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Mars Research in Polar Bear Country
Hans Amundsen
Hans Amundsen is a Norwegian geologist and the expedition leader of AMASE (Arctic Mars Analog Svalbard Expedition).

How Deep is the Gene Pool?
Anthony Poole
Anthony Poole, a molecular biologist at Stockholm University in Sweden discusses early life.

Earth’s Oldest Oils
Tomas Hode
Thomas Hode, cofounder of SWAN speaks about his research in astrobiology.

Radio Astrobiology
Axel Brandenburg
Host Simon Mitton interviews Axel Brandenburg, an astrobiologist at the Nordita research facility at Stockholm, Sweden.

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Swedish Astrobiology Network

Earth’s Oldest Oils

Interview with Tomas Hode

Astrobiology in Sweden commenced in 2000, when the Swedish National Space Board sponsored one of the first astrobiology meetings in the Nordic countries. That conference was a success, and it led to the formation of the SWedish Astrobiology Network, SWAN. A co-founder of SWAN, Tomas Hode, is now a geologist at Portland State University in Portland, Oregon. He was the first person in Sweden to be awarded a doctorate in astrobiology, for research carried out at the Swedish Museum of Natural History, Stockholm. He spoke to Simon Mitton about his research in astrobiology.

What sparked your interest in astrobiology?

Well, I’ve always been interested in the interface between geology, biology, and chemistry, so originally I wanted to become a carbonate sedimentologist. That interest evolved into petroleum geology. I studied in Norway for a year, and I was about to start a PhD project in petroleum geology when I found out about astrobiology and the NASA Astrobiology Institute.  This was back in 1999. I wrote to NASA and said that I was a great guy, and asked if they wanted to collaborate – to my surprise I actually got an answer, and that’s how it all started.

Sweden has the largest impact structure in Western Europe, the Siljan ring, which was 65 km in diameter when formed 370 million years ago. As a geologist you investigated the formation history of this structure, and you had a particular interest in its hydrothermal system – the hot water associated with the enormous energy released by the impact. How do your findings contribute to astrobiology?

Siljan impact crater

Siljan impact crater. Several lakes trace the remnants of the eroded impact crater that was formed by a meteorite impact about 370 million years ago. With a diameter of 65 km Siljan Impact Structure is the largest impact structure in Western Europe.

Image: NASA WorldWide Landsat 7

The principal idea of studying the Siljan impact structures was to investigate the temperature regimes of the impact-induced hydrothermal system, and to see if any hydrothermal minerals formed under temperature conditions that were favorable for life. Once we found the right minerals  -- in this case hydrothermal calcite veins -- we started looking for fossil evidence of hyperthermophilic life, that is to say, life that could flourish in very hot water. It was a bit tricky, but we finally confirmed that there were traces of fossilized extracellular polymeric substances (EPS), which is a slime that is often secreted by microbes and that holds microbial mats together.

Dr Tomas Hode

" large meteorite impact structures could be favorable places to look for traces of life on Mars."

But does finding EPS count as the detection of life as such?

Well, sort of. Finding fossilized EPS is not the same thing as finding actual fossilized cells, but it is a sign of life, or biosignature, that has recently gained attention in the scientific literature.

The overall purpose of the study was to confirm that large meteorite impact structures could be favorable places to look for traces of life on Mars. Impact structures are easy to identify on Mars, and we now know that the hydrothermal systems associated with these impacts are able to preserve traces of life. These findings should primarily be of interest for future sample return missions.

What are the implications for the possibility of life on Mars?

If life ever started on Mars, the main implications are related to the chances of finding traces of life, and not so much to the possibility of life emerging in the first place. Assuming that a biosphere existed at some point in the Martian history, impact structures should be promising targets to look at, particularly in the ancient southern terrain.


" large meteorite impact structures could be favorable places to look for traces of life on Mars."

Finally, what are your current interests in astrobiology?

My current interests mainly relate to the development of new micro-analytical techniques. One of the most exciting projects involves analysis of organic biomarkers in natural oils. My PhD student, Sandra Siljeström, at the SP Technical Research Institute of Sweden, is currently developing the method, which is based on an extremely sensitive instrument with the technical name 'time-of-flight secondary ion mass spectrometry’.

We are really pushing the detection limits of biomarker analysis in natural samples! We hope that the method will enable us to analyze some of the oldest oils on Earth. The oldest oils on the planet are exclusively found in fluid inclusions, and are therefore very difficult to accurately analyze with traditional methods. We hope this will provide new insights into the earliest life on Earth