The formation of terrains antipodal to major impacts

Watts, Alison; Greeley, R.; Melosh, H. J.

doi:10.1016/0019-1035(91)90170-x

Cited by 43 publications

(28 citation statements)

References 8 publications

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“…As the antipodes of these impact basins are expected to undergo kilometer-scale surface displacements with accelerations approaching that of the Moon's surface gravity [Hughes et al, 1977;Watts et al, 1991], some form of surface modification is to be expected. We acknowledge that the focusing of seismic energy may help to subdue the surface topography of features antipodal to a basin.…”

Section: Seismic Modification At the Antipodes Of Impact Basinsmentioning

confidence: 99%

A Serenitatis origin for the Imbrian grooves and South Pole‐Aitken thorium anomaly

Wieczorek¹,

Zuber²

2001

J. Geophys. Res.

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Abstract. The northwest comer of the Moon's South Pole-Aitken (SPA) basin contains a high abundance of thorium and a unique Imbrian aged geomorphologic unit that consists of"grooves and mounds" (referred to here as the Imbrian grooves). Because the location of these features are almost antipodal to the Imbrium basin, where high-thorium ejecta and seismic energy are expected to have converged, an Imbrium origin for these units has long seemed certain. By modeling the deposition of impact ejecta on the Moon, we have investigated whether the convergence of Imbrium's ejecta at its antipode could be the origin of both the Imbrian grooves and SPA thorium anomaly. As a result of the Moon's rotation, our results show that ejecta from this basin should converge more than 12 ø west of its antipode. Both the Imbrian grooves and thorium anomaly within SPA, however, reside slightly to the east of Imbrium's antipode. In an attempt to reconcile this disparity, the effects of a putative oblique Imbrium impact have been qualitatively investigated. While this model can distribute ejecta in the general vicinity of the Imbrian grooves, the planform of our modeled antipodal ejecta is distinctly different from that which is observed. As an alternative explanation for the origin of these features, we find that the modeled distribution of ejecta from an oblique Serenitatis impact is surprisingly similar to the planform of the Imbrian grooves, with the exception that it is offset directly to the east. This eastward offset is likely to be an artifact of our not being able to properly include the effects of the Moon's rotation in our oblique impact models. We conclude that the Imbrium grooves and SPA thorium anomaly are most consistent with having an origin from the convergence of ejecta antipodal to the Serenitatis basin. If this conclusion can be substantiated once quantitative ejecta scaling relations for oblique impacts are determined, then this implies that (1) the Serenitatis target contained a high abundance of thorium and (2) the convergence of seismic energy at the antipodes of either the Imbrium or Serenitatis basin was not sufficient to cause substantial surface modification. Extrapolating this result to Mercury suggests that the "hilly and lineated" terrain antipodal to the Caloris basin was formed by the convergence of ejecta, and not seismic waves.

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Section: Seismic Modification At the Antipodes Of Impact Basinsmentioning

confidence: 99%

A Serenitatis origin for the Imbrian grooves and South Pole‐Aitken thorium anomaly

Wieczorek¹,

Zuber²

2001

J. Geophys. Res.

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“…There is also indirect geological evidence for the ocean: Voyager and Galileo mission image analyses demonstrated that Callisto is the most densely cratered object in the Solar System, with no volcanic or tectonic landforms, and with a crust age dating back as far as 4 Gyr. The antipodal zone of the greatest impact crater, Valhalla, is indistinguishable from the rest of the surface, whereas in similar-sized bodies such as Mercury or the Moon impacts of comparable magnitude always create important tectonic deformations and hummocky terrains in the surface crust of the crater antipode, suggesting that the subsurface ocean absorbed the impact energy and then dissipated the seismic waves (Watts et al 1991;Williams et al 2001). Possibly, the ocean is generated by the decay of radioactive elements, is some 20 km thick, and stays hidden 100 km below the surface, comprised between two great ice layers (two solid convecting regions, Khurana et al 1998) that preclude heat circulation.…”

Section: Subsurface Oceans In Ganymede and Callistomentioning

confidence: 99%

Extraterrestrial hydrogeology

et al. 2005

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Subsurface water processes are common for planetary bodies in the solar system and are highly probable for exoplanets (planets outside the solar system). For many solar system objects, the subsurface water exists as ice. For Earth and Mars, subsurface saturated zones have occurred throughout their planetary histories. Earth is mostly clement with the recharge of most groundwater reservoirs from ample precipitation during transient iceand hot-house conditions, as recorded through the geologic and fossilized records. On the other hand, Mars is mostly in an ice-house stage, which is interrupted by endogenic-driven activity. This activity catastrophically drives short-lived hydrological cycling and associated climatic perturbations. Regional aquifers in the Martian highlands that developed during past, more Earth-like conditions delivered water to the northern plains. Water was also cycled to the South Polar Region during changes in climate induced by endogenic activity and/or by changes in Mars' orbital parameters. Venus very likely had a warm hydrosphere for hundreds of millions of years, before the development of its current extremely hot atmosphere and surface. Subsequently, Venus lost its hydrosphere as solar luminosity increased and a run-away moist greenhouse took effect. Subsurface oceans of water or ammonia-water composition, induced by tidal forces and radiogenic heating, probably occur on the larger satellites Europa, Ganymede, Callisto, Titan, and Triton. Tidal forces operating between some of the small bodies of the outer solar system could also promote the fusion of ice and the stability of inner liquid-water oceans.RØsumØ Les processus de subsurface impliquant l'eau sont communs pour les corps planØtaires du syst me solaire et sont tr s probables sur les exoplan tes (plan tes en dehors du syst me solaire). Pour plusieurs objets du syst mes solaire, l'eau de subsurface est prØsente sous forme de glace. Pour la Terre et Mars, les zones saturØes de subsurface apparaissent à travers toute leur histoire planØtaire. La Terre est particuli rement clØmente avec la recharge des rØservoirs, avec de amples prØcipitations, des conditions glaciaires et de fortes chaleurs, comme l'atteste les enregistrements gØologiques et palØontologiques. D'un autre côtØ, Mars se trouve dans une phase essentiellement glaciaire, qui est interrompue par des activitØs contraintes par les phØnom nes endogØniques. Cette activitØ conduit de mani re catastrophique à des cycles hydrologiques et à des perturbations climatiques brutaux. Les aquif res rØgionaux dans les haute terres martiennes qui se sont formØs dans des conditions similaires aux conditions terrestres, alimentent les plaines du Nord. Resumen Los procesos hídricos subsuperficiales son comunes en cuerpos planetarios del sistema solar y son altamente probables para exoplanetas (planetas fuera del sistema solar). Para muchos cuerpos del sistema solar, el agua subsuperficial existe como hielo. Para la Tierra y Marte han ocurrido zonas saturadas subsuperficiales a travØ...

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“…Furthermore, it is common to encounter uncertainties up to orders of magnitude with scaling laws in impact cratering studies. The uncertainty remains high in part because the equation applies to the transient cavity, which is difficult to assess for actual craters observed on planetary surfaces (Watts et al, 1991). Due to the depth of burial H for impact, studies on the Meteor Crater, Arizona, estimated the value varying from less than the diameter to 4-5 times of the diameter of the projectile (Melosh, 1989).…”

Section: Basin-forming Impactmentioning

confidence: 99%

“…Previous studies have addressed the formation of disrupted terrains antipodal to major impacts in general (Watts et al, 1991) and to the Caloris impact on Mercury in particular (Schultz and Gault, 1975;Hughes et al, 1977;Watts et al, 1991). Our study utilizes 1-D internal structure models of Mercury to investigate the relevance of Mercury's internal state, with emphasis on the core, and the antipodal seismic response to the Caloris impact.…”

Section: Comparison With Previous Studiesmentioning

confidence: 99%

“…The most uncertain aspect of the investigation is the characterization of the impact source. Previous studies basically treated the seismic wave as a single saw-toothed wave (Schultz and Gault, 1975) and assumed that a fraction of the projectile's kinetic energy was imparted to radiated seismic waves (Schultz and Gault, 1975;Hughes et al, 1977;Watts et al, 1991;Williams and Greeley, 1994). The actual form of the seismic waves is typically a series of complex oscillatory ground motions resulting from wave dispersion.…”

Section: Comparison With Previous Studiesmentioning

confidence: 99%

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