Kepler-452b: The Importance and Reality of the “Earth 2.0” Discovery

Yesterdays announcement by the NASA Kepler mission confirmed many new exoplanets discovered by the impressive telescope. Among these is the press self-proclaimed “Earth 2.0” or Kepler-452b. There are reasons to both get excited and be hesitant about these announcements.

The raw facts released in the paper published to Astrophysical Journal – http://www.nasa.gov/sites/default/files/atoms/files/ms-r1b.pdf – suggests that this planet is orbiting around a star which is of a similar class to the sun, with an equivalent effective surface temperature, however slightly older (further through it’s main sequence life-cycle) (6+/-2 Gyrs) and slightly larger (1.1 R_solar).

By using photometric transit detection followed by spectroscopy different parameters of the planet have been modeled using a Bayesian statistical frame. These further lead to the picture of a planet slightly larger than Earth (1.6 R_earth), with an orbital period comparable to our year and a positioning within the habitable zone, meaning a surface temperature of around zero degrees celcius (265 +15/-13 K).

At first glance these results appear to match the Earth quite well and with a greater age of the star, the exciting news stories about potential advanced civilised worlds seem reasonably well founded. But by digging through the results a little harder it is indicated that the chance of the planet being rocky in composition, by the use of mass-radius scaling relations, was only ~50%. Factor in a composition similar to the Earth with a rocky exterior and iron core and this dropped significantly further to only ~20%.

These results mean that until technology advances and different methods can be used, the actual composition of Kepler- 452b cannot be well understood. Whether an Earth-like planet or not; the discovery of a planet this size, with an orbital period comparable to a year and the close proximity to the habitable zone is still very much exciting.

For the past 20 years many exoplanets have been found but because the method used to find them utilises measuring the reduction of light received during the transit of a planet in front of it’s host star, it was mostly large planets close to their stars which were observed (dubbed “Hot Jupiters”). So many were found in comparison to terrestrial sized planets that people started to wonder whether our planet/solar system model was perhaps very different to the normal, in the Universe.

But with the recent surge in the detection of smaller planets, I feel that the discovery of exoplanets like Kepler-452b finally signals the end of the “Hot Jupiter Bias” era. I am sure it will soon become apparent that the most abundant planet class will be similar to the inner terrestrial planets in our solar system.

Although judging by the results published it is unlikely that Kepler-452b may host life and be the “Earth 2.0” that people have suggested, continued discoveries must mean that a true earth-like planet discovery may be just around the corner!

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