Astronomers Used Old Hubble Data To Confirm Extrasolar Planets
October 6, 2011

Astronomers Used Old Hubble Data To Confirm Extrasolar Planets

NASA said on Thursday that astronomers have found evidence for two extrasolar planets using Hubble Space Telescope data from 1998.

Using old Hubble images gives astronomers an invaluable time machine for comparing earlier planet orbital motion data to more recent observations, according to the space agency.

Star HR8799 has four giant planets orbiting around it, three of which were discovered in 2007 and 2008 in near-infrared ground-based images taken by astronomers at W.M. Keck Observatory and the Gemini North telescope.

Christian Marois of the National Research Council in Canada and his team then uncovered the fourth and innermost planet in 2010.

David Lafreniere of the University of Montreal recovered a hidden exoplanet in 2009 using data from Hubble images taken in 1998.  He identified the position of the outermost planet known to orbit the star.

NASA said by finding the planets in multiple images space over years of time, the orbits of the planets can be tracked.

"From the Hubble images we can determine the shape of their orbits, which brings insight into the system stability, planet masses and eccentricities, and also the inclination of the system," Remi Soummer of the Space Telescope Science Institute in Baltimore said in a press release.

The three outer gas-giant planets have about 100-, 200-, and 400-year orbits, which means astronomers need to wait a long time to see how the planets move along their paths.

"The archive got us 10 years of science right now," Soummer said in a press release. "Without this data we would have had to wait another decade. It's 10 years of science for free."

The planets were not found in 1998 when the Hubble first made the observations because the methods used to detect them were not available then.

Lafreniere developed a way to improve the method for detecting planets by using a library of reference stars to more precisely remove the "fingerprint" glow of the central star.

Soummer's team took Lafreniere's method further by using 466 images of reference stars taken from a library containing over 10 years of observations assembled by Glenn Schneider of the University of Arizona.

Soummer plans to analyze about 400 other stars in the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) archive with the same technique.

"We wanted to revisit surveys taken of young, nearby stars, as these are prime targets for imaging exoplanets," Laurent Pueyo, a NASA Sagan Fellow working with Soummer, said in a press release. "Stars with evidence of circumstellar dust will also be good targets, as this is commonly linked with planet formation."

Soummer's team will use NICMOS data to assemble a list of planetary candidates to be confirmed by ground-based telescopes.


Image Caption: Left: This is an image of the star HR 8799 taken by Hubble's Near Infrared Camera and Multi-Object Spectrometer (NICMOS) in 1998. A mask within the camera (coronagraph) blocks most of the light from the star. In addition, software has been used to digitally subtract more starlight. Nevertheless, scattered light from HR 8799 dominates the image, obscuring the faint planets.

Center: Recent, sophisticated software processing of the NICMOS data removes most of the scattered starlight to reveal three planets orbiting HR 8799. Astronomers used this decade-old image to calculate the orbits of the planets.

Right: This is an illustration of the HR 8799 exoplanet system based on the reanalysis of Hubble NICMOS data and ground-based observations. The positions of the star and the orbits of the four known planets are shown schematically. The sizes of the dots are not to scale with the planet's true sizes. The three outermost planets, b, c, and d, are detected in both the NICMOS and ground-based data. A fourth, inner planet, e, was detected in ground-based observations. The orbits appear elongated because of a slight tilt of the plane of the orbits relative to our line of sight. The size of the HR 8799 planetary system is comparable to our solar system, as indicated by the orbit of Neptune, shown to scale.

Credit: NASA, ESA, and R. Soummer (STScI)


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