Abstract
A fundamental goal of cometary studies is to determine the exact relationship between these bodies and the Solar System – the question(s) can be summarised as follows: did comets originate during the same events that spawned the Sun and planets, are they more primitive bodies that record a pre-solar history, or are they interstellar materials collected in relatively more recent times? Now, whatever the origin of comets, it is entirely possible that they could, in part, contain interstellar or pre-solar components – indeed, it seems rather likely in light of the fact that primitive meteorites contain such entities. These particular components are likely to be refractory (dust, macromolecular organic complexes, etc.). Of more relevance to the issues above are the volatile constituents, which make up the bulk of a comet's mass. Since these materials, by their very nature, volatilise during perihelion passage of a comet they can, in some instances, be detected and measured spectroscopically. Perhaps the most useful species for isotopic investigations are C2, HCN and CN. Unfortunately, spectroscopic measurements can only currently be made with accuracies of ±10 to ±20%. As such it is very often not practical to conclude anything further than the fact that isotopic measurements are compatible with ‘`solar’' values, which tends to imply an origin from the margins of the solar accretion disk. But there is another problem with the spectroscopic measurements – since these are made on gaseous species in the coma (and relatively minor species at that) it is impossible to be certain that these represent the true nuclear values. In other words, if the processes of sublimation, active jetting, and photochemistry in the coma impart isotopic fractionation, the spectroscopic measurements could give a false impression of the true isotope ratios. What is required is an experiment capable of measuring isotopic ratios at the very surface of a comet. Herein we describe the Ptolemy instrument, which is included on the Philae lander as part of the Rosetta mission to 67P/Churyumov-Gerasimenko. The major objective of Ptolemy is a detailed appraisal of the nature and isotopic compositions of all materials present at the surface of a comet.
References
Barber, S. J.: 1998, Development of a quadrupole ion trap mass spectrometer for the determination of stable isotope ratios: application to a space-flight opportunity. PhD Thesis, The Open University, UK.
Balsiger, H., Altwegg, K., Arijis, E., Bertaux, J.-L., Berthelier, J.-J., Bochsler, P., Carignan, G. R., Eberhardt, P., Fisk, L. A., Fuselier, S. A., Ghielmetti, A. G., Gliem, F., Gombosi, T. I., Kopp, E., Korth, A., Livi, S., Mazelle, C., Rème, H., Sauvard, J. A., Shelley, E. G., Waite, J. H., Wilken, B., Woch, J., Wollnik, H., Wurz, P., and Young, D. T.: 1998, Adv. Space Res. 21, 1527–1535.
Bradley, J. P. and Brownlee, D. E.: 1986, Science 231, 542–544.
Brownlee, D. E.: 1985, Ann. Rev. Earth Planet. Sci. 13, 147–173.
Goesmann, F., Rosenbauer, H., Roll, R., Szopa, C., Raulin, F., Sternberg, R., Israel, G., Meierhenrich, U., Thiemann, W., and Munoz-Caro, G.: 2006, COSAC, the COmetary SAmpling and Composition experiment on Philae. doi: 10.1007/s11214-006-9000-6.
Grün, E., and Jessberger, E. K.: 1990, Dust. In: Huebner, W. F. (ed.), Physics and Chemistry of Comets, Springer-Verlag, Berlin, pp. 115–176.
Hall, D. N. B.: 1973, Ap. J. 182, 977–982.
Jaworski, J. A. and Tatum, J. B.: 1991, Astrophysical J. 377(1), 306–317.
Jessberger, E. K.: 1989, Meteoritics 24, 281.
Jewitt, D. C., Matthews, H. E., Owen, T., and Meier, R.: 1997, Science 278, 90–93.
Kerridge, S. J., Muirhead, B. K., Neugebauer, M., Mauritz, A., TanWang, G., Sabahi, D., Green, J. R., Grimes, J., Moura, D. J. P., Bonneau, F., Chaffaut, F. X., Rangeard, P., Rocard, F., and Bibring, J. P.: 1997, Acta Astronautica 40, 585–595.
Kleine, M., Wyckoff, S., Wehinger, P. A., and Peterson, B. A.: 1995, Astrophysical J. 439(2), 1021–1033.
Lis, D., Gardner, M., Phillips, T. G., Brocklee-Morvan, D., Biver, N., Crovoisier, J., and Colom, P.: 1997, Comet A/1995 O1. IAU Circular, 6566.
McKeegan, K. D.: 1987, Science 237, 1468–1471.
McKeegan K. D., Walker R. M., and Zinner E.: 1985, Geochim. Cosmochim. Acta. 49, 1971–1987.
Messenger, S. and Walker, R. M.: 1998, Lunar Planet. Sci. 1906.pdf.
Neugebauer, M. and Bibring, J.-P.: 1998, Adv. Space Res. 21, 1567–1575.
Solc, M., Vanysek, V., and Kissel, J.: 1987, Astron. Astrophys. 187, 385–387.
Thomas, K. L., Blandford, G. E., Keller, L. P., Klöck, W., and McKay, D. S.: 1993, Geochim. Cosmochim. Acta 57, 1551–1566.
Urey, H. C.: 1947, J. Chem. Soc. 562–581.
Verdant, M. and Schwehm, G. H.: 1998, ESA Bull. 93, 38–50.
Weissman, P.: 1997, Lunar Planet. Sci. XXVIII, 1527.
Wilson, T. L. and Rood, R. J.: 1994, Ann. Rev. Astron. Astrophys. 32, 191–226.
Wright, I. P. and Pillinger, C. T.: 1998, Adv. Space Res. 21, 1537–1545.
Wyckoff, S., Lindholm, E., Wehinger, P. A., Peterson, B. A., Zucconi, J.-M., and Festou, M. C.: 1989, Ap. J. 339, 488–500.
Author information
Authors and Affiliations
Corresponding author
Additional information
This paper is dedicated to the memory of Professor Ray Turner, whose tireless efforts at the early stages of the project laid the foundations for the successful delivery of the Ptolemy instrument.
Rights and permissions
About this article
Cite this article
Wright, I.P., Barber, S.J., Morgan, G.H. et al. Ptolemy – an Instrument to Measure Stable Isotopic Ratios of Key Volatiles on a Cometary Nucleus. Space Sci Rev 128, 363–381 (2007). https://doi.org/10.1007/s11214-006-9001-5
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s11214-006-9001-5