In situ measurements of the physical characteristics of Titan's environment

Abstract

On the basis of previous ground-based and fly-by information, we knew that Titan's atmosphere was mainly nitrogen, with some methane, but its temperature and pressure profiles were poorly constrained because of uncertainties in the detailed composition. The extent of atmospheric electricity (‘lightning’) was also hitherto unknown. Here we report the temperature and density profiles, as determined by the Huygens Atmospheric Structure Instrument (HASI), from an altitude of 1,400 km down to the surface. In the upper part of the atmosphere, the temperature and density were both higher than expected. There is a lower ionospheric layer between 140 km and 40 km, with electrical conductivity peaking near 60 km. We may also have seen the signature of lightning. At the surface, the temperature was 93.65 ± 0.25 K, and the pressure was 1,467 ± 1 hPa.

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Figure 1: The atmospheric density profile of Titan as measured by HASI.
Figure 2: The atmospheric temperature profile.
Figure 3: The temperature lapse rate.
Figure 4: Pressure profile of the lower atmosphere as measured by the Pressure Profile Instrument (PPI)28.
Figure 5: Temperature profile of the lower atmosphere as measured by the temperature sensors, TEM 27 (expanded from Fig. 2).
Figure 6: The temperature lapse rate for the low atmosphere (expanded from Fig. 3).
Figure 7: A synopsis of PWA data: the signature of the ionosphere.
Figure 8: A synopsis of PWA data: electric field, acoustic pressure and radar measurements.
Figure 9: The HASI signature of the impact trace, at 200 samples per second.

References

  1. 1

    McKay, C. P., Pollack, J. B. & Courtin, R. The thermal structure of Titan's atmosphere. Icarus 80, 23–53 (1989)

    CAS  Article  ADS  PubMed  Google Scholar 

  2. 2

    Lindal, G. F. et al. The atmosphere of Titan—an analysis of the Voyager 1 radio occultation measurements. Icarus 53, 348–363 (1983)

    CAS  Article  ADS  Google Scholar 

  3. 3

    Lellouch, E. et al. Titan's atmosphere and hypothesized ocean: a reanalysis of the Voyager 1 radio-occultation and IRIS 7.7 µm data. Icarus 79, 328–349 (1989)

    CAS  Article  ADS  Google Scholar 

  4. 4

    Vervack, R. J., Sandel, B. R. & Strobel, D. F. New perspectives on Titan's upper atmosphere from a reanalysis of the Voyager 1 UVS solar occultations. Icarus 170, 91–112 (2004)

    CAS  Article  ADS  Google Scholar 

  5. 5

    Coustenis, A. et al. Titan's atmosphere from ISO mid-infrared spectroscopy. Icarus 161, 383–403 (2003)

    CAS  Article  ADS  Google Scholar 

  6. 6

    Hubbard, W. B. et al. Results for Titan's atmosphere from its occultation of 28 Sagittarii. Nature 343, 353–355 (1990)

    Article  ADS  Google Scholar 

  7. 7

    Sicardy, B. et al. The structure of Titan's stratosphere from the 28 Sgr occultation. Icarus 142, 357–390 (1999)

    Article  ADS  Google Scholar 

  8. 8

    Tracadas, P. W., Hammel, H. B., Thomas-Osip, J. E. & Elliot, J. L. Probing Titan's atmosphere with the 1995 August stellar occultation. Icarus 153, 285–294 (2001)

    Article  ADS  Google Scholar 

  9. 9

    Bouchez, A. H. et al. Adaptive optics imaging of a double stellar occultation by Titan. Bull. Am. Astron. Soc. 34, 881 (2002)

    Google Scholar 

  10. 10

    Sicardy, B. et al. The two stellar occultations of November 14, 2003: revealing Titan's stratosphere at sub-km resolution. Bull. Am. Astron. Soc. 36, 1119 (2004)

    ADS  Google Scholar 

  11. 11

    Lellouch, E., Hunten, D., Kockarts, G. & Coustenis, A. Titan's thermosphere profile. Icarus 83, 308–324 (1990)

    Article  ADS  Google Scholar 

  12. 12

    Yelle, R. V. Non-LTE models of Titan's upper atmosphere. Astrophys. J. 383, 380–400 (1991)

    CAS  Article  ADS  Google Scholar 

  13. 13

    Yelle, R. V., Strobel, D. F., Lellouch, E. & Gautier, D. Engineering Models for Titan's Atmosphere 243–256 (ESA SP-1177, European Space Agency, Noordwijk, 1997)

    Google Scholar 

  14. 14

    Campbell, D. B., Black, G. J., Carter, L. M. & Ostro, S. J. Radar evidence for liquid surfaces on Titan. Science 302, 431–434 (2003)

    CAS  Article  ADS  Google Scholar 

  15. 15

    Coustenis, A. et al. Maps of Titan's surface from 1 to 2.5 µm. Icarus 177, 89–105 (2005)

    Article  ADS  Google Scholar 

  16. 16

    Meier, R., Smith, B. A., Owen, T. C. & Terrile, R. J. The surface of Titan from NICMOS observations with the Hubble Space Telescope. Icarus 145, 462–473 (2000)

    Article  ADS  Google Scholar 

  17. 17

    Porco, C. C. et al. Imaging of Titan from the Cassini spacecraft. Nature 434, 159–168 (2005)

    CAS  Article  ADS  Google Scholar 

  18. 18

    Brown, R. H. et al. Cassini Visual and Infrared Mapping Spectrometer (VIMS): Results for the SOI- and near-SOI period of the Cassini orbital tour. Astron. Astrophys. (submitted)

  19. 19

    Elachi, C. et al. Cassini radar views the surface of Titan. Science 308, 970–974 (2005)

    CAS  Article  ADS  Google Scholar 

  20. 20

    Grard, R. et al. An experimental investigation of atmospheric electricity and lightning activity to be performed during the descent of the Huygens probe onto Titan. J. Atmos. Terr. Phys. 57, 575–578 (1995)

    Article  ADS  Google Scholar 

  21. 21

    Desch, S. J., Borucki, W. J., Russell, C. T. & Bar-Nun, A. Progress in planetary lightning. Rep. Prog. Phys. 65, 955–997 (2002)

    CAS  Article  ADS  Google Scholar 

  22. 22

    Tokano, T., Molina-Cuberos, G. J., Lammer, H. & Stumptner, W. Modelling of thunderclouds and lightning generation on Titan. Planet. Space Sci. 49, 539–560 (2001)

    CAS  Article  ADS  Google Scholar 

  23. 23

    Lebreton, J.-P. & Matson, D. L. The Huygens probe: science, payload and mission overview. Space Sci. Rev. 104, 59–100 (2002)

    Article  ADS  Google Scholar 

  24. 24

    Fulchignoni, M. et al. The characterization of Titan's atmospheric physical properties by the Huygens Atmospheric Structure Instrument (HASI). Space Sci. Rev. 104, 395–431 (2002)

    Article  ADS  Google Scholar 

  25. 25

    Zarnecki, J. C. et al. In-Flight Performances of the Servo Accelerometer and Implication for Results at Titan 71–76 (ESA SP-544, European Space Agency, Noordwijk, 2004)

    Google Scholar 

  26. 26

    Lebreton, J. P. et al. An overview of the descent and landing of the Huygens probe on Titan. Nature doi:10.1038/nature04347 (this issue)

  27. 27

    Ruffino, G. et al. The temperature sensor on the Huygens probe for the Cassini mission: Design, manufacture, calibration and tests of the laboratory prototype. Planet. Space Sci. 44–10, 1149–1162 (1996)

    Article  ADS  Google Scholar 

  28. 28

    Harri, A.-M. et al. Scientific objectives and implementation of the Pressure Profile Instrument (PPI/HASI) for the Huygens spacecraft. Planet. Space Sci. 46, 1383–1392 (1998)

    Article  ADS  Google Scholar 

  29. 29

    Mäkinen, T. Processing the HASI measurements. Adv. Space Res. 17, 217–222 (1996)

    Article  ADS  Google Scholar 

  30. 30

    Niemann, H. B. et al. The abundances of constituents of Titan's atmosphere from the GCMS instrument on the Huygens probe. Nature doi:10.1038/nature04122 (this issue)

  31. 31

    Hinson, D. P. & Tyler, G. L. Internal gravity waves in Titan's atmosphere observed by Voyager radio occultation. Icarus 54, 337–352 (1983)

    Article  ADS  Google Scholar 

  32. 32

    Friedson, A. J. Gravity waves in Titan's atmosphere. Icarus 109, 40–57 (1994)

    Article  ADS  Google Scholar 

  33. 33

    Bird, M. K. et al. The vertical profile of winds on Titan. Nature doi:10.1038/nature04060 (this issue)

  34. 34

    Molina-Cuberos, G. J., López-Moreno, J. J., Rodrigo, R. & Lara, L. M. Chemistry of the galactic cosmic ray induced ionosphere of Titan. J. Geophys. Res. 104, 21997–22024 (1999)

    CAS  Article  ADS  Google Scholar 

  35. 35

    Borucki, W. J. et al. Predictions of the electrical conductivity and charging of the aerosols in Titan's atmosphere. Icarus 72, 604–622 (1987)

    CAS  Article  ADS  Google Scholar 

  36. 36

    Borucki, W. J., Whitten, R. C., Bakes, E. L. O., Barth, E. & Tripathi, S. Predictions of the electrical conductivity and charging of the aerosols in Titan's atmosphere. Icarus (in the press)

  37. 37

    Molina-Cuberos, G. J., López-Moreno, J. J., Rodrigo, R. & Schwingenschuh, K. Capability of the Cassini/Huygens PWA-HASI to measure electrical conductivity in Titan. Adv. Space Res. 28, 1511–1516 (2001)

    Article  ADS  Google Scholar 

  38. 38

    Schwingenschuh, K. et al. Propagation of electromagnetic waves in the lower ionosphere of Titan. Adv. Space Res. 28, 1505–1510 (2001)

    Article  ADS  Google Scholar 

  39. 39

    Nickolaenko, A. P., Besser, B. P. & Schwingenschuh, K. Model computations of Schumann resonance on Titan. Planet. Space Sci. 51, 853–862 (2003)

    Article  ADS  Google Scholar 

  40. 40

    Morente, J. A., Molina-Cuberos, G. J., Portí, J. A., Schwingenschuh, K. & Besser, B. P. A study of the propagation of electromagnetic waves in Titan's atmosphere with the TLM numerical method. Icarus 162, 374–384 (2003)

    Article  ADS  Google Scholar 

  41. 41

    Lunine, J. I., Stevenson, D. J. & Yung, Y. L. Ethane ocean on Titan. Science 222, 1229–1230 (1983)

    CAS  Article  ADS  Google Scholar 

  42. 42

    Zarnecki, J. C. et al. A soft solid surface on Titan as revealed by the Huygens Surface Science Package. Nature doi:10.1038/nature04211 (this issue)

  43. 43

    Hamelin, M. et al. Surface and sub-surface electrical measurement of Titan with the PWA-HASI experiment on Huygens. Adv. Space Res. 26, 1697–1704 (2000)

    Article  ADS  Google Scholar 

  44. 44

    Coustenis, A. & Bézard, B. Titan's atmosphere from Voyager infrared observations. IV. Latitudinal variations of temperature and composition. Icarus 115, 126–140 (1995)

    CAS  Article  ADS  Google Scholar 

  45. 45

    Flasar, F. M. et al. Titan's atmospheric temperatures, winds, and composition. Science 308, 975–978 (2005)

    CAS  Article  ADS  PubMed  PubMed Central  Google Scholar 

  46. 46

    Brown, M. E., Bouchez, A. H. & Griffith, C. A. Direct detection of variable tropospheric clouds near Titan's south pole. Nature 420, 7995–7997 (2002)

    Google Scholar 

  47. 47

    Tokano, T. Meteorological assessment of the surface temperatures on Titan: constraints on the surface type. Icarus 173, 222–242 (2005)

    CAS  Article  ADS  Google Scholar 

  48. 48

    Kliore, A. J. et al. Cassini Radio Science. Space Sci. Rev. 115, 1–70 (2004)

    Article  ADS  Google Scholar 

  49. 49

    Tomasko, M. G. et al. Rain, winds and haze during the Huygens probe's descent to Titan's surface. Nature doi:10.1038/nature04126 (this issue)

  50. 50

    Ksanfomaliti, L. V. et al. Acoustic measurements of the wind velocity at the Venera 13 and Venera 14 landing sites. Sov. Astron. Lett 8(4), 227–229 (1982)

    ADS  Google Scholar 

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Acknowledgements

We thank the following people for their contributions to the realization of the HASI experiment: A. Buccheri, R. DeVidi, and M. Cosi of Galileo Avionica, A. Aboudan, S. Bastianello and M. Fabris of CISAS, M. Chabassière of LPCE, V. Brown, J.M. Jeronimo and L.M. Lara of IAA, R. Hofe of IWF, A. Smit, L. Smit and J. Van der Hooke from RSSD-ESTEC, H. Jolly from the UK, R. Pellinen, G. Leppelmeier, T. Siili, P. Salminen from FMI, and at the Aerodynamics Laboratory of Helsinki University of Technology T. Siikonen and B. Fagerström. HASI has been realised and operated by CISAS under a contract with the Italian Space Agency (ASI), with the participation of RSSD, FMI, IAA, IWF, LPCE and PSSRI sponsored by the respective agencies: ESA, TEKES, CSIC, BM:BWK, CNES and PPARC. We also acknowledge the long years of work by some hundreds of people in the development and design of the Huygens probe. The Huygens probe is part of the Cassini-Huygens mission, a joint endeavour of the National Aeronautics and Space Administration (NASA), the European Space Agency (ESA) and the Italian Space Agency (ASI).

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Correspondence to F. Ferri.

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Fulchignoni, M., Ferri, F., Angrilli, F. et al. In situ measurements of the physical characteristics of Titan's environment. Nature 438, 785–791 (2005). https://doi.org/10.1038/nature04314

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