Detections of PAHs within the Jezero Crater on Mars
Organic molecules play a central role in understanding the past habitability of Mars. These are compounds built primarily from carbon that serve as the foundation of life on Earth. Previous missions have hinted at their presence, but their origins and the mechanisms by which they survive on the harsh Martian surface remain unclear.
Now, a new study led by Teresa Fornaro reports the strongest evidence yet for polycyclic aromatic hydrocarbons (PAHs) detected on Mars. PAHs are carbon-based organic molecules composed of many interconnected benzene (C6H6) rings. On Earth, they can arise during many processes ranging from volcanic emissions to byproducts of incomplete combustion of biological material. Their detection on Mars was made possible by NASA’s Perseverance rover, during its exploration of the Jezero crater. This ancient lake and river delta system is currently considered one of the most promising sites to find traces of biological life.
The key observations came from the on-board 'Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals' (SHERLOC) instrument, a deep-ultraviolet fluorescence and ‘Raman’ spectrometer mounted to Perseverance’s robotic arm. Raman spectroscopy works by shining a deep ultra-violet (~248.6 nm) laser pulse directly onto a rock sample and subsequently collecting any back-scattered light. While most photons will undergo typical Rayleigh scattering, a select few instead undergo Raman scattering, wherein the incident photon gains or loses some energy, corresponding to a transition within the molecule’s vibrational modes. This energy shift in certain photons can be measured, and the molecular composition is then inferred based on the lines visible in the spectrum.
In this case, SHERLOC recorded signals in the ranges 1,300–1,500 cm⁻¹ and 1,600–1,700 cm⁻¹, regions strongly associated with aromatic organic compounds. Crucially, these features were found in rocks containing sulphates.
To verify these findings, the team compared SHERLOC data with laboratory experiments. They prepared mixtures of sulfates with candidate organic compounds and studied them using Earth-based spectrometers designed to replicate SHERLOC’s performance. These analogues revealed that sulfates can indeed host PAHs, subtly shifting their spectral features while protecting them from degradation. Computational models of vibrational spectra further confirmed that the features observed in these surface samples likely originate from PAHs.
On Earth, it has been well documented that certain salts are able to preserve the structure of organic molecules. Furthermore, it has long been suspected that sulphates may play a similar role on Mars. Previous tentative detections of organic compounds have historically been accompanied by sulphates, and this time is no different. This reinforces the idea that sulphates may help protect more fragile organics, by shielding them from ultraviolet radiation and chemical breakdown on the Martian surface.
If confirmed, the presence of PAHs bound to sulfates provides evidence of a stable carbon reservoir on Mars. This reservoir may have shaped the Martian carbon cycle, influencing both chemical and potentially biological processes. However, distinguishing between abiotic and biotic origins requires analyses beyond Perseverance’s onboard capabilities.
The rover has already cached relevant rock cores for eventual retrieval through the NASA–ESA Mars Sample Return campaign. Laboratory studies on Earth, with their higher sensitivity and broader range of techniques, will be able to confirm the presence of PAHs as well as provide more insight into their origins.
--
Journal Source: T. Fornaro et al., Evidence for polycyclic aromatic hydrocarbons detected in sulfates at Jezero crater by the Perseverance rover, Nature Astronomy, (2025), DOI: https://doi.org/10.1038/s41550-025-02638-z
Cover Image Credit: NASA/Perseverance