In 2010, the most recent and only the sixth giant storm on Saturn observed by humans began stirring. It quickly grew to superstorm proportions, reaching 15,000 kilometers (more than 9,300 miles) in width and visible to amateur astronomers on Earth as a great white spot dancing across the surface of the planet.
Now, thanks to near-infrared spectral measurements taken by NASA's Cassini orbiter and analysis of near-infrared color signatures by researchers at the University of Wisconsin-Madison, Saturn's superstorm is helping scientists flesh out a picture of the composition of the planet's atmosphere at depths typically obscured by a thick high-altitude haze.
The key finding: cloud particles at the top of the great storm are composed of a mix of three substances: water ice, ammonia ice, and an uncertain third constituent that is possibly ammonium hydrosulfide. According to the Wisconsin researchers, the observations are consistent with clouds of different chemical compositions existing side-by-side, although a more likely scenario is that the individual cloud particles are composed of two or all three of the materials.
Writing in the current edition (Sept. 9, 2013) of the journal Icarus, a team led by UW-Madison Space Science and Engineering Center planetary scientists Lawrence Sromovsky, and including Kevin Baines and Patrick Fry, reports the discovery of the icy forms of water and ammonia. Water in the form of ice has never before been observed on Saturn.
"We think this huge thunderstorm is driving these cloud particles upward, sort of like a volcano bringing up material from the depths and making it visible from outside the atmosphere," explains Sromovsky, a senior scientist at UW-Madison and an expert on planetary atmospheres. "The upper haze is so optically pretty thick that it is only in the stormy regions where the haze is penetrated by powerful updrafts that you can see evidence for the ammonia ice and the water ice. Those storm particles have an infrared color signature that is very different from the haze particles in the surrounding atmosphere."
Scientists believe Saturn's atmosphere is a layered sandwich of sorts, with a deck of water clouds at the bottom, ammonia hydrosulfide clouds in the middle, and ammonia clouds near the top, just below an upper tropospheric haze of unknown composition that obscures almost everything.
The latest great storm on Saturn and the presence of the Cassini probe now orbiting the planet gave scientists a chance to peek beneath the haze and learn more about the dynamics and chemical composition of the planet's deep atmosphere.
First noticed by amateur astronomers, the massive storm works like the much smaller convective events on Earth, where air and water vapor are pushed high into the atmosphere, resulting in the towering, billowing clouds of a thunderstorm. On Saturn, not only are the storms much bigger, they are far more violent, with models predicting vertical winds of more than 300 miles per hour for these rare giant storms.
The effect, Sromovsky says, is to loft the aerosols found deep in the atmosphere to the visible cloud tops, providing a rare glimpse of normally hidden materials. "It starts at the water cloud level and develops a huge convective tower. It is similar to a big thunderstorm, only 10 to 20 times taller and covering an even greater area," he explains.
The new work helps validate the models of Saturn's great storms as well as previous observations that detected water and ammonia in vapor form. The presence of water ice, he says, supports the idea that Saturn's superstorms are powered by condensation of water and originate deep in the atmosphere, about 200 kilometers below the visible cloud deck.
"The water could only have risen from below, driven upward by powerful convection originating deep in the atmosphere. The water vapor condenses and freezes as it rises. It then likely becomes coated with more volatile materials like ammonium hydrosulfide and ammonia as the temperature decreases with their ascent," Sromovsky adds.
The interesting effect, he notes, is that in Saturn's massive storm, at least, the observations can be matched by having particles of mixed composition, or clouds of water ice existing side-by-side with clouds of ammonia ice. In the latter scenario, water ice would make up 22 percent of the cloud head and ammonia ice 55 percent. The remaining fraction would be made up by the third constituent, which though less certain, is believed to be ammonia hydrosulfide.
"Up until now, there have been no quantitative calculations of spectra for cloud structures and compositions that matched the observed spectrum of an actual storm cloud feature," says Sromovsky.
Lawrence Sromovsky | Source: EurekAlert!
Further information: www.wisc.edu
Further Reports about: amateur astronomers > ammonia hydrosulfide > ammonia hydrosulfide clouds > Cassini > chemical composition > cloud particles > Earth's magnetic field > huge thunderstorm > near-infrared spectral measurements > planetary atmospheres > Saturn > upper tropospheric haze > water clouds > water ice > water vapor
More articles from Physics and Astronomy:
CU-Boulder scientist: 2012 solar storm points up need for society to prepare
10.12.2013 | University of Colorado at Boulder
3D printing used as a tool to explain theoretical physics
09.12.2013 | Institute of Physics
The molecular architecture of three key proteins and their complexes reveals how plants fine-tune their immune response to pathogens
Plants rarely get sick in their natural environment. When the threat of infection arises, a quick decision is made about the necessary countermeasures. The course is set by a protein which forms complexes with its partner proteins for this purpose.
Jane Parker from the Max Planck Institute for Plant Breeding ...
Researchers studying speciation of butterfly orchids on the Azores have been startled to discover that the answer to a long-debated question "Do the islands support one species or two species?" is actually "three species".
Hochstetter's Butterfly-orchid, newly recognized following application of a battery of scientific techniques and reveling in a complex taxonomic history worthy of Sherlock Holmes, is arguably Europe's rarest orchid species. Under threat in its mountain-top retreat, the orchid urgently requires conservation recognition.
A lavishly illustrated publication, titled "Systematic revision of Platanthera in ...
Researchers from Brown University and the University of Hawaii have found some mineralogical surprises in the Moon's largest impact crater.
Data from the Moon Mineralogy Mapper that flew aboard India's Chandrayaan-1 lunar orbiter shows a diverse mineralogy in the subsurface of the giant South Pole Aitken basin.
The differing mineral signatures could be reflective of the minerals dredged up at the time of the giant impact 4 billion years ago, ...
In power electronics systems bonded connections create the central electrical connections between adjoining surfaces.
The quality of these bonded connections is one of the main factors that determines the reliability and availability of drive systems in electric vehicles, and hence constitutes a major design challenge for German auto manufacturers aiming to electrify their vehicles.
Now the partners participating in the RoBE (Robust Bonds in ...
International team of scientists develops new feedback method for optimizing the laser pulse shapes used in the control of chemical reactions
In many ways, traditional chemical synthesis is similar to cooking. To alter the final product, you can change the ingredients or their ratio, change the method of mixing ingredients, or change the temperature or pressure of the environment of the ingredients.
Like an accomplished chef, chemists have become very skilled ...
11.12.2013 | Information Technology
11.12.2013 | Life Sciences
11.12.2013 | Agricultural and Forestry Science
11.12.2013 | Event News
10.12.2013 | Event News
05.12.2013 | Event News