Mars Obliquity History Constrained by Elliptic Crater Orientations

Samuel J. Holo (University of Chicago), Edwin S. Kite (University of Chicago), Stuart J. Robbins (Southwest Research Institute)

(Submitted on 17 Apr 2019)

The dynamics of Mars’ obliquity are believed to be chaotic, and the historical ~3.5 Gyr (late-Hesperian onward) obliquity probability density function (PDF) is high uncertain and cannot be inferred from direct simulation alone. Obliquity is also a strong control on post-Noachian Martian climate, enhancing the potential for equatorial ice/snow melting and runoff at high obliquities (> 40°) and enhancing the potential for desiccation of deep aquifers at low obliquities (< 25°). We developed a new technique using the orientations of elliptical craters to constrain the true late-Hesperian-onward obliquity PDF. To do so, we developed a forward model of the effect of obliquity on elliptic crater orientations using ensembles of simulated Mars impactors and ~3.5 Gyr-long Mars obliquity simulations. In our model, the inclinations and speeds of Mars crossing objects bias the preferred orientation of elliptic craters which are formed by low-angle impacts. Comparison of our simulation predictions with a validated database of elliptic crater orientations allowed us to invert for best-fitting obliquity history. We found that since the onset of the late-Hesperian, Mars' mean obliquity was likely low, between ~10° and ~30°, and the fraction of time spent at high obliquities > 40° was likely < 20%.

Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Geophysics (physics.geo-ph)

Journal reference: Earth and Planetary Science Letters, v. 496, p. 206-214 (2018)

DOI: 10.1016/j.epsl.2018.05.046

Cite as: arXiv:1904.08446 [astro-ph.EP] (or arXiv:1904.08446v1 [astro-ph.EP] for this version)

Submission history

From: Samuel Holo 

[v1] Wed, 17 Apr 2019 18:31:55 UTC (1,688 KB)

https://arxiv.org/abs/1904.08446