Aliens used to be considered merely science fiction, found in books and movies but never considered part of everyday life. However, signs of unidentified flying objects (UFOs) have become commonplace in the news stream as of late, with congressional hearings in the United States to discuss numerous unexplained sightings of craft flying at tremendous speeds, particularly around nuclear weapons sites. Scientists have always wished to understand whether we are alone in the universe, and with so much unexplained activity, this question has now brought extraterrestrial research to the lab.

What would extraterrestrial life need to look like (biochemically)?

To think of life beyond Earth, it’s worth exploring the biophysical nature of living organisms on our own planet. In a review by Dr Shunsuke Tagami from the RIKEN Center for Biosystems Dynamics Research in Kanagawa, Japan, he explains that the nature of biomolecules, and what makes them so adaptable, is the ability of polymers to fold around hydrophobic cores and adopt various structures. He expands by noting that rigidity is needed in the main chains of the polymers, such that the structures formed from our macromolecules would avoid being merely random. Of course, the molecules that fulfill these criteria are proteins, and any newly discovered alien polymers would also be proteins or something very similar in biomolecular structure.¹

Dr Tagami concludes his article by noting that while many assume that any newly identified alien life should be advanced in its evolutionary scale, many might be much simpler, with bodies composed of “non-ideal” molecules that may have preceded complex systems like our own and which may have been found during the more primordial time on Earth, billions of years ago.¹

Can life grow in outer space?

Though no one has ever shown the existence of alien microorganisms, it doesn’t hurt to ask whether their existence in space would be possible. One group, led by Dr Charles Cockell of the University of Edinburgh, asked if such life could ever incorporate the carbon found in extraterrestrial sources by examining the integration of isotope-labeled carbon obtained from meteoritic material into bacteria. Using the carbonaceous chondrite Aguas Zarcas as the sole source of energy and nutrients, they showed via spectroscopy that the radiolabeled carbon was efficiently incorporated into the proteins of the cultured bacteria. They also found that multiple kinds of bacteria could grow in such a culture, from pseudomonas to enterobacteria and micrococcales.²

The search for life on Mars and beyond

Planetary exploration, though currently limited due to existing space travel technology, may one day have the ability to find evidence of existing or extinct alien microorganisms. Through analysis of the near-Earth carbonaceous asteroid (162173) Ryugu, an asteroid of which samples were collected during the Japanese mission Hayabusa2, researchers have found minor signs already, as scientists from a number of different institutes across Japan have characterized small traces of uracil, one of the bases of ribonucleic acid. Other compounds were found as well, including niacin (a B₃ vitamin), alkylamines, acetic acid, and polycyclic aromatic carbons, indicating that while life has yet to be established extraterrestrially, molecules preceding life can still be found produced on asteroids and potentially other planets.^3,4

To aid in the search for alien species, several groups are currently looking into different methods of developing biomarkers for life detection. Among them, one group led by scientists at the Universidad de Alcalá in Spain performed a bioinformatics search for well-conserved ancient peptides and developed antibodies to detect them via fluorescence microarray immunoassays. They also showed that these peptides have the potential to be detected in space using Earthbound minerals and rocks with similar composition to those found on Mars.⁵ Similarly, a group led by scientists from Spain, USA, and Canada developed the Signs of Life Detector-Life Detector Chip (SOLID-LDChip), an antibody microarray-based sensor that was recently tested in a Mars drilling simulation campaign, located in the Atacama Desert. The SOLID-LDChip identified markers from proteobacteria, acidobacteria, bacteroidetes, actinobacteria, firmicutes, and cyanobacteria at a depth of 40-50 cm below the Earth.⁶

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References:

1. Tagami S. Why we are made of proteins and nucleic acids: Structural biology views on extraterrestrial life. Biophys Physicobiol. 2023;20(2):e200026.
2. Waajen AC, et al. Life on Earth can grow on extraterrestrial organic carbon. Sci Rep. 2024;14(1):3691.
3. Oba Y, et al. Uracil in the carbonaceous asteroid (162173) Ryugu. Nat Commun. 2023;14(1):1292.
4. Oba Y, et al. Ryugu astroid sample return provides a natural laboratory for primordial chemical evolution. Nat Commun. 2023;14(1):3107.
5. Mustieles-Del-Ser P, et al. Immunoanalytical Detection of Conserved Peptides: Refining the Universe of Biomarker Targets in Planetary Exploration. Anal Chem. 2024;96(12):4764-4773.
6. Moreno-Paz M, et al. Life Detection and Microbial Biomarker Profiling with Signs of Life Detector-Life Detector Chip During a Mars Drilling Simulation Campaign in the Hyperarid Core of the Atacama Desert. Astrobiology. 2023;23(12):1259-1283.