Comets probably didn't deliver life's ingredients to Earth — and that sharpens the search elsewhere

It is one of science's favourite stories: comets rained down the ingredients of life on the young Earth. New modelling from a University of Cambridge-led team, published in Scientific Reports, tests that story hard — and finds it wanting. Comets strike too fast and too steeply; fragile molecules such as hydrogen cyanide, a building block in prebiotic chemistry, would almost always vaporise on impact rather than pool where life's chemistry could begin. Intriguingly, the same physics makes Mars a slightly less unlikely recipient, thanks to its smaller size and thinner atmosphere. A negative result, but a useful one: when the next generation of telescopes, such as the proposed Habitable Worlds Observatory, hunts for life-friendly systems, it will know better where cometary delivery could actually work.