There is a speed limit for detecting biosignatures in space

Mass spectrometers hurtling through space in search of life may need to stick to a speed limit, according to research presented at the American Geophysical Union (AGU) Fall Meeting 2022.

NASA’s Cassini spacecraft flew through a plume of ice erupting from subsurface oceans on Saturn’s moon Enceladus. With the spacecraft traveling at 7–17 km/s, molecules within the plume ionized on impact. This impact-induced ionization made it possible for a mass spectrometer aboard Cassini to detect chemical clues about the molecular makeup of the icy moon’s seas. “The problem is, when it comes to biosignatures, that may be a little too fast,” Morgan Cable, a research scientist at the NASA Jet Propulsion Laboratory, said in a presentation on Dec. 14. Previous research has suggested that much like a butterfly hitting the windshield of a truck, delicate compounds may fragment beyond recognition in high-speed collisions with spacecraft, she said.

To investigate, Cable and her colleagues used a combination of Earth-bound mass spectrometry measurements and computational simulations to see how impact speed affects molecular fragmentation of small biomolecules such as amino acids. The researchers found that at speeds below 3 km/s, the molecules bounce off the mass spec’s detector without ionizing. At speeds above about 6 km/s, the amino acids break apart. For researchers designing fly-by missions to search for signs of life on Enceladus and other ocean worlds, “you really want to keep it to about 3–6 km/s,” Cable said.