NASA’s Curiosity rover has unearthed the largest organic molecules ever detected on Mars—possible fragments of fatty acids—hinting at the tantalizing possibility that prebiotic chemistry on the Red Planet may have been more advanced than previously thought.

While the presence of these molecules is not proof of ancient life on Mars, scientists say it shows we could detect chemical signatures of past life, if it ever existed.

The molecules may be remnants of fatty acids, which form cell membranes in Earth’s organisms, though they might have formed through a non-biological process