Using a method called reconstructive speckle imaging, a team of astronomers at the Gemini Observatory has captured the sharpest ground-based image ever obtained of Pluto and Charon in visible light.
“The Pluto-Charon result is of timely interest to those of us wanting to understand the orbital dynamics of this pair for the 2015 encounter by NASA’s New Horizons spacecraft,” said Dr Steve Howell of the NASA Ames Research Center, lead author of a paper to be published next month in the journal Publications of the Astronomical Society of the Pacific.
“NASA’s Kepler mission, which has already proven a powerful exoplanet discovery tool, will benefit greatly from this technique,” Dr Howell noted.
The astronomers said the speckle imaging with the Gemini North 8-meter 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 Dr Howell’s team made at Gemini. “This is an enormous gain in the effort underway to confirm small Earth-size planets,” Dr Howell said.
The team temporarily installed a camera, called the Differential Speckle Survey Instrument (DSSI), among the suite of instruments mounted on the Gemini telescope.
“This was a fantastic opportunity to bring DSSI to Gemini North this past July,” said co-author Dr Elliott Horch of the Southern Connecticut State University. “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 only the light from the actual objects remains constant, and the artifacts reveal their transient nature, eventually canceling each other out.
Bibliographic information: Howell S. et al. 2012. To appear in the Publications of the Astronomical Society of the Pacific