First, a little about the mission, The Kepler spacecraft is a mission launched in March 2009 which was designed to search for small exoplanets by measuring almost constantly the brightness of more than 156,000 stars in a small patch of the sky. The 0.95m-telescope is able to detect a dip in the light coming from the host stars which could be due to the transit of an exoplanet passing between its star and us, like the Moon passes between the Earth and the Sun during a solar eclipse. When this happens it can give us a direct estimate of the size and orbit of the eoxplanet.


Keplers over 1200 Planet candidates sorted by size

The Kepler mission has released 1,200 exoplanet candidates from data collected with the Kepler spacecraft around 150 days of observation time. This marks a new age in astronomy, there will be before and after Kepler era.

The FOV of view of Kepler with the location of the exoplanet candidates and their family classification per size (credit: NASA-Kepler team)

The Kepler team released the data from the first 150 or so days of operation. A careful statistical analysis done by the team concludes that 80-90% of these candidates are probably real. The total count of explanets currently contains 519 exoplanets which were discovered over 15 years of observations. In almost 4 months of operation, the Kepler mission has found 1,200 exoplanets!

The figure summarizes the candidate size versus orbital period and candidate equilibrium temperature. The horizontal lines mark the limit between these families of exoplanets.

Many of these exoplanets orbit around smaller and cooler stars than our Sun. The surface temperature of the exoplanets could allow liquid water to exist on the surface of these planets. In their paper, the Kepler team lists ~60 candidates with sizes ranging from Earth-size to larger than that of Jupiter which are in the Habitability Zone of their host star. This is one of the most extraordinary result of this survey! If we wish to find Earth-like planets with water on them, we need to look for exoplanets in the Habitability Zone, an area which isn’t too hot or too cold for water to exist. This zone is also called the Goldilocks Zone.

With these results, we can now say that stars in the Milky Way galaxy are more likely to have small exoplanets since 70% of the exoplanets discovered are smaller than Neptune, with a peak of exoplanets only 2-3 times larger than Earth. Using model predictions the team calculated that 6% of the stars in our Milky way have Earth and super-Earth size exoplanets. Since the Milky Way has around ~200 billion stas, that makes it ~12,000,000,000 stars with Earth-like planets!

The Kepler mission is still in operation and collecting new data. In a few years time, we can expect to have a more accurate and complete catalogue, which might contain smaller exoplanets, exoplanets orbiting further from their host star and even the exomoons of these exoplanets. Different groups of astronomers are now going to go through the catalogue and study the vast variety of worlds found. We can expect a lot of exciting news in the coming weeks. To start it off, here’s a very cool mini solar system with a lot more still to come.

Artistic illustration of the multiple planetary system Kepler-11 (credit: Nature / NASA / Ames / JPL-Caltech / T. Pyle)

If you go out tonight, take some time out to look at the sky and think that among the 2,500 stars that you can see with the naked eye, a third of them may have an exoplanet. Worlds which might be very different or very similar to ours, how many different worlds can you think of?

There are a lot of interesting worlds out there, now we just need to explore them. Welcome to the golden age of astronomy.


Astronomers have now confirmed that an object imaged back in 2008 is a direct image of an exoplanet orbiting a star.

This image, taken in 2008 by the Gemini North telescope in Hawaii, shows the star 1RXS J160929.1-210524 (I’ll call it 1RXS 1609) in the center, and the planet (1RXS 1609b) indicated by the red circle. The star is a bit smaller and slightly cooler than our sun.

The problem was, that the object might have been a background object like a star or a background galaxy. It has happened before. However, follow-up observations have shown that it is neither a star nor a galaxy, it is indeed a planet orbiting the star.

Credit: Gemini Observatory/AURA/David Lafrenière (University of Montreal),Ray Jayawardhana (University of Toronto), and Marten van Kerkwijk (University of Toronto)

On this graph, the separation of the object and the star are shown in the y-axis, and time is shown on the x.  The star is moving slowly as it orbits the centre of our galaxy. If the object was moving separately it would be near the or on the purple line, changing as they moved separately. If the object were a planet the separation wouldn’t change much as they moved together across the sky. The observation of the planet is shown as black dots in this picture, they fall right on the line making it an object orbiting a star, which pretty much makes this a planet.

The star is about 500 light years away and the planet has a mass 8 times that of Jupiter, it orbits the star 47 billion kilometres away, that’s about 300 times the distance of Earth form the sun and has a temperature of about 1500 C. The star is a bit less massive than the sun and not nearly hot enough to heat the planet up to that temperature. The reason the planet is so hot is that it’s very young.  The contraction of the planet under its own gravity during its formation quickly raised its temperature to thousands of degrees. Once this contraction phase is over, the planet will slowly cool down by radiating infrared light. In billions of years, the planet will eventually reach a temperature similar to that of Jupiter.

This discovery is a great technological achievement because the planet and the star are very close together, it’s very difficult to separate them. From the ground the Earth’s atmosphere blurs out the image and scatters the light of the star, making it very difficult to see objects like this. Even more remarkable thing is that they even got the spectra of the planet and used that to determine the temperature of the planet.

However, it’s not he the first the first planet which has been directly imaged. That title belongs to planet 2M1207b, which orbits a brown dwarf about 230 light years away. While brown dwarfs are cooler and smaller than the Sun, and they don’t fuse hydrogen into helium in their core, some people don’t consider them real stars. So it’s not really a sun-like star. But a planet orbiting a sun-like star has already been observed by telescopes in space. Since this observation was made from a ground based telescope, it is the first planet directly observed orbiting another star from a ground based telescope, which is very cool. It’s easier to make observations from space than it is from the ground, on the ground there is a lot of atmospheric scattering which makes the task a lot more difficult and that makes it much more remarkable.

We’re directly seeing worlds orbiting other stars from our world…THAT’S AWESOME!