Astronomers using Keck Observatory discover rain falling from Saturn's rings

Apr 10, 2013
Credit: NASA/JPL-Caltech/Space Science Institute/University of Leicester

(Phys.org) —NASA funded observations on the W. M. Keck Observatory with analysis led by the University of Leicester, England tracked the "rain" of charged water particles into the atmosphere of Saturn and found the extent of the ring-rain is far greater, and falls across larger areas of the planet, than previously thought. The work reveals the rain influences the composition and temperature structure of parts of Saturn's upper atmosphere. The paper appears in this week's issue of the journal Nature.

"Saturn is the first planet to show significant interaction between its atmosphere and ring system," said James O'Donoghue, the paper's lead author and a postgraduate researcher at Leicester. "The main effect of ring rain is that it acts to 'quench' the ionosphere of Saturn, severely reducing the electron densities in regions in which it falls."

O'Donoghue said the ring's effect on electron densities is important because it explains why, for many decades, observations have shown electron densities to be unusually low at some latitudes at Saturn.

"It turns out a major driver of Saturn's ionospheric environment and climate across vast reaches of the planet are ring particles located 120,000 miles [200,000 kilometers] overhead," said Kevin Baines, a co-author on the paper, based at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "The ring particles affect which species of particles are in this part of the ."

In the early 1980s, images from NASA's showed two to three dark bands on Saturn and scientists theorized that water could have been showering down into those bands from the rings. Those bands were not seen again until 2011 when the the team observed the planet with 's NIRSPEC, a unique, near- that combines broad wavelength coverage with high , allowing the observers to clearly see subtle emissions from the bright parts of Saturn.

The ring rain's effect occurs in Saturn's ionosphere (Earth has a similar ionosphere), where charged particles are produced when the otherwise neutral atmosphere is exposed to a flow of energetic particles or solar radiation. When the scientists tracked the pattern of emissions of a particular hydrogen molecule consisting of three hydrogen atoms (rather than the usual two), they expected to see a uniform planet-wide infrared glow. What they observed instead was a series of light and dark bands with a pattern mimicking the planet's rings. Saturn's magnetic field "maps" the water-rich rings and the water-free gaps between rings onto the planet's atmosphere.

They surmised that charged from the planet's rings were being drawn towards the planet by Saturn's magnetic field and neutralizing the glowing triatomic hydrogen ions. This leaves large "shadows" in what would otherwise be a planet-wide infrared glow. These shadows cover 30 to 43 percent of the planet's surface from around 25 to 55 degrees latitude. This is a significantly larger area than suggested by the Voyager images.

Both Earth and Jupiter have a very uniformly glowing equatorial region. Scientists expected this pattern at Saturn, too, but they instead saw dramatic differences at different latitudes.

"Where Jupiter is glowing evenly across its equatorial regions, Saturn has dark bands where the water is falling in, darkening the ionosphere," said Tom Stallard, one of the paper's co-authors at Leicester. "We're now also trying to investigate these features with an instrument on NASA's Cassini spacecraft. If we're successful, Cassini may allow us to view in more detail the way that water is removing ionized , such as any changes in the altitude or effects that come with the time of day."

Explore further: Memory reformat planned for Opportunity Mars rover

More information: Paper: dx.doi.org/10.1038/nature12049

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cantdrive85
1 / 5 (10) Apr 10, 2013
So, electric currents affect the ring plane and ionosphere? Who'da thunk it?

"It seems almost incredible that such a ring of cosmic dust should be able to exist for ever, so to speak, without other governing forces than gravitation…"

— Kristian Birkeland 1913

Oh, Birkeland did, a HUNDRED YEARS AGO!
robeph
5 / 5 (5) Apr 10, 2013
Oh poor cantdrive, always cherry picking words ignoring the rest of the article
James_O_D
3.7 / 5 (3) Apr 10, 2013
Thanks Robeph! My colleague told me not to read comments on my work ;).
I'm not sure Birkeland mentioned that water fell on one-third of Saturn's atmospheric surface, feel free to quote though! :)
Best wishes,
James O' D.
HannesAlfven
1.5 / 5 (8) Apr 10, 2013
Re: "Thanks Robeph! My colleague told me not to read comments on my work"

It's not exactly news that the academic world exists within a bubble. Jeff Schmidt was ignored when he warned that the physics discipline rewards ass-kissers and memorizers over people who stop to think about what it is that they are memorizing. Hannes Alfven's warnings about cosmic plasma models were ignored even as he was giving his Nobel acceptance speech for his creation of MHD. University professors generally ignore the entire discipline of physics education research -- maybe because it reminds them that there's no actual theory behind the lecture format (?). Wal Thornhill was ignored even after his suggestion that the Deep Impact impactor would create two separate flashes was observed. Gerrit Verschuur continues to be ignored to this day when he notes that the interstellar "clouds" are not at all cloud-like, but are instead highly filamentary and exhibit CIV's at the knots.

Welcome to the club!
James_O_D
4 / 5 (4) Apr 10, 2013
Ring rain hasn't been believed entirely for 30 years, I'm aware of being ignored too. It's a shame it happens and I am happy to have had sufficient evidence for my result.
HannesAlfven
1.4 / 5 (10) Apr 10, 2013
Re: "Oh poor cantdrive, always cherry picking words ignoring the rest of the article"

Questioning assumptions and re-interpreting a press release through the lens of another paradigm are actually features of critical thinking.

What is happening, unfortunately, in our graduate physics programs is that students are asked to memorize stacks of problem sets. Jeff Schmidt argues in Disciplined Minds that if you memorize enough problem sets, you'll eventually stop asking certain poignant questions about what it is that you're "learning".

People need to stop acting as though science doesn't need critics or critical thinkers. Whatever your thoughts about the theory, the ways in which teach people science -- as well as the public responses to critique -- can all have an incredible effect upon peoples' beliefs within science. Ostracism elicits particular effects within those who observe it. You might want to do a google on "physorg ostracism" ...
HannesAlfven
1.4 / 5 (10) Apr 10, 2013
Re: "Ring rain hasn't been believed entirely for 30 years, I'm aware of being ignored :)"

It's too bad though that you guys decided to stick with a concept label that comes with so much baggage. With all of the interstellar "clouds", the solar "wind" and now "ring rain", one could be forgiven for thinking that space is more like a typical day in the Bahamas than a plasma.
HannesAlfven
1 / 5 (3) Apr 11, 2013
Did anybody else notice the apparent morphological similarity to the Van Allen Radiation belts? And did anybody else notice the observation back in March that the Van Allen radiation belts have been hiding a stash of electrons from us ...

http://www.spaced...999.html

One of the most common responses to the claim that the Sun might be electrically powered is to suggest that if the electrons were there, we'd clearly already have observed them. And yet, far closer to home, we can see that the movement and collection of electrons is going to require actual effort to observe. Within the context of these two recent findings, it should be clear that if electrons are indeed streaming towards the Sun, they very possibly have a specific morphology which we'll have to figure out.
HannesAlfven
1 / 5 (3) Apr 11, 2013
BTW:

"A Note on the Acceleration of the Solar Wind"
DE Scott
http://electric-c...Wind.pdf

And from here ...

"WIND observations of coherent electrostatic waves in the solar wind"
http://www.ann-ge...1999.pdf

... a 400-600 V potential is proposed at 1 AU.

Don Scott is talking more in the range of a 3000 V potential, so is this really so crazy?

What typically happens in this sort of a situation is that a barrage of mathematicians goes to work trying to build a variety of models to see what could be made to work.

What is becoming clear is the extent to which personal preferences and the pressures of the discipline play in the decision to direct that barrage of mathematicians. We are told that, "Mathematics represents objective knowledge, which allows us to break free of dogmas and prejudices."

(from http://www.slate....sn_feed)

Really?