Giant telescope takes a close look at a lava lake on Jupiter's moon Io
Summary: With the first detailed observations through imaging interferometry of a lava lake on a moon of Jupiter, the Large Binocular Telescope Observatory places itself as the forerunner of the next generation of Extremely Large Telescopes.
Io, the innermost of the four moons of Jupiter discovered by Galileo in January 1610, is only slightly bigger than our own Moon but is the most geologically active body in our solar system. Hundreds of volcanic areas dot its surface, which is mostly covered with sulfur and sulfur dioxide.
The largest of these volcanic features, named Loki after the Norse god often associated with fire and chaos, is a volcanic depression called patera in which the denser lava crust solidifying on top of a lava lake episodically sinks in the lake, yielding a rise in the thermal emission which has been regularly observed from Earth. Loki, only 200km in diameter and at least 600 million km from Earth, was, up to recently, too small to be looked at in detail from any ground based optical/infrared telescope.
With its two 8.4 m mirrors set on the same mount 6 m apart, the Large Binocular Telescope (LBT), by combining the light through interferometry, provide images at the same level of detail a 22.8 m telescope would reach. Thanks to the Large Binocular Telescope Interferometer (LBTI), an international team of researchers was able to look at Loki Patera, revealing details as never before seen from Earth; their study is published today in the Astronomical Journal (link here).
"We combine the light from two very large mirrors coherently so that they become a single, extremely, large mirror,” says Al Conrad, the lead of the study and a Scientist at the Large Binocular Telescope Observatory (LBTO). “In this way, for the first time we can measure the brightness coming from different regions within the lake."
For Phil Hinz, who leads the LBTI project at the University of Arizona Steward Observatory, this result is the outcome of a nearly fifteen year development. "We built LBTI to form extremely sharp images. It is gratifying to see the system work so well." Hinz notes that this is only one of the unique aspects of LBTI. "We built the system both to form sharp images and to detect dust and planets around nearby stars at extremely high dynamic range. Recent results from LBTI on eta Crv and HR 8799 are great examples of its potential."
LMIRcam, the camera recording the images at the very heart of LBTI in the 3 to 5 micrometers near-infrared band, was the thesis work of Jarron Leisenring as graduate student at the University of Virginia. For Leisenring, now an instrument scientist for NIRCam (the Near InfraRed CAMera for the James Webb Space Telescope) at Steward Observatory, "these observations mark a major milestone for me and the instrument team. LMIRcam has already been very productive these past few years; now, interferometric combination provides the last step in harnessing LBTI’s full potential and enabling a whole host of new scientific opportunities."
Many raw images delivered by LMIRcam are combined to form a single high-resolution image. "LBTI raw images are crossed by interference fringes. Therefore, these raw images do not look very sharp", explains Gerd Weigelt, a Professor at the Max-Planck-Institut für Radioastronomie (Bonn, Germany). "However, modern image reconstruction (deconvolution) methods allow us to overcome the interference fringes and achieve a spectacular image resolution.”
"Data processing based on deconvolution methods", adds Mario Bertero, a professor in Information Science at the University of Genova (Italy), "are basic for detecting details not directly distinguishable in the interferometric images. However they can generate artifacts and, for this reason, it is important to process the images with different methods for discriminating between relevant details and artifacts.
"While we have seen bright emissions – always one unresolved spot – “pop-up” at different locations in Loki Patera over the years”, explains Imke de Pater, a Professor at the University of California in Berkeley, "these exquisite images from the LBTI show for the first time in groundbased images that emissions arise simultaneously from different sites in Loki Patera. This strongly suggests that the horseshoe-shaped feature is most likely an active overturning lava lake, as hypothesized in the past.”
"Two of the volcanic features are at newly-active locations", explains Katherine de Kleer, a graduate student at the University of California at Berkeley. "They are located in a region called the Colchis Regio, where an enormous eruption took place just a few months earlier, and may represent the aftermath of that eruption. The high resolution of the LBTI allows us to resolve the residual activity in this region into specific active sites, which could be lava flows or nearby eruptions."
"Studying the very dynamic volcanic activity on Io, which is constantly reshaping the moon 's surface, provides clues to the interior structure and plumbing of this moon," remarked team member Chick Woodward of the University of Minnesota, "helping to pave the way for future NASA missions such as the Io Volcano Observer. Io's highly elliptical orbit close to Jupiter is constantly tidally stressing the moon, like the squeezing of a ripe orange, where the juice can escape through cracks in the peel."
For Christian Veillet, Director of the Large Binocular Telescope Observatory (LBTO), "this study marks a very important milestone for the Observatory. The unique feature of the binocular design of the telescope, originally proposed more than 25 years ago, is its ability to provide images with the level of detail (resolution) only a single-aperture telescope at least 22.8m in diameter could reach. The spectacular observations of Io published today are a tribute to the many who believed in the LBT concept and worked very hard over more than two decades to reach this milestone."
Veillet adds: "While there is still much work ahead to make the LBT/LBTI combination a fully operational instrument, we can safely state that the Large Binocular Telescope is truly a forerunner of the next generation of Extremely Large Telescopes slated to see first light in a decade (or more) from now."
The LBT is an international collaboration among institutions in the U.S., Italy and Germany. LBT Corporation partners are: The University of Arizona on behalf of the Arizona Board of Regents; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; The Ohio State University, and The Research Corporation, on behalf of The University of Notre Dame, University of Minnesota and University of Virginia. The Large Binocular Telescope Interferometer is funded by NASA as part of its Exoplanet Exploration program. LMIRcam is funded by the National Science Foundation through grant NSF AST-0705296. The research was partially supported by the National Science Foundation, NSF Grant AST-1313485 to UC Berkeley, and by the National Science Foundation Graduate Research Fellowship under Grant DGE-1106400.
Astronomical Journal Publication
Spatially resolved M-band emission from Io's Loki Patera - Fizeau imaging at the 22.8 meter LBT
Albert Conrad, Katherine de Kleer, Jarron Leisenring, Andrea La Camera, Carmelo Arcidiacono, Mario Bertero, Patrizia Boccacci, Denis Defrère, Imke de Pater, Philip Hinz, Karl-Heinz Hofmann, Martin Kürster, Julie Rathbun, Dieter Schertl, Andy Skemer, Michael Skrutskie, John Spencer, Christian Veillet, Gerd Weigelt, Charles E. Woodward
Local copy (pdf)
Io seen by LBT (left) on 2013 December 24 (left) compared to a USGS map (right) based on images from NASA’s Voyager 1 and 2 missions (acquired in 1979) as well as the Galileo orbiter (1995-2003).
Loki Patera is the bright red spot on the LBT image. Credit: LBTO-USGS
A raw LMIRcam image of Io showing the fringes on Loki Patera (bright spot) and on fainter active volcanic areas. Credit: LBTO
Comparison between a simulated view of Io through an 8-meter telescope (left) and the final real LBTI reconstruction (right) - Credit: LBTO
The LBT image of Loki Patera (orange ) laid over a Voyager image of the volcanic depression.The emission (in orange color) appears spread out in the north-south direction due to the telescope point-spread function; it is mainly localized to the southern corners of the lake. The original 4.8 μm LBT image has been smoothed to better indicate the location of the two distinct emission features.
Credit: LBTO- NASA
A serendipitous movie of an occultation of Io by its neighboring moon Europa when the team re-observed Io on the night of March 7, 2015 for a follow up to the work done for the published study. Europa happened to pass in front of Io as observed from Earth (see here for more details).
Loki is the bright volcano on the left and Pele the other one on the lower right. Europa appears dark because the water ice on its surface absorbs the incident sunlight at the wavelength used.
LBTO (AZ, USA)
Max-Planck-Institut für Radioastronomie (Germany)
Steward Observatory - University of Arizona (AZ, USA)
University of California, Berkeley (CA, USA)
University of Genova (Italy)
University of Minnesota (MN, USA)