Learn about how our understanding of comets has transformed since Rosetta began its journey more than 10 years ago. The NASA mission Deep Impact helped develop our knowledge of cometary compositions and density. The mission Stardust brought back comet dust from the coma of Wild 2, and within one of these grains, an amino acid was found. Amino acids are the building blocks of proteins, essential to life. Rosetta and Philae hope to find more of these amino acids within the comet and in doing so add weight to the theory that comets helped deliver these essential ingredients to Earth billions of years ago.