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Fraser
2005-May-25, 06:30 PM
SUMMARY: Based on new observations from the Chandra X-Ray Observatory, Saturn could act as a mirror to help determine when massive X-ray flares are going off on the Sun. Chandra observed Saturn before and then during a flare and could clearly see X-rays reflected back. A similar situation also happens with Jupiter, so scientists could use the two planets as remote sensing tools to monitor events on the opposite side of the Sun.

View full article (http://www.universetoday.com/am/publish/saturn_reflects_xrays_sun.html)

What do you think about this story? Post your comments below.

om@umr.edu
2005-May-25, 07:14 PM
Using Saturn and Jupiter as mirrors to see what is happening on the back side of the Sun is an interesting new development.

I had never thought about the possibility of these planets reflecting back x-rays from the Sun.

With kind regards,

Oliver
http://www.umr.edu/~om

VanderL
2005-May-25, 08:33 PM
Is there any idea how this works exactly, these planets are gas giants, without a solid surface, I expect rocky or icy moons to reflect but reflecting gas?

Cheers.

antoniseb
2005-May-25, 08:42 PM
Originally posted by VanderL@May 25 2005, 08:33 PM
Is there any idea how this works exactly, these planets are gas giants, without a solid surface
I imagine that xrays are short enough wavelength that suspended aerosol particles could reflect them. This is just a guess. I do not know the mechanism the researchers here think is happening.

dave_f
2005-May-25, 09:36 PM
Originally posted by VanderL@May 25 2005, 03:33 PM
Is there any idea how this works exactly, these planets are gas giants, without a solid surface, I expect rocky or icy moons to reflect but reflecting gas?

Cheers.
Good question: Gas Giants reflect all sorts of light. If they didn't, they would either be transparent or black in color.

Guest
2005-May-25, 09:45 PM
Thanks for the replies,

I would expect these planets to absorb the radiation and emit in the specific frequencies of it's constituents, that way we would see changes in frequencies, not reflection, so the question to me remains how this scatter/absorption/emission can lead to X-rays being reflected. If at all it would be an infinitesimal fraction, I don't know of any "gas mirrors".

Cheers.

dave_f
2005-May-26, 05:35 PM
Originally posted by Guest@May 25 2005, 04:45 PM
Thanks for the replies,

I would expect these planets to absorb the radiation and emit in the specific frequencies of it's constituents, that way we would see changes in frequencies, not reflection, so the question to me remains how this scatter/absorption/emission can lead to X-rays being reflected. If at all it would be an infinitesimal fraction, I don't know of any "gas mirrors".

Cheers.
They aren't "mirrors" any more than a piece of paper is a mirror. So these measurements will tell us little more than how powerful these flares are that we can't see directly. It's not much, but enough to give us a little warning if a major sunspot system is coming 'round the corner.

If anything we'll have advanced warning on potentially beautiful aurora days or weeks before they happen. ;)

alfchemist
2005-May-27, 11:26 AM
Hhmm. This is intriguing. There's something about the two gas giants that the rest don't have that's reflecting the x-rays or maybe the rest are reflecting x-rays too but not so considerable or observable.

Anil Bhardwaj
2005-May-30, 10:41 PM
I just saw email from Ola Dudin (was on travel) inviting me to reply on queries posted at this site.
Let me explain how gas giants Jupiter and Saturn shine in X-rays.
As we understand, to a large extend, both these giant planets shine in soft (~0.2-2.0 keV) X-rays by resonant (elastic) and fluorescent scattering of solar X-rays by the atoms and molecules in their atmospheres. It’s largely (~90%) resonant (elastic) and partially (<10%) fluorescent (K-shell) scattering of solar X-rays from their upper atmospheres. The scattering process is called “Thomson Scattering” of photons by electrons in the atom/molecules in the atmospheres of the gas giants. At the altitudes (heights) where they efficiently scatter back the solar X-rays, these planets have molecular hydrogen as pre-dominant (~85-95%) gas with small contribution from Helium (~5-15%). Fluorescent (K-shell excitation) scattering occurs from carbon atom in methane molecules in the atmosphere (CH4 to H2 ratio is about 0.2%).

Note: not all the solar X-rays are scattered by these planets. On an average, just one in few thousand solar X-ray photons in ~0.2-2.0 keV are scattered from atmospheres: enabling these giant planets to glow in X-rays.

cheers, :)
- Anil Bhardwaj

VanderL
2005-May-31, 08:41 PM
Hi Anil Bhardwaj,

Thanks for the explanation of the (back)scattering of solar X-rays. Apparently the 0.07 % reflection is enough to show up in the X-ray detectors. Can all planets be used as a sort of mirror for solar activity, or is it only possible for the gas giants? I saw the plots of the events in the article, and I am curious about the Chandra data. There aren&#39;t many data points for Jupiter&#39;s (and also for Saturn&#39;s) X-rays, it would be much more informtive to have the timing of the events (flares) as accurately as possible, to show the time-delay that is calculated for the Earth/Sun/Jupiter/Saturn distances to be correct. Will there be follow-up observation with more data points?
Are the raw data used for the plots publicly available?

Another question is the use of the planets to forecast solar activity, wouldn&#39;t this be very difficult, and only possible if the planets are in the right spots?

Cheers.