[meteorite-list] Titan's Building Blocks Might Pre-date Saturn

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 24 Jun 2014 10:47:48 -0700 (PDT)
Message-ID: <201406241747.s5OHlm98011136_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.php?release=2014-200

Titan's Building Blocks Might Pre-date Saturn
Jet Propulsion Laboratory
June 23, 2014

A combined NASA and European Space Agency (ESA)-funded study has found
firm evidence that nitrogen in the atmosphere of Saturn's moon Titan
originated in conditions similar to the cold birthplace of the most
ancient comets from the Oort cloud. The finding rules out the
possibility that Titan's building blocks formed within the warm disk of
material thought to have surrounded the infant planet Saturn during its
formation.

The main implication of this new research is that Titan's building
blocks formed early in the solar system's history, in the cold disk of
gas and dust that formed the sun. This was also the birthplace of many
comets, which retain a primitive, or largely unchanged, composition today.

The research, led by Kathleen Mandt of Southwest Research Institute in
San Antonio, and including an international team of researchers, was
published this week in the Astrophysical Journal Letters.

Nitrogen is the main ingredient in the atmosphere of Earth, as well as
on Titan. The planet-sized moon of Saturn is frequently compared to an
early version of Earth, locked in a deep freeze.

The paper suggests that information about Titan's original building
blocks is still present in the icy moon's atmosphere, allowing
researchers to test different ideas about how the moon might have
formed. Mandt and colleagues demonstrate that a particular chemical hint
as to the origin of Titan's nitrogen should be essentially the same
today as when this moon formed, up to 4.6 billion years ago. That hint
is the ratio of one isotope, or form, of nitrogen, called nitrogen-14,
to another isotope, called nitrogen-15.

The team finds that our solar system is not old enough for this nitrogen
isotope ratio to have changed significantly. This is contrary to what
scientists commonly have assumed.

"When we looked closely at how this ratio could evolve with time, we
found that it was impossible for it to change significantly. 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," Mandt said.

The small amount of change in this isotope ratio over long time periods
makes it possible for researchers to compare Titan's original building
blocks to other solar system objects in search of connections between them.

As planetary scientists investigate the mystery of how the solar system
formed, isotope ratios are one of the most valuable types of clues they
are able to collect. In planetary atmospheres and surface materials, the
specific amount of one form of an element, like nitrogen, relative to
another form of that same element can be a powerful diagnostic tool
because it is closely tied to the conditions under which materials form.

The study also has implications for Earth. It supports the emerging view
that ammonia ice from comets is not likely to be the primary source of
Earth's nitrogen. In the past, researchers assumed a connection between
comets, Titan and Earth, and supposed the nitrogen isotope ratio in
Titan's original atmosphere was the same as that ratio is on Earth
today. Measurements of the nitrogen isotope ratio at Titan by several
instruments of the NASA and ESA Cassini-Huygens mission showed that this
is not the case -- meaning this ratio is different on Titan and Earth --
while measurements of the ratio in comets have borne out their
connection to Titan. This means the sources of Earth's and Titan's
nitrogen must have been different.

Other researchers previously had shown that Earth's nitrogen isotope
ratio likely has not changed significantly since our planet formed.

"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.

Mandt and colleagues are eager to see whether their findings are
supported by data from ESA's Rosetta mission, when it studies comet 67P/
Churyumov-Gerasimenko beginning later this year. If their analysis is
correct, the comet should have a lower ratio of two isotopes -- in this
case of hydrogen in methane ice -- than the ratio on Titan. In essence,
they believe this chemical ratio on Titan is more similar to Oort cloud
comets than comets born in the Kuiper Belt, which begins near the orbit
of Neptune (67P/ Churyumov-Gerasimenko is a Kuiper Belt comet).

"This exciting result is a key example of Cassini science informing our
knowledge of the history of solar system and how the Earth formed," said
Scott Edgington, Cassini deputy project scientist at NASA's Jet
Propulsion Laboratory, Pasadena, California.

The Cassini-Huygens mission is a cooperative project of NASA, ESA and
the Italian Space Agency. JPL, a division of the California Institute of
Technology, Pasadena, manages the mission for NASA's Science Mission
Directorate in Washington.

Rosetta is an ESA mission with contributions from its member states and
NASA. JPL manages the U.S. contribution of the Rosetta mission for
NASA's Science Mission Directorate in Washington.

More information about Cassini is available at the following sites:

http://www.nasa.gov/cassini

http://saturn.jpl.nasa.gov

Preston Dyches/Whitney Clavin
NASA's Jet Propulsion Laboratory, Pasadena, Calif.
818-354-7013/818-354-4673
preston.dyches at jpl.nasa.gov/whitney.clavin at jpl.nasa.gov

2014-200
Received on Tue 24 Jun 2014 01:47:48 PM PDT