DID LIFE COME FROM COMETS?
They race in and out of our Solar System, and according to evidence, they could have brought life with them
Reported by Colin Stuart
© Tobias Roetsch
Comet impacts formed glycine
Laboratory experiments suggest amino acids, such as glycine, may form on comets as they are struck by other flying space debris.
In the void between planets, huge snowballs tumble across the Solar System. These comets - relics from an age before large worlds circled the Sun - have been patrolling our local neighbourhood for 4.6 billion years. Hidden away in their icy layers are clues to what our Solar System was like all that time ago, along with teasers as to how our family of planets formed. But their real bounty could be knowledge of how one of the Solar System’s stand-out features came to pass: life. Could comets have played a role in delivering biology to Earth? Scientists are starting to think so.
Perhaps the single biggest factor in our planet’s suitability for life is the presence of water. Thanks to our temperate position around the Sun, water can exist largely in liquid form. Yet still fresh from the violent collisions that gave birth to it, the early Earth would have been too hot for any water molecules to escape evaporation. “The impact that formed the Moon would have gotten rid of any ocean or atmosphere too,” says Kathrin Altwegg from the University of Bern in Switzerland. The fact that we live on a wet planet today suggests that more water must have arrived some time later. Given that Earth is thought to have developed oceans within 500 million years, and life is thought to have popped up within 800 million years, it must have come fairly quickly and in abundance.
Naturally astronomers turned their attention to the objects in space known to have a high water content: comets. Often compared to ‘dirty snowballs’, these small objects were formed far from the Sun when gravity gathered up grains of dust and ice into objects several kilometres across. Many of these comets crashed into the planets and their moons in the Solar System’s youth.