02 Feb 2022
Research
6 minute read

The first atomic-resolution images of extraterrestrial molecules

Meteorites are fragments of asteroids (and, potentially, comets) that reach the Earth’s surface intact. They’re leftovers from the solar system’s formation, providing clues to its history in the molecules they contain. Thanks to our latest research, published today in Meteoritics and Planetary Science, we can now read those clues a little better.

Meteorites are fragments of asteroids (and, potentially, comets) that reach the Earth’s surface intact. They’re leftovers from the solar system’s formation, providing clues to its history in the molecules they contain. Thanks to our latest research, published today in Meteoritics and Planetary Science, we can now read those clues a little better.

Most primitive meteorites have remained practically unchanged since their formation billions of years ago. They’re like time machines that give us access to the remote past when the planets orbiting the sun first came to be. Part of the cargo that meteorites carry with them is organic matter, which could have been delivered to the early Earth, and might have played a role in the origins of life.

In our study,1 we used ultra-high resolution atomic force microscopy (AFM) to investigate meteoritic organic matter for the first time. We looked at samples of the famous Murchison meteorite, which fell in its namesake small Australian town in September, 1969. We took advantage of a unique strength of AFM — its single-molecule sensitivity — to visualize and identify individual molecules. Our findings, obtained by a multinational team of researchers, including our team at IBM Research in Zurich, provide a proof of concept that shows AFM can resolve and identify single molecules of meteoritic origin.

Molecules imaged from untreated Murchison sample.
Molecules imaged from untreated Murchison sample. On the left side: Scanning tunneling microscopy overview image of the surface on which the molecules are adsorbed. On the right side, individual molecules imaged with scale bars of 0.5 nm; in (d) – (h) AFM data (left) and high-pass filtered AFM data (right) is shown, reproduced from the MAPS publication.

The ability of AFM to identify a single molecule means that trace amounts of substances can be detected that might otherwise go unnoticed by other techniques. This strength becomes even more important when sample material is sparse, as in the case of meteorites, and even more so for material returned from space missions. While none of the molecules revealed now by AFM are new — in fact, they were all known to be present in the Murchison meteorite thanks to previous studies — resolving single molecules individually with AFM adds a new valuable tool for future analyses of extraterrestrial bodies.

Behind the first pictures of extraterrestrial molecules

Some 12 years ago, we advanced AFM to resolve single molecules with atomic resolution.2 By studying samples related to crude oil and soot, which contain a large diversity of molecules, we started taking advantage of the single-molecule sensitivity.

One of our hopes was to resolve individual molecules of extraterrestrial origin. We began looking for possible samples we could investigate, as well as collaborators with the expertise in meteoritic science who could help us obtain the right samples. We needed people who could help interpret our results and compare them with what’s known about the molecules in meteorites from other techniques. This led us to Scott Sandford and Aaron Burton from NASA, Henderson Cleaves from the Tokyo Institute of Technology and Gregoire Danger from Aix-Marseille Université. It was Scott who provided us with a sample of the Murchison meteorite.

We took advantage of a unique strength of AFM to visualize and identify individual molecules from the Murchison meteorite.

In our first experiments, we attempted to study molecules sublimed directly from unprocessed meteorite powder. This was challenging because meteorites contain a relatively small amount of organic material that we can resolve by AFM. Nevertheless, we still managed to resolve a few molecules, giving us confidence that we would indeed be able to image extraterrestrial organics by AFM.

Molecules imaged from the Murchison extract
Molecules imaged from the Murchison extract for each molecule AFM data (left), and high-pass filtered AFM data (right) is shown. Scale bars are 0.5 nm; reproduced from the MAPS publication.

Our longtime collaborators Diego Peña and Iago Pozo from the University of Santiago de Compostela devised a method to extract the kinds of molecules we thought could be well imaged with AFM.

The extractions were developed to target flat (planar) aromatic compounds, as well as some straight-chain hydrocarbon molecules. Using this optimized extraction process, we resolved many more molecules. Their structures were in agreement with the molecular structures determined using other techniques.

We also compared our results obtained by AFM with state-of-the-art mass spectrometry data, for which Julien Maillard from Normandie University and Carlos Afonso from Aix-Marseille Université joined the project. We had previously worked with Julien on a project where we looked at lab analogs of molecules from the atmosphere of Atomic force microscopy helped clear the haze surrounding Saturn’s moon, Titan. Read more.Saturn’s moon Titan.3 His mass spectrometry results indicated that the molecules we resolved with AFM are representative for the meteorite and the extracted fraction.

Individual resolved molecules
Individual molecules of the Murchison meteorite resolved by non-contact atomic force microscopy with a CO functionalized tip. Left: Individual resolved molecule (propylnaphthalene) of Murchison, untreated sample. Right: Individual resolved molecule (pyrene) of Murchison, extracted sample.

The next AFM frontier

Our study of the Murchison meteorite’s organic molecules showcases the capability of high-resolution AFM. It can be used to complement the well-established gold standards for molecular structure elucidation, NMR and mass spectrometry, in the isomer-specific identification of molecules from extraterrestrial samples.

So far, we haven’t resolved novel molecules in meteorites using AFM. However, due to its single-molecule sensitivity, AFM might in the near-future be used to reveal very rare molecules that haven’t yet been found in meteorite samples. There are also molecules that can only be resolved with the help of AFM where conventional techniques alone fall short.4

After this proof of concept, we hope to get larger samples of different meteorites to understand the effects of increasing water and heating on their parent asteroids, and potentially samples returned by missions to other objects in our solar system — including asteroids and even other planetary surfaces — to resolve single molecules and advance our knowledge about the molecules they carry. We are thrilled to contribute to a better understanding of the story these molecules can tell us, which could ultimately help paint a clearer picture of the very origin of our solar system and life on Earth.

Notes

  1. Note 1Atomic force microscopy helped clear the haze surrounding Saturn’s moon, Titan. Read more. ↩︎

References

  1. K. Kaiser, F. Schulz, J. F. Maillard, F. Hermann, I. Pozo, D. Peña, H. J. Cleaves, A. S. Burton, G. Danger, C. Afonso, S. Sandford, L. Gross. Visualization and identification of single meteoritic organic molecules by atomic force microscopy. Meteoritics and Planetary Science. (2022).
  2. L. Gross, F. Mohn, N. Moll, P. Liljeroth, G. Meyer. The Chemical Structure of a Molecule Resolved by Atomic Force Microscopy. Science. 325, 1110–1114 (2009).
  3. F. Schulz, J. Maillard, K. Kaiser, I. Schmitz-Afonso, T. Gautier, C. Afonso, N. Carrasco, L. Gross. Imaging Titan’s Organic Haze at Atomic Scale. Astrophys. J. Lett. 908, L13 (2021).
  4. K. O. Hanssen, B. Schuler, A. Williams, T. B. Demissie, E. Hansen, J. H. Andersen, J. Svenson, K. Blinov, M. Repisky, F. Mohn, G. Meyer, J.-S. Svendsen, R. Ruud, M. Elyashberg, L. Gross, M. Jaspars, J. Isaksson. A Combined Atomic Force Microscopy and Computational Approach for the Structural Elucidation of Breitfussin A and B: Highly Modified Halogenated Dipeptides from Thuiaria breitfussi. Angew. Chem. Int. Ed. 51, 12238–12241 (2012).