Astronomers have known about Wolf 1061, a nearby cool, dim star, since 1919. But hiding that entire time were three rocky planets, including one that's in the star's habitable zone. The new discovery, spotted at the European Southern Observatory in Chile, will be published in an upcoming Astrophysical Journal Letters.

At just 13.8 light years away, the new planet is the closest within the habitable zone of its star to Earth, and could provide an important test-bed for determining if it has the conditions ripe for life. For instance, astronomers could study the composition of the atmosphere if it passed in front of its star in the right way.

To be sure, Wolf 1061c is a lot different than Earth. It's four times more massive, and moves around its tiny M-dwarf star in just 17.9 days. Planets of similar size are often tidally locked to their parent stars due to the close proximity. Tidal locking is the process by which the same side of an object faces the object it orbits due to the larger mass of the sun or planet it orbits. And at the inner edge of its stars habitable zone, it is likely hotter than our home planet.

Of the three planets discovered, only Wolf 1061d has an orbit close to anything like in our solar system. It's orbit is 67.2 days long, still short of Mercury's 88 days. However, since it is around a cooler star than the sun, it's likely to be too frigid to sustain liquid water or life, lying just outside the habitable zone.

The new planet was found by using the radial velocity technique, which involves monitoring the red shift or blue shift (moving away or toward Earth) of a star to indicate the tug of an unseen planet. It uses the HARPS Spectrograph instrument to enable the detection of small planets, rather than the large, Jupiter-sized worlds typically found by radial velocity.

The University of New South Wales team who discovered the planets put together this demonstration of the system, with the green area marking the habitable zone. It was built in Universe Sandbox 2.

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