Popular Science: Investigations into traces of life on Mars
Jan Jehlička of the Institute of Geochemistry, Mineralogy and Mineral Resources at the Faculty of Science (Charles University in Prague) and his colleague Howell Edwards of the University of Bradford are the co-editors and authors of a number of articles published in Philosophical Transactions of Royal Society A, one of the world's most prestigious science journals. Established in 1655, Philosophical Transactions of Royal Society is the world's oldest science journal, with a track record of publications by a large number of big names, including, centuries ago, Isaac Newton.
The latest monothematic issue of PTRS explores the possibilities of using Raman spectroscopy, a spectroscopic method applied in analytical chemistry, in exobiological research. The Raman spectrometer is a hot candidate and part of a set of devices supposed to be used by future mobile labs in exploring the Red Planet, including on a rover that is being prepared to travel to Mars in 2018 under the ExoMars project. This exobiological mission is a joint project between the European Space Agency (ESA) and the Russian-based Roskosmos, and the NASA has similar plans, too.
A number of important questions have to be answered prior to commencing these enormously expensive missions. The question how to discover traces of life in some of the selected bodies of the Solar System (besides Mars, the objects of researchers' interest include Jupiter's moon Europa and Saturn's moons Titan and Enceladus) can be divided into several sub-questions, and the aforesaid monothematic issue of Philosophical Transactions of Royal Society A aims to answer some of them.
It is both necessary and advisable to conduct a number of studies and research sub-projects in Earth conditions, in locations where selected organisms prove to be strong enough to resist to adverse chemical and physical impacts and survive. Various groups perform major research projects in extreme conditions, and organisms that are able to survive such conditions include halophiles, acidophilic organisms, psychrophiles and organisms resistant to strong exposure to ultraviolet radiation. Sites offering such conditions include, for example, the McMurdo Dry Valleys in Antarctica and the Atacama Desert in Chile. "Extremophiles have been living on Earth for billions of years, and familiarising ourselves with their survival and adaptation strategies will help us understand how similar organisms could survive in extreme extraterrestrial conditions that used to exist on Mars", explains Mr. Jehlička.
The investigations into life on remote planets involve various technical, technological, research, field, laboratory and theoretical aspects, and the planned mission would be useless without pre-identifying substances that can be used as traces of organic life (biomarkers). Substances that in Raman spectres show specific signals need to be differentiated from the omnipresent "noise", as well as from signals of other organic compounds, including abiogenic ones. This matter is covered by the introductory article of the said PTRS issue ("Biomarkers and their Raman spectroscopic signatures: a spectral challenge for analytical astrobiology").
Some of the other articles aim to identify the most important arguments for using Raman spectrometry for this area and highlight the key benefits of this method, e.g. "Raman spectroscopy on Mars: Identification of geological and bio-geological signatures on Martian analogues using miniaturised Raman spectrometers" written by a team led by Ian Hutchinson, and also an article exploring the limits of the method concerned, "The potential and limits of Raman spectroscopy for carotenoid detection in microorganisms: implications for astrobiology" , by Jan Jehlička et al.
In searching for suitable candidates for distinct signatures of life, scientists explore organisms (bacteria) living in extreme conditions on Earth, such as halophiles described by microbiologist Aharon Oren in an article titled "Halophillic archaea on Earth and in space: growth and survival under extreme conditions".
As the rover and the devices to be carried by it will not return to Earth, the miniaturised Raman spectrometer has to be able to analyse samples in situ. Some of the articles describe tests of miniature devices designed to test key biomarkers in such conditions – on Earth for the time being (e.g. a study by teams led by Adam Culka and Petr Vítek of our Faculty of Science). The objective of these efforts is to ascertain whether miniaturised Raman devices will be able to detect these biomolecules in rock materials coming from brine evaporation tanks in Eilat and/or the Atacama and Mojave deserts.
Last but not least, it is necessary to spectroscopically characterise the selected molecules, make a list of them and create an atlas of interpreted spectra that is going to be used for correct identification of measurement results to be sent by the mobile Raman spectrometer. The substances to be explored include, for example, pigments that support bacterial photosynthesis and protect bacteria from high UV radiation (for example, scytonemin is the subject matter of a study conducted by Tereza Varnali and Howell Edwards).