OCR Text |
Show place worthy of future Mars landers and sample returns, largely because it is one of the few possible lake features that most of the Mars science community can agree upon. Many more possible ancient lakebeds have been identified and summarized by Goldspiel and Squyres [ 11], Scott et al [ 12], De Hon [ 13], Wharton et al [ 14], and Parker and Currey [ 15]. Most of the proposed lakebeds are areas of low elevation where one or more channels appear to terminate at the location of a smooth, flat- lying deposit. In some cases, the smooth deposit has been eroded to form buttes and mesas. Other lake features are identified on the basis of thick, layered deposits [ 16]; or high- albedo deposits on crater floors, interpreted to be possible evaporites [ 17]. Parker [ 18, 19] has continued the approach of looking for Bonneville- like paleoshore features, but has moved from looking at the margins of great northern plains to the large ( 100' s to 1000' s of km) impact basins. Edgett and Parker [ 20] recently proposed that a vast portion of ancient cratered highlands terrain in the martian region of western Arabia was once part of a vast, northern hemisphere ocean that was bigger than previously envisioned by anyone. Upcoming Missions: NASA's decade- long Mars Surveyor Program is focused on the theme of " water." The program's emphasis recently shifted toward the search for evidence of martian life. One of the main types of sites desired for exobiologic investigation is " sublacustrine spring deposits and evaporites/ lacustrine shales" [ 1]. New high resolution images ( 1.5 m/ pixel) and thermal infrared mineral spectra will be obtained by Mars Global Surveyor instruments during its primary mission ( March 1998- January 2000)- these are both expected to contribute greatly toward the identification of lacustrine features. In addition, the Mars Global Surveyor laser altimeter may confirm topographic continuity of shore features identified by Parker et al. [ 6, 7]. Additional orbiters with complimentary capabilities will launch in 1998 and 2001. Rovers designed to cache samples for return to Earth will land in 2002 and 2004, and at least one of these is expected to go to a lacustrine site. Knowledge of North America's Great Basin lacustrine geomorphology will contribute greatly to the exploration of this new frontier in the 21st Century. References: [ 1] An Exobiological Strategy for Mars Exploration ( 1995) NASA SP- 530, 56 p. [ 2] Lowell, P. ( lZ96) Pop. Astron., 4, 289- 296. [ 3] Clifford, S. M., etal (\ 9SS) Eos, Trans. AGU, 69, 1585, 1595- 1596. [ 4] McEwen, A. S. ( 1991) Rev. Geophys. Suppl, 29, 290- 296. [ 5] Parker, T. J. et al. ( 1987) pp. 96- 98 mMars: Evolution of its Climate and Atmosphere, LPI Tech Rept. 87- 01, Houston, TX. [ 6] Parker, T. J. et al. ( 1989) Icarus, 82,111- 145. [ 7] Parker, T. J. etal. ( 1993) J. Geophys. Res., 98, 11061- 11078. [ 8] Baker, V. R., etal. ( 1991) Nature, 352, 589- 594. [ 9] Carr, M. H. ( 1991) Bull. Amer. Astron. Soc, 23, 1206. [ 10] DeHon, R. A. ( 1987) Lunar Planet. Sci. XIX, 261- 262. [ 11] Goldspiel, J. M. and S. W. Squyres ( 1991) Icarus, 89, 392- 410. [ 12] Scott, D. H. etal. ( 1991) Origins Life Evol. Biosph., 21, 189- 198. [ 13] DeHon, R. A. ( 1992) Earth, Moon, Planets, 56, 95- 122. [ 14] Wharton, R. A. et al. ( 1995) J. Paleolimn., 13, 267- 283. [ 15] Parker, T. J., and D. R. Currey ( in press) Extraterrestrial coastal geomorphology, Geomorphology. [ 16] Nedell, S. S., etal ( 1987) Icarus, 70,409- 441. [ 17] Williams, S. H., and J. R. Zimbelman ( 1994) Geology, 22,107- 110. [ 18] Parker, T. J. ( 1996) Lunar Planet. Sci. XXVII, 1003- 1004. [ 19] Parker, T. J. ( 1997) pp. 65- 66 in Conference on Early Mars, Lunar Planet. Inst., Houston, TX. [ 20] Edgett, K. S., and T. J. Parker ( 1997) pp. 27- 28 in Conference on Early Mars, Lunar Planet. Inst., Houston, TX. |