What makes comets special?

Churyumov Gerasimenko 67P Comet

Comets are like time capsules, preserving the molecules from the beginning of our solar system’s formation, filling in the information gap between star stuff and planets, and possibly the origins of life. Most comets used to orbit at the frigid outer reaches of the solar system where they formed from the cloud that swirled around the infant Sun.

Far from the radiation and heat of the Sun, their chemistry has changed little from the beginning of the solar system. Occasionally, one drifts in toward the Sun, pulled by gravity, and passes through the inner solar system where we can see it in our night sky. This gives us the opportunity to send spacecraft like CAESAR to study these planetary fossils up close.

Previous missions have confirmed that comets contain large amounts of ice, as well as ammonia, simple organic compounds like methane, and even more complex ones like tholins and the amino acid glycine. So comets impacting the newly formed Earth may have seeded the surface with water and key building blocks of life. Indeed, life as we know it may not have been possible without the help of comets.