Astronomers find elusive planets in decade-old Hubble data

Astronomers find elusive planets in decade-old Hubble data
The left image shows the star HR 8799 as seen by Hubble's Near Infrared Camera and Multi-Object Spectrometer (NICMOS) in 1998. The center image shows recent processing of the NICMOS data with newer, sophisticated software. The processing removes most of the scattered starlight to reveal three planets orbiting HR 8799. Based on the reanalysis of NICMOS data and ground-based observations, the illustration on the right shows the positions of the star and the orbits of its four known planets. (Credit: NASA; ESA; STScI, R. Soummer)
( -- In a painstaking re-analysis of Hubble Space Telescope images from 1998, astronomers have found visual evidence for two extrasolar planets that went undetected back then.

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.

Four are known to orbit the young, massive star HR 8799, which is130 light-years away. In 2007 and 2008 the first three planets were discovered in near-infrared ground-based images taken with the W.M. and the Gemini North telescope by Christian Marois of the National Research Council in Canada and his team. Marois and his colleagues then uncovered a fourth innermost planet in 2010. This 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). He identified the position of the outermost planet known to orbit the star. This first demonstrated the power of a new data-processing technique for retrieving faint planets buried in the glow of the central star.

A new analysis of the same archival NICMOS data by Remi Soummer of the Science Institute in Baltimore has recovered all three of the outer planets. The fourth, innermost planet is 1.5 billion miles from the star and cannot be seen because it is on the edge of the NICMOS coronagraphic spot that blocks the light from the central star.

By finding the planets in multiple images spaced over years of time, the orbits of the planets can be tracked. Knowing the orbits is critical to understanding the behavior of multiple-planet systems because can perturb each other's orbits. "From the 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," says Soummer.

These results are to be published in the Astrophysical Journal.

The three outer gas-giant planets have approximately 100-, 200-, and 400-year orbits. This means that astronomers need to wait a very long time to see how the planets move along their paths. The added time span from the Hubble data helps enormously. "The archive got us 10 years of science right now," he says. "Without this data we would have had to wait another decade. It's 10 years of science for free."

Nevertheless, the slowest-moving, outermost planet has barely changed position in 10 years. "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," says Soummer.

The planets weren't found in 1998 when the Hubble observations were first taken because the methods used to detect them were not available at that time. When astronomers subtracted the light from the central star to look for the residual glow of planets, the residual light scatter was still overwhelming the faint planets.

Lafreniere developed a way to improve this type of analysis 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 a step further and used 466 images of reference stars taken from a library containing over 10 years of NICMOS observations assembled by Glenn Schneider of the University of Arizona.

Soummer's team further increased contrast and minimized residual starlight. They completely removed the diffraction spikes, which are artifacts common to telescope imaging systems. This allowed them to see two of the faint inner planets in the Hubble data. The planets recovered in the NICMOS data are about 1/100,000th the brightness of the parent star when viewed in near-infrared light.

Soummer next plans to analyze approximately 400 other stars in the NICMOS archive with the same technique, improving image quality by a factor of 10 over the imaging methods used when the data were obtained.

Soummer's work demonstrates the power of the data archive, which harbors images and spectral information from over twenty years of Hubble observations. Astronomers tap into this library to complement new observations with a wealth of invaluable data already gathered, yielding much more discovery potential than new observations alone.

From the NICMOS archive data Soummer's team will assemble a list of planetary candidates to be confirmed by ground-based telescopes. If new are discovered they will once again have several years' worth of orbital motion to measure.

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Hubble Finds Hidden Exoplanet in Archival Data

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Oct 06, 2011
This is so fascinating. I defy anyone to see a downside in this. I think its great astronomers got a break like this.

Oct 06, 2011
The downside is that we haven't figured to do this before. BAM!

Oct 06, 2011
This is one of the reasons I love astronomy. They can squeeze so much information out of so little resources. I'm a biochemist and it's obscene how much resources it takes to learn so little, and how much data is never utilized. The fact that they can now store every image taken by every telescope perfectly is just amazing. Also, I think this supports my argument that we should be investing in more telescopes, spaced-based and ground based, in every possible spectrum. We're all alone, isolated on this fragile planet, surrounded by extremely hostile (to biological life) conditions. It makes sense that we keep looking at what's going on out there and see what we can find.

Oct 06, 2011
I'll be interested to learn how they use the data from "reference stars" to subtract the glare from the HR 8799 image.

Oct 06, 2011
This is certainly great news, but I do hope that all the candidate planets actually pan out, given the short time interval of the observations (as seen with, recently, Fomalhaut b): http://news.disco...926.html

Oct 07, 2011
I'll be interested to learn how they use the data from "reference stars" to subtract the glare from the HR 8799 image.

It looks like they did this similarly how radiographic/CT pictures with artifacts (e.g. metal artifacts) are treated. You model the artifact (the model being derived from standardized metal artifact phantom images) and then you substract that artifact from your initial image.

This doesn't add any information, though. Information lost due to glare from artifacts cannot be restored. but it can heighten the contrast of small details that are not part of the artifact (e.g. the planets in the Hubble pictures or the tooth decay next to a metall filling in a dental picture)

Oct 07, 2011
@ paul -- Hubble is not what i would consider a little resource

Oct 07, 2011
@ el nose - I would. It's not a natural resource, but that doesn't disqualify it as a scientific resource. It is a resource for gathering high quality images and scientific data.

Oct 09, 2011
I am saying Hubble is a giant resource. It has incurred costs in the billions, development, creations, launch, maintenence and has been a Huge success. this article is about how the data from Hubble collected over twenty years can still be used to make new discoveries. This is not my definition of little resource. Seems like a huge resource to me, in money and time. How many biology experiments costs in the billions excluding pharmacueticals??

Oct 09, 2011
You are right that space telescopes increase our knowledge of what's out there.

However, I would not call them a "huge resource" at this point in time.

So far, no modern space telescope has ever paid for itself by discovering, say, some unknown law of physics or some super-material that improved human life.

Dark Matter, Dark Energy, but untill somebody makes a "Dark Energy Engine" or something similar, you can't even count that as a "resource".

I.E. nobody has ever made a profit or a tool or engine or computer or other technology based on the discovery of DM or DE, so those don't even count.

Discover electricity and magnetism, and you can make electric and magnetic appliances.

Do something like that with DM and DE, then the telescope will be a "resource".

Until then, it's mostly entertainment.

Oct 10, 2011
do you realize how much money the military and our government give away every year to our supposed allies who really dislike us but we pay them out the ass to set up bases in their countries and all that? Whats 5-10 billion to greatly improve our understanding of the universe compared to the billions we give away every month to people who hate us but pretend to be our allies?

Oct 11, 2011
This is so fascinating. I defy anyone to see a downside in this. I think its great astronomers got a break like this.

This is one of the things I love the most about research, being able to re-analyze previous data and find new diamonds in the rough.

Oct 12, 2011
@Nanobanano, that's like saying the microscope was a useless tool upon its invention. Space telescopes allow us to observe things we wouldn't otherwise be able to observe. We build things like this to build a knowledge database in the hopes that it will someday lead to discovery.

Science does not need to be profitable to be useful... and many things that are profitable are not very useful.

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