The raw materials that form Titan, Saturn’s largest moon, might have been locked up in ice that condensed before Saturn began its formation, according to a new study.
Scientists from NASA and the European Space Agency have studied the nitrogen in Titan’s atmosphere and found strong evidence it originated in the cold disk of gas and dust that formed the Sun. This is also the origin of the building blocks of most of the ancient comets in the Oort cloud – a spherical cloud of frozen objects that surrounds the Sun at the very edge of our solar system. The discovery rules out the theory that Titan’s building blocks formed within the warm disk of material that surrounded Saturn as it formed, according to the team, which was led by Kathleen Mandt of Southwest Research Institute in Texas, US.
The research is published in Astrophysical Journal Letters, and could also shed light on how the Earth formed. Nitrogen is the main component in both the atmospheres of Titan and Earth, and Titan is often compared to an early version of Earth locked in a deep freeze. The study looked at the ratio of one isotope, or form, of nitrogen, called nitrogen-14, to isotope nitrogen-15.
The team found that this ratio wouldn’t have had time to change since Titan first formed – even if it was as old as the solar system itself – and so they could compare it to the ratio of other solar system objects to try to work out the origin of Titan’s building blocks. What they found was that the building blocks of comets and Saturn’s largest moon appeared to form under similar conditions in the disk of gas and dust that produced the Sun. They also found that, contrary to popular theories, the atmospheric nitrogen isotope ratio on Titan is different to that of Earth today. This means that the sources of Earth’s and Titan’s nitrogen must have been different, and supports the emerging view that ammonia ice from comets isn’t likely to be the primary source of Earth’s nitrogen.
“Some have suggested that meteorites brought nitrogen to Earth, or that nitrogen was captured directly from the disk of gas that formed the sun. This is an interesting puzzle for future investigations,” Mandt said in a NASA press release. Via Titan’s building blocks might be older than Saturn