Ice chemistry on the Galilean satellites

Abstract

Abstract. Jupiter's icy satellites Europa, Ganymede, and Callisto are subject to energy fluxes from electrons, photons, and magnetospheric plasma ion bombardment. As water ice and CO2 ice are thought to be present on their surfaces, the radiolysis of these materials over time should produce more complicated CHO-containing molecules. These may include CH3OH, H2CO , CH2CO , C302, HCOOH, CH3COOH, H2CO3, HCOOCH, (CH3)2CO , CH3CH2OH , HOCH2CH2OH , polymeric C302, and polymeric H2CO. The water fragmentation products OH, 0 2, HO2, H202, and 03 should also be produced. The molecules formed should be detectable with ground-based intruments because of their many active infrared bands. Another product produced is CO, which will have a high vapor pressure over a Galilean satellite surface at typical temperatures. The vapor pressure of CO at the nighttime temperature of 70 K could be as high as 150 mbar. Ganymede's unique dipolar magnetic field should induce more chemistry in its polar regions due to the focusing of radiation to higher latitudes. The observed lack of leading/ trailing asymmetry in its SO2 absorption correlates with this redirection of plasma ions toward the poles. The observance of O atom emissions at high latitudes by Hall et al.[1998] is also consistent with this picture. The ratio of plasma energies directed to the poles to those directed to the equatorial regions is ---4.

Possible ecosystems and the search for life on Europa

“…The radiation also destroys exposed molecules, leading to steady-state concentrations (56,57). Erosion due to sputtering occurs when charged particles eject material (60,61).…”

“…Chyba (58,59) therefore took oxidants and organic molecules to be lost through sputtering before they were gardened down to depths at which they would be protected against further radiation processing or sputtering loss. He took the relevant radiationprocessed depth at Europa's surface to be Ϸ1 mm, the stopping depth of incident electrons (56,57), but the results of Cooper et al (61) suggest that substantial radiation processing extends to depths Ͼ1 cm for a surface age of 10 million years.…”

“…Charged-particle interactions with water ice should produce molecular oxygen, hydrogen peroxide, and other oxidants (55)(56)(57)60 This value may be compared with that from a simple production calculation based on radiation flux F, H 2 O 2 G value (molecules produced per 100 eV), and irradiation time. The column density expected is given by n ϭ FGt (56,57,61) yr, production must be substrate-limited.…”

“…The column density expected is given by n ϭ FGt (56,57,61) yr, production must be substrate-limited. The production quantities of H 2 O 2 and O 2 could be orders of magnitude higher than those we find here (61) if the upper meter of Europa's surface was recirculated downward, so that fresh material were regularly being exposed to the surface radiation flux.…”

Ionizing Radiation and Life

“…Irradiation of the europan surface water ice would produce oxidants, such as oxygen and hydrogen peroxide, and radiolysis of carbon dioxide in the ice and subsequent freeradical chemistry is expected to also generate reduced organic molecules such as formaldehyde (Delitsky and Lane, 1998;Chyba and Phillips, 2001). Such a radiolytically generated disequilibrium of oxidized and reduced chemical species could power a chemoautotrophic-based biosphere if these redox couples can be washed into the europan ocean, as discussed further below.…”