The European Space Agency (ESA) announced today that its Rosetta spacecraft has made the first in situ<\/i> detection of oxygen molecules outgassing from a comet, a surprising observation that suggests they were incorporated into the comet during its formation.<\/p>\n
\u201cWe weren\u2019t really expecting to detect O2<\/sub> at the comet \u2013 and in such high abundance \u2013 because it is so chemically reactive, so it was quite a surprise,\u201d says Kathrin Altwegg of the University of Bern, and principal investigator of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis instrument, ROSINA.<\/p>\n Her team explored various possibilities to explain the presence and consistently high abundance of O2\u00a0<\/sub>and its relationship to water, as well as the lack of ozone. They first considering whether processes called photolysis and radiolysis of water ice could have converted ice into oxygen. They seemed\u00a0the most likely sources, but finally they rejected these mechanisms.<\/p>\n \u201cThe instantaneous generation of O2<\/sub> also seems unlikely, as that should lead to variable O2<\/sub> ratios under different illumination conditions. Instead, it seems more likely that primordial O2<\/sub> was somehow incorporated into the comet\u2019s ices during its formation, and is being released with the water vapour today.\u201d<\/p>\n In one scenario, gaseous O2 <\/sub>would first be incorporated into water ice in the early protosolar nebula stage of our Solar System. Chemical models of protoplanetary discs predict that high abundances of gaseous O2<\/sub> could be available in the comet forming zone, but rapid cooling from temperatures above \u2013173\u00baC to less than \u2013243\u00baC would be required to form water ice with O2<\/sub> trapped on dust grains. The grains would then have to be incorporated into the comet without being chemically altered.<\/p>\n \u201cOther possibilities include the Solar System being formed in an unusually warm part of a dense molecular cloud, at temperatures of 10\u201320\u00baC above the \u2013263\u00baC or so typically expected for such clouds,\u201d says Ewine van Dishoeck of Leiden Observatory in the Netherlands, co-author of the paper cited below.<\/p>\n \u201cThis is still consistent with estimates for the comet formation conditions in the outer solar nebula, and also with previous findings at Rosetta\u2019s comet regarding the low abundance of N2<\/sub>.\u201d<\/a><\/p>\n Alternatively, radiolysis of icy dust grains could have taken place prior to the comet\u2019s accretion into a larger body. In this case, the O2<\/sub> would remain trapped in the voids of the water ice on the grains while the hydrogen diffused out, preventing the reformation of O2<\/sub> to water, and resulting in an increased and stable level of O2<\/sub> in the solid ice.\u00a0Incorporation of such icy grains into the nucleus could explain the observed strong correlation with H2<\/sub>O observed at the comet today.<\/p>\n \u201cRegardless of how it was made, the O2<\/sub> was also somehow protected during the accretion stage of the comet: this must have happened gently to avoid the O2<\/sub> being destroyed by further chemical reactions,\u201d adds Kathrin.<\/p>\n \u201cThis is an intriguing result for studies both within and beyond the comet community, with possible implications for our models of Solar System evolution,\u201d says Matt Taylor, ESA\u2019s Rosetta project scientist.<\/p>\n \u201cAbundant molecular oxygen in the coma of 67P\/Churyumov\u2013Gerasimenko<\/a>,\u201d by A. Bieler et al is published in the 29 October 2015 issue of the journal Nature<\/i>.<\/p>\n http:\/\/www.esa.int\/Our_Activities\/Space_Science\/Rosetta\/First_detection_of_molecular_oxygen_at_a_comet<\/a><\/p>\n","protected":false},"excerpt":{"rendered":" The European Space Agency (ESA) announced today that its Rosetta spacecraft has made the first in situ detection of oxygen molecules outgassing from a comet, a surprising observation that suggests they were incorporated into the comet during its formation. \u201cWe … Continue reading Photolysis and radiolysis of water ice rejected<\/h3>\n
Oxygen dissolved in water ice rejected<\/h3>\n
Possible warm molecular cloud<\/h3>\n
Radiolysis on dust grains also possible<\/h3>\n
References<\/h3>\n