New Technique Allows Astronomers to Discover Exoplanets in Old Hubble Images

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The Hubble Space Telescope has recently provided us with some astonishing images of exoplanets orbiting distant stars. This is a departure from the indirect detection of exoplanets by measuring the “wobble” of stars (revealing the gravitational presence of a massive planetary body) or the transit of exoplanets through the line of sight of the parent star (causing its brightness to dim). Scientists have refined Hubble’s exoplanet hunting abilities to directly image these alien worlds in visible light. However, astronomers now have another trick to find these mysterious worlds. A new imaging technique is allowing us to see exoplanets already hiding in archival Hubble data…

It has been estimated that another 100 previously unknown exoplanets could be discovered in old Hubble data. The technique being tested by astronomers at the University of Toronto could be a very powerful new way to reveal the existence of a huge number of buried jewels buried by the glare of star light.

In November 2008, a spate of direct imagery of exoplanets showed the world how advanced our ground and space-based observatories were becoming. One such discovery was an observing campaign of the young star HR 8799 by the near-infrared adaptive optics observations of the Gemini and Keck telescopes. HR 8799 (140 light years away, approximately 50% more massive than our Sun) plays host to three massive gas giants (10, 10 and 7 times the size of Jupiter). Now that HR 8799 is known to have large exoplanets orbiting around it, the University of Toronto astronomers, headed by David Lafrenière, have re-examined images taken by Hubble of that same star in 1998, to see if there is any trace of these exoplanets in the old data. In 1998, HR 8799 appeared to be a lonely star, with no associated exoplanets.

Using a new technique to extract the weak exoplanet emission in the Hubble image, Lafrenière’s team have been able to cut down the glare of the parent star to reveal the presence of the outermost exoplanet of the trio known to be orbiting HR 8799 (pictured top). The other two exoplanets remain too close to the star to be resolved.

The University of Toronto result “definitely indicates that we should reanalyze all the existing Hubble images of young stars with the new approach — there’s probably 100 to 200 stars where planets could be seen,” comments planet-hunter Bruce Macintosh of the Lawrence Livermore National Laboratory in California. Many of these stars have already been studied by the powerful Keck observatory in Hawaii, so astronomers now have an exciting and powerful new analysis tool to hopefully reveal more overlooked exoplanets.

However, this most recent result was achieved by using a space-based observatory, as some of the near-infrared emission from the exoplanet will be absorbed by the Earth’s atmosphere.

The new exoplanet discovery potential has excited many astronomers, and it has highlighted the importance of maintaining a good archive of astronomical observations. “The first thing it tells you is how valuable maintaining long-term archives can be. Here is a major discovery that’s been lurking in the data for about 10 years!” said Matt Mountain, director of the Space Telescope Science Institute in Baltimore. “The second thing its tells you is having a well calibrated archive is necessary but not sufficient to make breakthroughs — it also takes a very innovative group of people to develop very smart extraction routines that can get rid of all the artifacts to reveal the planet hidden under all that telescope and detector structure.”

Hopefully we’ll be seeing even more exoplanet discoveries over the coming months, not just from new observing campaigns, but possibly from old observations using archived observatory data. Exciting times!

Source: Science News