[X] My Assistant

[Guest_Richard Trigaux_*]

Hello all


This spectrum,, obtained by Cassini's ion and neutral mass spectrometer, shows a lithium ray (ordinate= 7)

and also this figure, a mass spectrogram from the same instrument, also show lithium (abscissa=7)

First of all, I wonder if these rays are real, or if they are intrument defects or artifacts. Otherwise only lithium could have a mass of 7 daltons.

The presence of lithium is not really astonishing by itself (there was sodium in Io's atmosphere) but it implies that Titan's atmosphere would be much more reducing than with hydrogen alone. Also there are no traces of oxygen or water in these spectrograms (oxygen and water are linked through oxydation and photo-dissociation)

In a medium where there is an excess of hydrogen, all the available oxygen is reduced, so that this medium becomes reducing. But lithium is much more reducing than hydrogen, so it would take the oxygen in priority. So the presence of lithium implies that there is a source of lithium in excess over Titan's atmospheric oxygen, and that Titan's atmosphere is much more reducing than with only the presence of hydrogen and hydrocarbons...

Where could this lithium come from? It looks as if Titan's hydrogen would be formed directly from an interstellar cloud, and thus would contain some lithium. But if so, it would also contain helium... which is nearby absent! Right on the countrary the mainstream hypothesis is that this hydrogen comes from the photo-dissociation of methane. Maybe there would be some volcanism, releasing together methane and lithium. But this is incompatible with the presence of an ice surface or underground ocean, as lithium and water react violently.

So, if these rays are not instrument artifacts, they are a complete mystery. As far as I know, there was no comment on this.

Anybody have some idea?

Richard

[deglr6328]

I suspect Alan is absolutely correct. Don't make too much of the definition of a Dalton, its just another word for atomic mass unit. They are very nearly identical. There is no special meaning of "elementary particle charge" either, a single proton has an elementary charge of +1. The ion and neutral mass spectrometer is (to GROSSLY oversimplify) basically a fancy and I think directional (though maybe that's just MIMI) quadrupole mass spectrometer. It works by taking charged atoms (ions) and subjecting them to a varying electric field then "watching" how they're deflected. The more massive an atom is the less it will be deflected by a given electric field. However this assumes the atoms all have identical charge (eg. a loss of 1 electron so the ions are all charged +1) if an atom is doubly ionized to a +2 charge for instance, then it will experience twice the pull toward (or 2x the push away) from the electric field its in, thus giving the "illusion" that the atom weighs half as much as it actually does. (I'm pretty sure this is all right )

[Guest_Richard Trigaux_*]

Thank you deglr6328 for your precisions.

Following your post I found some stetchy explanations of the INMR working on the Cassini INMR page. (Please note that this instrument is NOT the MIMI or Huygen's mass spectrometer).

This page confirms that the INMS works by first ionising the collected particles into positive ions (two methods can be selected). These ions are then deflected and detected by their electrical influence into a set of four electrodes. There are still many details left, but with such a system we can really expect that double ionisation may occur, so that we could find double ionized nitrogen atoms mistakenly detected as a mass of 7 in place of 14, as Alan indicated. But this depends of the overal geometry, this geometry could be set so that double ionization may have a different effect.


This could be most satisfying explanation of the lithium ray.

So we just have to wait for confirmation of Volcanopele's friend Roger (or other people well knowing the instrument).

What astonished me in this affair was that nobody commented this lithium ray. But if they reasonably knew it was just an artifact, there was no need to comment it.

Pity, my hypothesis of radiogenic lithium was nice, I think.