanets cataloged, and only 15 systems are known to have three worlds or more. Most of the planets found, alone or in groups, are more like Jupiter than Earth. That’s because technological limitations make small, rocky worlds harder to spot.

But we suspect there must be plenty out there, including some in the so-called habitable zone, the magic region just far enough from a star to host liquid water.

In fact, finding habitable Earths is the primary goal of a NASA space telescope called Kepler, which is searching for planets based on transits, looking for dips in starlight as a planet passes in front of its host star, as seen from Earth.

So does it make a difference if any soon-to-be-discovered Earths are part of larger planetary systems? Would life on Earth cease, for example, if Venus winked out of existence?

Probably not. But studies have shown that Jupiter, with its gassy enormity, has been acting as a sort of shield for Earth, gravitationally deflecting asteroids and comets that hold the potential to trigger mass extinctions.

And there’s still plenty to be found out about how planets form and how that process influences the evolution of star systems.

Some exoplanet discoveries suggest that not all worlds stay where they were born, and that planets can migrate, tilt, and even get expelled over the course of a few billion years.

In other words, it’s a strange universe out there, and parallel Earths have so far proven elusive. But that won’t stop astronomers from trying to find them, or people across the globe from getting thrilled at the prospect.