A direct picture of a planet orbiting an alien star confirmed!

July 2, 2010

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!


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