Friday, September 19, 2008

First planet imaged around a sun-like star

The enormous 8 meter North Gemini telescope in Hawaii captured what appears to be the first image of a planet orbiting a sun-like star(the planet is circled in the image shown).

According to spectra obtained from the image, the dim object is a planet and not a background star like it may seem at first glance.  The planet weighs in at a whopping 8 Jupiter masses and was 330 AU (Earth's distance from sun: 93 million miles = 1 AU)  from its parent star which was 500 light years away from Earth when this image was taken.

Astronomers are hoping to get a follow-up study on this planet to determine an orbit and learn more about this large world.

Normally, Astronomers take careful measurements of a star's movement as it gets tugged by a nearby planet by seeing if the light is slightly blue or slightly red shifted (called a Doppler shift).  This method works best for very large Jupiter-like planets that orbit really close to their star.  The reason Astronomers haven't been able to image planets like this with ease is not just because they're all too faint, it's because the light from their parent star outshines them and blocks out the light.   It's similar to detecting a spotlight and a firefly a few feet apart on the moon.  Planets are similar to that firefly, they're really hard to see!

Using infrared imaging we can see warm planets like this (it has a temperature of around 1800K or 1500°C) next to a star easily since stars give off less light in the infrared than the visible part of the spectrum.

The star - which was creatively named 1RXS J160929.1-210524 - and its planet are very young, astronomically speaking, at only 5 million years old.  This leaves the planet nice and warm and easy to detect since it gives off a lot of infrared light.

Jupiter sized planets aren't supposed to form so far out from their parent star, according to our current theories, so it's most likely that it formed in closer to its parent star and then slowly migrated outward into the orbit it has today.  Van Kerkwijk (one of the authors of the paper announcing the discovery) thinks that this Jupiter-like planet is uncommon and may only be found in one in every 100 stars.

If you want to read more into this interesting find, click here to read the paper announcing the discovery.  The paper is called "Direct Imaging and Spectroscopy of a Planetary Mass Candidate Companion to a Young Solar Analog" and was written by David Lafrenière, Ray Jayawardhana, and Marten H. Van Kerkwijk.

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