Hubble has done it again. The 21-year-old space telescope has managed to pick out the impossibly faint glow from three worlds orbiting another star! However, this is a discovery with a huge difference: The image containing the star and its family of exoplanets was acquired in 1998.
1998? Why is this discovery only just being announced 13 years later? Well, that's where the clever bit comes in.
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Time for a little background: In 2008, an incredible thing happened -- the first direct observations of exoplanets from two astronomical studies swamped the world's media. Although exoplanets had been detected indirectly before, the Hubble optical light photo of the star Fomalhaut and the Keck/Gemini observatories' infrared imagery of the star HR 8799 showed tiny pinpricks of light orbiting the stars.
In the case of Fomalhaut, a single world -- with the imaginative name "Fomalhaut b" -- was seen nestled inside a stellar disk of dust. For HR 8799, a whole system of three gas giant worlds were seen. (It is now known that a fourth exoplanet orbits HR 8799, but it is too close to its star for observatories to observe it directly.)
Now, wind back the clock to 1998, when astronomers, searching for exoplanets, imaged HR 8799. Hubble saw no worlds orbiting the star -- the starlight was simply too bright in the images it acquired, and the starlight-subtraction methods hadn't been developed sufficiently.
But on Thursday, researchers using the 1998 data from Hubble's Near Infrared Camera and Multi-Object Spectrometer applied a new technique for teasing out the faint infrared signal emitted by the worlds orbiting HR 8799. This time, the three exoplanets emerged from the background noise.
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In 2009, David Lafrenière and his University of Toronto team took a look at old Hubble images and "rediscovered" HR 8799's outermost world by reanalyzing the 1998 data. Today, the other two have been spotted after further development of starlight-subtraction methods.
OK, so Hubble has "rediscovered" the exoplanets that were already known to be orbiting HR 8799. Great! But it gets better.
Keep in mind that the Hubble image is from 1998. The Keck/Gemini image is from 2008. Overnight, astronomers have acquired 10 years of orbital data for an entire star system!
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"The (Hubble data) archive got us 10 years of science right now," said Remi Soummer, of the Space Telescope Science Institute in Baltimore, who led the reanalysis. "Without this data, we would have had to wait another decade. It's 10 years of science for free."
As can be seen by the image above, the orbits of the three exoplanets are huge (the orbit of Neptune, with an orbital period of 164 years around our sun, is displayed as a comparison). HR 8799's worlds have 100-, 200- and 400-year orbits. The outermost exoplanet has barely moved, "but if we go to the next inner planet we see a little bit of an orbit, and the third inner planet we actually see a lot of motion," said Soummer.
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The Hubble Space Telescope has a huge number of images of other stars in its archive; I wonder how many other worlds -- and whole systems of worlds -- lie hidden in old data just waiting to be teased out of the starlight.
Image: The 1998 NIMCOS image (left) after being processed by Soummer's team (center). The HR 8799 system and exoplanet orbits (right). Credit: NASA, ESA and R. Soummer (STScI).
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