Notes and references

1. Laplace, P. S. (1809) The System of the World (trans. J. Pond), Richard Phillips, Book 1, p. 69.

2. The standard reference remains Mercury (eds. F. Vilas etal., 1988), University of Arizona Press. Detailed descriptions of the planet may be found in the report on the Mariner 10 mission given in The Planet Mercury: Mariner 10mission. JGR 80, 2341-514 (1975) and in the proceedings of conferences on Mercury given in Icarus 28, 429-609 (1976); PEPI15, 113-314 (1977) and The Mercury 2001 Workshop in MPS 37, 1165-283 (2002). See also Planet. Space Sci. 45, 1-167 (1997) for information mainly on the magnetic field of Mercury. A special issue of Planet. Space Sci. 49, 1395-632 (2001) provides some valuable summaries of the understanding of Mercury prior to the Messenger (NASA) and the projected Bepi Colombo (ESA) missions as well as details of the missions and spacecraft. A detailed summary of the scientific rationale for the Messenger mission is given by Solomon, S. C. et al. (2001) The Messenger mission to Mercury: scientific objectives and implementation. Planet. Space Sci. 49, 1445-65. See also Balogh, A. and Giampieri, G. (2002) Mercury: The planet and its orbit. Rep. Prog. Phys. 65, 529-60 and Taylor, G. J. and Scott, E. R. D. (2004) Mercury, in Treatise on Geochemistry (eds. H. D. Holland and K. K. Turekian), Elsevier, vol. 1, pp. 477-85. A more popular account is Strom, R. G. and Sprague, A. L. (2004) Exploring Mercury: The Iron Planet, Springer Proxis Books. The photographic coverage of the planet from the Mariner 10 mission was restricted to about 45%. Reliable image resolution over this area is about 1-2 km, comparable to Earth-based telescopic views of the Moon. About 25% of the surface was imaged at Sun angles that were low enough to enable terrain analysis. Avery small number of high-resolution (100 m) views are available.

3. The planet was apparently captured into a 3/2 resonance as the most favored outcome of an orbital history that has included high eccentricities in the past. Correla, A. C. M. and Laskar, J. (2004) Mercury's capture into a 3/2 spin-orbit resonance as a result of its chaotic dynamics. Nature 429, 848-50. Variations in the orbit of Mercury have often suggested that another planet, Vulcan, might lurk sunward of Mercury. This notion was prompted by the successful discovery of Neptune in the nineteenth century due to its effects on the orbit of Uranus. This led to a long search for Vulcan. Nothing was found and eventually the problems of the motion of Mercury were resolved by Einstein's general theory of relativity, rather than by the classical approach using Newtonian gravitational astronomy. Baum, R. and Sheehan, W. (1997) In Search of Planet Vulcan: The Ghost in Newton's Clockwork Universe, Plenum. For a detailed discussion, see Balogh, A. and Giampieri, G. (2002) Mercury: The planet and its orbit. Rep. Prog. Phys. 65, 529-60.

4. Comets are a debatable source on account of their high impact velocities so close to the Sun. Paige, R. (1992) The thermal stability of water ice at the poles of Mercury. Science 258, 643-6. This observation seems to be more securely based than the debatable presence of ice on the Moon but may only be recording trapped solar wind hydrogen.

Feldman, W. C. et al. (2001) Evidence for water ice near the lunar poles. JGR 106, 23,231-52, but see Campbell, B. A. et al. (2003) Radar mapping of the lunar poles.

Nature 426, 137-8.

5. Spohn, T. et al. (2001) The interior structure of Mercury. Planet. Space Sci. 49, 1561-70.

6. Hauck, S. A. et al. (2004) Internal and tectonic evolution of Mercury. EPSL 222, 71328. The identification of iron, rather than nickel, ruthenium, platinum or even lead as the dominant core-forming element in this and other planets is because, as a consequence of nucleosynthesis, iron is by far the most abundant metallic element. It is for similar reasons that magnesium-iron rather than titanium or barium silicates dominate the rocky mantles of the terrestrial planets.

7. Schubert, G. (1988) Mercury's thermal history and the generation of its magnetic field, in Mercury (eds. F. Vilas et al.), University of Arizona Press, pp. 429-60. See also the review in Planet. Space Sci. 45, 1-167 (1997).

8. Older conjectures about the origin of the magnetism have been supplanted by evidence that the outer core is indeed partially molten, so allowing for dynamo models to generate the field. Margot, J. L. et al. (2007) Large longitude libration of Mercury reveals a molten core. Science 316, 710-14. One explanation for the weakness of the field is that the dynamo is deep. Christensen, U. R. (2006) A deep dynamo generating Mercury's magnetic field. Nature 444, 1056-8.

9. See Lodders, K. and Fegley, B. (1998) The Planetary Scientists Companion, Oxford University Press, Table 4.4, p. 106.

10. e.g. Lewis, J. S. (1972) Metal-silicate fractionation in the Solar System. EPSL 15, 286-90; (1988) Origin and composition of Mercury, in Mercury (eds. F. Vilas et al.), University of Arizona Press, pp. 651-69.

11. Fegley, B. and Cameron, A. G. W. (1987) A vaporization model for iron/silicate fractionation in the Mercury protoplanet. EPSL 82, 207-22.

12. Benz, W. et al. (1988) Collisional stripping of Mercury's mantle. Icarus 74, 516-28.

13. Taylor, S. R. et al. (2006) The Moon: A Taylor perspective. GCA 70, 5904-18.

14. Planetary Th values are in general more readily established than the more mobile and analytically more challenging U, as experience on Mars shows. Boynton, W. V. et al. (2004) The Mars Odyssey gamma-ray spectrometer instrument suite. Space Sci. Rev. 110, 37-83.

15. Neukum, G. et al. (2001) Geologic evolution and cratering history of Mercury. Planet. Space Sci. 49, 1507-21.

16. Strom, R. G. and Neukum, G. (1988) The cratering record on Mercury and the origin of the impacting objects in Mercury (eds. F. Vilas et al.), University of Arizona Press, pp. 336-73; Neukum, G. et al. (2001) Geologic evolution and cratering history of Mercury. Planet. Space Sci. 49, 1507-21.

17. Chapman, C. R. and McKinnon, W. B. (1986) Cratering on planetary satellites, in Satellites (eds. J. A. Burns and M. S. Matthews), University of Arizona Press, pp. 492580. The craters are similar in general morphology to those on the Moon. All the features of a surface dominated by impacts such as ejecta blankets, terraces, central peaks and peak rings and secondary crater fields are present. Differences due to gravity, possible target strength, average impact velocity, and the source of the impacting objects lead to minor variations.

18. Trask, N. J. and Guest, J. E. (1975) Preliminary geologic terrain map of Mercury. JGR 80, 2461 -77. The oldest impact basin superimposed on the intercrater plains is Dostoevskij, followed by Tolstoj and Beethoven, that is about 625 km in diameter and so comparable in size to Mare Serenitatis on the Moon.

19. Although Caloris is often regarded as the largest basin on Mercury, the Borealis Basin in the north polar region is 1500 km in diameter, while other giants may lurk on the unseen side. McCauley, J. F. (1979) Orientale and Caloris. PEPI 15, 220-50.

20. Hughes, G. H. et al. (1977) Global seismic effects of basin-forming impacts. PEPI15, 251-63; Wieczorek, M. A. and Zuber, M. T. (2001) A Serenitatis origin for the Imbrian grooves and South Pole-Aitken thorium anomaly. JGR 106, 27,853-64; Spudis, P. D. and Guest, J. E. (1988) Stratigraphy and geologic history of Mercury, in Mercury (eds. F. Vilas et al.), University of Arizona Press, p. 139.

21. Neukum, G. et al. (2001) Geologic evolution and cratering history of Mercury. Planet. Space Sci. 49, 1507-21.

22. Strom, R. G. et al. (2005) The origin of planetary impactors in the inner Solar System. Science 309, 1847-50.

23. Strom, R. G. and Neukum, G. (1988) The cratering record on Mercury and the origin of the impacting objects, in Mercury (eds. F. Vilasetal.), University of Arizona Press, pp. 336-73.

24. Milkovich, S. M. et al. (2002) Identification of mercurian volcanism: Resolution effects and implications for Messenger. MPS 37, 1209-22.

25. Spudis, P. D. and Guest, J. E. (1988) Stratigraphy and geologic history of Mercury, in Mercury (eds. F. Vilas et al.), University of Arizona Press, pp. 118-64.

26. Wilhelms, D. E. (1976) Mercurian volcanism questioned. Icarus, 28, 551-8.

27. Neukum, G. et al. (2001) Geologic evolution and cratering history of Mercury. Planet. Space Sci. 49, 1507-21; and see Ref. 26 above.

28. Hapke, B. et al. (1976) Photometric observations of Mercury from Mariner 10. JGR 80, 2431-43.

29. Robinson, M. S. and Lucey, P. G. (1997) Recalibrated Mariner 10 color mosaics: Implications for mercurian volcanism. Science 275, 197-200.

30. Sprague, A. L. et al. (1994) Mercury: Evidence for anorthosite and basalt from mid-infrared (7.3-13.5 ^m) spectroscopy. Icarus 109, 156-67.

31. Wilhelms, D. E. (1976) Mercurian volcanism questioned. Icarus 28, 556.

32. Strom, R. G. (1977) Origin and relative age of lunar and Mercurian intercrater plains. PEPI 15, 156-72.

33. Milkovich, S. M. etal. (2002) Identification of mercurian volcanism: Resolution effects and implications for Messenger. MPS 37, 1209-22.

34. Watters, T. R. et al. (2001) Large-scale lobate scarps in the southern hemisphere of Mercury. Planet. Space Sci. 49, 1523-30.

35. Melosh, H. J. and McKinnon, W. B. (1988) The tectonics of Mercury, in Mercury (eds. F. Vilas et al.), University of Arizona Press, pp. 374-400.

36. Watters, T. R. et al. (1998) Topography of lobate scarps on Mercury: New constraints of the planet's contraction. Geology 26, 991-4.

37. Dzurisin, D. (1978) The tectonic and volcanic history of Mercury as inferred from studies of scarps, ridges, troughs, and other lineaments. JGR 83, 4902.

38. Nimmo, F. (2002) Constraining the crustal thickness of Mercury from viscous topographic relaxation. GRL 29, doi: 10.1029/2001Gl013883; Nimmo, F. and Watters, T. R. (2004) Depth of faulting on Mercury: Implications for heat flux and crustal and effective elastic thickness. GRL 31, doi: 10.1029/2003GL018847.

39. Scott, R. F. (1977) Review of "Lunar Soil Science" (I. I. Cherkasov and V. V. Shvarev). Earth Sci. Rev. 13, 379.

40. Vilas, F. (1988) Surface composition of Mercury from reflectance spectrophotometry in Mercury (eds. F. Vilas et al.), University of Arizona Press, pp. 59-76.

41. Sprague, A. L. and Roush, T. L. (1998) Comparison of laboratory emission spectra with Mercury telescopic data. Icarus 133, 174-83; Sprague, A. L. et al. (1994) Mercury:

Evidence for anorthosite and basalt from mid-infrared (7.3-13.5 p.m) spectroscopy. Icarus 109, 156-67; Sprague, A. L. et al. (1997) Mercury's feldspar connection: Mid-IR measurements suggest plagioclase. Adv. Space Res. 19, 1507-10; Sprague, A. L. et al. (2000) Mid-infrared (8.1-12.5 ^m) imaging of Mercury. Icarus 147, 421-32.

42. Mitchell, D. L. and De Pater, I. (1994) Microwave imaging of Mercury's thermal emission at wavelengths from 0.3 to 20.5 cm. Icarus 110,2-32. Jeanloz. R. et al. (1995) Evidence for a basalt-free surface on Mercury and implications for internal heat. Science 268, 1455-7.

43. Blewett, D. T. et al. (2002) Lunar pure anorthosite as a spectral analog for Mercury. MPS 37, 1255-68. The reflectance spectra are best matched by a "3:1 labradorite (An60) to enstatite regolith" with about 1% FeO and no TiO2 and "the abundances of both these oxides must be near zero for Mercury". Warell, J. and Blewett, D. T. (2004) Properties of the Hermean regolith: V. New optical reflectance spectra, comparison with lunar anorthosites, and mineralogical modeling. Icarus 168, 257-76.

44. Jeanloz, R. et al. (1995) Evidence for a basalt-free surface on Mercury and implications for internal heat. Science 268, 1456. It is sometimes suggested that the angrite class of differentiated basaltic meteorites might be derived from Mercury. e.g. Irving, A. J. et al. (2005) Unique angrite NWA 2999: The case for samples from Mercury. AGU Fall Meeting, San Francisco, CA, December 5-9, 2005, Abst. P51A-0898. Angrites have ages close to Tzero but are basic-ultrabasic rocks with FeO contents around 10-20% (e.g. Mittlefehldt, D. et al. (1998) in Planetary Materials (ed. J. J. Papike), Reviews of Mineralogy and Geochemistry 36, Table 40, p. 4-138), making it exceedingly unlikely that they are derived from the low-FeO mercurian surface.

45. Hapke, B. (1993) Theory of Reflectance and Emittance Spectroscopy, Cambridge University Press; Hapke, B. (2001) Space weathering from Mercury to the asteroid belt. JGR 106, 10,039-73. However the magnetic field of Mercury, although weak, may shield the surface.

46. Sprague, A. L. et al. (1997) Distribution and abundance of sodium in Mercury's atmosphere, 1985-1988. Icarus 129, 506-27; Killen, R. M. et al. (2005) The calcium exosphere of Mercury. Icarus 173, 300-11.

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