The composition of the neutral gas comas of most comets is dominated by H2O, CO and CO2, typically comprising as much as 95 per cent of the total gas density1. In addition, cometary comas have been found to contain a rich array of other molecules, including sulfuric compounds and complex hydrocarbons. Molecular oxygen (O2), however, despite its detection on other icy bodies such as the moons of Jupiter and Saturn2, 3, has remained undetected in cometary comas. Here we report in situ measurement of O2 in the coma of comet 67P/Churyumov–Gerasimenko, with local abundances ranging from one per cent to ten per cent relative to H2O and with a mean value of 3.80 ± 0.85 per cent. Our observations indicate that the O2/H2O ratio is isotropic in the coma and does not change systematically with heliocentric distance. This suggests that primordial O2 was incorporated into the nucleus during the comet’s formation, which is unexpected given the low upper limits from remote sensing observations4. Current Solar System formation models do not predict conditions that would allow this to occur.
At a glance
- 391–423 (Univ. Arizona Press, 2004) , & in Comets II (eds , & )
- Detection of an oxygen atmosphere on Jupiter’s moon Europa. Nature 373, 677–679 (1995) , , , &
- Production, ionization and redistribution of O2 in Saturn’s ring atmosphere. Icarus 180, 393–402 (2006) et al.
- Herschel measurements of molecular oxygen in Orion. Astrophys. J. 737, 96 (2011) et al.
- ROSINA — ROSETTA orbiter spectrometer for ion and neutral analysis. Space Sci. Rev. 128, 745–801 (2007) et al.
- Time variability and heterogeneity in the coma of 67P/Churyumov-Gerasimenko. Science 347, aaa0276 (2015) et al.
- Composition-dependent outgassing of comet 67P/Churyumov-Gerasimenko from ROSINA/DFMS — implications for nucleus heterogeneity? Astron. Astrophys. http://dx.doi.org/10.1051/0004-6361/201526205 (2015) et al.
- The diurnal cycle of water ice on comet 67P/Churyumov–Gerasimenko. Nature 525, 500–503 (2015) et al.
- The organic-rich surface of comet 67P/Churyumov-Gerasimenko as seen by VIRTIS/Rosetta. Science 347, aaa0628 (2015) et al.
- Erosion and molecular formation in condensed gas films by electronic energy loss of fast ions. Nucl. Instrum. Methods 198, 1–8 (1982) et al.
- Hydrogen peroxide on the surface of Europa. Science 283, 2062–2064 (1999) et al.
- Charge-coupled device spectra of the Galilean satellites: molecular oxygen on Ganymede. J. Geophys. Res. 100, 19049–19056 (1995) , &
- Condensed O2 on Europa and Callisto. Astron. J. 124, 3400–3403 (2002) &
- Constraints on the abundance of solid O2 in dense clouds from ISO-SWS and ground-based observations. Astron. Astrophys. 346, L57–L60 (1999) et al.
- A 3–5 μm VLT spectroscopic survey of embedded young low mass stars I. Structure of the CO ice. Astron. Astrophys. 408, 981–1007 (2003) et al.
- Multi-line detection of O2 toward ρ Ophiuchi A. Astron. Astrophys. 541, A73 (2012) et al.
- Molecular oxygen in the Ophiuchi cloud. Astron. Astrophys. 466, 999–1003 (2007) et al.
- Deep observations of O2 toward a low-mass protostar with Herschel-HIFI. Astron. Astrophys. 558, A58 (2013) et al.
- Multilayer modeling of porous grain surface chemistry. I. The GRAINOBLE model. Astron. Astrophys. 538, A42 (2012) , &
- Detection of interstellar hydrogen peroxide. Astron. Astrophys. 531, L8 (2011) et al.
- Detection of the hydroperoxyl radical HO2 toward ρ Ophiuchi A. Additional constraints on the water chemical network. Astron. Astrophys. 541, L11 (2012) , &
- Production of interstellar hydrogen peroxide (H2O2) on the surface of dust grains. Astron. Astrophys. 538, A91 (2012) , &
- Molecular nitrogen in comet 67P/Churyumov-Gerasimenko indicates a low formation temperature. Science 348, 232–235 (2015) et al.
- The molecular composition of the planet-forming regions of protoplanetary disks across the luminosity range. Astron. Astrophys. 582, A88 (2015) , &
- O2/O3 microatmospheres in the surface of Ganymede. Astrophys. J. 480, L79–L82 (1997) &
- The ancient heritage of water ice in the solar system. Science 345, 1590–1593 (2014) et al.
- 67P/Churyumov-Gerasimenko, a Jupiter family comet with a high D/H ratio. Science 347, http://dx.doi.org/10.1126/science.1261952 (2015) et al.
- Influence of spacecraft outgassing on the exploration of tenuous atmospheres with in situ mass spectrometry. J. Geophys. Res. 115, A12313 (2010) et al.
- Electron impact dissociative ionization of CO2: measurements with a focusing time-of-flight mass spectrometer. J. Chem. Phys. 108, 927 (1998) &
- ROSINA/DFMS and IES observations of 67P: ion-neutral chemistry in the coma of a weakly outgassing comet. Astron. Astrophys http://dx.doi.org/10.1051/0004-6361/201526210 (2015) et al.
- Formation of hydrogen, oxygen and hydrogen peroxide in electron-irradiated crystalline water ice. Astrophys. J. 639, 534–548 (2006) , &
- Heliospheric cosmic ray irradiation of Kuiper belt comets. Adv. Space Res. 21, 1611–1614 (1998) , &
- The importance of pores in the electron stimulated production of D2 and O2 in low temperature ice. Surf. Sci. 593, 180–186 (2005) &
- The recent dynamical history of comet 67P/Churyumov-Gerasimenko. Astron. Astrophys. 579, A78 (2015)
- Solar wind sputtering of dust on the surface of 67P/Churyumov-Gerasimenko. Astron. Astrophys http://dx.doi.org/10.1051/0004-6361/201525980 (2015) et al.