The discovery of new planets is coming thick and fast. Astronomers have now confirmed more than 800 planets beyond our own solar system. The unconfirmed tally is as high as 1800, with more than half found by the Kepler space telescope.

The latest find is known as Kepler-186f. So far five planets have been found in the system. Estimates are that this planet is only around 10% bigger than Earth – bringing it closer to the ‘Earth Twin’ that seems to be the Holy Grail of planet-finding. This is the latest discovery from the treasure-trove of data generated by the Kepler space telescope.

The exciting thing is that this planet is in the habitable zone of the Kepler system, meaning it is in a position relative to its star where water will remain liquid.

The newly discovered planet orbits around 52 million kilometers from it sun. This is around one third of the distant that Earth orbits our own sun, but since Kepler is a smaller, dimmer star, the orbit still falls in the sweet spot. Kepler has 0.48 the mass of Earth, and is a dwarf red star (type M1).

The new planet is in the outer limit of the Kepler habitable zone, so much would depend on the composition of its atmosphere. A thicker atmosphere would allow enough heat to be retained to prevent water from freezing.

Interestingly, Mars is in the outer limit of our own Sun’s habitable zone. In the case of the Red Planet, there is not enough atmosphere to keep in the heat. Mars is far smaller than Earth, with lower gravity, and less ability to keep atmospheric gases from escaping into space. Not surprisingly, planned terraforming of Mars revolves around thickening the atmosphere to allow liquid water to exist there (and melt the poles).

It is not known if this latest planet is a rocky world like our own Earth, but astronomers, such as Berkley’s Geoff Marcy consider it likely.

So it’s down to analysing the mass of data from Kepler to look for Earth’s true ‘twin’ – an Earth-like star in the habitable zone of a Sun-like star. It should only be a matter of time. The Kepler telescope has already shown that small, rocky planets like Earthy are common throughout the galaxy. Before Kepler discoveries has been confined to large ‘hot’ Jupiters.

Kepler, launched in 2009, was designed to enable astronomers to detect new planets using the ‘transit’ method – the reduction in brightness that occurs when a planet crosses the face of its star.

Kepler’s planet-hunting ended last may when its telescope went out of alignment. Despite this, the finds keep coming from the data it had already generated. There are an estimated additional 3000 additional planet candidates remaining to be analysed. Let’s hope the golden age of planet hunting keep rolling on, despite the end of Kepler’s first run at collecting data.

There is a new mission called K2 that would enable Kepler to start a new phase of observation to discover exoplanets and other stellar phenomena such as supernova, asteroids and comets. Let hope K2 gets the green light.