Enceladus Spray-Paints Its Neighbors Yards
Saturn’s moon Enceladus is not only Yellowstone unto itself. Its shares the National Park experience with its neighbors. The geyser spray coats nearby moons white like snow. Space.com and National Geographic are calling this a case of “cosmic graffiti.” How did scientists catch the tagger?
The original paper in Science describes how on 13 Jan. 2005, on a rare night when the Sun, Earth and Saturn were almost perfectly aligned, scientists used the Hubble Space Telescope to measure the “geometric albedo” of Saturn’s moons. This is the brightness of a body at the moment the sun’s phase angle approaches zero. The albedo of the 11 moons embedded in Saturn’s E-ring turned out to be much brighter than expected – by a factor of about 1.5. The only way they could explain this is by hypothesizing that the ice particles ejected by Enceladus (07/11/2006) are sandblasting the nearby moons and coating them with a whitewash of ice. The bodies affected include the large moons Rhea and Dione as well as smaller ones Tethys, Mimas and others.
The original paper said nothing about life, but National Geographic couldn’t resist. “Enceladus’s geysers have made the moon a hot spot for astronomers looking for signs of life in space,” the article said. “If the geysers are drawing from pockets of water below the moon’s surface, as some theories suggest, those reservoirs could harbor an intriguing variety of primitive life-forms much like those found in Earth’s deep-ocean hydrothermal vents.” One of the scientists cautioned against speculation, though, saying that we don’t yet understand the nature of the geysers.
Saturn is nicely placed in the sky right now, according to a JPL press release. At opposition (opposite the sun from Earth), it’s high in the sky all night till April, and the rings are nearly wide open. Many people have remembered their first view of Saturn through a telescope as a thrilling experience. Some astronomers made their career choice because of it.
1Anne Verbiscer, Richard French, Mark Showalter, Paul Helfenstein, “Enceladus: Cosmic Graffiti Artist Caught in the Act,” Science, 9 February 2007: Vol. 315. no. 5813, p. 815, DOI: 10.1126/science.1134681.
How long could this spray-painting be going on? Is it plausible that Enceladus has been doing this for 4.5 billion years? If not, why is it doing it now? This is the question nobody seems to be asking.