APOD: Unusual Auroras Over Saturn's North Pole (2008 Nov 19)

[BMAONE23]

COOL SITE
I got a zero though IS THAT OUT OF 100?

[apodman]

I got a zero ...

Congratulations on your 0. I'm sure my eyes are perfect, too (my monitor and room lighting are to blame).

... IS THAT OUT OF 100?

No, if you just score the test without rearranging the colors at all, you get something like 1026. If you click the right link, it shows other scores for the age and gender you choose, one worse than 1400, though it only shows 0-100 on the graphical scale.

COOL SITE

I found the link on some other astronomy discussion site, too many clicks away to remember now.

But who needs to remember when technology does it for me?

http://forum.ourdarkskies.com/index.php?showforum=2

http://forum.ourdarkskies.com/

[neufer]

The caption clearly stated "... Infrared images by the robotic Cassini spacecraft of the north pole of Saturn ...".
Following the provided link gives detailed information about the composition.

Infrared images: <<Energetic particles, crashing into the upper atmosphere cause the aurora, shown in blue, to glow brightly at 4 microns (six times the wavelength visible to the human eye). The image shows both a bright ring, as seen from Earth, as well as an example of bright auroral emission within the polar cap that had been undetected until the advent of Cassini. This aurora, which defies past predictions of what was expected, has been observed to grow even brighter than is shown here. Silhouetted by the glow (cast here to the color red) of the hot interior of Saturn (clearly seen at a wavelength of 5 microns, or seven times the wavelength visible to the human eye) are the clouds and haze that underlie this auroral region.>>
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For something to glow at 4 microns BUT NOT at 5 microns REQUIRES
a vibrational molecular IR band as the source...such at that of H3+ :

... which is observed in emission at Jupiter:
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Jupiter VIS+IR full disk reflectance
http://www.ifsi-roma.inaf.it/vims/index ... egoryid=18

<<By using the signal from both VIS (blue) and IR (red) channels of VIMS was possible to retrieve the full-disk integrated reflectance spectrum of Jupiter. In the following plot is possible to note as in the IR range the methane absorption bands are very strong and saturated completely between 2.2-2.4 microns and between 3.2-3.8 microns. At about 4.0 microns (i.e., 4000 nm) are visible some emission lines of H3+. Over 4.5 microns the thermal emission of the planet is easily visible.>>



http://avogadro.bitacoras.com/archivos/2006/01/16/h3
http://frhewww.physik.uni-freiburg.de/k ... es_d3h.gif
http://fermi.uchicago.edu/~bjmccall/pro ... gures.html
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[neufer]

IRTF Images of Jupiter


<<These near-infrared images of Jupiter were taken as a part of a campaign to observe changes in Jupiter's atmospheric conditions using instrumentation at NASA's Infrared Telescope Facility, located at the summit of Mauna Kea, Hawaii. North is toward the top in these images; Jupiter rotates from left to right. These wavelengths sample cloud reflectivity (1.58 microns), haze and cloud particles in the upper troposphere (3.8 microns) and lower stratosphere (2.3 microns) and thermal emission from cloud tops (4.85 microns). Auroral emission is also seen near the poles at 3.8 microns.

At a wavelength of 1.58 microns, we sense sunlight reflected from cloud particles with virtually no absorption by Jupiter's gases. Thus, the variations from one region to the next indicate changes of the reflectivity (albedo) of cloud particles. The appearance of the planet at 1.58 microns is the closest near-infrared analogue of its visible (red) appearance.

At a wavelength of 3.8 microns, we sense two sources of radiation. One is sunlight reflected from cloud particles in Jupiter's upper troposphere which has not been extinguished by weak methane (CH4) gas absorption. The Great Red Spot is seen as a high cloud on the right, just below the center; the brightest reflection - and probably the highest cloud particles in this region - are detected in discrete plumes just north of the equator, close to the latitude in which the Galileo Probe will enter on December 7. The other source of radiation comes from emission by H3+ from an airglow which covers the planet and is most pronounced at the edge of the disk (the limb) and from auroral emission near the poles. This image has captured oval-shaped H3+ auroral emission near the south pole.

At a wavelength of 2.3 microns, we sense sunlight reflected from cloud and haze particles higher up - in Jupiter's lower stratosphere - which have not been extinguished by methane (CH4) and molecular hydrogen (H2) gas absorption. The most prominent features are the particulate caps covering the poles (in this image, the dark spot in the middle of the south polar cap is an artifact of the NSFCAM optics at the time). From mid-latitudes toward the south pole, the moderate reflecting particulates are mostly remnants of particles remaining from impacts of Comet Shoemaker-Levy 9 fragments near 45 deg.S lat., now distributed rather uniformly over longitudes and migrating far to the south and somewhat to the north of the impact latitude.

At a wavelength of 4.85 microns, we are sensing heat from Jupiter, which we indicate by the false red shading. The darkest regions correspond to emission from temperatures near 185 Kelvins (-190 deg. F) and the warmest regions to temperatures near 255 Kelvins (-64 deg. F), indicating emission from 1 - 5 bars of atmospheric pressure in Jupiter. The absence of strong gaseous absorption at this wavelength means that we are sensing temperatures near the tops of clouds in the atmosphere. The brightest spots are discrete regions which are locally clear of obscuring clouds, known as ``hot spots''; they are one of the special targets planned for the atmospheric investigations by the Galileo Orbiter instrument teams. Note that there is a relatively bright (clear) but broken band to the north of the Great Red Spot. There are also bright rings around several of the visibly white oval features south of the Great Red Spot.
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http://www.sciencedaily.com/releases/20 ... 131158.htm
http://tinyurl.com/5a8c8g

Science News
Really Big Planets: When Do Gas Giants Reach The Point Of No Return?

ScienceDaily (Dec. 7, 2007) — <<Planetary scientists at UCL have identified the point at which a star causes the atmosphere of an orbiting gas giant to become critically unstable, as reported in this week's Nature (December 6). Depending upon their proximity to a host star, giant Jupiter-like planets have atmospheres which are either stable and thin, or unstable and rapidly expanding. This new research enables us to work out whether planets in other systems are stable or unstable by using a three dimensional model to characterise their upper atmospheres.

Tommi Koskinen of UCL's Physics & Astronomy Department is lead author of the paper and says: "We know that Jupiter has a thin, stable atmosphere and orbits the Sun at five Astronomical Units (AU) - or five times the distance between the Sun and the Earth. In contrast, we also know that closely orbiting exoplanets like HD209458b - which orbits about 100 times closer to its sun than Jupiter does - has a very expanded atmosphere which is boiling off into space. Our team wanted to find out at what point this change takes place, and how it happens.

"Our paper shows that if you brought Jupiter inside the Earth's orbit, to 0.16AU, it would remain Jupiter-like, with a stable atmosphere. But if you brought it just a little bit closer to the Sun, to 0.14AU, its atmosphere would suddenly start to expand, become unstable and escape. This dramatic change takes place because the cooling mechanism that we identified breaks down, leading to the atmosphere around the planet heating up uncontrollably."

Professor Alan Aylward, co-author of the paper, explains some of the factors which the team incorporated in order to make the breakthrough: "For the first time we've used 3D-modelling to help us understand the whole heating process which takes place as you move a gas giant closer to its sun. The model incorporates the cooling effect of winds blowing around the planet - not just those blowing off the surface and escaping.

"Crucially, the model also makes proper allowances for the effects of H3+ in the atmosphere of a planet. This is an electrically-charged form of hydrogen which strongly radiates sunlight back into space and which is created in increasing quantities as you heat a planet by bringing it closer to its star.

"We found that 0.15AU is the significant point of no return. If you take a planet even slightly beyond this, molecular hydrogen becomes unstable and no more H3+ is produced. The self-regulating, 'thermostatic' effect then disintegrates and the atmosphere begins to heat up uncontrollably."

Professor Steve Miller, the final contributing author to the paper, puts the discovery into context: "This gives us an insight to the evolution of giant planets, which typically form as an ice core out in the cold depths of space before migrating in towards their host star over a period of several million years. Now we know that at some point they all probably cross this point of no return and undergo a catastrophic breakdown.

"Just twelve years ago astronomers were searching for evidence of the first extrasolar planet. It's amazing to think that since then we've not only found more than 250 of them, but we're also in a much better position to understand where they came from and what happens to them during their lifetime.">>
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[bystander]

Aurorae on Mars found not at poles, as on Earth, Jupiter and Saturn, but around pockets of magnetic rocks in Mars crust.

Mars Express maps aurorae on the Red Planet
Provided by European Space Agency
Astronomy.com - 2008 Nov 21

Aurorae seem to be located near regions where the martian magnetic field is the strongest.
Artist's impression

[NoelC]

False colour should be much more clearly indentified in alterations.

Yes, yes, YES! Hear hear! This bit of information is missing from SO many images.

Laypeople don't realize that such a thing as "false color" even exists, and so tend to take what they see as a representation of visual reality. Even non-laypeople on occasion make this mistake.

Editors of APOD: Please include a note describing an image as being in "false color" unless it's a fair representation of the actual visual color we'd see if only we could get out there with eyes the size of ash cans.

-Noel

[bystander]

Yes, yes, YES! Hear hear! This bit of information is missing from SO many images.

Laypeople don't realize that such a thing as "false color" even exists, and so tend to take what they see as a representation of visual reality. Even non-laypeople on occasion make this mistake.

So, what part of infrared image do you not understand.

[NoelC]

Ask 10 laypeople on the street that question. They'll hear the "red" part.

APOD's mission seems to be to educate the public about astro stuff. I just ask that some plain English wording be added to make it clear to a first-time viewer who doesn't know "infrared" from "glowing red".

-Noel

[apodman]

When I was a (young) kid, I thought "infrared" was pronounced like it rhymed with "prepared". I thought it was one of those "in-" words like "inflamed". "Infrare" my steak until it is well done. Just hit it with some of those "infrared" rays.

On one hand, there are many technical aspects and terms in a typical APOD description, and we can't define them all every time. Though an attempt is made: goodness knows all those links go a long way toward filling in background. And the surfer of today's web can't really cry "foul" and that they can't find a dictionary, google, or wikipedia.

On the other hand, it doesn't hurt to put in a phrase like "infrared (beyond the long end of the spectrum of visible light)" once in a while.

On the third hand, you can't reach everyone no matter how completely you describe something. Many readers won't associate "beyond the visible spectrum" with false color, either.

APOD descriptions are kept to one paragraph. If you explain more of one thing, you have to sacrifice detail on something else. I think the trade-offs chosen by the editors are fine.

[Frenchy]

Any talk of whether or not rotating and revolving asteroids can cause electromagnetic waves that would cause these auroras?

and

the differential atmospheric patterns on these two planets? (i.e. Saturn and Jupiter)

[Chris Peterson]

Any talk of whether or not rotating and revolving asteroids can cause electromagnetic waves that would cause these auroras?

They can't. Auroras are not caused by electromagnetic waves, they are caused by high energy particles interacting with atmospheric gas. Any field lines that the particles are following are clearly being produced on the planet. In any case, asteroids don't have a significant magnetic field, and they don't move fast, and they aren't large, and they aren't very conductive, and they don't cut through large electric fields. So they have no way to produce much in the way of electromagnetic waves.

[Frenchy]

What is the blip in the graph previously listed? (Just to the left of 3000nm)

[Doum]

What is the blip in the graph previously listed? (Just to the left of 3000nm)

Look at this link:

http://en.wikipedia.org/wiki/Electromag ... e_spectrum
It look to be in the near infrared. 3000nm is also 3um. In the graph the blip is at about 2750nm or 2,75 um. It is still in the near infrared.

[Frenchy]

Thanks for the information Doum...

Is there a way to eliminate electromagnetic interference?