Rosetta became the first spacecraft to orbit a space iceball when it reached Comet 67P/Churyumov- Gerasimenko in 2014. This year we learned even more about the ancient object and, in turn, the solar system.
“Comets have been stored far from the sun in a deep freeze,” says Rosetta principal investigator Alan Stern of the Southwest Research Institute. “They represent samples of the original material out of which planets were formed.”
Rosetta’s been telling the comet’s secrets ever since its May 2014 arrival, starting with its rubber duckshaped body, 4.1 miles long with a head 1.6 miles wide. Fluffy dust up to 16 feet thick coats the comet’s surface and acts like sunscreen, protecting the vulnerable ice from the sun’s heat. This has kept 67P together despite its millions of close encounters with the sun, around which it orbits every 6.6 years.
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.
During its brief but productive life, Philae detected 16 organic molecules, confirming the orbiter’s findings and showing that the chemicals of life can form and survive in space. The lander also found the comet has no magnetic field, meaning magnetism doesn’t affect how the early solar system’s building blocks came together, contrary to several models.
Just after Philae’s momentary resurrection, 67P roared to life. On July 29, the comet released a huge jet of gas and dust moving at 22 mph. On Aug. 13, the comet reached perihelion — its closest approach to the sun — and released two bathtubs’ worth of water every second. Engineers moved Rosetta farther away from the comet to protect it from the deluge and dust.
Since its close encounter, 67P has been spewing less and cooling off, getting ready to return to its cosmic freezer, with Rosetta in tow. The probe will continue to watch the show until its mission ends in September 2016, when scientists will likely send it to rest onon the comet’s surface.