Three‐dimensional simulations of the southern polar giant impact hypothesis for the origin of the Martian dichotomy

Abstract

We demonstrate via numerical simulations that the impact of a~lunar-sized body with Mars is capable of creating a hemispherical magma ocean that upon cooling and solidification resulted in the formation of the southern highlands and thus the Martian dichotomy. The giant impact may have contributed a significant amount of iron to the Martian core and generated a deep thermal anomaly that led to the onset and development of the volcanism in the southern highlands. Our model predicts several mantle plumes converging to the South Pole from the equatorial regions as well as new plumes forming in the equatorial region and also an absence of significant large-scale volcanism in the northern lowlands. The core heat flux evolution obtained from our numerical models is consistent with the decline of the magnetic field. We argue that such a scenario is more consistent with a range of observations than a northern giant impact (excavating the Borealis basin) for the formation of the Martian dichotomy.

Mangala Valles, Mars: A reassessment of formation processes based on a new geomorphological and stratigraphic analysis of the geological units

“…The observational evidence shows that the Asp3 lava flows were channelized into Mangala Fossa through Daedalia Planum, so it is difficult that the volcanism of Arsia Mons might have been prolonged until the Amazonian (Leone, 2016). The self-consistent hypothesis of formation for the Martian dichotomy and the consequent onset of volcanism (Leone et al, 2014), validated by the discovery of twelve volcanic alignments (Leone, 2016), suggests that the volcanic activity of Arsia Mons and Sirenum Mons, from which the units Asp2 and Asp3 within Mangala Valles derived, peaked in the Pre-Noachian (4.5-4.1), declined in the Noachian (4.1-3.9 Ga), and completely ended in the Hesperian (3.5 Ga ago at the latest). Keske et al (2015) estimated a volcanism of Amazonian ages through crater counts but they did not make any correlation to the thermal history of Mars to see if there is any consistency.…”

“…Lastly, this work will discuss the formation of Mangala Valles in the context of the overall volcanic history of Mars, which is now enriched of new important information (Leone et al, 2014;Leone, 2016). This work will provide a better understanding of the formation of single features at regional scale, focusing particularly on the nature of Mangala Fossa (e.g.…”

Hemispheric Dichotomy in Lithosphere Thickness on Mars Caused by Differences in Crustal Structure and Composition

“…The origin of this surface dichotomy remains debated and various formation mechanisms have been proposed such as a heterogeneous fractionation of an early magma ocean (Solomon et al, 2005), a mantle overturn (Elkins-Tanton et al, 2005), a degree 1 mantle convection pattern (Roberts & Zhong, 2006;Yoshida & Kageyama, 2006), or an impact origin either in the north (Andrews-Hanna et al, 2008;Marinova et al, 2008) or in the south (Golabek et al, 2011;Leone et al, 2014;Reese et al, 2010). In any case, the dichotomy formation would probably date back to the early stages of Mars evolution, between 4.5 and 4 Gyr (Bottke & Andrews-Hanna, 2017;Brasser & Mojzsis, 2017;Frey, 2008;Nimmo & Tanaka, 2005;Nyquist et al, 2001).…”

The Absence of an Ocean and the Fate of Water all Over the Martian History

“…These estimates about past water might even be too optimistic because the current low atmospheric pressure may have already been present since the early ages of Mars due to the erosion by primordial impacts (Melosh & Vickery, 1989). This hypothesis includes the giant impact that formed the Martian dichotomy, regardless whether occurring in the Northern (i.e., Wilhelms & Squyres, 1984) or in the Southern Hemisphere (i.e., Leone et al, 2014). Several studies of isotopic hydrogen showed how Mars lost much of its water already in its first 500 Ma (Gillmann et al, 2011; Krasnopolsky, 2015; Kurokawa et al, 2014; Villanueva et al, 2015).…”

“…The giant impact event that formed the Martian dichotomy must have removed much of the primordial atmosphere and part of the water that survived after the accretion (Leone et al, 2014). The remaining water was then lost to space (Gillmann et al, 2011; Krasnopolsky, 2015; Kurokawa et al, 2014; Villanueva et al, 2015) through degassing from a still wet mantle (Balta & McSween, 2013; Leone, 2017).…”