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The title of the thesis: On water vapor observations and modeling on planet Mars

Thesis defender: Jouni Polkko
Opponent: Prof. Stephen Lewis, Open University, UK
Custos: Prof. Esa Kallio, Aalto University School of Electrical Engineering

On water vapor observations and modeling on planet Mars

Jouni Polkko’s dissertation examined how water vapour behaves in the lowest layers of the Martian atmosphere and what this reveals about the planet’s climate and potential habitability. The study focuses particularly on Jezero Crater, where NASA’s Mars 2020 Perseverance rover is investigating conditions in an ancient crater basin and collect samples for later recovery to Earth. The thesis also assessed how well low-power miniature capacitive polymer sensors – used in the rover’s MEDA‑HS humidity instrument – are suited to measuring atmospheric humidity in the cold and extremely dry conditions on Mars. The work lies in the fields of planetary science and space technology.
Humidity measurements from Perseverance’s instruments were combined with a simplified atmospheric model, which was used to track the amount and vertical distribution of water vapour during roughly the first thousand Martian days of the rover’s operations.

On the basis of the results, these compact humidity sensors are capable of producing scientifically useful observations of the lowest, near-surface layer of the Martian atmosphere. The measurements reveal that over the course of a day, water vapour moves back and forth between the atmosphere and the surface material, the regolith: at night moisture is taken up by the porous surface soil, and during the day it is released back into the air. The observed seasonal variability matches well with satellite measurements obtained from the same region at the same time, which strengthens confidence in both the modelling approach and the instruments.

The water-vapour observations and the modelling fitted to them show that the present surface temperatures and water availability in the surface material at Jezero Crater are too low to sustain Earth‑like, metabolically active microbial life. In the past, however, Mars has most likely been considerably wetter and warmer and closer to being habitable.

The thesis also estimated the amount of water vapour in the headspace of the sample tubes containing rock cores collected by Perseverance, helping to understand how the sample collection may be preserved or altered before a possible return to Earth. The measurement and modelling methods developed in the study can be applied in future research projects that investigate Mars’s climate and environmental conditions and search for signs of possible early life.

Key words: Mars, humidity, water, water vapor, planetary boundary layer, Perseverance, Jezero

Thesis available for public display 7 days prior to the defence at .

Contact: 
jouni.polkko@aalto.fi
050-5266661