Organic matter on Mars was formed from atmospheric formaldehyde | Science & Technology

Organic matter refers to the remains of living things such as plants and animals, or the byproduct of certain chemical reactions. Whatever the case, the stable carbon isotope ratio (¹³C/¹²C) found in organic matter provides valuable clues about how these building blocks of life were originally formed, giving scientists a window into the past. As such, it has become a point of interest for Mars expeditions. For example, the Mars rover Curiosity (operated by NASA) revealed that organic matter found in sediments from that era on Mars are unusually depleted in ¹³C. It was also discovered that the carbon isotope ratios varied significantly between samples. However, the reason for this variability was a mystery.

To expand on these findings, a research group led by Shungo Koyama, Tatsuya Yoshida, and Naoki Terada from Tohoku University developed a Martian atmospheric evolution model. The model focused on formaldehyde (H₂CO), which members of this research team previously determined could feasibly be produced in the ancient Martian atmosphere. The reason for this choice is that formaldehyde can generate complex organic compounds such as sugars, which are essential for life. In other words, formaldehyde may be the missing factor that could explain the anomalous values of the Curiosity rover samples. It could also be a sign of past life.

This model combined a photochemical model with a climate model to estimate the changes in the carbon isotope ratio of formaldehyde on Mars, dating back 3 to 4 billion years. It revealed that the depletion of ¹³C in formaldehyde is due to the photodissociation of CO₂ by…