The search for so-called 'exoplanets' , planets orbiting other stars, has been led by the Kepler Space Telescope, launched in 2009, as well as other missions including the Hubble and Spizter Space Telescopes. To date an incredible number of exoplanets have been discovered (1706 confirmed at the time of writing, with another 2903 possibles), of all sizes and descriptions, many in multi-planet systems - you can see a few examples in the diagrams above.
The majority are so-called 'Hot Jupiters', large gas giants very near their star and far too hot to host life, so the discovery of Kepler 186f, is a major step forward in the search for places which could potentially host life.
That's all very well, you may be thinking, but how they actually find these planets? Bear in mind that most stars, however bright, appear as just dots in even the most powerful telescopes, let alone planets which are much smaller and dimmer.
In fact, the vast majority of exoplanets have been discovered by observing the effect they have on the light and movement of their star, rather than spotting them directly.
For example, a planet exerts a gravitational pull on its star, which can cause the star to wobble very slightly.
Another effect of gravity is called 'microlensing' - when a planet passes in front of its star (a movement known as 'transit'), the gravity of the planet can cause the star's light to be temporarily focussed and it brightens.
Also, when a planet transits, it blocks out a little of the star's light, causing a temporary dip in brightness.
All these effects are minute and can only be detected by very sensitive instruments, but the size of the planet and the distance that it orbits from the sun can then be calculated from this data. Clever stuff, don't you agree?
Direct imaging
It is extremely difficult to directly observe and image a planet due to its tiny size compared with a star, and because of the dazzling brightness of the star. However, a few have been spotted by using of a a coronagraph (see my earlier blog about the aurora), where a disk is used to mask the star itself, so that the star's immediate surroundings can be seen.
Check out this amazing image by the Hubble Space Telescope of a planet orbiting the star Formalhaut (the dark area in the centre covers the masked-out star).
For a planet to be habitable (at least for life as we know it), there needs to be liquid water on the surface. Too close to the star and any water will vaporise (think Mercury), too far away and it will turn in to a ball of ice. The narrow band between these two extremes, known as the 'habitable zone', has also been nicknamed the Goldilocks Zone (not too hot, not too cold). It's marked in green on this image, which compares our planet and solar system with that of the newly discovered Kepler 186f and its system.
The distance of the habitable zone from the star naturally depends on the size of the star - the hotter the star, the more distant the habitable zone.
So could there be life on Kepler 186f?
The short answer is 'maybe'. All that is known about this planet so far is its distance from the star, and its size. Size matters – too large and the atmosphere will be too thick, too small and there will be no atmosphere at all.
But other crucial factors are still unknown, for example, what the planet and its atmosphere are actually made of. Analysis of chemical signatures in the light is needed to provide more answers. Watch this space
Next week: Galaxies
http://planetquest.jpl.nasa.gov
http://www.nasa.gov/ames/kepler/nasas-kepler-discovers-first-earth-size-planet-in-the-habitable-zone-of-another-star
http://www.astrobio.net/news-exclusive/investigating-exoplanet-surfaces/
Image Credits:
1. NASA Ames/UC Santa Cruz
2. NASA, ESA, and P. Kalas (University of California, Berkeley and SETI Institute)
3. NASA Ames/SETI Institute/JPL-Caltech