It’s only slightly bigger than our own moon, but Jupiter’s Io is the most geologically active body in our entire solar system. It’s home to hundreds of volcanic areas covered with sulfur and sulfur dioxide, and the largest of these is Loki, named after the Norse god often linked to fire and chaos (and yes, Thor’s brother in some versions). Loki is a 200-kilometer-diameter (124-mile-diameter) volcanic depression, called a patera, with a dense lava crust that’s solidifying atop a horse-shoe shaped lava lake. Occasionally, when the top sinks into the lake, we can see a rise in thermal emissions here, from 600 kilometers (370 miles) away.
But until recently, Loki was too small for us to observe in detail using ground-based telescopes. Now, thanks to two mirrors that are each 8.4 meters (26.5 feet) across and 6 meters (20 feet) apart, the Large Binocular Telescope (LBT, pictured) in Arizona has produced images with as much detail as more massive, single-aperture telescopes. This is the first time researchers have been able to measure the brightness coming from different and specific regions within the lava lake. Their observations were published in The Astronomical Journal last week.
University of Arizona’s Al Conrad and the Large Binocular Telescope Observatory (LBTO) team utilized interferometry, which combines light coming from each of the two main mirrors in a way that makes the image look like it’s coming from a single mirror as big as the farthest edges of the two—rather than the 8.4 meters of each, you’ve got 22.8 meters (75 feet). “If we want to look in the vicinity of a star to find dust or planets, we use the information coming from both mirrors in a way that will 'erase' the bright star and allow us to look at faint objects around the star such as planets or a disk of dust,” LBTO’s Christian Veillet explains in a news release.
“These exquisite images from the LBTI show for the first time in ground-based images that emissions arise simultaneously from different sites in Loki Patera,” UC Berkeley’s Imke de Pater says. “This strongly suggests that the horseshoe-shaped feature is most likely an active overturning lava lake, as hypothesized in the past." Here’s a comparison between a simulated view of Io through an 8-meter (26-foot) telescope on the left and the final, real reconstruction using the Large Binocular Telescope Interferometer (LBTI) on the right:
Furthermore, the images revealed 15 other emission sites on the hemisphere of Io that’s visible to us. This includes two never-before-seen hot spots in an area called Colchis Regio, and they may be residual activity from a massive eruption that took place there a few months prior.
"Studying the very dynamic volcanic activity on Io, which is constantly reshaping the moon's surface, provides clues to the interior structure and plumbing," University of Minnesota's Chick Woodward explains. “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."
Images: LBTO-NASA (top), LBTO (middle, bottom)