But as it approaches the sun, the comet does release into space some dust and gas, which form its tails. Astronomers were surprised to see molecular oxygen, the kind humans breathe, blasting from the comet. The comet also released about 24 times as much water as oxygen, as well as a great deal of carbon monoxide and carbon dioxide. The liberated dust contains many organic molecules, showing that comets may have seeded our planet with the chemistry that life needs to thrive. The probe further revealed the comet is less than half as dense as water and three-quarters empty space.
Scientists had also long suspected that comets’ crashing into Earth had given our planet its water stores, but Rosetta found otherwise. The water on Comet 67P has more neutrons than earthly water, suggesting different origins.
To get a closer look, in November 2014 Rosetta deployed its lander, Philae. Instead of landing smoothly on the surface, the solar-fueled lander bounced and rolled away, coming to rest in the shade where it soon lost power. While scientists did revive Philae in June 2015 and confirmed that all its instruments had a pulse, they couldn’t get those instruments to actually do anything. It went silent a week later.