Electric Comets II. Of Water & Ice

First, I want to say congratulations to the team that built and operated Rosetta & Philae to a successful rendezvous and landing on the nucleus of comet 67P/Churyumov–Gerasimenko (Wikipedia).

The really funny part about this is that if the space environment around the Sun were really as different from the mainstream science model as Electric Universe advocates want to claim (see Challenges for Electric Universe 'Theorists'...), the Rosetta mission would not have been the level of success that it has been so far - the spacecraft would have been fried long ago from the voltages induced within by the various 'Electric Sun' models (particularly those noted in Death by Electric Universe. II. The Solar Capacitor Model,   Death by Electric Universe. IV. The Z-Pinch (Solar Resistor) Model).

The simple explanation is that the Electric Universe model for the heliospheric environment and comets is blatantly wrong.

Probably because of this event, my first Electric Comet page (Electric Comets: Failures of the Electric Comet Model) has been receiving a lot of traffic of late, so it seemed time to assemble some additional items I've collected for an update. 

Stuart Robbins has also put together a podcast on James McCanney's "Electric Comet" claims (Exposing PseudoAstronomy: Episode 120: James McCanney’s Views on Comets, Part 1).  Stuart does a detailed explanation of how we determine the temperature of comets and know that they are cold, not hot.  He also talks about how McCanney denies that water has been found in previous (and current) comet observations, as well as McCanney's failed predictions for the passages of comets ISON (wikipedia) and Siding Spring (wikipedia) near Mars.

In spite of the denials of Electric Comet advocates, Rosetta has made a number observations that fit major predictions of the  standard "dirty snowball" comet (Wikipedia: Comet), most notably the detection of water vapor and carbon dioxide, very close to the comet.

• ESA, June 2014: First detection of water from 67P/C-G
• ESA, September 2014: MIRO bathes in water vapour
• ESA, November 2014: VIRTIS detects water and carbon dioxide in comet’s coma.  Note the production rate is increasing as it gets closer to the Sun (0.3 liters/second in June 2014, increasing to 1-5 liters/second in July-August 2014)

Wal Thornhill has created a little 'story' to explain these observations but for his model, the combination of the raw atomic material to form water must take place further out (see Thunderbolts: Predictions for Comet Science After Rosetta):

In our recent Space News on Rosetta, we noted that electrochemical processes, not dissimilar to those proposed in peer-reviewed papers for Mercury’s putative ice deposits and water in the lunar soil, may in fact be responsible for the signal of “water” appearing in the comet’s coma—a potential game changer in comet science. As Wal Thornhill explains, “The cathode jets strip and ionize atoms of oxygen from minerals on the comet and accelerate the negative ions away in a fine jet. The oxygen ions then combine with the protons in the solar wind to form the hydroxyl radical, OH, which was mistakenly assumed to be evidence of an ultraviolet breakdown product of water molecules from the comet. Oxygen and hydrogen have both been found in the comet’s coma, by the Rosetta ultraviolet spectrometer.”

But there's some more predictions implied by this model which Thornhill ignores, or evades...

• How much hydrogen would need to be collected from the solar wind by the nucleus to explain the observed rate of water produced each second?  Note for the case of Mercury and the Moon, water is forming on a rocky world over billions of years, while the comet expels quite a lot with each orbit of the Sun.
• How much charge would need to be on the nucleus to collect this amount of hydrogen? 

I've also heard some claims that the low density (0.4 gm/cm^3, less than water) of the comet nucleus inferred from the spacecraft motion could be the result of electrostatic repulsion between the spacecraft and nucleus. 

Both of these claims provide information on the alleged charge of the comet nucleus, and the spacecraft.  Once you have that, there are a number of other forces, such as the Lorentz force (Wikipedia: Lorentz Force), which will act on both the spacecraft and the comet and would alter it compared to the predominantly gravitational trajectory assumed for piloting Rosetta to 67P/Churyumov–Gerasimenko.  More on these in a future post.

Should We Expect to See Patches of Ice on a Comet Nucleus?

Some people, including some astronomers, have commented that they were surprised that they did not find patches of ice in close-up views of the comet nucleus.  But one needs to ask, would you expect to see surface ice in the standard comet model?

Consider the measured surface temperature for 67P using the VIRTIS instrument (ESA: VIRTIS maps comet 'hot spots') was 205K (-68 C = -91 F) in mid-July 2014 when the comet was about 3.75 AU from the Sun, definitely still a bit of a deep freeze.  A simple radiation balance calculation (Wikipedia: Effective Temperature) for the temperature of an object at this distance from the Sun gives (using 0.00468Astronomical Units for the solar radius):

5780K * sqrt( 0.00468AU / 3.75AU ) = 204K

which is pretty good agreement for an object of low albedo (about 4%) and high emissivity.  For perihelion for 67P, at 1.24AU, we might expect the temperature to reach 355K (82 C = 180F), assuming emissivity and albedo remain about the same (which we can be pretty certain will not hold true).

To make ice patches on the comet would require temperatures and pressures high enough for liquid water to form from the ice, collect into patches, and then re-freeze.  At temperatures below 0 C and pressures below 0.006 atmospheres, water cannot exist in liquid form as we note from the phase diagram (Wikipedia: Phase Diagram).

Phase Diagram for Water (Credit: Wikipedia)

In these ranges of temperature and pressure along the bottom of the graph, common in the space environment, water goes directly from a solid to a gas.  Near perihelion, the temperature will be high enough to form liquid at higher atmospheric pressures, but against the vacuum of space, water would sublimate to a gas before liquifying.  So even when the temperature got above 0 C, the pressure in space, even close to the Sun, will not get high enough to form liquid water that could refreeze into an obvious patch of ice.

In the low-gravity environment of the comet nucleus, another question is how would the water collect into a puddle to make an ice-patch?  Water molecules do have attractive forces between them which are the basis of surface tension, the reason why water makes a meniscus (wikipedia) in containers and collects into spheres on the International Space Station (YouTube: Space Station Astronauts Grow a Water Bubble in Space).

The water and other volatiles out-gassing are so mixed in the with the other material of the nucleus that they may not appear to emit from a distinct patch of the comet.

But next we could ask: Is there a way the pressure and temperature on the comet could increase sufficiently for liquid water to form and subsequently re-freeze to ice? 

I can imagine possible impact scenarios where temperatures and pressures during a collision might be sufficient to convert water into liquid form that could refreeze, however, I've not yet done a detailed calculation for that scenario. 

Some astronomers have made this claim and it has been picked up by a number of pseudo-sciences.  But it is fair to ask if the idea is  based on an actual examination of the physics of the conditions, or a seat-of-the-pants guess or speculation, most likely based on our everyday experience with water and ice in our Earth-temperatures and atmospheric pressure?