New analysis of data collected by Nasa's Kepler telescope "demonstrates that habitable zone planets are probably very common through the galaxy", says Professor Don Pollacco of the University of Warwick's Astrophsyics group.

Scientists involved with the research say that the planet Kepler-452b could be the most Earh-like planet yet discovered, but Professor Pollacco cautions that whilst "Kepler-452b has a host star very similar to the sun while the planet itself has a radius of about 1.6 times that of the earth" and that it "lies in the habitable zone of this star and has a orbital period or year of about 384days" to "say anything further (eg planetary or atmospheric composition etc) is much more difficult as there is no substantive data" and that to "say anything about "life" is pure conjecture."

Prof Pollacco's comment in full:

A new analysis of the Kepler data brings out a more habitable zone planet candidates, roughly doubling the number known. This is important as it demonstrates that habitable zone planets are probably very common through the galaxy.

Kepler data allows you to estimate the size of a planet relative to its host star, so if you know the size of the host, you can determine the size of the planet.

However, to go further (eg. is it rocky?) involves measuring the planetary mass and this is much more difficult to do. Kepler stars are pretty far away and consequently quite faint so measuring the planetary orbit and its mass is extremely challenging (in fact this has only been done for a few Kepler candidates).

Kepler-452b has a host star very similar to the sun while the planet itself has a radius of about 1.6 times that of the earth. It lies in the habitable zone of this star and has a orbital period or year of about 384days. Its composition and whether it has an atmosphere is unknown. So in reality we have no idea what this planet is made of: it could be rock but it could be a small gassy ball or something more exotic maybe. The "Earth 2.0" label used here really refers to the likelihood that this is a small planet revolving around a sun-like star with a period of roughly a year which places it in the habitable zone of this star (a distance at which water could exist as a liquid). There are other Kepler planets that probably more closely resemble the Earth.

To say anything further (eg planetary or atmospheric composition etc) is much more difficult as there is no substantive data. To say anything about "life" is pure conjecture.

These measurements are important because it allows us to estimate the frequency of different sized planets but to say anything more about earth sized planets needs PLATO and ESA mission (launch 2024) that looks at much closer planets where the mass measurements, while still difficult, can actually be made.

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