Secondary impact craters as absolute stratigraphic markers on the Moon and Mars

Summary

Impact cratering is ubiquitous across the Solar System. Due to their abundance, impact craters are key to understanding the evolution of planetary surfaces. This project will exploit the vast secondary crater population to investigate a range of features and processes on Mars and the Moon. This work will involve refining the method of primary and secondary crater identification in remote sensing data, before developing a modern workflow of their use as absolute stratigraphic markers. This novel approach will be applied to a range of key science questions on Mars and the Moon. The outcome of this project will be a new, widely applicable, and open method of deriving absolute surface ages.

Project Description

Stratigraphy is at the heart of understanding the evolution of all solid planetary bodies. Beyond the Earth, despite being arguably the most important factor, time is inherently difficult to determine. The limited number of samples available for detailed geochronological analysis in laboratories severely limits the locations in the Solar System for which we have absolute ages. Instead, planetary science is rooted in applying superposition theory (relative ages) and extrapolated impact crater chronologies (“crater counting”). The only way to derive an age of a planetary surface through remote sensing methods is through crater size-frequency distribution (CSFD) analysis, a powerful, widely applicable, and common technique across the entire Solar System [1], but one that has been inherently limited to studies of sufficiently large areas. 

Secondary impact craters (“secondaries”) are produced during the excavation stage of the cratering process, from material ejected from the primary crater [2]. A single impact can generate up to 10⁷ secondaries [3]. These secondary craters are often removed as problematic in studies of the age of planetary surfaces. This project will instead exploit the secondary crater population as absolute stratigraphic markers, to make new insights into a range of processes on Mars and the Moon.

This project will refine the method for identifying primary and secondary craters on planetary surfaces, before developing a modern application of secondary impact craters as absolute stratigraphic markers. Three main projects will help develop and apply this approach:

1.     Determine the rate of ice flow on Mars. Understanding the absolute age and thermal state of water ice is an important goal of Mars exploration. This project will identify and determine a formation age for a primary crater whose secondary craters have formed on ice-rich deposits. By measuring the deformation of these secondary craters, the rate at which the ice has flowed can be determined. This will provide the first confident estimate of the ice flow rate, which will allow for better modelling of the thermal state of the ice deposit, and also the relative abundance of ice and rock.

2.     Quantify secondary cratering at the Artemis III landing sites. Using secondary craters to indirectly date distant features was used successfully during the Apollo missions, to determine the ages of both the Copernicus and Tycho impact events. This project will use a similar theory refined for the possible future Artemis III landing sites in order to (1) identify potential source regions for material brought into the landing sites through impact ejecta processes, to better understand possible chemical mixing processes, and (2) where possible, provide absolute ages to geological units in the exploration areas.

3.     Refine numerical models linking primary and secondary craters. Identifying secondary craters, and their associated primaries, is not trivial. At relatively short distances from their primaries, secondaries often show distinctive elements of asymmetry (e.g. depth, crater rim height, ejecta distribution); however, at relatively large distances, these diagnostic features are usually not present. This project will refine methods of identifying secondary craters  [e.g. 4], and their associated primary craters, using machine-learning crater identification, GIS-based clustering methods, and numerical impact modelling using a shock physics code  [e.g. 5].

Suggested Skills and Background

This project will use techniques from different disciplines, providing the student with training in the use of remote sensing data for Mars and the Moon, GIS software (e.g. ArcGIS, ENVI, SocetSet), and numerical modelling and programming languages (e.g. iSALE, Python). The project would suit an enthusiastic individual with a background in geosciences in general, and geology and/or planetary science in particular.

The student will be registered at the University of Manchester.

For informal enquiries or further information, please contact Peter Grindrod (p.grindrod@nhm.ac.uk).

Application Process

Deadline: Sunday 4^th February 2024.

Please upload the following documents here

• Curriculum vitae
• Covering letter outlining your interest in the PhD project, relevant skills training, experience and qualifications, and a statement of how this PhD project fits your career development plans.
• Transcripts of undergraduate and Masters’ degree results.
• Two academic references including (if applicable) Masters’ project supervisor.

We strongly recommend contacting potential supervisors in advance, so that you can ask any questions, and also meet the supervisory team before you apply. This project is eligible for funding from the Science and Technology Facilities Council, who provide information for students: https://www.ukri.org/what-we-do/developing-people-and-skills/stfc/training/studentship-information-for-students/

This is a competitive application process. All applications will be reviewed by the project supervisory team and an academic panel. Shortlisted applicants will be invited for an interview, which usually lasts 30-60 minutes. As part of the process, shortlisted applicants will also be offered the opportunity to visit the NHM, to meet the wider research group, and tour relevant facilities. Shortlisted applicants will usually find out the outcome a few days after all interviews have been held.