New Technique Allows Astronomers to Discover Exoplanets in Old Hubble Images


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

21 Replies to “New Technique Allows Astronomers to Discover Exoplanets in Old Hubble Images”

  1. That is just too cool. Actually being able to see pictures of exoplanets is so awesome.

    Maybe Bob’s (on the Skeptics Guide to the Universe podcast) guess that 100 exoplanets will be discovered this year will become true.

    The North-East indicator in the images changes angles in nearly the same way as the planet moved between the two pictures… hmm…

  2. Another fine reason for going back out and servicing the Hubble Space Telescope! That is, IF debris from those colliding satellites can be accurately tracked..

  3. Neptune’s existence and position were predicted mathematically from decades worth of observations of Uranus, so scouring old data to find new planets is a practise with a long and proud history.

  4. Really exciting news. And the image we see here looks like the image of the mini star system discoverd from Gemini few months ago, this new technique seems to be very efficient.

  5. I almost spilled over my tea reading this…to realise that we had directly imaged these systems for 10 long yrs ago….
    Great work!!

  6. You’re right ReevesAstroomy, there is no planet movement between the two images. I superimposed one on the other and rotated to match the compass and the tick-marks of the planets exaclty line up.

    It seems these are two seperate Hubble images taken about the same time 11 years ago and not a comparison of one now and then.


  7. Ian, is there any problem with thw 365 days of astronomy podcast ? I can’t see the page…

  8. @Martin and ReevesAstronomy

    If I’m right in interpreting the two images, it’s just the same photo, subject to the same graphical treatment in two different orientations, to make sure the blob of the planet isn’t some artifact created by the manipulation, since from the dark diagonal spikes seems obvious that the technique used has orientation issues.

    So, if I’m right, they just rotate the image and check to see if any faint signal that arises after the treatment remains and rotates the same way. If the answer is yes, then it’s a real object, not just a ghost with no real existence.

    What I don’t get is how can they be sure this is a planet and not just some faint background star. I wouldn’t expect this to be possible without several photos of the same object showing its rotation over time.

    I suppose that’s what happened and this is just one of several pictures available, but the original article in Science News is moot about that.

  9. @Jorge:

    I’m pretty sure it’s two different pictures (taken one after the other). The diagonal spikes are the remains of diffraction spikes from HST’s secondary mirror mounting, and I’m pretty sure they rolled the telescope in between observations.

  10. OK, now you forced me to go check for myself if the difference between the two images is only rotation or if there is something else. So, I dowloaded the picture, split it in two, overlapped them in two layers, set the blending mode to “difference”, rotated the top layer to make the axis coincide, moved it to overlap the centres of the central crosses, and…

    … there is movement in the planet. It does move slightly, perhaps some 2-3º. So, problem solved, and Don Alexander is right.

  11. Yes – this is very misleading. Anyone reading this article would infer right or wrong that it is based on two images 11 years apart showing movement. This analysis is based on images collected 11 years ago. The source document at discusses a 29.9 deg roll angle used to collect the images. Ian – go to your corner in Bad Astromony for a time out.

  12. *puts hands up* My bad, sorry, I should have explained the images. To be honest, my source material didn’t focus on the either picture, so I got carried away with the “thatissodamncool! I need to write about that ASAP!” attitude. Still, my mentality is “they have just discovered a frakin’ exoplanet in Hubble’s old data!”

    Next time I’ll nail it… next time…

    Cheers all! Ian 🙂

  13. Now THIS is “beating things into a bloody pulp of understanding!” – Dr. Gay’s ever-so-nice description of Science.

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