Now that oxygen has been found coming from one comet, other comets want in on the action. Comet 1P/Halley might have been venting O2 the last time it visited the inner solar system, researchers report in the Dec. 10 Astrophysical Journal Letters. The finding follows a recent detection of oxygen streaming from comet 67P/Churyumov-Gerasimenko (SN: 11/28/15, p. 6) and implies that many comets carry around oxygen that has been buried since the dawn of the solar system.
When Halley buzzed the sun in 1986, an armada of spacecraft flew out to greet it, including the European Space Agency probe Giotto. Martin Rubin, a planetary scientist at the University of Bern in Switzerland, and colleagues took a new look at data from Giotto using more sophisticated algorithms than were available at the time. The researchers found that Halley probably has roughly the same relative abundance of oxygen (compared with water) as 67P.
Halley and 67P come from different regions of the solar system. Comet 67P originated in the Kuiper belt, a bit beyond Neptune. Halley hails from the far more distant Oort cloud, a shell of frozen fossils that envelops the solar system. If oxygen is buried in two comets with such divergent histories, the researchers argue, those molecules were probably present in primordial ice grains that seeded the solar system well before the planets took shape.