Sharpest-ever ground-based images of Pluto and Charon

Sep 26, 2012
Pluto/Charon poses for sharpest ground-based images ever
Speckle image reconstruction of Pluto and Charon obtained in visible light at 692 nanometers (red) with the Gemini North 8-meter telescope using the Differential Speckle Survey Instrument (DSSI). Resolution of the image is about 20 milliarcseconds rms (root mean square). This is the first speckle reconstructed image for Pluto and Charon from which astronomers obtained not only the separation and position angle for Charon, but also the diameters of the two bodies. North is up, east is to the left, and the image section shown here is 1.39 arcseconds across. Credit: Gemini Observatory/NSF/NASA/AURA

(Phys.org)—Despite being infamously demoted from its status as a major planet, Pluto (and its largest companion Charon) recently posed as a surrogate extrasolar planetary system to help astronomers produce exceptionally high-resolution images with the Gemini North 8-meter telescope. Using a method called reconstructive speckle imaging, the researchers took the sharpest ground-based snapshots ever obtained of Pluto and Charon in visible light, which hint at the exoplanet verification power of a large state-of-the-art telescope when combined with speckle imaging techniques. The data also verified and refined previous orbital characteristics for Pluto and Charon while revealing the pair's precise diameters.

"The Pluto-Charon result is of timely interest to those of us wanting to understand the orbital dynamics of this pair for the upcoming NASA New Horizons mission to Pluto," said Steve Howell of the NASA Ames Research Center, who led the study. In addition, Howell notes that NASA's , which has already proven a powerful exoplanet discovery tool, will benefit greatly from this technique.

Kepler identifies by repeatedly measuring the change in brightness of more than 150,000 stars to detect when a planet passes in front of, or affects the brightness of, its host star. Speckle imaging with the Gemini telescope will provide Kepler's follow-up program with a doubling in its ability to resolve objects and validate Earth-like planets. It also offers a 3- to 4-magnitude sensitivity increase for the sources observed by the team. That's about a 50-fold increase in sensitivity in the observations Howell and his team made at Gemini. "This is an enormous gain in the effort underway to confirm small Earth-size planets," Howell added.

To institute this effort Howell and his team –– which included Elliott Horch (Southern Connecticut State University), Mark Everett (National Optical Astronomy Observatory), and David Ciardi (NASA Exoplanet Science Institute/Caltech) –– temporarily installed a camera, called the Differential Speckle Survey Instrument (DSSI), among the suite of instruments mounted on the .

"This was a fantastic opportunity to bring DSSI to Gemini North this past July," said Horch. "In just a little over half an hour of Pluto observations, collecting light with the large Gemini mirror, we obtained the best resolution ever with the DSSI instrument –– it was stunning!"

The resolution obtained in the observations, about 20 milliarcseconds, easily corresponds to separating a pair of automobile headlights in Providence, Rhode Island, from San Francisco, California. To achieve this level of definition, Gemini obtained a large number of very quick "snapshots" of Pluto and Charon. The researchers then reconstructed them into a single image after subtracting the blurring effects and ever-changing speckled artifacts caused by turbulence in the atmosphere and other optical aberrations. With enough snapshots (each image was exposed for only 60 milliseconds or about 1/20 of a second) only the light from the actual objects remains constant, and the artifacts reveal their transient nature, eventually canceling each other out.

DSSI was built at SCSU between 2007-2008 as a part of a United States National Science Foundation Astronomical Instrumentation grant and mounted on the Gemini North telescope for a limited observing run. The instrument is likely to return to Gemini North for observations in mid-2013 for general user programs from across the international Gemini partnership. Any such arrangement will be announced along with the call for proposals for Semester 13B, in February 2013.

This work was funded in part by the National Science Foundation and NASA's Kepler discovery mission and will be published in the journal Publications of the Astronomical Society of the Pacific in October 2012.

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plutosavior
1 / 5 (5) Sep 26, 2012
Pluto IS still a major planet. That infamous demotion remains a matter of ongoing debate, as it was done by only four percent of the IAU, most of whom are not planetary scientists, and was opposed by hundreds of professional astronomers in a formal petition. The Dawn mission has shown that Vesta, which is much smaller than Pluto, is far more planet than asteroid in its complexity. New Horizons will likely reveal similar complexity on Pluto comparable to that of the other major planets.
Sinister1811
1 / 5 (4) Sep 27, 2012
Pluto bears more resemblance to the rest of the Kuiper belt (which it's actually a part of) than it does to the Terrestrial and Jovian planets. It's still a recognized planet, however, they've just given it a new category. Just as Jupiter is of a different planetary category to Mars. This new category includes its larger Kuiper belt sibling - Eris, and its asteroid cousin Ceres (as well as a few other planet-like objects).

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