No. 4 A planet like Earth?

Top Ten Stories of 2015

An artist’s impression of Kepler-452b. Image: NASA Ames/JPL–Caltech/T Pyle.
An artist’s impression of Kepler-452b. Image: NASA Ames/JPL–Caltech/T Pyle.

There was great media excitement in July when it was announced that the Kepler Space Telescope had discovered the most Earth-like planet yet, but appearances can be deceiving.

Called Kepler-452b, the exoplanet is 60 percent larger than Earth, but crucially, orbits in its star’s habitable zone, which is a region around the star where the temperature is just right for liquid water to exist on a planet’s surface – assuming it has an atmosphere. Kepler-452b orbits its star every 385 days, while the star itself is very much like our Sun, but a billion-and-a-half years older. The two exist around 1,400 light years away in the constellation Cygnus.

That is all astronomers are able to say about this mysterious world. Whether it has an atmosphere, or water, is unknown, although because its star is older, the star will be hotter, meaning the planet could be undergoing a runaway greenhouse effect. Its size may also work against it — a report published around the same time by Caltech’s Leslie Rogers suggests that planets one-and-a-half times larger than Earth will not be rocky, but gaseous instead. The Kepler team, however, are confident in their assertion that Kepler-452b is the first rocky world we have found in a habitable zone. For now, our imagination will have to fill in the gaps.

Inside the magazine

Our top ten greatest stories of 2015 first appeared in the December edition of Astronomy Now.

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