Since oxygen is chemically very reactive, scientists have previously assumed that the element in the early solar system would have combined with the abundant hydrogen to water. Therefore, it was considered excluded that there are O 2 on comets. Previous data also seemed to confirm this: in spectroscopic measurements by telescopes, no comet oxygen was detected. Apparently, field measurements using the Rosetta probe ROSINA mass spectrometer were needed for this discovery: between the expected peaks of sulfur and methanol values, the trace gases of oxygen molecules (O 2 ) were observed in the investigation of comet gases, Altwegg and her report Colleagues. After water (H 2 O), carbon monoxide (CO) and carbon dioxide (CO 2 ), oxygen comes fourth in the order of the most important gases.
"It was also amazing to us that the ratio of water to oxygen changed neither with the location on the comet nor with time - so there is a stable correlation between water and oxygen, " says Altwegg. In contrast to comets, oxygen molecules from the moons of Jupiter and Saturn are already well known. There are high-energy particles originating from the respective parent planet. In the case of Comet 67P / Churyumov-Gerasimenko, however, this possible cause of oxygen does not exist.
What's up with the oxygen?
The possible cause could be the high-energy cosmic ray particles that have been bombarding the comet for 4.6 billion years. These particles can split water, which, among other things, produces oxygen, hydrogen and ozone. However, the particles of cosmic radiation can penetrate only a few meters into the surface of the comet. But this one also seems to have the oxygen at depth, say the researchers. This shows the fact that the comet is peeled regularly: it loses on its orbit around the sun with each revolution between one to ten meters in circumference. Since his last encounter with Jupiter in 1959 - which pushed him to today's track - he has therefore already lost more than 100 meters circumference.
So the researchers now come to the supposition: The oxygen was created very early, before the formation of the solar system. At that time, high-energy particles might have encountered grains of ice in the cold and dense birthplaces of stars, the so-called dark molecular clouds, and split water molecules, resulting in hydrogen and oxygen molecules. The oxygen was then preserved. The oxygen measurements suggest that at least a large part of the comet material is older than our solar system and the composition is typical for dark molecular clouds, from which solar fog and later planetary systems arise. "This indication of oxygen as ancient material is likely to upset some theoretical models about the formation of the solar system, " says Altwegg. display
Original work of the researchers:
- Nature, doi: 10.1038 / nature15707, Communication from the University of Bern