Astrobiology Revealed #2: Maryse Napoleoni
Maryse Napoleoni chases biosignatures in ejecta from icy moons
By Aubrey Zerkle
This week we had the pleasure of interviewing Maryse Napoleoni, a 3rd year PhD student in the Planetary Sciences and Remote Sensing group at Freie Universität Berlin. For her recent paper, “Mass Spectrometric Fingerprints of Organic Compounds in NaCl-Rich Ice Grains from Europa and Enceladus”, Maryse used special instruments on Earth to simulate what similar devices on space missions might see in plume material from icy moons. In this Q&A, Maryse describes the challenges of experimental astrobiology and how her data could someday help find life beneath their frozen shells. (This interview has been edited for length and clarity)
How did you first become interested in icy moons?
I am originally from Grenoble in the French Alps, where I studied Geosciences for my Bachelor. I chose this field since I have had a passion for the mountains since I was a kid. This region is such a cool playground for geology and I spent most of my free time there while growing up!
I first got interested in Astrobiology in a geomicrobiology class. I was fascinated to learn about the interactions of microbial life and geology, and how the evolution of Earth has been interconnected with the evolution of terrestrial life for billions of years, ranging from the minerals formed as a direct result of biological processes to global changes in Earth’s atmosphere and climate.
Thinking of Earth as a planet among billions of others brought me to study planetary sciences in a Master program in Paris. Icy moons are such a fascinating topic to study, mostly thanks to their huge diversity and their potential to maybe host alien life. Besides, many space missions (such as JUICE or Europa Clipper) are going to explore [icy moons] in the near future, making it a super exciting topic. And I’m sure we will discover many more in the future while looking at exoplanets: the icy moons that we know in the solar system are just a tiny tip of the iceberg!
What questions were you trying to answer with this particular project?
On icy moons, ice grains can be ejected from the surface ice by micrometeorite bombardment or from the subsurface ocean by plumes, as seen on Enceladus. With this paper, we wanted to characterize the detectability of organic material embedded in such ice grains. This organic material could originate from the subsurface ocean and could contain traces of lifeforms, potentially in the form of organic biomolecules.
Mass spectrometers such as the Surface Dust Analyzer (SUDA) onboard NASA’s Europa Clipper mission can give the chemical composition of these ice grains and could detect organic material inside. However, we know that there are lots of salts and other inorganic compounds on icy moons, and this might complicate the detection of organics with these instruments: the salts could “hide” or modify the signal of the organics in the [resulting] mass spectra. In this project, we focused on these modifications to characterize how organics interact with salts.
Could you describe the approach you used to fingerprint the organic-salt mixtures?
We performed lab experiments where we simulated the mass spectra of spectrometers like SUDA, to create analogue data for these instruments. The technique we use in the lab is called Laser Induced Liquid Beam Ion Desorption (LILBID), and it allows us to simulate many different types of ice grain compositions. To do so, we chose a range of organic species from different chemical families (containing oxygen, nitrogen, aromatics, carboxylic acids, etc.) and mixed those with a salt, sodium chloride (NaCl). We then recorded analogue mass spectra of these mixtures with a time-of-flight mass spectrometer, to obtain spectra very similar to what SUDA would record from an ice grain with that composition.
Artist's rendering of NASA's Europa Clipper spacecraft. From NASA/JPL-Caltech.
What was the most challenging aspect of the project?
Many measurements were needed. It was quite a long measurement campaign in the lab! Besides, interpreting the data was also sometimes challenging, because one has to think of the realistic interactions of organic molecules with the salt matrix in the experiments.
What would you say was the most important or most surprising result from your data?
The main result of this paper is a large amount of analogue mass spectra which can later be used to interpret the data from space missions. We now have a growing database of data for the detection of organics on ice grains from icy moons. It will maybe allow a discovery of organic material on icy moons in the future! This work will be particularly useful for Europa Clipper in a couple of years [when we have similar data to interpret from that mission].
How will your data help in the search for life on icy moons?
The discovery of more organic material on icy moons is only one step away! And by characterizing this organic material, we could discover that its origin is biogenic.
Our results are also valuable for the preparation of space missions. For example, we can evaluate which instrumental parameters are most useful, such as using the cation or anion mode of the mass spectrometer [on the mission probes]. Moreover, some ice compositions will be particularly efficient for the detection of organic material, and this information could be used to target specific areas on an icy moon during a space mission.
What are the next steps in this project, in terms of detecting these organics?
We are continuing this project with more experiments with different types of salts and inorganics typical from Europa’s surface. Such experiments are focused on [interpreting data from] the SUDA instrument onboard Europa Clipper.
Another follow up on this research is to evaluate the effects of ionizing radiation on organic material at the surface of Europa. We know that Europa, because it is so close to Jupiter, receives a huge amount of harsh radiation on its surface, and this will affect the organic material by provoking many reactions, potentially changing its composition. These effects could modify organic biosignatures, so it would be harder to detect them in material which has been exposed for a long time to the radiation. We aim to characterize these modifications with more lab experiments.
Is there anything else you’d like to mention that I haven't asked about?
In a different project we are also characterizing the fingerprints of microbial life with our experimental setup. It is also interesting to consider biosignatures that we know here on Earth. If there were [actual] micro-organisms in the oceans of icy moons, how could we detect them? If they were ejected from a subsurface ocean by a plume, they could then be sampled by a spacecraft doing flybys through the plume… and mass spectrometers onboard could potentially identify them.
To simulate ice grains containing biosignatures [and actual microbes] from a subsurface ocean, we measured analogue spectra of biosignature molecules such as amino acids, peptides and fatty acids, and then also measured bacterial material. In that paper we characterized the mass spectral characteristics of cells from two different bacterial species. We provided analogue spectra for ice grains containing bacteria originating from an icy moon’s subsurface ocean, and showed that instruments like SUDA would be able to detect bacterial cells even at very low concentrations.