General Meeting: Alunite in Cross Crater, Mars: Evidence for a Possible Site of Ancient Life

Open to members and non-members alike, the Monthly General Meetings feature club announcements, member observing reports, and a headline guest speaker. Speakers typically hail from one of Colorado’s many science or technical organizations and share their experiences on a wide range of astronomy topics.

Location: In-person at Regis University’s Peter Claver Hall, Room 328. 

Meeting attendees can arrive at Regis starting at 6:30 p.m.
* Park in Lot 4, Lowell Boulevard, between 52nd and 53rd Avenue

• New Member and Guest Introductions
• Announcements
• Presentation by Dr. Ranalli & Dr. Swayze
• Observing Reports

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Presentation Abstract:

Cross Crater is a 65 km impact crater located in the Noachian highlands of the Terra Sirenum region of Mars. Geochemical modeling indicates that alunite detected on the southwest wall of Cross Crater could have been formed by a fumarole upwelling into Cross Crater Lake and could indicate that an environment favorable to the development of life may have existed there billions of years ago. Alunite did not form when Noachian precipitation reacted with basalt, nor when the sediments and groundwater resulting from this reaction reacted with a fumarole. Only when Cross Crater Lake water was equilibrated with sulfuric acid, thought to be a significant component of the atmosphere in the Hesperian, following reaction with fumarole groundwater, did alunite precipitate from solution. Kaolinite, silica, or an Al-smectite such as montmorillonite, detected by Tetracorder mapping of CRISM data of the southwest wall of Cross Crater, also formed.

The proximity of Cross Crater to the Tharsis volcanic region relative to Columbus Crater may have resulted in larger amounts of magmatic water input to the lake from sources along fractures that extend westward from Tharsus. This could explain the more extensive deposit of alunite at Cross Crater relative to Columbus Crater.

Our Speakers:

Tony Ranalli received his Ph.D. in Geochemistry from the Colorado School of Mines in 2005. He has worked as a geochemist for the U.S. Geological Survey from 1985 to 2015. Eight of those years were spent in collaboration with U.S. EPA Region 8, working with various tribes to assist them in developing their water quality programs, and the last few years at the USGS consisted of geochemical modeling of different aspects of uranium geochemistry. This is his first attempt at Martian geochemistry.

Gregg Swayze received his Ph.D. in Geology from the University of Colorado at Boulder in 1997. He has worked as a research geophysicist for the U.S. Geological Survey from 1985 to 2022, specializing in imaging spectroscopy of mine waste, naturally occurring asbestos, Mars surface mineralogy, hydrothermal alteration, rare earth minerals, and disaster sites. He was a Scientific Collaborator with the NASA Mars Reconnaissance Orbiter CRISM team and a Co-I of the NASA EMIT imaging spectrometer team.

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