Rosetta measures production of water at comet over two years

Rosetta measures production of water at comet over two years
Comet 67P/C-G on 11 September 2015 - NavCam. Credit: ESA/Rosetta/NAVCAM, CC BY-SA IGO 3.0

Over the past two years, Rosetta has kept a close eye on many properties of Comet 67P/Churyumov-Gerasimenko, tracking how these changed along the comet's orbit. A very crucial aspect concerns how much water vapour a comet releases into space, and how the water production rate varies at different distances from the Sun. For the first time, Rosetta enabled scientists to monitor this quantity and its evolution in situ over two years.

In a new study led by Kenneth C. Hansen of the University of Michigan, in the US, measurements of water production rate based on data from ROSINA, the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis, are compared with water measurements from other Rosetta instruments.

The combination of all instruments shows an overall increase of the production of water, from a few tens of thousands of kg per day when Rosetta first reached the comet, in August 2014, to almost 100 000 000 kg per day around perihelion, the closest point to the Sun along the comet's orbit, in August 2015. In addition, ROSINA data show that the peak in water production is followed by a rather steep decrease in the months following perihelion.

"We were pleasantly surprised to find such a good agreement between the data collected by all the various instruments in this unprecedented study of the water production rate's evolution for a Jupiter-family comet," says Hansen.

The scientists analysed almost two years' worth of data from ROSINA, which detects neutral water molecules with its Double-Focussing Mass Spectrometer (DFMS).

Rosetta measures production of water at comet over two years
Water production rate measured by different instruments at Comet 67P/C-G. Credit: Hansen et al. (2016)

"This is by no means trivial: ROSINA performs measurements locally, at specific points around the comet, and we need a model to extend them to the entire atmosphere," adds Hansen.

The simplest model would be a spherical distribution of the outgassing centred around the nucleus but, given the complex shape and season cycle of Comet 67P/C-G, this would be a very crude approximation. For this reason, the ROSINA team developed a series of numerical simulations to accurately describe the comet's production of water, which are presented in a separate study led by Nicolas Fougere also of the University of Michigan.

From these simulations, which showed that the water production rate at a comet like 67P/C-G is highly inhomogeneous, Hansen and his colleagues derived an empirical model, which they then used to transform the local ROSINA measurements into estimates of the overall water production rate.

The results revealed that, during the first several months of observations, when the comet was at distances between 3.5 and 1.7 astronomical units (au) from the Sun, water was predominantly produced in the comet's northern hemisphere.

Then, in May 2015, the equinox marked the end of the 5.5-year long northern summer and the beginning of the short and intense southern summer. At that time, the comet was about 1.7 au from the Sun, and scientists expected that the peak of water production would drift slowly from the northern to the southern hemisphere; instead, this transition happened more abruptly than predicted. This was likely due to the complex shape of the nucleus, which causes highly variable illumination conditions including self-shadowing effects.

Rosetta measures production of water at comet over two years
Simulation of comet 67P's water production rate during northern summer. Images adapted from Hansen et al. (2016). Credit: K.C. Hansen

As expected, the production of water peaked between the end of August and early September 2015, about three weeks after the comet's perihelion, which took place on 13 August, 1.24 au from the Sun. The data hint at possible variations in the water production rate at this epoch: these might be due to the spacecraft's motion relative to the comet, but could also be an indication of actual changes to the outgassing dynamics, and will be subject of future in-depth investigation.

In addition to the ROSINA measurements, Hansen and his colleagues collated a series of previously published measurements of the water production rate at 67P/C-G. These include observations performed with the Microwave Instrument for the Rosetta Orbiter (MIRO) shortly before and after Rosetta had reached the comet, data from the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) obtained between November 2014 and January 2015, and measurements from the Ion Composition Analyser, part of the Rosetta Plasma Consortium (RPC) suite of instruments, obtained between October 2014 and April 2015.

RPC-ICA does not detect water directly, but rather measures the ratio of differently ionised Helium ions; since He+ ions arise mainly from collisions between alpha particles (He2+) from the solar wind and neutral molecules, such as water, found in the comet's atmosphere, this ratio can be used to estimate the amount of water produced at the comet.

Hansen and his collaborators have found some small discrepancies between the various data sets: for example, the measurements from ROSINA yield systematically higher values than those from VIRTIS. One possible reason for this is the different nature of the two experiments: ROSINA samples the gas in the coma at the spacecraft's position, while VIRTIS tends to observe closer to the nucleus, where the water production activity is potentially more confined than it is further out in the coma. The difference in measurements techniques and the discrepancy could potentially indicate an extended source of water in the coma itself, for example icy grains that are lifted into the coma and turn into gas a few kilometers above the surface.

Another difference was found between the MIRO measurements, which indicate a rising trend in the water production rate from June to September 2014, and the first months of ROSINA data, starting in August, pointing to an almost constant rate in the same period.

Rosetta measures production of water at comet over two years
Simulation of comet 67P's water production rate around perihelion. Images adapted from Hansen et al. (2016). Credit: K.C. Hansen

"This could be explained if a sudden surge in the water production happened around the time of the first MIRO measurement, a few weeks before Rosetta's rendezvous with 67P/C-G, and the beginning of ROSINA observations," says Hansen.

The scientists also compared the comet's production rate of water to that of dust, which can be measured via ground-based observations and was recently reported in a study led by Colin Snodgrass of the Open University, UK. These observations were performed with a number of robotic telescopes across the globe, from Chile to Hawaii and the Canary Islands.

"The correlation between the production rate of water and dust, both before and after perihelion, is impressive, suggesting that the gas-to-dust ratio remained constant over this long period," explains Hansen.

Based on the water production rate, the team estimated that the comet lost some 6.4 billion kg of water to space over the period monitored by Rosetta, with the most intense mass loss happening near perihelion. The total mass loss, taking into account other gas molecules and in particular the dust, could be roughly 10 times larger than that and, if distributed uniformly across the , it would translate into a reduction of 2 to 4 metres.

"This study shows how cross comparison between different instruments and simulations is beginning to reveal the further," says Matt Taylor, Rosetta project scientist at ESA.

"Connecting in-situ measurements from Rosetta with ground-based observations was a major science goal for the mission and it is wonderful to see this cooperation in action," concludes Kathrin Altwegg, ROSINA principal investigator.


Explore further

Video: Rosetta's journey around Comet 67P/Churyumov–Gerasimenko

More information: Kenneth C. Hansen et al. Evolution of water production of 67P/Churyumov-Gerasimenko: An empirical model and a multi-instrument study, Monthly Notices of the Royal Astronomical Society (2016). DOI: 10.1093/mnras/stw2413
Citation: Rosetta measures production of water at comet over two years (2016, September 29) retrieved 18 September 2019 from https://phys.org/news/2016-09-rosetta-production-comet-years.html
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Sep 29, 2016
Hansen and his collaborators have found some small discrepancies between the various data sets: for example, the measurements from ROSINA yield systematically higher values than those from VIRTIS. One possible reason for this is the different nature of the two experiments: ROSINA samples the gas in the coma at the spacecraft's position, while VIRTIS tends to observe closer to the nucleus,

So the data show the likelihood that h2o is being produced in the coma electrochemically, but not "electrochemically"...

Oct 04, 2016
So the data show the likelihood that h2o is being produced in the coma electrochemically, but not "electrochemically"...
@eu cult leader
please show, in this linked study above (or here: http://mnras.oxfo...pdf+html ) where this is mentioned

17 pages
number of times electric is mentioned: once (an electrical engineer school reference in the author list)
number of times "electrochemical" or "electrochemically" is mentioned: zero

number of times "plasma" is mentioned: 3
number of times this study has been misinterpreted by a cult for confirmation bias because the word "plasma" is in it: every time they read it
how many times has it been read by the eu cult?
n general, the agreement between the instruments is very good
or
based on in situ and remote sensing measurements made by Rosetta nstruments
number of times the eu can claim the above quote, especially WRT comets or astrophysics: ZERO


Oct 04, 2016
Did you say something Cap'n Stoopid?
Captain Stumpy5 / 5 (1) 1 hour ago
Comment posted by a person you have ignored ...

Perfect!

Oct 04, 2016
Did you say something Cap'n
fascinating

so... if you can't actually produce evidence ...
and if the electrical engineers are actually making claims that are directly against what you're saying...
and you can't refute the science with equivalent or superior validated data...

then why, exactly are you here?

is it for the coffers of the cult?
seeking like minded nutjobs?
or is it attempted validation through sharing on a science news aggregate for the uninitiated or illiterate?

read it and weep, spark-cult
http://journals.p....0075637

Oct 04, 2016
So the data show the likelihood that h2o is being produced in the coma electrochemically, but not "electrochemically"...


Jesus, you talk some crap. Why didn't you just read the paper? I guess that would mean actually having to understand it, eh?
Please explain how this "electrochemistry" is working. Bear in mind that the solar wind was getting nowhere near the nucleus for at least 8 months (i.e. at the peak of H2O production). Combine this with what the plasma instruments on board have actually seen (and, more to the point, haven't seen).
I keep asking you fruit loops, show us the theory. You know, actual figures, mechanisms, evidence for said mechanisms, etc, etc, etc.
I'll save you the trouble of looking; there isn't one. Just more mythology inspired woo from the cranks at Dunderdolts.
You are possibly the last person on the planet that still believes this crap. I'm not even sure Wallace & Gromit ever believed it!

Oct 04, 2016
@CS,
read it and weep, spark-cult
http://journals.p....0075637


Quite! Even one of their heroes, Anthony Peratt referred to EU as anti-science: http://plasmauniverse.info/
"The Plasma Universe and Plasma Cosmology have no ties to the anti-
science blogsites of the holoscience 'electric universe'."

If Alfven was still around, he wouldn't touch it with a barge pole. They make a lot of noise, but unfortunately for them, nobody is listening. The few scientists that are aware of them only mention it to show how stupid and unscientific it is.


Oct 06, 2016
Why didn't you just read the paper? I guess that would mean actually having to understand it, eh?

You mean where it said;
"There does appear to be a systematic off-set of the VIRTIS-H data below the ROSINA data of about
a factor of 2. One possibility for the difference between the VIRTIS-H and ROSINA production rates may be the difference in acquisition techniques – during this period ROSINA measures in situ between 20-30 km from the nucleus, while VIRTIS-H measures water emission along lines-of-sight that pass much closer to the nucleus."

For some reason there seems to be more h2o at 30km than the surface by a factor of two. And it's been show

Oct 06, 2016

......... during this period ROSINA measures in situ between 20-30 km from the nucleus, while VIRTIS-H measures water emission along lines-of-sight that pass much closer to the nucleus."

For some reason there seems to be more h2o at 30km than the surface by a factor of two. And it's been show


And your point is? Given that two very different techniques were used, and the VIRTIS-H was on its way out due to a cryogenic cooler failure. And there may well be extended sources causing the mismatch? There have been recent papers on the discovery of icy particles within the coma, up to decimetre scale (as seen at Hartley 2). As I asked, what is your proposal for how it is different? Based on actual science, and taking into account the lack of the solar wind (not that the SW could explain even 1 billionth of 1 litre of water production)? How is EU explaining this? The only things reaching the nucleus for long periods are photons. Start from there.

Oct 06, 2016
@cd,
Anyway, it's bit rich arguing about the amount of water at x km compared to y km, when the idiot Thornhill told us:

But a much different vantage point on the water question is possible. When astronomers view the comas of comets spectroscopically, what they actually see is the hydroxyl radical (OH), which they assume to be a residue of water (H2O) broken down by the ultraviolet light of the Sun (photolysis). This assumption is not only unwarranted, it requires a speed of "processing" by solar radiation beyond anything that can be demonstrated experimentally.


This despite numerous unambiguous detections of H2O in the comae of comets, going all the way back to 1986! OH has a very different spectroscopic signature from H2O. Why didn't he know that? Why would somebody that ignorant think that he can tell many dozens of scientists that they've got it all wrong?
No skin off my nose, but I feel sorry for the chumps that were taken in by that crap.

Oct 06, 2016
That the Sun's plasma can reach the coma.

Oct 06, 2016
That the Sun's plasma can reach the coma.


Sorry, what has that got to do with the price of fish? What do you think it will do? It wasn't reaching the coma at the distance these measurements were taken anyway. And what do you think it will do when it gets there? Do you honestly believe that H+ SW ions are actually going to combine, at 400 km/s, with anything? Have a look at the energetics involved! Have a look at the numbers involved. NOT GOING TO HAPPEN! And what is it impossibly combining with? O-, presumably? Where has that been seen?
Sorry, but it is yet one more demonstration that Thornhill and his disciples simply haven't got the vaguest clue about the science that they think they are trying to overturn.
It is complete and utter rubbish. Totally unscientific rubbish, at that. All to try and prove that comets are rocks (wrong) that were blasted off of rocky planets. To anybody remotely scientifically literate it is lolworthy!

Oct 06, 2016
@cd,

Anyway, it's bit rich arguing about the amount of water at x km compared to y km, when the idiot Thornhill told us:

But a much different vantage point on the water question is possible. When astronomers view the comas of comets spectroscopically, what they actually see is the hydroxyl radical (OH), which they assume to be a residue of water (H2O) broken down by the ultraviolet light of the Sun (photolysis)

From the paper;
"While in some cases these species may serve as proxies for the production of water or other more volatile species and may even themselves provide important clues to the understanding of cometary evolution, "
"Otherwise, water production rates are most often inferred from either ground-based (e.g. Schleicher (2006)) or space-based observations of OH (e.g. Weaver et al. (1981)) or from space-based observations of atomic H (Combi et al. 2005). "

It would seem jonesdumb is either lying or ignorant, most likely both.

Oct 06, 2016
^^^ Just to add some context; in Sept 2015, about a month after perihelion, the craft took an excursion out to 1500 km in the sunward direction. The solar wind was not detected at 1500 km. They didn't see it until the impact of a CME in October, while at 800 km. By the way, there was no flaring, or any increase in volatile production due to this or other CMEs, flares, etc.
Surely, if the volatile production is dependent on SW density, then the volatile rate that is detected should be up and down like a whore's drawers, based on the ambient SW flux?

Oct 06, 2016


It would seem jonesdumb is either lying or ignorant, most likely both.


WRONG. H2O has been detected unambiguously at comets since the first detection by the KAO and Vega at Halley in 1986. Way back, they used OH as a proxy for H2O (which everybody, including Alfven, knew had to be there). It was seen unambiguously many times between '86 and 2006 (when T & T wrote their crap). I've listed them on here before. This was due to IR that could see different rotational lines of H2O, and therefore didn't suffer from extinction by the Earth's atmosphere. These are not lines that are possible in OH. It was also detected in sub-mm at ~557 GHz numerous times. That is H2O. Unambiguously. Of course, it was also detected at Tempel 1 and Hartley 2. Unambiguously. Along with solid ice grains in the coma.
You want to accuse somebody of lying, you useless troll, at least get your facts straight.

Oct 06, 2016
Hale-Bopp 1997 (HDO); http://www.lesia....ence.pdf
19/P Borrelly 2001; http://www.ursi.o...0903.pdf]http://www.ursi.o...0903.pdf[/url]
C/2000 WM1 Linear 2001/2; http://www.ursi.o...0903.pdf]http://www.ursi.o...0903.pdf[/url]
C/1999 H1 Lee 1999; http://iopscience...#artAbst]http://iopscience...#artAbst[/url]]http://iopscience...#artAbst[/url]
C/1999 S4 Linear 2000; http://iopscience...#artAbst]http://iopscience...#artAbst[/url]]http://iopscience...#artAbst[/url]
C/2001 A2 Linear 2001; http://iopscience...#artAbst]http://iopscience...#artAbst[/url]]http://iopscience...#artAbst[/url]
21P/Giacobini-Zinner 1998; http://www.scienc...99962188
153/P Ikeya-Zhang 2002; http://www.homepa...DM04.pdf
C/1996 B2 Hyakutake 1996; https://www.resea...24388297
1986I Wilson 1987; https://inis.iaea...20067254
1P/Halley 1986; http://science.sc...23.short

Those were just some of the unambiguous detections. Who is lying?


Oct 06, 2016
It would also be interesting to know why T & T concentrated on a non-existent pre-impact flash at Tempel 1, whilst totally failing to inform their scientifically illiterate acolytes, that what said impact excavated was, along with dust, solid H2O ice grains. Didn't fit the script, I guess. Never any mention, either, that there was also a shed load of solid ice being excavated from Hartley 2 by the vigorous CO2 jets at that comet, in 2011.
I think it's high time cantthink had a good think about who has been doing the lying about comets. And why.

Oct 06, 2016
Sorry, what has that got to do with the price of fish? What do you think it will do? It wasn't reaching the coma at the distance these measurements were taken anyway. And what do you think it will do when it gets there? Do you honestly believe that H+ SW ions are actually going to combine, at 400 km/s, with anything? Have a look at the energetics involved! Have a look at the numbers involved. NOT GOING TO HAPPEN! And what is it impossibly combining with? O-, presumably? Where has that been seen?


Still haven't answered this.

Oct 06, 2016

From the paper;
"While in some cases these species may serve as proxies for the production of water or other more volatile species and may even themselves provide important clues to the understanding of cometary evolution, "
"Otherwise, water production rates are most often inferred from either ground-based (e.g. Schleicher (2006)) or space-based observations of OH (e.g. Weaver et al. (1981)) or from space-based observations of atomic H (Combi et al. 2005). "

It would seem jonesdumb is either lying or ignorant, most likely both.


And to show that in context, and fill in the bits that cantthink didn't mention:
"Direct ground-based infrared measurements of water in comets are quite good at yielding water production rates for moderate to bright comets at moderate to small heliocentric distances
Water has also been directly measured at longer microwave wavelengths from various space-based platforms." More obfuscation by EU.

Oct 06, 2016
And just to fix the links in a previous comment that got fuxxed up:

19/P Borrelly; C/2001 A2 Linear; C/2000 WM1 Linear. All 2001, all in sum-mm (microwave) by the Odin satellite:
http://www.ursi.o...0903.pdf

C/1999 H1 (Lee), C/1999 S4 (LINEAR), and C/2001 A2 (LINEAR);
http://iopscience...#artAbst

That list is by no means the full record detections between 1986 & 2006. Why did T & T either not know this, or choose not to mention it?
More lying, methinks.

Oct 06, 2016
@cd,
Ever wondered what your hero Alfven thought was the origin of the H and OH in comets? As opposed to the terminally scientifically challenged Wallace & Gromit?

As a different interpretation of the Lyman-alpha. emission from comets, Lai proposed [21] thermalization and recombination of solar protons at collision with the cometary dust in the coma and tail, followed by diffusion and excitation of hydrogen in the observed Lyman-o; halo. This view might seem to be contraindicated by the fact that roughly matching amounts of oxygen are deduced from observed/OH emission. ***Most workers would take this as a support for the concept of water molecules as the source for both dissociated hydrogen and hydroxyl radicals.***


My emphasis.

Arrhenius, Alfven, Fitzgerald; Asteroid and Comet Exploration, 1973
http://ntrs.nasa....8994.pdf

Oct 06, 2016
Funny how these buggers always go quiet when you ask for **actual** science to back up their mythology, eh? Just an observation.

Oct 07, 2016
Funny how these buggers always go quiet when you ask for **actual** science to back up their mythology, eh? Just an observation.
@Jonesdave
not really a surprise...

you're talking about a cult that ignores the measured, observed tracked meteor/meteoroid strikes on the moon to claim EDM made the craters
...and worse stuff that that, especially WRT the grand canyon, dust devils or comet D/1993 F2 striking Jupiter !! LMFAO

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