Images of Io at different near-infrared wavelengths. The name of the filter used is indicated in the black box at the start of each section. The bright spots are thermal emissions from Io's myriad volcanoes. Note the increasing number of hot spots detected at longer wavelengths, i.e. towards the bottom of the figure. Credit: Katherine de Kleer and Imke de Pater, UC Berkeley
The longest-running, high-resolution observations of the moon's thermal emission confirm that Jupiter's moon, Io, is the most volcanically active body in our solar system.
Astronomers from the
University of California, Berkeley have used near-infrared adaptive optics on two of the largest telescopes, the 8-meter Gemini North and the 10-meter Keck II located near the summit of Maunakea in Hawaii, to track 48 volcanic hot spots on the surface for 29 months from August 2013 till the end of 2015.
The adaptive optic technology is used to remove the atmospheric blur in order to sharpen the image, and without this, Io is just a blurry ball. This technique can separate features just a few hundreds of kilometers away from the 3,600-kilometer-diameter surface of Io.
Video showing all hot spots detected from August 2013 through December 2015, displayed on a full map of Io and illustrating the approximate length of time they were visible. The size of the circle corresponds logarithmically to the intensity. Loki Patera is at 310 West longitude, 10 North latitude and Kurdalagon Patera is at 220 West longitude, 50 South latitude. (Credit: Katherine de Kleer and Imke de Pater, UC Berkeley)
On a given night, we may see half a dozen or more different hot spots. Of Io's hundreds of active volcanoes, we have been able to track the 50 that were the most powerful over the past few years.
Katherine de Kleer, Graduate Student,
De Kleer and Imke de Pater, a professor of astronomy and of earth and planetary science at UC Berkeley, detected the heat coming off from active volcanic eruptions in addition to cooling lava flows and determined the temperature and specific power output of individual eruptions. They tracked their progress for days, weeks and even years.
Interestingly, some of the volcanic eruptions appeared to spread across the surface over time, as if one caused another 500 kilometers away.
"While it stretches the imagination to devise a mechanism that could operate over distances of 500 kilometers, Io's volcanism is far more extreme than anything we have on Earth and continues to amaze and baffle us," de Kleer said.
On Oct. 20, De Kleer and de Pater will talk about their observations at a media briefing during a joint meeting of the European Planetary Science Congress and the American Astronomical Society's Division for Planetary Sciences in Pasadena, California. The research papers explaining the observations have been accepted for publication in the journal Icarus.
The intense volcanic activity of Io is caused by tidal heating that generated from friction in Io's interior as the intense gravitational pull of Jupiter changes along Io's orbit by small amounts. Models for how this tidal heating occur project that most of emission of Io’s total volcanic power takes place either near the equator or near the poles, and that the pattern has to be symmetric between the backward- and forward-facing hemispheres in Io's orbit (that is to say, at longitudes of 0-180 degrees versus 180-360 degrees).
However, this is not what they observed. During the observational period from August 2013 through December 2015, the researchers attained images of Io on 100 nights. Although they observed a surprising number intense but short-lived eruptions that emerged and subsided in few days, each eruptions occurred on the trailing face of Io (that is, at longitudes of 180-360 degrees) rather than the leading face, and at much higher latitudes than more normal eruptions.
The distribution of the eruptions is a poor match to the model predictions, b ut future observations will tell us whether this is just because the sample size is too small, or because the models are too simplified. Or perhaps we'll learn that local geological factors play a much greater role in determining where and when the volcanoes erupt than the physics of tidal heating do.
Katherine de Kleer , Graduate Student, UC Berkeley
Loki Patera, Io's most powerful persistent volcano, was one of main target of interest. It is an irregular crater and brightens by more than a factor of 10 every year or two.
Many researchers believe that Loki Patera is a massive subterranean lava lake and that this intense brightening event occurs due to crust overturning, like the lava lakes on Earth. Actually, the heat emitted from Loki Patera appears to move around the lake, as if a massive wave of lava traveling around the lake causing the destabilization and sinking of some portions of crust. This circular motion of the brightening events, as of 2002, seemed to travel around the lake in a counter-clockwise direction.
De Pater observed a renewed activity in 2009 after a clear cessation of brightening events after 2002.
"With the renewed activity, the waves traveled clockwise around the lava lake," she noted.
Kurdalagon Patera, another volcano, generated hot eruptions twofold in the spring of 2015 and this coincided with the brightening event of a large cloud of neutral material orbiting Jupiter. De Kleer said that this offers circumstantial evidence that hot eruptions on the surface are main source of variability in the neutral cloud, although it is uncertain why other eruptions were not linked to the brightening event.
De Kleer also said that the Keck and Gemini telescopes, located atop the inactive volcano Maunakea, complement each other. Keck's instruments are sensitive to longer wavelengths (5 microns), revealing the cooler features like older lava flows that not visible in the Gemini observations, on the other hand, Gemini North's queue scheduling allows more regular observations.
The astronomers are frequently observing Io in order to provide a long-term database of high resolution images that were not captured by Galileo, which tracked Jupiter for eight years.