This week’s Cometwatch entry was taken by Rosetta’s NAVCAM on 22 November 2015 when the spacecraft was 127.7 km from the nucleus of Comet 67P/Churyumov-Gerasimenko.
Single frame enhanced NAVCAM image of Comet 67P/C-G taken on 22 November 2015. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
The scale is 10.9 m/pixel and the image measures 11.1 km across. The contrast has been lightly enhanced to bring out the comet’s activity without losing details of the nucleus.
A prominent active region is clearly visible towards the horizon on the right of the nucleus in this orientation, close to the comet’s ‘neck’.
Although faint, several diffuse jets of activity can also be seen emanating from the Imhotep region, which is cast in shadow in the foreground. Stretching the contrast of the image even further will reveal these active regions more clearly (but will wash out the nucleus).
The comet nucleus is oriented with much of the southern hemisphere visible, facing ‘up’. On the small lobe in the background, the relatively flat region of Wosret can be identified, with a transition through Sobek on the neck into Anhur on the large lobe in the foreground.
The original 1024 x 1024 image of today’s CometWatch is provided below:
Discussion: 106 comments
I see that what are probably the roundish features on Imhotep are still active well after sunset, as they have been since March. It’s clearly a very active region due to being one onion layer deeper into the comet than the surrounding layers.
Breathtaking, Emily. Missing this perspective since arrival. Thanks also to H. NAVCAM Team.
Yep Emily as you say jets from the shadow region clearly evident and clearly intrinsically illuminated as in glow discharge. Any data from these jets? Temperature ? ion content ?
Here a strongly enhanced version of the image, showing both, features on the comet, and the more subtle dust jets:
https://imgur.com/3w3Gj27
To my eyes, the basis of the jets in the shadowed side is in the shadow itself.
Interesting would be, whether the jets have still been active, after the basis entered the shadow, or whether the visible jets are just relics of the jets when the basis has been in sunlight.
Interesting also, the white blips.
CRs, camera artifacts, or grains. I guess, most of them grains, but of which size? Are some large grains (cobbles/boulders) still orbiting the comet in close orbits, after some of the outbursts?
Gerald
Good observation. I presume you mean the jets may emanate from the still-lit portion and are only visible from the point where they pass in front of the shadowed Imhotep area? If that’s the case they’d have to be emitted tangentially from the terminator area. That’s possible seeing as there are end-on fracture planes (torn onion layers) at that point on the southern hemisphere. However, my comment above is based on the jet emanating from the same place in past photos of the shadowed Imhotep. Your shadow would therefore be crossing that point by coincidence. Maybe not a big coincidence because it’s difficult to judge the roundish feature recess to within less than 300 metres in this photo. It could emanate from just beyond the shadow line and therefore be invisible.
Did you notice while processing that Aker looks uncannily like Apis at the diametrically opposite end of the diamond-shaped base of the comet? Same shape, same size, same orientation, same curved edges, same surface texture, same tearing away of strata from three sides, same depth of tear (or depth of erosion as some would dutifully say).
Whoops, forget my last paragraph. I was toggling between this post and Cometwatch 17th November. Got mixed up.
Good question, where the jets exactly originate.
Either the source has still been lit, or several minutes before.
I’m preferring the erosion version, like a path crossed by a small river.
Then already erosively masked effects of a collision, then mere coincidence, then immediate results of contact binary formation, then some versions of stretch, then vandalism of aliens, then electric combustion voodoo, preference descending in this order.
My brain still swells, Cooper. Could you bring a link to that other side?
Big, traced blips should be 🙂
Long time claim for missing ‘jet’ sources no more sustainable.
“To my eyes, the basis of the jets in the shadowed side is in the shadow itself.”.
…and that would bring arguments about electron sources 🙂
@OJ
Not intrinsically lit. Just pareidolia at work again. As usual. Ion content? Did you not see the blog post around perihelion after one of the explosive outbursts? Very nice graphic of the species that were seen to increase in the coma after the event. Neutral species.
Every time MIRO, and other instruments, have looked at these jets they see two things; Neutral gas and dust.
No electric woo.
If electrons, also ions, ianw16 🙂
Blog’s cacophony restricted to scale of phenomena.
https://blogs.esa.int/rosetta/2015/06/02/ultraviolet-study-reveals-surprises-in-comet-coma/
If photographed in short UV [1k A] strongly collimated jets would be the most ‘intrinsically’ lit features.
But up there light and heat are different beasts 🙂
As Dave said: “Glowing Paper,
great detective work”.
It does not take any imagination to see that the illumination is intrinsic, ian. The source is in the shadow, obviously.
As for measured species in the jets of course you only find neutrals if that is all your instruments can detect. See MIRO comment below.
Originaljohn: “It does not take any imagination to see that the illumination is intrinsic”
To the contrary: It’s pure imagination.
The illumination is actually by sunlight.
Not sure about the intrinsic illumination, but today’s OSIRIS picture, 12/12/15, clearly shows 4 jets or plumes, maybe 5 originating in shadow. I don’t think there’s any doubt that a lot of the theoretical sublimation takes place in the shadows.
Logan commented on this in an older post after reading the paper “GIADA: shining a light on the monitoring of the comet dust production from the nucleus of 67P/Churyumov-Gerasimenko”. He said:
“There is a ‘dust acceleration region’ according to at least GIADA Team. Cold Sep14-Feb15 period, accelerated by what?”
I posted a reply there, but still awaiting moderation, so will repost here in more current and topic related article. The GIADA results paper, which is linked below, says the following:
“We classified the dust speed data into three subgroups according to the cometocentric distance: up to 15 km (labeled as 10 km), from 15 to 25 km (labeled as 20 km) and from 25 to 35 km (labeled as 30 km). Each set of data was grouped into speed bins (Figs. 9b−d). We fitted the data with Maxwell distributions due to the data skewness. We determined the speed confidence intervals by means of the bootstrap method and obtained (2.5 ± 0.8) m s-1, (3.0 ± 1.0) m s-1, and (4.3 ± 0.9) m s-1 for 10, 20, and 30 km, respectively. These results suggest a possible speed increase between 10 and 30 km.”
Now, I’m not a scientist, but it does seem to be saying that dust leaves the comet at one speed for up to about 10 km, then it actually INCREASES speed starting at around 10 km. But, if that’s not correct, please let me know.
Then, in the Summary, they address this issue starting just above the large equations, but I can’t tell if they are simply outlining what they found, or are including some kind of explanation. So, any input from the science types (or Emily) would be appreciated. Seems this is unusual activity, and sort of big news, and yet it’s not something I remember seeing on any of the posts before yours, Logan. Perhaps it’s easily explained and anticipated behavior, but you apparently don’t think so.
Here’s a direct link to the paper:
https://www.aanda.org/articles/aa/full_html/2015/11/aa26208-15/aa26208-15.html
PS…Didn’t mean to imply you’re not a “science type,” Emily, was of course referring to those other guys that post here, mainly Gerald and Harvey.
🙂
Sovereign Slave,
the paper describes three possible causes for velocity changes of dust particles:
– deceleration by 67P’s gravity (like a stone on Earth thrown up),
– acceleration by drag of emanating gas (like leafs in the wind)
– acceleration by radiation pressure from the Sun; this applies only to very fine dust. That’s an effect which usually is barely noticible on Earth, but only in vacuum.
(The paper doesn’t mention an effect on dust, which appears like radiation pressure, but is of different kind: That’s acceleration of dust due to heating from one side, inducing pressure increase of the immediately surrounding gas on the illuminated side of the grain.
https://en.wikipedia.org/wiki/Crookes_radiometer)
The trend to velocity increasing with distance points towards gas drag being stronger than gravity.
But the larger the grains, the more the gravity will win.
Things are more easy to calculate for spherical comet models.
Since 67P isn’t spherical, these easy models are expected to fail close to the comet. At larger distances, this non-spherical propery is less important for modeling.
The paper says, that the results are preliminary, and represent a snapshot of work in progress.
Sorry, dust drag and acceleration not contradictory as I said in above post, just not a prove explanation. As to your three possible explanations presented above, the first, deceleration, does not seem to have anything to do with acceleration of the dust later. Acceleration by gas drag – has the behavior of the gas been positively determined 10-30km from the comet? Apparently not. And seems like it would require some pretty uniform behavior for gas over a very great distance. Finally, acceleration by radiation pressure. However, as far as I can tell, the acceleration zone isn’t limited to behind the comet, but all sides, including in front of the comet’s orbital trajectory and toward the sun itself. If dust is leaving the comet directly toward the sun, seems like it should be a continual slowdown based on that explanation, not an acceleration. Not sure at what distance at the front of the comet the solar wind bends the dust traveling ahead of the comet back around, but I guess not before 30 km. Anyway, sublimation seems to keep being a one trick pony that’s being touted as the only act in a three ring circus. But, the cometary “atmosphere” does seem quite active, perhaps more light will be shed on the dust accelerating as more data is uncovered. But as of now, I guess all explanations are highly speculative.
Sovereign Slave,
the approach of the paper regarding dust acceleration looks very straightforward to me, based on effects which are present without any doubt.
Speculative would be the presence of additional unknown factors. Those unknown factors would require observational evidence.
The paper stays conservative, and on the safe side.
I don’t share your exaggerated scepticism here.
Some additional effects might be discovered, but as of the observations used for the paper, not evidenced.
The only addtional effect to be considered, is a velocity change close to Rosetta due to the dust and Rosetta being electrically charged with a few volts. At those slow velocities, even small voltages, as caused by photoelectricity or solar wind, are able to modify trajectories of the small fluffy dust grains, or disrupt them. But the effect of disruptions is roughly the same in all directions. So you don’t get much change in average velocity vectors, just a higher standard deviation.
The voltages proposed by “electric comet” would result in a totally different behaviour, no way consistent with observations.
SS
I looked at the paper and the math.
I must say it is a bit easy to get the wrong end of the stick so to speak.
If you look at eqn 1, the left hand side is simply a slightly odd way to write the acceleration of the dust particle as v.dv/dr. That has units of (m/s)*(m/(m.s))=m/s.s, an acceleration.
On the right hand side we have two accelerations.
The first, positive term is due to gas drag accelerating the particle.
The second, negative term is due to 67P’s Gravity.
But note that *both* terms vary as 1/r^2. It’s obvious in the second term, r^2 on the bottom line; but the first term has an r on the bottom line of the () term which is squared. So it’s also 1/r^2
So the two terms have *exactly the same variation with distance from the comet*. If the first term is bigger – positive net acceleration away from the comet – it will always be bigger, and vice versa. And the net effect only gets smaller as you move away.
Because the net term decays as 1/r^2 the integral to infinity is finite, and so is the velocity. This is what eqn (3) says. If you let r go to infinity, R/r goes to zero, and the v^2-vo^2 term just becomes a constant equal to the terms to the right of the (1-R/r) bracket. In practice, by the time you are out at say ten comet radii, about 25km, you have done 90% of the net change in the squared velocity difference.
(Eqn 2 is just how he gets s from 1 to 3 really.)
So there is no ‘acceleration/decceleration zone’ at some magic distance. A particle leaves the surface at v0. It then accelerates or decelerates depending on whether (1) is positive or negative, and it’s final velocity at a large distance (ignoring sunlight photon pressure!) is given by (3). It makes the chance continuously, smoothly and ever more slowly. Of course if it hasn’t reach d escape velocity, it falls back.
The figures for the velocities all have pretty wide error bars, which actually overlap for the various distances. Also they were taken inevitably at differing heliocentric distances etc. The math approximates the comet to a sphere – very poor when close in, but gets better as an approximation at large r. Also photon pressure is not included. It can’t be in (1) in a simple manner. The gas acceleration and gravitational accelerations are colinear but opposite directions, so can be added as scalars; but the photon pressure acts in a different direction, it would be a vector sum.
Overall, I don’t see any problem here, although the increase in speed at larger r does seem rather high. It does read a bit as if something odd is going on and the dust magically accelerates faster further out. But in reality it’s almost certainly just the limitations of the data and the analysis. Remember it’s not *the same* particles they are measuring, following as they go out, different times, conditions.
It is quite easy to read it as if there is something really wired going on, but I don’t think that’s the case.
Does that help?
If you look at the actual velocity distributions, it’s clear, that interpreting the data as an acceleration has been tentative:
https://www.aanda.org/articles/aa/full_html/2015/11/aa26208-15/F9.html
They took best fits of Maxwell distributions (https://en.wikipedia.org/wiki/Maxwell%E2%80%93Boltzmann_distribution).
Using other skewed distributions might have returned a different result.
The basis for using Maxwell distributions is certainly fragile, since dust with different grain sizes doesn’t need to follow the same rules as an ideal gas in a straightforward way.
And we see low number statistics, which doesn’t allow to determine the actual velocity distribution.
The paper hence describes the data as available at that time.
But the statistics is too sparse to allow for strict conclusions.
So don’t over-interprete.
@Harvey
Yes it helps, at least as much as clarifying a mostly incomprehensible paper with a mostly incomprehensible explanation can help, lol. But your bottom line seems clear enough. I think I’m just going to punt and blame Logan for ever raising the issue at all 😉
Speed increase at 10-20Km: 0.5km/s. Speed increase at 20-30km 1.3km/s!
Additional scenarios could also be related to grains/’aero-gels’/clathrates explosively eroding.
Logan – m/s, not km/s
It’s not that fast!
(For SS too.)
And you are just quoting the mean; look at the error bars.
2.5 is +/- 0.8 that is 1.7 to 3.3
3 is +/-1 that is 2 to 4
4.3 is +/- 0.9 that is 3.4 to 5.2
So the first ‘increase’ is anywhere from -1.3 (a decrease!) to + 2.3
The second ‘increase’ is from – 0.6 (a decrease!) to +3.2
So the ranges overlap.
Taking differences of similar numbers with large error bars is dangerous!
There are probably one standard deviation error bars, the real error could be bigger!
Asking pardon to Blog about this ‘Km’ issue, total acceleration 1.8 m/s, from 10 to 30 km.
All related posts of mine, after and before should not contain this error.
Purpose of the argumentation is that a small field able to increase dust speed by 1.8 m/s in 20km, should be able to accelerate those cold, new electrons to very energetic speeds.
And accepting Harvey comment, nature of dust/grain population could be very different along the sampling.
Still not discarding plausibility of an electric field toping hundred(s) volts. As suggested at some moment by OriginalJohn. Due to Coma/Core differential electrodynamics.
As for the error bars. Your signaling is for the ‘extreme’ 🙂 reading possible, Harvey.
“The error of the speed measurement is 6%.”
Logan – that’s the measurement, systematic error. you have a 6% error on the absolute value iPod everything.
But then you have a wide distribution, roughly fitted to a Maxwellian distribution (not sure why!) and they then quote the +/- error of the mean velocity. That’s to do with the statistics and fitting, not the measurement error. As you can’t follow a single particle out and watch what it does, you have to use the mean and its quoted error bar.
(Not sure from memory if they used mean or peak, but it doesn’t change the argument.)
So the big error bars are the ones to use in considering the acceleration etc, not the 6%
SS
An object of mass m falling to Earth is being accelerated by gravity with a force f=mg where g is the acceleration due to gravity.
In the opposite direction is the drag force F due to atmospheric resistance.
F= -0.5pv^2ACd.
p is the density of the atmosphere, v is the velocity, A is the surface area of the object and Cd is the drag coefficient.
The total force on the object is f+F = ma= mg – 0.5pv^2ACd. where “a” is the acceleration.
Dust particles ejected from the comet nucleus are being accelerated along with the sublimation gasses. The dust particles are experiencing drag from the gasses.
Gas density decreases with increasing distance from the nucleus. This results in decreasing drag forces on the accelerating dust particles.
Hence it is not surprising the velocity of the dust particles increases with distance.
This is of course a simplistic explanation based on atmospheric resistance but it does provide an insight into the dust velocity behaviour of comets.
To avoid any confusion here, the velocity of the dust particles is the average particle velocity based on a Maxwellian distribution.
Sorry, I’m obviously missing something here as none of these explanations makes any sense at all (or, to borrow Ian’s favorite redundancy word, it all sounds like so much woo). Fire a bullet into the air, it will slow down due to air resistance, gravity, and whatever else, and then let’s say it keeps going and hits the vacuum of space, it won’t then suddenly start accelerating again based on its initial force of propulsion, it will just remain at whatever speed it is when it hit the vacuum, and will continue to travel at that speed unless some other new force acts upon it. According to the paper, the acceleration happens STARTING at 10km out. Until then, it is being suggested that the gas is both accelerating the dust but also causing a drag, which is contradictory. At best, the gas would initially PROPEL the dust, but then just continually slow it down until it was free of whatever the supposed drag forces are, and then continue on at that same speed. The gas would certainly not be responsible for causing the dust to start accelerating again at 10km+ out. The dust wouldn’t start accelerating unless some new force acted upon it, or the dust has it’s own propulsion system that then allows it to accelerate once it’s past the supposed interference of gravity, gas drag, etc. And self propulsion does seem to be one possible explanation being proposed , aero-gels’/clathrates explosively eroding, but that seems highly speculative and questionable, and would surely make the dust trajectory omni-directional, counterbalancing, back and forth, and highly erratic as erosion would no doubt be happening on more than one dust surface – in fact, highly doubtful any dust would be able to travel in a straight line long enough to make it past 10km. So, nice attempt at trying to again normalize a surprising (even shocking? …the dust is actually changing speed and SPEEDING UP!) and unexplained and highly problematic finding (more move along, nothing to see here because we really have no idea what it is, so don’t pay attention to it) with rather ridiculous explanations, but this finding is anything but “not surprising,” and yet again calls into question the one size fits all explanation of frozen volatiles and sublimation being the only possible explanation for the comet’s activities. SOMETHING ELSE IS HAPPENING HERE. The question is, what is the new force that is acting upon the dust between 10-30km that results in it accelerating?
Was reading gas drag as inhibiting, not propelling, the dust, so disregard that part of above post. Guess the question then though is how gas continually and I guess uniformly propels dust away from the comet for over 30 km, with acceleration between20-30km?
SS wrote
“Was reading gas drag as inhibiting, not propelling, the dust, so disregard that part of above post. Guess the question then though is how gas continually and I guess uniformly propels dust away from the comet for over 30 km, with acceleration between20-30km?”
SS there are a few misconceptions floating around.
Firstly the idea that particle acceleration is a done deal is wrong given the paper explicitly states the acceleration as a possibility (refer Section 3.2)
Secondly as explained in a previous post the quoted velocity values for each distance range are “most probable velocities”.
These are statistically inferred and are not actual velocity measurements.
This plus the fact that the data sample number is very small leads to the cautious statement by the authors.
Thirdly equation (1) while relating to a symmetrical model doesn’t require the use of exotic and unknown forces to explain the acceleration. The overall force is based on a very simple principle of summing all the forces acting on the particle.
The term on the left hand side is the acceleration
(the dust mass term is cancelled out on both sides of the equation).
The first term on the right hand side is a combination of inertial and drag forces on the particles, the second term is the counterbalancing gravitational force of the comet trying to overcome the inertial force.
Equation (3) is the approximate solution to equation (1).
The theoretical velocity values from this solution agree well with the most probable velocity values for the 10 and 20 km distances but deviates considerably at 30 km due to the non symmetry.
This deviation could be due to the lower gas density which is not accounted for in the model resulting in decoupling of the dust from the gas.
.
Sovereign Slave,
this one sounds better.
First ingredient: The evolving gas has been very dilute during the observation period. So the drag on the dust has been present, but it has been very weak.
Think at a polished large sphere on a flat smooth even surface on Earth, very gently accelerated by wind. Then reduce pressure of air and size of sphere. Repeat though experiment.
Second ingredient: The gas is about 100-times faster than the dust (with respect to the comet), since there is no outer boundary/confinement, where the gas molecules could bounce off. The velocity of gas molecules is several 100 m/s, so the bulk velocity of the gas is several 100 m/s, similar to an explosion in vacuum. Details are a little more complicated, but not necessary for a basic understanding. Dust moved with just a few m/s.
Both ingredients result in very long acceleration paths for dust grains, just sufficient to overcome gravity near the comet, but insufficient for dust to get remotely close to the speed of the gas within the considered distance.
SS
See previous comments about error bars etc.
The mechanism by which the particles are accelerated is a bit less obvious than simple ‘drag’, which is our ‘high pressure’ earth bound one bar and more perspective.
At high pressures which we are used to, the mean distance a molecule travels before colliding with another molecule is extremely small, and much smaller than the size of the particles. This is the ‘viscous flow regime’, and the one all our experience and senses are used to. The gas sort of ‘behave collectively’, molecules affect each other.
But quite a short distance out from 67P (don’t have an exact figure, but not far) as the pressure drops the mean distance between collisions rises, and molecular collisions become rarer. Each one hits 67P individually. This is ‘molecular flow’ – and absolutely routine in the lab.
The net ‘push’ on 67P now becomes a statistical average over a huge number of individual tiny bumps. The sideways ones average to zero, but there are slightly more ‘from behind’ than ‘from in front’ in an outward flowing gas stream whose density reduces as you move away from the comet. So a tiny outward acceleration.
There is nothing weird here at all, nothing not verified in a lab times over.
BTW I think you rather misunderstand the ‘lab’ issue from a scientists perspective.
I have spent my entire career making measurements in labs; very often on processes which are completely undetectable to any direct human sense. Much of it goes on in apparently empty vacuum chambers, produces light I cannot see (infrared), happens in unimaginably short times, fS say.
So I’m entirely used to looking at data reported to me by instruments; which I take a great deal of care choosing, call grating, understanding, cross checking. But ultimately virtually everything is reported to me by an instrument.
Rosetta, Philae, etc are no different. They are just instruments that don’t happen to be in my lab, cost ££££, took years to build and a decade to get there, can’t be fixed if they fail. But, conceptually, just an instrument, whose calibrations I must check, limitations I must live with.
The *real* different is not about ‘in the lab’ or not. It’s that for most Astro, cosmo…… systems we cannot do meaningful experiments in which we ‘poke the system and see what happens’ (the Temple impactor was a rare exception.)
We can’t say ‘I predict it will respond with X if I impose Y on it’ as we do all the time in the lab. We can only sit and watch, and hope that nature changes X for us.
The real difference of lab science as opposed to planetary, cosmological experiments is not location; it’s the inability, in the vast majority of cases, to do experiments in which we deliberately perturb the system and look at the response. We can only sit and watch.
Gas transonic. Drag dominantly ‘upwards’ [Most Coma Return blanketing is going to occur later].
-But, on favoring our arguments, as Harvey said, Coma is dominated by molecular flow. Viscous behavior plausible only at out-bursts.
Also, even if dust acceleration scalar [thermo-translational] means adding to scape velocity, anyway [as is for gas molecules].
Stand by electric field plausibility.
Surface’s flow_resistivity and heterogeneity plausibly bring the ‘nozzling’ necessary to get dust airborne.
[If Ducky perfectly, uniformly porous, is my speculation that She could get only very fluffy material ‘airborne’].
This advantage doesn’t exist at 10,20, or 30 km high. Outflow is NOT ENOUGH to keep the dense particulate airborne there. The less to keep accelerating that enormous dust charge. Harvey’s ‘Percolating’ is not a dominant issue up there.
Sovereign Slave,
the dust in the emanating gas behaves more similar to the bullet in the gun than in the air, since the emanating gasses near the comet need to be fast, a litte less than Mach three.
That’s a consequence of kinetic gas theory.
Since the gasses near the comet are very dilute, the acceleration process of the dust takes much longer.
Well, difficult for me to decipher the paper, so would appreciate it if you humored me and tell me if I’ve got this right, and answer some other questions based on yours and sjastro’s explanations.
So the dust, which is engrained more or less evenly with the frozen volatiles, is accelerated away from the surface by the gas, which is also being accelerated away from the comet as it sublimates.
– am wondering how much of this is theory (that dust mixed with volatiles accelerates the dust away from a surface in a vacuum as the gas sublimates), and how much has been undeniably confirmed by actual real data or experiments
– does the gas initially accelerate away from the comet in a more or less perpendicular direction to the surface when it sublimates, or is it omni-directional?
Due to the continued influence of the (expanding) gas, the dust is more or less being continually accelerated away from the comets surface, while other factors may come to bare to also contribute, like sunlight, lessoning gravitational influence, etc.
– have the trajectory, speeds and distances covered by the gas been measured as it travels away from the comet, or is it just assumed that since the dust is accelerating up to 30km away from the comet, then the dust must be as well?
Sjastro, as I’m reading your explanation, seems you’re indicating that the acceleration is not actually true acceleration, but is more due to a basically statistical averaging process or something to that effect, rather than actual dust acceleration. Not sure why they call it a dust acceleration zone in the paper then. Regardless, these explanations seem to hinge on having a very good understanding of how unconfined gases behave in the vacuum of space near a comet while trying to take into account all the other possible influences that might come to bear on the gas, and I still haven’t gotten a sense that this level of understanding really exists yet, though I could be wrong. I do see how it’s a very good fit for sublimation theory though.
.
Sovereign Slave, your understanding is roughly correct.
First, there exist theoretical and experimental basics on Earth, since more than 60 years:
Theoretical work:
“The Motion of a Gas Cloud Expanding into a Vacuum”, D.C.Pack, 1952,
https://adsabs.harvard.edu/full/1953MNRAS.113…43P
page 43:
Reference to J.M.Burgers, 1946: “The face of the gas moves forward into the vacuum with velocity 3a, where a is the speed of sound in the gas cloud in its initial state.”
page 51:
“It is shown that, when the the flow remains continuous, the wave-front ultimately moves with velocity 3a. When a shock wave appears in the flow the wave-front attains an even higher velocity.”
“The Expansion of a Gas-cloud into a Vacuum”, R.C.Khare,
https://adsabs.harvard.edu/full/1953ZA…..33..251K
page 266:
“The face of the cloud advances into the vacuum with a constant velocity varying from eight times to three times that of local velocity of sound in gas at rest according as gamma varies from 5/4 to 5/3.”
On experiments:
https://www.chem.utah.edu/_documents/faculty/morse/84.pdf
page 23:
“For an ideal monoatomic gas C_p = 5/2 R, and Eq. (2.4) predicts terminal velocities of … 7.86 x 10^4 … cm/s for … Ne …, expanding from a reservoir of 300 K.
In practice, velocities closely approaching these values are readily achieved.”
[7.86 x 10^4 cm/s = 786 m/s]
“Experimentally, it is not difficult to achieve Mach numbers of 20 or greater in a supersonic expansion.”
Those high Mach numbers are due to adiabatic cooling, and hence slowing down of the local speed of sound.
The molecules/atoms of the gas move almost parallel.
… Propulsion systems for space probes are based on the assumption, that physics on Earth and in space are the same.
https://eotvos.dm.unipi.it/TASI%20GG%20Presentation%20June09/coldgas.pdf
Since these systems work as predicted, there is abundant evidence, that gasses behave in a space environment consistent with according experiments on Earth.
Experiments on Earth fit with the according theory.
So by transitivity, theory of gasses applies to gasses in a space environment, as well.
Part three:
Sovereign Slave: “have the trajectory, speeds and distances covered by the gas been measured as it travels away from the comet, or is it just assumed that since the dust is accelerating up to 30km away from the comet, then the dust must be as well?”
The Rosina instrument is able to determine gas velocities at the location of Rosetta, according to its science objectives:
An excerpt of the Rosina instrument description:
“Ability to determine cometary gas and ion outflow flow velocities and temperatures”.
https://sci.esa.int/rosetta/35061-instruments/?fbodylongid=1650
Other excerpts:
“two pressure gauges (COPS) provide density and velocity measurements of the cometary gas”
“ROSINA’s primary objective is to determine the elemental, isotopic and molecular composition of the comet’s atmosphere and ionosphere, as well as the temperature and bulk velocity of the gas and the homogeneous and inhomogeneous reactions of the gas and ions in the dusty cometary atmosphere and ionosphere.”
https://www2.mps.mpg.de/de/projekte/rosetta/rosina/
Read the article carefully, the dust particles are “not speeding up”.
Fire a hundred bullets in the air and you will get a range of velocities. The velocities are grouped into a distribution.
In the model the dust particles have a velocity distribution based on a Maxwellian curve. The particles do not have the same velocity.
If you look at the respective fitted Maxwellian distributions at 10, 20 and 30 km
(https://www.aanda.org/articles/aa/full_html/2015/11/aa26208-15/F9.html),
you will notice the fitted distribution is shifted towards the right with increasing distance.
The “midpoint” of the curves gives the MOST PROBABLE VELOCITY.
The AVERAGE VELOCITY is 1.13 X PROBABLE VELOCITY.
Analysis of the data show indicates the particle velocity is proportional to (mass)^-0.32+/-0.18. This provides an important clue as to why the curves shift to the right with increasing distance.
The greater the mass, the smaller the velocity due to effects such as inertia and drag.
The incidence of the lower velocity particles will decrease with increasing distance which pushes the Maxwellian distribution to the right.
Hence the most probable and average velocity for the distribution will increase as the distance from the comet increases.
Dust mass so focused at -7.4 Log10 kg at that Fig. 9. Could that be the mass of the grains at the sampling?
Gerald, surely you must be joking…5-dimensional relativity? Really? That’s what is so much better than EU?
@ Gerald,
Lost track of threads. Above response is in reply to your post below of…
Gerald says:
11/12/2015 at 10:53
Sovereign Slave,
a unified gravity-electromagnetism theory exists, it’s called Kaluza-Klein theory.
First version elaborated in 1919, as an extension of General Relativity::
https://en.wikipedia.org/wiki/Kaluza%E2%80%93Klein_theory
“Electric universe” cannot remotely compete.
Sovereign Slave,
not a joke.
The Kaluza-Klein theories are consistent with all observed and theoretical subtleties of gravity and electromagnetism.
Still not claimed to be “the” truth.
Nicely detailed refutation, SS, of what you correctly interpret as the usual mainstream wool-pulling-over-eyes stunt… This is indeed a major finding which, as you comment, has gone curiously unsung. It’s not easy being a standard theory comet scientist nowadays…
I have nothing to add except perhaps:
As dust shoots off like a sand-blaster,
It’s seen to go faster and faster.
The experts are frantic
At Chury’s new antic
They’re getting aghast and aghaster!
Sorry THOMAS,
As I have said before, there are many phenomena about comets, which have required awkward hind casting evidence and saving hypotheses based on primordial formation….
This is not one of them. The velocity distribution is well within predictions based on incumbent mechanisms.
Strange how the wool only seems to be pulled over the eyes of those that don’t understand the Science or Maths.
Dust grains got less accelerated
as previous models anticipated.
Serendipidity,
early activity.
Finally data, models refined, experts excited!
Not sure about the refutation, just hard to understand all the science presented in the papers and trying to get a handle on what’s what. It is understandable though that whichever structure of ideas and models and theories a person holds to, they’ll obviously want to try to remain consistent to that structure to make sense of things, otherwise it’s all just a jumbled mess, and no one really wants that. As I see it, mainstream and EU start with a presumption of trying to determine “what makes sense” based on observations, patterns, data, discoveries, and what other specialists have proposed, and whatever experiments have been done that may be applicable. Dust acceleration via gas is basically internally consistent, “makes sense,” within the framework of sublimation, which is great. However, without the checks and balances of the lab (which is mostly impossible for most phenomena in space), you have to rely on interpreting data and making sense of it (again, what makes sense?). By necessity, the things that make sense lead to other things that then make sense on and on (endless if/then’s) until they turn into huge intellectual constructs. Working one’s way back to the original things, the fundamental things, that make sense, then questioning those things is very difficult, and questioning all those stacks of other things that make sense which are based on those fundamental things can be even more difficult because they logically extend from them. And it is nearly impossible for anyone to weed out all their assumptions from what are actually facts. But as I see it, neither mainstream nor EU can move very far beyond a simple “what makes sense” approach to cosmology because it’s still an infant science that just doesn’t have the required star trek type technology to go places and really analyze what’s going on. For EU, gravity and gas and shock waves, etc don’t nearly explain enough, and for mainstream, you can’t be making electricity explain everything. And neither seems to be able to give verifiable detailed explanations very well, and virtually nothing can be tested. But bottom line, few people are going to overthrow what makes sense to them without a pretty major epiphany. Regardless, for me personally, the idea of an electric universe is very appealing on many levels, and it’s a very fun idea indeed and worth exploring for many reasons I think. At the very least it proposes to submit a new type of question into the arena, even if it is considered a hair-brained question by most. But I would not trust much at all, at least not at this stage in the development of cosmology science, which claims to either prove or disprove the electric universe idea. Best to hold it as an enticing possibility that still has a huge amount of work ahead of it to get anywhere. I see a similar thing in archeology with the Ancient Aliens proposal. Regardless of how much one might “believe” (or not believe) in ancient aliens and their suggested influence on history, it has raised questions that simply weren’t being asked before, it highlights gaps or inadequacies in the mainstream archeology narrative, and it presents the opportunity to view much of history in a fundamentally new way. I have strong doubts about their premise, but I think in many ways it’s been a very useful idea that has led to legitimate new insights, investigation and debate. Looking at the world through the glasses of a new idea can be very useful. But new “radical” ideas are always resisted and marginalized and ridiculed and offensive to the protectors of the “truth,” and yet they are as inevitable as the rising sun, and the best ones will fundamentally shift a person’s whole perspective, whether they can be proven to be true or not.
SS: One has to begin with explaining the basics. The electric theory might be appealing and great fun for some people, but it cannot explain how a comet goes around the Sun. The electric theorists ignored these basics and tried to apply their ideas directly to the formation of comet jets, proposing a discharge mechanism. Observations of 67p over a year have not shown any evidence of such a mechanism on the scale required to link it to the comet’s output. The focus has shifted from the positive goal of showing the electric theory is right to the negative one of looking for the one contrary observation that can bring the mainstream theories crashing down.
Not only over our eyes, also under our feet, Sjastro 😉
Sovereign Slave,
a unified gravity-electromagnetism theory exists, it’s called Kaluza-Klein theory.
First version elaborated in 1919, as an extension of General Relativity::
https://en.wikipedia.org/wiki/Kaluza%E2%80%93Klein_theory
“Electric universe” cannot remotely compete.
More raven than duck, at this lighting.
MIRO, ian, is programmed to measure four neutral molecules plus two additional water isotope neutral molecules. That is all. Interesting that you cite results from an instrument that cannot detect ions as evidence of no ions and therefore an ions/neutrals ratio of 0%/100%. Easily satisfied as I said.
Could COSIMA Team give us an appetizer of advances on ‘jumping’ grains?
Here is an abstract from DPS:
https://adsabs.harvard.edu/abs/2015DPS….4750308B
And an abstract from AGU:
https://agu.confex.com/agu/fm15/meetingapp.cgi/Paper/59643
But would welcome an appetizer!
Thanks Kamal 🙂 The abstract talks of more surprises.
“…about as large as Jupiter but roughly one one-hundredth of its mass[: Super-puff Planets]”.
As suggested by Eve Lee, Eugene Chiang et al.
https://www.sciencenews.org/article/super-earths-meet-superpuffs-lighter-weight-class-planet
https://arxiv.org/abs/1510.08855
Even these newest lines of thought are going to be challenged by ROSETTA’s outcome.
Gerald: We have a .gif of a CSM, from a Red Giant [CW Leo]. Apparently, nothing else remains. Hypnotic.
https://cdn.phys.org/newman/gfx/news/2015/studentdisco.gif
Following a technique with resemblance to Jakub’s work on the 7 shots of Philae’s landing.
From graduate student Paul Stewart, under guidance of his Pofr. Peter Tuthill, who comment: “In trying to find an underlying structure to the clumps and blobs, we have seen little more than our own preconceptions reflected back at us—like a giant celestial Rorschach Ink Blot Test.”
https://phys.org/news/2015-12-student-stellar-chamaeleon-astronomers-years.html
How much am I telling about 67P, out of my preconceptions?
450 light years distance will certainly result in a rather bright supernova in the sky.
Some of the dust may eventually travel to our solar system as interstellar dust grains.
Would be interesting, whether larger bodies are accreting already.
What would happen to them on a consecutive supernova?
Why Gerald, when thinking of the next container, your first choice is another Supernova? Of all cosmic Objects?
Logan,
those giant stars are the final state of short-lived instable massive stars, just before undergoing core collapse and supernova explosion. And they are key ingredients for our existence; they provide all heavy elements starting with iron, and they trigger formation of solar/stellar systems.
So when thinking about what will happen next, thinking at the supernova is immadiate. Since it’s so close to Earth, the next thought is, what will happen to Earth? Will the event be as bright as the Sun, or more like the moon, or like Venus? Will Earth be hit, when, and by fragments of which size and velocity?
It’s a while since the latest nearby supernova. The 1054 event leading to the crab nebula was 6500 ly away (https://en.wikipedia.org/wiki/Crab_Nebula). At 450 ly it would be more than 100-times brighter, by far the brightest object in the night sky, and probably visible at day, as well.
” According to the Song Huiyao the visibility of the guest star was for only 23 days, but this is after mentioning visibility during daylight.” (https://en.wikipedia.org/wiki/SN_1054#Chinese_astronomy)
Then, “ok, it’s not really dangerous”, but maybe some previous supernova created an expanding hull, we can sample right now as interstellar dust grains. (That’s actually done.)
How would the interstellar dust grain population change when the debris cloud of the expected new supernova arrives at Earth, in maybe several thousand years?
Would be quite THE sky show of the millennium.
Grateful about the patience, Gerald 🙂
If a new civilization just starting space exploration, they would say THAT dust is our local, interplanetary dust 😉
… verified CW Leonis. Wikipedia (https://en.wikipedia.org/wiki/IRC_%2B10216) says, it’s a carbon star of a too low mass to undergo a supernova, but just a nova with a white dwarf remnant.
No big fireworks in the sky. Sleeping better now.
Nowadays -according to authors- one of the most brilliant IR objects in the sky!
[Objects of this kind could be very relevant to Comet-ology].
Seeing 8 years of a Hot shock wave evolving, in a few seconds. Cold dust is not being showed [How could?].
ERRATA. “…which is now believed to be buried in its own dust”. CW Leo is actually somewhere inside this Hot structure. Behind a curtain of Cold Dust!!
Respect, from Student to Professor, on respecting Science Principia.
“…Seeing rabbits or elephants in the clouds is okay for my 4-year old boy, but it seems that this time a dusty star in Leo has caught all the astronomers out daydreaming at their work.”
More Souls daydreaming, Ram 🙂
https://www.astronomy.com/news/2015/12/curious-inkblot-star-outed-for-trolling-the-astronomers
“…The big problem with all the [tested -and failed] models is the scaffolding that they tried to impose onto the system,” said Stewart.
“…It is pretty clear that the new images tell us is that CW Leo has just been ejecting clumps and plumes of hot dust at random all this time…”
When all models fail, Random ends being the most honest model.
Don’t understand wording. Pretty clear to me those clumps and plumes are not ejecta. Those are the dust bow shocks of noveau ejecta with CSM. Extremely difficult to model.
ERRATA: Nova, Nouveau
Those new images have been produced by superresolution techniques. I’d be cautious not to see too much of structure in ink blots, again.
Accepting, Gerald 🙂 As the Team, will leave it as random, as the best fitting model to actual data.
As an (instrument rated) amateur pilot, I shall get very worried if I start seeing any rabbits, let alone elephants, in the clouds!
🙂
A Team of physicists at the Relativistic Heavy Ion Collider is exploring ways to make super-cool [so super-focused] ion ‘blastings’, via super-cooled ‘dancing’ electrons…
My speculation: An Oxygen laser could be worked in that way, also. An Oxygen Laser and a Telescope with a mono-wavelength filter duo could start a grosso modo active search and cataloging of Hidden Oxygen at our Neighborhood.
This is fiction.
Logan
A number of laser transitions are known in monatomic oxygen and ions up to O4+.
All in discharges, some only seen in a 77K cooled from an old gas laser line list.
Can’t find any note of a *molecular* oxygen laser. For reasonabe gain, I think it would have to be the B-X Schumann-Runge band I mentioned before, where it has resolved structure. Just maybe one could find a way to invert some combination of v’ & v” with a decent Franck-Condon factor, but I cant see that its been done.
(Molecular O2 has no ro-vibrational infrared transitions.)
High energy density pump mechanisms will tend to dissociate the O2 to O and ionise it. For an O2 laser you need to be relatively gentle & keep your molecules intact.
If trying to detect O2, an O, O+1 etc laser is of no particular use.
“…(Molecular O2 has no ro-vibrational infrared transitions.)”
So, that why you are searching on radio spectra 🙂 Masers?
Nothing about crystal structures on Wikipedia. Would be to wild to expect 02 crystals? At receding tides of molecular nebulas?
Logan
In a normal, classical sense O2 can have no permanent electric dipole moment and no transition moment because of its symmetry. If you make it rotate, or if you make it vibrate, there is no oscillating electric dipole, so it cannot interact with an oscillating electric field.
Now because of the unpaired spins, there is a very weak oscillating magnetic dipole if it rotates, so there is a very, very weak rotational spectrum where the usual electric dipole one would occur, widely spread across the microwave spectrum. See
https://www.jstor.org/stable/pdf/2416233.pdf?acceptTC=true
The lines are very spread out from 12cm-1 or 360GHz to 62cm-1 or some 1.86THz
But for rather complicated reasons in O2 there is an additional, stronger band near 60GHz see
https://radiometrics.com/data/uploads/2012/11/Tretyakova_JMS_05.pdf
Again it’s to do with the spin.
These lines all lie between about 55 and 65GHz.
This causes strong absorption in the atmosphere, because it’s 20% O2 and one bar – LOTS of oxygen!
For completeness, at very high pressures the vibrational bands can be observed, because the symmetry is broken in the collisions. But that takes pressures far above one bar.
So yes, I over simplified for brevity!
Oh, detail, I don’t deal with magnetic dipole transitions much!
The magnetic dipole lines occur in the same * region* as the electric dipole transitions would, but differ because the K selection rule differs.
Also it’s not really ‘microwave’, but mm/sub mm, now usually called the THz region.
60GHz on the other ha pond is classical microwave.
“…because the symmetry is broken in the collisions.”
Amazed at the faintness of the footprints Science is trying to catch! 🙂
Thanks Harvey 🙂 Quite a lone wolf O2…
SS.
In a long post, I pick out:
“As I see it, mainstream and EU start with a presumption of trying to determine “what makes sense” based on observations, patterns, data, discoveries, and what other specialists have proposed, and whatever experiments have been done that may be applicable.”
*ABSOLUTELY NOT.*
The mainstream does more or less that.
If something doesn’t fit, we tear up the old theory and find a better one.
Furthermore it insists on quantitative theories. It emphasises verifiable, quantitative predictions that can be tested.
EU does no such thing.
It completely ignores a huge range of well established basic physics, and any data that doesn’t fit it’s preconceptions. It never makes quantitative predictions.
It is not in any normal sense a ‘scientific theory’ at all, but a mess of verbal assertions supported largely by visually perceived similarities to discharges etc occurring under utterly different conditions.
Hi Harvey,
I disagree with the assertion about the mainstream “if something doesn’t fit, we tear up the old theory and find a better one”
The mainstream makes a lot of noise about not being wedded to incumbent paradigms but it is just lip service.
EU is of course far worse in that when something doesn’t fit there is just complete denial that it doesn’t fit. Incoherent ideas do not need saving hypotheses as you can just keep asserting that it actually does fit.
The problem for the mainstream is really that “finding a new one” bit. The O2 didn’t fit, so there was head scratching for months, until a suitable narrative of a saving hypothesis was found. This is kind of “hind cast” into the models, at least with the thought that O2 is going to be typically found in comets and that we should have predicted it.
I think the number of contradictory saving hypotheses based on comet formation (Is it the Oort Cloud,, the Kuiper belt, collisionally relaxed or in a dense cloud with constant collisions, is it mixed with elements born in fire, like CAIs and if so, when?) already justifies scientists to say ” we are not too sure about the paradigm” and perhaps say that paradigms such as panspermia “we are not too sure about how wrong or whether it is wrong”
A lot of things should be up for grabs, and the lack of skepticism about the incumbent paradigm is unhelpful, because it puts incoherent alternatives like EU as just as wrong as coherent ones like panspermia (say as explanations for the O2)
Well said Marco Parigi
Regards
Marco
I would agree that there can sometimes (not always) be resistance to ripping up the old theory; it can take a bit of time. Sometimes pressure builds for a while until it’s obvious a new theory is needed and people jump on it when it appears.
But in the end, if the evidence against is good, it *does* get ripped up.
No, it’s not ‘lip service’ but there can be a degree of conservatism.
Hi Harvey,
The main issue is that I think we should be happy to rip up a theory *without* a complete, final replacement. All we need is a fragment of a replacement that is both consistent with all known physics and more reliably predicts new facts. I would even be happy if we just became less dogmatically convinced about elements of the incumbent paradigm – Like the way Bibring says “we are not too sure about that” It is not less conservative, just more skeptical about current paradigms.
Hi Marco,
such maximum-likelihood methods are actually used.
https://en.wikipedia.org/wiki/Maximum_likelihood
But maximum likely doesn’t necessarily need to mean evident. So something may be maximum likely, but still spurious, and not evident.
Applying maximum likelihood methods to each bit of incoming data may result in a somewhat erratic behaviour of the conclusions.
So for the sake of smoothness, it’s better to add some damping (conservatism) to science results, hence to wait for some reasonable statistical confidence level, before building too much of fragile conclusions.
As a change from Limericks, let’s try a form I like better; getting 5/7/5 in English is hard.
Argument rages
About dust velocity
Driven by error.
With a bit of deliberate ‘double entendre’ in the last like!
But no ‘seasonal reference’ I fear.
Cometary dust
Know low number statistics
Summer will improve.
3/5/3 pidgin haiku:
Dust fine-grained
Low number large gaps
Heat will change.
良いですよ。
私には俳句が大好きです。
Not fluent, and I don’t know a lot of kanji, but I can get by.
Of course the required ‘seasonal reference’ is a bit tricky on 67P!
domo arigato gozaimasu Harvey-san.
Yes, I’ve tried to use the approach of the comet to the sun as a reference to a season.
Seems a comet is a
ほうき星 [ほうきぼし (houkiboshi)], a ‘broom star’
Or a
彗星 [すいせい (suisei)], a ‘comet star’ (which seems a bit recursive!)
BTW ‘Rosetta’ can be transliterated directly into Japanese.
In katakana it is
ロゼッタ
Churyumov-Gerasimenko is a bit tricky.
Actually you can do Gerashimenko, and Churyumo…..but no way to get a terminal v sound; it would have to be ‘bi’ in classical kana.
So チュリュモビ—ゲラシメンコ. I suppose
Churyumobi-Gerashimenko.
Maybe just omit the -bi ビ would be better. churyumo.
There are some new katakana symbols which do include the v-vowel sound like vi, ヴィ, but not everybody knows them, and there is no way at all to get……mov that I can see.
67P is sort of ok, 六七ピ, Roku nana pi, (or Roku shichi pi), 67Pi.
It’s a sort of hobby, I go to Japan a lot!
You might use the kana ‘fu’ for the ‘v’, since sometimes the cyrillic/russian “в” is transliterated by ‘ff’.
So we get chu-ryu-mo-fu in kana.
Maybe better using the long ‘ryū’ instead, such that we get
chu-ryū-mo-fu
I’ve no IME installed, so can’t typewrite it in katakana/hiragana. Quite a long time ago since I’ve learned (some) Japanese; no much practice right now.
Sorry for the late answer, I’ve been very busy with another (tricky) project.