1 / 15

First Measurement of the HDO/H 2 O ratio in a Jupiter Family Comet

First Measurement of the HDO/H 2 O ratio in a Jupiter Family Comet. N. Biver and D. Bockelée-Morvan,… LESIA, Observatoire de Paris. Based on Hartogh et al. (2011) to be published in Nature (online on 5 Oct. 2011). Why studying the D/H ratio in cometary water.

liesel
Download Presentation

First Measurement of the HDO/H 2 O ratio in a Jupiter Family Comet

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. First Measurement of the HDO/H2O ratio in a Jupiter Family Comet N. Biver and D. Bockelée-Morvan,… LESIA, Observatoire de Paris Based on Hartogh et al. (2011) to be published in Nature (online on 5 Oct. 2011)

  2. Why studying the D/H ratio in cometary water • - Comets are relics of the chemistry in the outer regions of the primitive Solar Nebula • - They are relics of the planetesimals that formed outer planets and icy satellites, and may have contributed to Earth oceans •  The composition of comets can constrain the chemistry and processes at work in the early Solar System • What is the origin of comet material: • - interstellar chemistry ? - product of nebular chemistry ? - role of coma processing + comet aging ? • The study of the chemical diversity of comets is important to investigate chemical differences related to different formation regions or aging • How do the different dynamical classes compare ? • long-period comets (Oort cloud) origin: Saturn-Neptune region • Jupiter-family comets (Kuiper Belt/Scattered disk) beyond Neptune

  3. Comet 103P/Hartley 2 in november 2010 A JFC at 0.13 AU from Herschel! Dust seen by Herschel Nucleus seen by EPOXI PACS 70 mm HIFI 557 GHz PACS 1661 GHz 360 000 km SPIRE 500 mm 5400 km 1x1,5 106 km H2O by Herschel

  4. Water lines observed with Herschel About 30 water lines have been detected in comet 103P/Hartley 2 SPIRE spectrum PACS, spectrum, SED mode HIFI spectra

  5. Problems to avoid to measure an accurate HDO/H2O ratio: • Time Variability: • Comet outgassing can vary quickly: • Outbursts: e.g. 17P/Holmes QH2O x10000 ~12h •  Periodic variation: • e.g. C/2007 N3 Q±40% in 42h, •  Irregular activity: • Odin before Herschel obs. => QH2O(t) in 103P

  6. Problems to avoid to measure an accurate HDO/H2O ratio: Coma sampling Asymetry, jets, in cometary coma  no easy comparison if different field of view:  Observe at a similar frequency, with the same telescope Opacity effect • The main H2O line corresponds to a column density ~2000x higher than HDO  high opacity of submm lines of H2O (t=5 to 40) • Properly model the water emission ? • Use optically thinner proxy, e.g. H218O

  7. HIFI observations to measure D/H in H2O in comet 103P/Hartley 2: 17 november 2010: Alternate 11 observations of H2O (557 GHz) + H218O (548 GHz) with 10 of HDO (509 GHz) and five maps of H2O: total 66 + 320 + 80min (~8h) Same receiver  similar field of view (~39’’ ) Observed variation: smooth decrease by ~20% of QH2O during the observation

  8. Result: Hartogh et al. (2011) 110-101 509 GHz 110-101 548 GHz S/N = 10 S/N = 60

  9. Analysis of the observations Excitation model : collisions with H2O + e- + infrared pumping, gas temperature determined by other observation (e.g. methanol lines at IRAM/CSO)  the HDO/H218O production rate ratio is not very sensitive to the model parameters (similar transition: JKaKc = 110-101)  H2O maps still need to be fully interpreted (opacity not well modeled at the center – variable T?) Hypothesis : 16O/18O = 500 (+/- 10%) (VSMOW) (520±30 in 4 comets with Odin) => D/H = (1.61 ± 0.24) x 10-4 D/H(VSMOW) = 1.56 x 10-4

  10. Measurements of D/H in cometary water: • Measurements in Oort cloudcomets • 1P/Halley, Hyakutake, Hale-Bopp : • D/H ~3 x 10-4 (Earth value x2) New D/H measurements in water from Oort cloud comets From OD/OHcomet C/2002 T7 (LINEAR) (UVES at ESO-VLT - Hutsemekers et al. 2008) FromD/H Ly-acomet C/2001 Q4 (NEAT) (STIS on the Hubble Space Telescope - Weaver et al.) HDO/H2O high-res IR observations comet 8P/Tuttle (Keck, VLT - Villanueva et al. 2008) • D/H ~3-4 x 10-4 Other upper limits in Oort cloud comets: HDO at CSO + H2O/H218O Odin:comet 153P/Ikeya-Zhang comet C/2004 Q2 (Machholz) • D/H < 2.5 x 10-4

  11. Deuterium in water in the Solar System 153P

  12. Model Predictions for D/H in comets Kaveelars et al. (2011) JF OC = Oort Cloud JF = Jupiter family 103P OC OC J S Takes into account planet migration

  13. Why would the D/H ratio in water be terrestrial in JFCs and twice larger in Oort Cloud comets? Hypotheses to explore: Ices condensed close to the Sun would be more deuterated? e.g., Out of equilibirium chemistry at high T H2/H2O/OH/H/O (Thi et al. 2010) – but seems incompatible with D/H in carbonaceous chondrites The origin of JFCs and Oort Cloud comets must be revisited? e.g. JFC = Troyans formed in the vicinity of Jupiter (Horner et al. 2007) e.g. 90% of Oort cloud comets from in other stars vicinity (Levisson et al. (2010), to reproduce the actual population and location of the Oort cloud) Other explanations?

  14. Conclusions… The D/H ratio in the water of the Jupiter Family comet 103P/Hartley 2 is equal to that of the Earth – in line with the similarities seen between carbocaneous chondrites and cometary material (e.g. 81P/Wild 2) The difference found with Oort cloud comets (D/H twice higher), will require more theoretical modeling to explain it! New D/H measurements are planned with Herschel…

  15. Isotopic ratios in volatiles : nitrogen Measurements in HCN • 14N/15N ratio in 17P/Holmes: • 14N/15N = 139 ± 26 • consistent value in CN • HCN and other major parent • of CN are equally enriched in • 15N Bockelée-Morvan et al. 2008 N chemical fractionation in the presolar cloud or solar nebula ? (Charnley & Rodgers 2008), but no observational evidence yet in the ISM (Gérin et al. 2009)

More Related