X-rays from solar system objects

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X-rays from solar system objects

Unread postby Nereid » Sun Dec 12, 2010 9:18 pm

That's the title of a recent ("[v1] Mon, 6 Dec 2010 07:42:45 GMT") preprint on the arXiv server.

The authors are: Anil Bhardwaj, Ronald F. Elsner, G. Randall Gladstone, Thomas E. Cravens, Carey M. Lisse, Konrad Dennerl, Graziella Branduardi-Raymont, Bradford J. Wargelin, J. Hunter Waite, Ina Robertson, Nikolai Ostgaard, Peter Beiersdorfer, Steven L. Snowden, and Vasili Kharchenko.

Here is the abstract:
Bhardwaj et al. wrote:During the last few years our knowledge about the X-ray emission from bodies within the solar system has significantly improved. Several new solar system objects are now known to shine in X-rays at energies below 2 keV. Apart from the Sun, the known X-ray emitters now include planets (Venus, Earth, Mars, Jupiter, and Saturn), planetary satellites (Moon, Io, Europa, and Ganymede), all active comets, the Io plasma torus (IPT), the rings of Saturn, the coronae (exospheres) of Earth and Mars, and the heliosphere. The advent of higher-resolution X-ray spectroscopy with the Chandra and XMM-Newton X-ray observatories has been of great benefit in advancing the field of planetary X-ray astronomy. Progress in modeling X-ray emission, laboratory studies of X-ray production, and theoretical calculations of cross-sections, have all contributed to our understanding of processes that produce X-rays from the solar system bodies. At Jupiter and Earth, both auroral and non-auroral disk X-ray emissions have been observed. X-rays have been detected from Saturn's disk, but no convincing evidence of an X-ray aurora has been observed. The first soft (0.1- 2 keV) X-ray observation of Earth's aurora by Chandra shows that it is highly variable. The non-auroral X-ray emissions from Jupiter, Saturn, and Earth, those from the disk of Mars, Venus, and Moon, and from the rings of Saturn, are mainly produced by scattering of solar X-rays. The spectral characteristics of X-ray emission from comets, the heliosphere, the geocorona, and the Martian halo are quite similar, but they appear to be quite different from those of Jovian auroral X-rays. X-rays from the Galilean satellites and the IPT are mostly driven by impact of Jovian magnetospheric particles. This paper reviews studies of the soft X-ray emission from the solar system bodies, excluding the Sun.

Lots of good data that might be used to quantitatively test models based on EU theory! :)
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Re: X-rays from solar system objects

Unread postby DustyDevil » Mon Dec 13, 2010 5:49 am

This preprint may have only been uploaded on Dec. 6, 2010; however, this paper was published in Planetary and Space Science in 2007. For those who may find the published figures more informative, the following is a link to the published article:

http://web.ift.uib.no/~nikost/papers/bh ... 07_onl.pdf

Enjoy!

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Re: X-rays from solar system objects

Unread postby mharratsc » Mon Dec 13, 2010 7:38 am

Thanks for posting that, Ms. Nereid. :)

Say, regarding the whole 'proof in pudding' thing- I obviously know how the EU model explains X-ray emissions (regardless of whether it's sticky tape or galactic cores), but what exactly is the most prevalent 'mainstream' explanation for X-ray emissions within the solar system, and from comets for that matter, too? o.O

Would you happen to be familiar with that offhand? I guess I'm a bit interested in seeing where the focus of current investigations into this phenomena might be pointed at currently.
Mike H.

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Re: X-rays from solar system objects

Unread postby Nereid » Mon Dec 13, 2010 8:48 am

Thanks very much DustyDevil! :)

Mike, Section 10 is entitled "Comets"; it's ~5 pages long, and the first paragraph is as follows:
Bhardwaj et al. wrote:The discovery of high-energy X-ray emission in 1996 from C/1996 B2 (Hyakutake) has revealed the existence of a new class of X-ray emitting objects (Lisse et al., 1996). Observations since 1996 have shown that the very soft (Eo1 keV) emission is due to an interaction between the solar wind and the comet’s atmosphere, and that X-ray emission is a fundamental property of comets. Theoretical and observational work has demonstrated that CX collisions of highly charged solar wind ions with cometary neutral species is the best explanation for the emission. Now a rapidly changing and expanding field, the study of cometary X-ray emission appears to be able to lead us to a better understanding of a number of physical phenomena: the nature of the cometary coma, other sources of X-ray emission in the solar system, the structure of the solar wind in the heliosphere, and the source of the local soft X-ray background. We mostly focus here on X-ray comet observations made up to 2003.

"CX collisions" are "charge exchange" collisions, in which an ion collides with a neutral (usually an atom) and charge is exchanged.

The last sentence suggests that there's an awful lot more material (published papers) on observations of x-ray emission by comets than the few pages that follow this sentence!

More generally, I think you'd enjoy this paper (as DD says), so why not download it, read it at your leisure, and ask any questions you want (I will try to answer them, but I'm sure there are others here who can also).
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Re: X-rays from solar system objects

Unread postby mharratsc » Mon Dec 13, 2010 12:08 pm

Whups! My bad- I didn't see Dusty sneak in under my radar there when I'd posted. :oops:

This is a pretty thorough and informative paper, but wow- is this guy ever playing it 'politically correct'! :roll:

It has been suggested that these emissions are bremsstrahlung from upward-propagating, relativistic (MeV) electrons generated in a runaway electron discharge process above thunderclouds by the transient electric field following a positive cloud-to-ground lightning event...


That sure is a fancy way of saying 'flow of current from the Earth to space'. Even with knowing about the "magnetic flux tubes" connecting the Sun to the Earth, is it still taboo to mention 'current flow' regards to the Sun-Earth circuit? o.O
Mike H.

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Re: X-rays from solar system objects

Unread postby Nereid » Mon Dec 13, 2010 1:19 pm

mharratsc wrote:Whups! My bad- I didn't see Dusty sneak in under my radar there when I'd posted. :oops:

Don't you just hate it when that happens?! :P
This is a pretty thorough and informative paper, but wow- is this guy ever playing it 'politically correct'! :roll:

I'm afraid you're going to have to educate me mharratsc; what does "politically correct", enclosed within single quote marks, mean? :?:
It has been suggested that these emissions are bremsstrahlung from upward-propagating, relativistic (MeV) electrons generated in a runaway electron discharge process above thunderclouds by the transient electric field following a positive cloud-to-ground lightning event...


That sure is a fancy way of saying 'flow of current from the Earth to space'.
Actually, no, it isn't (as far as I know; I'll be the first to admit that I am still very ignorant of this field).

You see 'flow of current from the Earth to space' is very imprecise, while 'bremsstrahlung from upward-propagating, relativistic (MeV) electrons generated in a runaway electron discharge process above thunderclouds by the transient electric field following a positive cloud-to-ground lightning event' is not.

For example, the quote from the paper:
* specifies the charge carriers (your phrase does not)
* bounds the charge carriers' speeds (your phrase does not)
* proposes a mechanism by which the charge carriers, and acceleration of them, attain their (possible) speeds (your phrase does not)
* identifies where the acceleration likely takes place (ditto)
* proposes when the triggering circumstances may occur (ditto).
Even with knowing about the "magnetic flux tubes" connecting the Sun to the Earth,

But why would they mention it (assuming what you write is correct; do you have a reference? I mean to a published paper, not a Press Release)

Unless they had good, reliable, quantitative evidence that such a thing was directly relevant to the observed x-rays, wouldn't adding anything about such "magnetic flux tubes" be unfounded speculation?
is it still taboo to mention 'current flow' regards to the Sun-Earth circuit? o.O

Huh? There's a "Sun-Earth circuit"?!?! :o
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Re: X-rays from solar system objects

Unread postby Anaconda » Mon Dec 13, 2010 2:55 pm

Nereid wrote:Huh? There's a "Sun-Earth circuit"?!?! :o


There is some evidence that a "Sun-Earth circuit" can exist at times of intense coronal mass ejections (CME):

Here is a recent peer-reviewed paper discussing the electric circuit theory of CME's:

2009 peer-reviewed published paper: Central European Astrophysics Bulletin

GENERATION OF LARGE SCALE ELECTRIC FIELDS IN CORONAL FLARE CIRCUITS

Abstract:

A large number of energetic electrons are generated during solar flares. They carry a substantial part of the flare released energy but how these electrons are created is not fully understood yet. This paper suggests that plasma motion in an active region in the photosphere is the source of large electric currents. These currents can be described by macroscopic circuits. Under special circumstances currents can establish in the corona along magnetic field lines. The energy released by these currents when moderate assumptions for the local conditions are made, is found be comparable to the flare energy.


This paper presents the electric circuit theory championed by Hannes Alfven.

Quote from the above paper:

Currently several different electron acceleration mechanisms in the solar corona are known. All of these mechanisms have the principle of acceleration due to electric fields in common, but differ in the processes leading to the generation of the electric field. In the present paper the generation of a large scale DC electric field is discussed in terms of electric circuits, which is related to a current generated due to photopheric plasma motion (e.g., Alfven and Carlqvist, 1967; Sen and White, 1972; Martres et al., 1973; Heyvarts, 1974; Obayashi, 1975; Akasofu, 1979; Kan et al., 1983; Melrose, 1997; Zaitsev et al., 1998; Yang et al., 2004; Zaitsev, 2005). Motivated by these papers, the electric currents are investigated in order to obtain a mechanism for acceleration of electrons to high energies. The basic idea of this mechanism is to generate the flare energy by photopheric plasma motion in active regions. This is in contradiction to the reconnection model in which the magnetic field energy in the corona is taken for the flare.

http://arxiv.org/PS_cache/arxiv/pdf/090 ... 0813v1.pdf

The following NASA press release reports on a CME impacting the Earth's magnetosphere:

Science@NASA (Dec. 16, 2008) -- Giant Breach in Earth's Magnetic Field Discovered

NASA wrote:NASA's five THEMIS spacecraft have discovered a breach in Earth's magnetic field ten times larger than anything previously thought to exist. Solar wind can flow in through the opening to "load up" the magnetosphere for powerful geomagnetic storms. But the breach itself is not the biggest surprise. Researchers are even more amazed at the strange and unexpected way it forms, overturning long-held ideas of space physics.


And, here is the "surprise" expressed by the scientist:

NASA wrote:"At first I didn't believe it," says THEMIS project scientist David Sibeck of the Goddard Space Flight Center. "This finding fundamentally alters our understanding of the solar wind-magnetosphere interaction."


The NASA press release go on:

NASA wrote:The magnetosphere is a bubble of magnetism that surrounds Earth and protects us from solar wind. Exploring the bubble is a key goal of the THEMIS mission, launched in February 2007. The big discovery came on June 3, 2007, when the five probes serendipitously flew through the breach just as it was opening. Onboard sensors recorded a torrent of solar wind particles streaming into the magnetosphere, signaling an event of unexpected size and importance.


And, the scientists attempt to quantify the size of the event:

NASA wrote:"The opening was huge—four times wider than Earth itself," says Wenhui Li, a space physicist at the University of New Hampshire who has been analyzing the data. Li's colleague Jimmy Raeder, also of New Hampshire, says "1027 particles per second were flowing into the magnetosphere—that's a 1 followed by 27 zeros. This kind of influx is an order of magnitude greater than what we thought was possible."

http://science.nasa.gov/science-news/sc ... antbreach/

It's important to investigate whether a connection exists between seperate observations & measurements, to see if it is possible to develop a hypothesis of an over all process or phenomenon, which encompasses the seperate physical observations & measurements.

To that effort, here is another Science@NASA press release describing the shape of CME's:

Science@NASA (April 14, 2009) -- The Surprising Shape of Solar Storms

NASA wrote:Researchers studying data from NASA's twin STEREO probes have found that ferocious solar storms called CMEs (coronal mass ejections) are shaped like a French pastry. The elegance and simplicity of the new "croissant model" is expected to dramatically improve forecasts of severe space weather.


What is a croissant shaped like? Two twisted stands of pastry dough.

NASA wrote:Coronal mass ejections are billion-ton clouds of hot magnetized gas that explode away from the sun at speeds topping a million mph. Sometimes the clouds make a beeline for Earth and when they hit they can cause geomagnetic storms, satellite outages, auroras, and power blackouts. The ability to predict the speed and trajectory of a CME is key to space weather forecasting.

"This is an important advance," says Lika Guhathakurta, STEREO program scientist at NASA headquarters in Washington DC. "From a distance, CMEs appear to be a complicated and varied population. What we have discovered is that they are not so varied after all. Almost all of the 40-plus CMEs we have studied so far with STEREO have a common shape--akin to a croissant."

http://science.nasa.gov/science-news/sc ... apr_3dcme/

Why is the shape of CME's important?

Because the morphology is suggestive of magnetic flux tubes, sometimes called Birkeland currents:

A Birkeland current usually refers to the electric currents in a planet's ionosphere that follows magnetic field lines (ie field-aligned currents), and sometimes used to described any field-aligned electric current in a space plasma. They are caused by the movement of a plasma perpendicular to a magnetic field. Birkeland currents often show filamentary, or twisted "rope-like" magnetic structure. They are also known as field-aligned currents, magnetic ropes and magnetic cables.

http://www.plasma-universe.com/Birkeland_current

Let's compare the descriptions given by NASA and the Birkeland current entry:

NASA wrote:[CME's]have a common shape--akin to a croissant."


Birkeland currents often show filamentary, or twisted "rope-like" magnetic structure.


It would seem the morphology is similar between CME's "croissant" like shape and Birkeland current's twisted "rope-like" shape.

Birkeland currents are part of a "circuit" and, per the peer-reviewed published paper, GENERATION OF LARGE SCALE ELECTRIC FIELDS IN CORONAL FLARE CIRCUITS, above, CME's are also part of an electrical "circuit".

The electric circuit theory championed by Hannes Alfven.

So, yes, there is evidence that at times, there is a "Sun-Earth circuit". :)
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Re: X-rays from solar system objects

Unread postby mharratsc » Mon Dec 13, 2010 3:19 pm

Or a more simplified format (i.e.- 'Mike speed' :P ) from UniverseToday:

New Finding Shows Super-Huge Space Tornados Power the Auroras

Also, the Thunderbolts versions:

The Interconnected Sun Part One


The Interconnected Sun Part Two


Essentially, if you have charge moving, you have current. If you have current, you have a circuit. That's how I understand it. o.O
Mike H.

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Re: X-rays from solar system objects

Unread postby Anaconda » Mon Dec 13, 2010 4:02 pm

Additional scientific paper:

DRIVING CURRENTS FOR FLUX ROPE CORONAL MASS EJECTIONS (2008):

Abstract: “We present a method for measuring electrical currents enclosed by flux rope structures that are ejected within solar coronal mass ejections (CMEs). Such currents are responsible for providing the Lorentz self-force that propels CMEs. Our estimates for the driving current are based on measurements of the propelling force obtained using data from the LASCO coronagraphs aboard the SOHO satellite. We find that upper limits on the currents enclosed by CMEs are typically around $10^{10}$ Amperes. We estimate that the magnetic flux enclosed by the CMEs in the LASCO field of view is a few $\times 10^{21}$ Mx.”

http://arxiv.org/PS_cache/arxiv/pdf/081 ... 4210v1.pdf

More evidence that there can be a "Sun-Earth circuit".
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Re: X-rays from solar system objects

Unread postby webolife » Wed Dec 15, 2010 6:07 pm

I've posted cautions elsewhere not to confuse the language of circuit and current of flowing plasma [or ions in space] with electrical wire circuity, in which a current is simply described by an electrical cause at one end of a wire and an electrical effect at the other, not as an actual [fluid-like] flow of electrons along the wire. The cause and effect in wired electricity are virtually simultaneous, while the flow of ions in space is clocked significantly more slowly in Km/s. Is this distinction relevant to the discussion of CME's?
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Re: X-rays from solar system objects

Unread postby jjohnson » Wed Dec 15, 2010 10:25 pm

Webolife, it is relevant. Time scales marking causal events and their consequences on a circuit board or in a house are indeed "virtually" instantaneous, because at the speed of propagation we can't detect with our senses any noticeable time lag, at least for things which don't intentionally build in a time lag. In a national grid system electric events are merely "very fast", measured in fractions of a second to seconds. In circumsolar space out to Earth, a "distance" of 8+ light minutes, it takes times measured in minutes to hours for physical events to propagate, such as a proton in the solar wind moving at a fairly high fraction of the speed of light, or a CME which, at best, takes over half a day to arrive near Earth.

From Wikipedia: Coronal mass ejections reach velocities between 20km/s to 3200km/s with an average speed of 489km/s, based on SOHO/LASCO measurements between 1996 and 2003. The average mass is 1.6×1012kg. The values are only lower limits, because coronagraph measurements provide only two-dimensional data analysis.


So when there might be conductive plasma filaments stretching parsecs, among stars or along galactic arms, it is reasonable for much longer timescales to prevail if field-aligned currents are moving in the distance scales plasma circuitry. I do not know how fast "electric" speed is in wires, nor what it may be in the much more conductive (never "perfectly conductive") plasma circuitry, but it is not typically at c. Hence, long response times, in most cases. However, when magnetic energy is stored in double layers, local current density can overload them just as it does in the magnetic fields of power lines during solar storms, and the result is astoundingly fast and violent, and can continue to be fed by current within the line itself after the initial release. Some think that such phenomena on a stellar scale may be able to explain novas and supernovas, with their fast rise time to max brilliance and months-long decay. Possibly CME's; I don't know.

Good, thorough response, Anaconda.
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Re: X-rays from solar system objects

Unread postby webolife » Sat Dec 18, 2010 10:11 pm

jjohnson, we agree.
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Re: X-rays from solar system objects

Unread postby Nereid » Tue Dec 21, 2010 8:42 am

Thanks for all the material and comments.

As has been noted, the use of the term "circuit" when describing, or explaining, phenomena observed in plasmas can be misleading (at best) and downright wrong (at worst); so, if you feel the need to use that word for things like what happens in the Sun's photosphere, or corona, or between the Sun and a planet, or in the interplanetary medium, etc, then it would be a VERY GOOD IDEA to take some time to describe, carefully, just what you mean.
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Re: X-rays from solar system objects

Unread postby mharratsc » Wed Dec 22, 2010 10:01 am

Reference.com defines an electrical circuit as "the complete path of an electric current, including the generating apparatus, intervening resistors, or capacitors."

Seems applicable? Charge carriers, even in motion (i.e.- solar 'wind'), will still require completion of a circuit for current flow. There IS a return path.
Mike H.

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Re: X-rays from solar system objects

Unread postby Nereid » Wed Dec 22, 2010 11:36 am

mharratsc wrote:Reference.com defines an electrical circuit as "the complete path of an electric current, including the generating apparatus, intervening resistors, or capacitors."

Indeed.

However, as jjohnson so clearly explained, this concept is quite problematic when applied in plasma physics, especially for plasmas that are not, in any real sense, bounded by non-plasmas (i.e. just about every part of the solar system!)

Seems applicable? Charge carriers, even in motion (i.e.- solar 'wind'), will still require completion of a circuit for current flow. There IS a return path.

All I can say, in response, is that those who learn plasma physics/space physics - even at the Swedish institution which bears Alfvén's name - learn that use of the term 'circuit' can be very misleading, with respect to space plasmas, and so they avoid it.
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