Galileo's first images of Jupiter and the Galilean satellites

Science

Volumn 274, Issue 5286, 1996, Pages 377-385

  Belton, M J S ^a   Head III, J W ^b   Ingersoll, A P ^c   Greeley, R ^d   McEwen, A S ^e   Klaasen, K P ^f   Senske, D ^f   Pappalardo, R ^b   Collins, G ^b   Vasavada, A R ^c   Sullivan, R ^d   Simonelli, D ^g   Geissler, P ^e   Carr, M H ^h   Davies, M E ⁱ   Veverka, J ^g   Gierasch, P J ^g   Banfield, D ^g   Bell, M ^g   Chapman, C R ^j   Anger, C ^k   Greenberg, R ^e   Neukum, G ^l   Pilcher, C B ^m   Beebe, R F ⁿ   Burns, J A ^g   Fanale, F ^o   Ip, W ^p   Johnson, T V ^f   Morrison, D ^q   Moore, J ^q   Orton, G S ^f   Thomas, P ^g   West, R A ^f   more..

^a NATIONAL OPTICAL ASTRONOMY OBSERVATORY   (United States)

^b BROWN UNIVERSITY   (United States)

^c CALIFORNIA INSTITUTE OF TECHNOLOGY   (United States)

^d ARIZONA STATE UNIVERSITY   (United States)

^e UNIVERSITY OF ARIZONA   (United States)

^f CALIFORNIA INSTITUTE OF TECHNOLOGY   (United States)

^g Department of Obstetrics Gynecology   (United States)

^h U S GEOLOGICAL SURVEY   (United States)

ⁱ RAND CORPORATION   (United States)

^j SOUTHWEST RESEARCH INSTITUTE   (United States)

^k ITTRES Ltd   (Canada)

^l Deutsches Zentrum F Luft R   (Germany)

^m NASA HEADQUARTERS   (United States)

ⁿ NEW MEXICO STATE UNIVERSITY   (United States)

^o UNIVERSITY OF HAWAII   (United States)

^p MAX PLANCK INSTITUT FÜR SONNENSYSTEMFORSCHUNG   (Germany)

^q NASA AMES RESEARCH CENTER   (United States)

more..

Author keywords

[No Author keywords available]

Indexed keywords

ARTICLE; ASTRONOMY; ATMOSPHERE; FILTER; GEOLOGY; IMAGING SYSTEM; PRIORITY JOURNAL; SPACE; TELECOMMUNICATION; VOLCANO;

CRATER; GALILEO; HOT SPOT; PLANETARY STRUCTURE;

EUROPA; GANYMEDE; IO; JUPITER;

EID: 0029659602     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.274.5286.377     Document Type: Article

References (81)

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2. M. J. S. Belton et al., ibid., p. 413; K. P. Klaasen et al., Opt. Eng. 23, no. 3, 334 (1984). The effective wavelengths of the SSI filters are dependent on the spectrum of the target. We name the filters according to their effective wavelength for integrated sunlight: Clear (628 nm); violet (414 nm); green (559 nm); red (664 nm); 731, 757, and 888 nm; and 1 μm (990 nm). Where the effective wavelengths differ appreciably for a given target we have noted the appropriate wavelength in the text.
3. M. J. S. Belton et al., ibid., p. 413; K. P. Klaasen et al., Opt. Eng. 23, no. 3, 334 (1984). The effective wavelengths of the SSI filters are dependent on the spectrum of the target. We name the filters according to their effective wavelength for integrated sunlight: Clear (628 nm); violet (414 nm); green (559 nm); red (664 nm); 731, 757, and 888 nm; and 1 μm (990 nm). Where the effective wavelengths differ appreciably for a given target we have noted the appropriate wavelength in the text.
4. The Galileo spacecraft achieved orbit on 7 December 1995. Although images of lo, Europa, and Jupiter were scheduled to be taken near this time, most of these were not recorded because of a tape recorder malfunction on 11 October 1995, just following the acquisition of the first Jupiter approach images. These Jupiter images remain on the tape but in a region that cannot be safely accessed. Galileo's central computer was reprogrammed partly to provide an essential capability to compress SSI images before their transmission to Earth on the spacecraft's law-gain antenna.
5. According to the initial spacecraft operational flight rules, only one pass through the tape recorder was to be allowed following the Ganymede 1 encounter. This would have limited the number of returned images to about 117 and excluded most of the Europa coverage. However, because of technical problems with other experiments, four such passes were performed.
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7. The Galileo nominal mission, which ends on 31 December 1997, after 10 orbits, should return about 1500 images. However, the option exists with the current predictions for propellent usage and lifetime against failure due to radiation damage to extend the mission by 2 years. The SSI has examined a concept (the Galileo Europa Mission) that would return an additional 1500 images, mainly of Europa but also including very high resolution images (∼10 m per pixel) of lo not possible during the prime mission.
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12. The exposure fault was discovered from the Europa mosaics, which were found to be underexposed by about a factor of 2 relative to predictions. This problem is understood and is being corrected. The BARC compressor problem, which is still not completely understood, was made evident by the large photometric contrast at high spatial frequencies seen in the Uruk Sulcus and Galileo Regio images of Ganymede. The compressor works by first truncating up to three least significant bits (LSBs) per pixel in an image line and then, if the compression achieved is not sufficient, truncating the last pixels' readout in a line. The photometric activity in these pictures was such that the compressor was pushed into truncating lines. Examination of the LSBs showed that the compressor did not consistently first truncate them to the three bit level. As a result, these images suffer from shortened lines, from the normal 800 samples per line to about 540.
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35. A. F. Cook et al., Science 211, 1419 (1981); the Voyager wide-angle camera was sensitive to emissions between 380 and 600 nm. The SSI camera is sensitive to emissions in a much wider band, 380 to 1050 nm.
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41. 3 Europa is comparable in many respects to Earth's moon but contains at least 5% by mass of water (32). Earth-based spectroscopy shows the surface to be predominantly water ice (33). Although the water could be contained mostly in hydrated minerals (34), most models of the interior involve an outer shell of water as thick as 100 km, parts of which could be liquid (35). Local darkening of the surface could result from ice weathering and contamination by rocky materials (36). The general paucity of impact craters observed in the Voyager data suggested a youthful surface and the possibility of recent, or even active, resurfacing.
42. 3 Europa is comparable in many respects to Earth's moon but contains at least 5% by mass of water (32). Earth-based spectroscopy shows the surface to be predominantly water ice (33). Although the water could be contained mostly in hydrated minerals (34), most models of the interior involve an outer shell of water as thick as 100 km, parts of which could be liquid (35). Local darkening of the surface could result from ice weathering and contamination by rocky materials (36). The general paucity of impact craters observed in the Voyager data suggested a youthful surface and the possibility of recent, or even active, resurfacing.
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59. Post-Voyager discussion of graben, modified tension fractures, and ductile necking features can be found in the following: J. Fink and R. Fletcher, NASA Tech. Memo. TM-34211 (1981), p. 51 ; E. Shoemaker et al., in The Satellites of Jupiter, D. Morrison, Ed. (Univ. of Arizona Press, Tucson, 1982), p. 435; E. M. Parmentier et al., Nature 395, 290 (1982); and S. W. Squyres, Icarus 52, 545 (1982). Mass wasting and differences in strain rate or thickness of the lithosphere are discussed by Parmentier et al. and Squyres. Constructional ice-volcanism or surface deformation due to ice plutonism in underlying fractures is discussed by S. Croft et al., Icarus 73, 279 (1988).
60. Post-Voyager discussion of graben, modified tension fractures, and ductile necking features can be found in the following: J. Fink and R. Fletcher, NASA Tech. Memo. TM-34211 (1981), p. 51 ; E. Shoemaker et al., in The Satellites of Jupiter, D. Morrison, Ed. (Univ. of Arizona Press, Tucson, 1982), p. 435; E. M. Parmentier et al., Nature 395, 290 (1982); and S. W. Squyres, Icarus 52, 545 (1982). Mass wasting and differences in strain rate or thickness of the lithosphere are discussed by Parmentier et al. and Squyres. Constructional ice-volcanism or surface deformation due to ice plutonism in underlying fractures is discussed by S. Croft et al., Icarus 73, 279 (1988).
61. Post-Voyager discussion of graben, modified tension fractures, and ductile necking features can be found in the following: J. Fink and R. Fletcher, NASA Tech. Memo. TM-34211 (1981), p. 51 ; E. Shoemaker et al., in The Satellites of Jupiter, D. Morrison, Ed. (Univ. of Arizona Press, Tucson, 1982), p. 435; E. M. Parmentier et al., Nature 395, 290 (1982); and S. W. Squyres, Icarus 52, 545 (1982). Mass wasting and differences in strain rate or thickness of the lithosphere are discussed by Parmentier et al. and Squyres. Constructional ice-volcanism or surface deformation due to ice plutonism in underlying fractures is discussed by S. Croft et al., Icarus 73, 279 (1988).
62. Post-Voyager discussion of graben, modified tension fractures, and ductile necking features can be found in the following: J. Fink and R. Fletcher, NASA Tech. Memo. TM-34211 (1981), p. 51 ; E. Shoemaker et al., in The Satellites of Jupiter, D. Morrison, Ed. (Univ. of Arizona Press, Tucson, 1982), p. 435; E. M. Parmentier et al., Nature 395, 290 (1982); and S. W. Squyres, Icarus 52, 545 (1982). Mass wasting and differences in strain rate or thickness of the lithosphere are discussed by Parmentier et al. and Squyres. Constructional ice-volcanism or surface deformation due to ice plutonism in underlying fractures is discussed by S. Croft et al., Icarus 73, 279 (1988).
63. Post-Voyager discussion of graben, modified tension fractures, and ductile necking features can be found in the following: J. Fink and R. Fletcher, NASA Tech. Memo. TM-34211 (1981), p. 51 ; E. Shoemaker et al., in The Satellites of Jupiter, D. Morrison, Ed. (Univ. of Arizona Press, Tucson, 1982), p. 435; E. M. Parmentier et al., Nature 395, 290 (1982); and S. W. Squyres, Icarus 52, 545 (1982). Mass wasting and differences in strain rate or thickness of the lithosphere are discussed by Parmentier et al. and Squyres. Constructional ice-volcanism or surface deformation due to ice plutonism in underlying fractures is discussed by S. Croft et al., Icarus 73, 279 (1988).
64. See, for example, the discussion by S. W. Squyres and S. K. Croft in Satellites, J. A. Burns and M. S. Matthews, Eds. (Univ. of Arizona Press, Tucson, 1990), p. 293.
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66. M. P. Golombek and M. Allison, Geophys. Res. Lett. 8, 1139 (1981); S. J. Murchie et al., J. Geophys. Res. 91, E222 (1990); E. M. Parmentier et al., Nature 295, 290 (1982).
67. M. P. Golombek and M. Allison, Geophys. Res. Lett. 8, 1139 (1981); S. J. Murchie et al., J. Geophys. Res. 91, E222 (1990); E. M. Parmentier et al., Nature 295, 290 (1982).
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69. S. J. Murchie et al., J. Geophys. Res. 91, E222 (1990); R. Cassachia and R. Strom, ibid. 89, B419 (1984); P. Shenk and W. McKinnon, Icarus 72, 209 (1987); M. Zube and E. Parmentier, ibid. 60, 200 (1984); E. M. Shumaker et al., in Satellites of Jupiter, D. Morrison, Ed. (Univ. of Arizona Press, Tucson, 1932), p. 435.
70. S. J. Murchie et al., J. Geophys. Res. 91, E222 (1990); R. Cassachia and R. Strom, ibid. 89, B419 (1984); P. Shenk and W. McKinnon, Icarus 72, 209 (1987); M. Zube and E. Parmentier, ibid. 60, 200 (1984); E. M. Shumaker et al., in Satellites of Jupiter, D. Morrison, Ed. (Univ. of Arizona Press, Tucson, 1932), p. 435.
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79. P. Helfenstein, thesis, Brown University, Providence, Rl (1990); Lunar Planet. Sci. XVII, 333 (1990); P. Schenk and W. McKinnon, Icarus 89, 318 (1989); S. J. Murchie et al., Lunar Planet. Sci. XXIII, 943 (1992).
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81. We thank the current project manager, W. J. O'Neil, and his predecessors J. R. Casani and R. J. Spehalski for their leadership; T. Brady and J. Marr for flight software development and its implementation; G. Levanas and his team for their diagnosis of the tape recorder problems and the creation of a safe way to operate this device; and W. Cunningham and his team who provided the new SSI camera flight software. T. Becker, E. Lee, R. Sucharski, and T. Rosanova provided the team with maps. Many associates of the team members contributed to the success of the SSI experiment; we thank N. Ausman, E.A. Alvarez del Castillo, K. Bender, H. Breneman, K. Buxbaum, T. Colvin, D. Deats, T. Denk, S. Fagents, A. Di Cicco, P. Helfenstein, S. Henderson, K. Homan, T. Jones, J.M. Kaufman, R. Krk, J. Klemaszewski, S. LaVoie, E. Lo, L, Lowes, K. Magee, W. Merline, R. Mitchell, H. Mortensen, B. Paczkowski, C. Phillips, K. Rages, A. Simon, D. Smonelli, J.N. Spitale, C. Stanley, E. Ustinov, D. Winther, D. Johnson, J. Van der Woude, J. Yatteau, A. Culver, D. Jensen, D. Alexander, and J. Yoshimizu. We acknowledge the contributions of absent colleagues H. Masursky, J. Pollack, C. Yeates and J. Dunne. A portion of this research was carried out by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. The National Optical Astronomy Observatories are operated by the Association of Universities for Research in Astronomy (AURA), under cooperative agreement with the National Science Foundation.