View Full Version : Atmospheric sputtering on Callisto et al.

2007-Sep-01, 11:14 PM
I got 332 hits when I searched "Callisto atmosphere" on BAUT, but I don't think this question has been floated yet:

I've read that Callisto's thin atmosphere is mostly CO2 with some oxygen present. But Ganymede and Europa are predominately oxygen. Is that known to be true? If so, begs the question, why the difference?

I understand that UV light splits water and the hydrogen is "sputtered" away by radiation flux from Jupiter, but is there a way to explain the CO2/O differences based on ice composition? Or radiation intensity?

2007-Sep-03, 10:49 AM
I think that the CO2 in the Callisto is caused by evaporation of dry ice.

2007-Sep-03, 11:50 AM
From the book Jupiter: The Planet, Satellites and Magnetosphere edited by Bagenal, Dowling & McKinnon (at the moment THE book for the Jovian system) I found the following constituents of the atmospheres of the icy moons and their column density (i.e. cm-2[sup])

species | Europa | Ganymede | Callisto
O2 | 2.4-14 10[sup]14 | 1-10 1014 | 3 1016
CO2 | - | - | 8 1014

This means that CO2 is not the major species in the Callisto atmosphere but O2, but at the > 1% level, not unimportant. The high O2 density, inferred from radio occultation of the spacecraft is a problem,though, as it is 100 times that of Europa and Ganymede.

I could not find so quickly what the source of the CO2 is, other than that it is included in the water ice on all three icy moons.

Maybe more later.

2007-Sep-03, 09:17 PM
Real data, thank you. Those units for column density for each component, are they molecules per square centimeter?

So is one possible conclusion: Callisto with some amount of CO2 ice on its surface and Ganymede and Europa pretty much CO2 free?

I know this is way out, but if you could somehow switch Callisto with Io, so Callisto experienced the same tidal forces, would it become Io-like? In other words do we know if all 4 of those moons started out with approximately the same compositions?

I'll try to find a copy of that book, else I'll have you reading it to me :)

2007-Sep-03, 09:43 PM
I think that the CO2 in the Callisto is caused by evaporation of dry ice.

Thats interesting because the 3 ice moons seem so similar in size and location at first glance. I think the radiation flux is much less for Callisto, so its tempting to conclude difference in gasses & ices be attributed to that. Mechanisms?

CO2 freezes out at about 190 kelvin. All 3 are much colder than that, but Callisto must be coldest of all over time. Yet it has more volatiles.

Neat laboratory, eh. Heck of a commute though.