After conducting a thorough re-analysis of decade-old images from the Hubble Space Telescope using new techniques, scientists have found visual evidence for two extrasolar planets that went undetected in 1998.

Finding these hidden gems in the Hubble archive gives astronomers an invaluable time machine for comparing much-earlier planet orbital motion data to more recent observations. It also demonstrates a novel approach for planet hunting in archival Hubble data, according to NASA.

New analysis of decade-old images from Hubble's Near Infrared Camera and Multi-Oblect Spectrometer, or NICMOS, confirmed the existence of planets orbiting HR 8799, a young star which is 130 light years from Earth in the constellation Pegasus.

There are four known planets orbiting HR 8799 but the imaging software available back then did not discover any planet. In 2008 and 2009, a team led by Christian Marois of Canada's National Research Council analyzed ground-based imagery of the star and discovered three planets.

Marois and his colleagues then uncovered a fourth innermost planet in 2010, which is the only multiple exoplanetary system for which astronomers have obtained direct snapshots.

In 2009, David Lafreniere of the University of Montreal recovered hidden exoplanet data in Hubble images of HR 8799 taken in 1998 with the Near Infrared Camera and Multi-Object Spectrometer (NICMOS), according to NASA.

A new analysis of the same data was conducted by Remi Soummer of the Space Telescope Science Institute in Baltimore, who successfully recovered all three of the outer planets.

He compared the technique to a time machine for seeking out planets beyond our solar system. NICMOS was used in the 1990s to seek out dusty planetary disks and brown dwarfs. The images were processed to remove any glare that remained and bring out dim details.

Researchers say they will be able to track the orbits of planets when they locate these in several images spaced out over years. Knowing the orbits is very important in understanding the behavior of multiple-planet systems, as massive planets can perturb each other's orbits.

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, said Soummer.

Researchers say the three outer gas-giant planets have approximately 100-, 200- and 400-year orbits that means astronomers need to wait a very long time to see how the planets move along their paths. The extra time span added by the decade-old Hubble data helps see the slow paths of the planets.

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

Despite the passage of time, HR 8799's slowest-moving, outermost planet has barely changed position, but the astronomers did notice some changes with the star's other worlds, Space.com reported.

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, Soummer said.

We worked long and hard to achieve this result, and what's really exciting now is that we're going to apply the same method to a bunch of other stars, and hopefully we'll make some discoveries of our own, Brendan Hagan, a recent graduate from Goucher College in Baltimore, and a member of Soummer's research team told Space.com.

Soummer and his colleagues now plan to analyze approximately 400 other stars in the NICMOS archive with the same technique.

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