building blocks of comets
June 24, 2014

Raw Materials For The Formation Of Titan May Have Been Locked In Ices That Condensed Before Saturn Began Forming

Brett Smith for - Your Universe Online

A joint research effort between NASA and the European Space Agency has found proof that nitrogen within the atmosphere of Saturn's moon Titan came from conditions very similar to those that formed most of the ancient comets in the Oort cloud, according to a new report in the Astrophysical Journal Letters.

The Oort cloud is a spherical cloud of predominantly icy space rocks believed to surround the Sun at a radius far outside the Solar System.

The team said their conclusion eliminates the possibility that Titan's foundations were produced in the warm disk of material believed to have surrounded a still-forming Saturn. The paper also suggested Titan's foundations established early in the solar system's history, in the cold disk of gas and dust that created the Sun. This was also the origin of many comets, which retain their ancient composition to this day.

The new study indicates that information on Titan's formation is still contained in the icy moon's atmosphere, allowing scientists to test various ideas on how the moon might have developed. The team focused on an explicit chemical sign – the ratio of one isotope, nitrogen-14, to a different isotope, nitrogen-15. The researchers said the ratio ought to be the same today as when this moon was established, up to 4.6 billion years ago.

"When we looked closely at how this ratio could evolve with time, we found that it was impossible for it to change significantly,” said study author Kathleen Mandt of Southwest Research Institute in San Antonio. “Titan's atmosphere contains so much nitrogen that no process can significantly modify this tracer even given more than four billion years of solar system history.”

This lack of significant change means scientists can compare Titan to other objects in the Solar System, like Earth, in search of a connection. The study team said their work supports the growing view that ammonia ice from comets is probably not the principal source of Earth's nitrogen. In the past, scientists suspected an association between comets, Titan and Earth, and supposed the nitrogen isotope ratio in Titan's original atmosphere was identical to the ratio found on Earth today. Data on the nitrogen isotope ratio at Titan by quite a number instruments from the NASA and ESA Cassini-Huygens mission revealed this is not true – meaning this ratio is distinct between Titan and Earth – while measurements of the ratio in comets have shown a connection to Titan. This indicates distinct sources of nitrogen for Earth and Titan.

Prior research has shown that Earth’s own nitrogen ration has not changed much since the planet’s formation.

"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.

Ongoing research surrounding the comet 67P/ Churyumov-Gerasimenko should reveal more information surrounding the origins of our solar system. If the new study is correct, the comet should have a lower ratio of hydrogen isotopes in methane ice than the ratio on Titan because 67P/ Churyumov-Gerasimenko is a comet from the much closer Kuiper Belt.

Image 2 (below): New research on the nitrogen in Titan's atmosphere indicates that the moon's raw materials might have been locked up in ices that condensed before Saturn began its formation. Credit: NASA/JPL-Caltech/Space Science Institute


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