Titan’s Atmosphere May be Older than Saturn, a New Study Suggests

by Shannon Hall on June 24, 2014

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Titan's atmosphere makes Saturn's largest moon look like a fuzzy orange ball in this natural-color view from the Cassini spacecraft. Cassini captured this image in 2012. Image Credit:  NASA/JPL-Caltech/Space Science Institute

Titan’s atmosphere makes Saturn’s largest moon look like a fuzzy orange ball. Image Credit: NASA / JPL-Caltech / Space Science Institute

It’s well accepted that moons form after planets. In fact, only a few months ago, astronomers spotted a new moon forming deep within Saturn’s rings, 4.5 billion years after the planet initially formed.

But new research suggests Saturn’s icy moon Titan — famous for its rivers and lakes of liquid methane — may have formed before its parent planet, contradicting the theory that Titan formed within the warm disk surrounding an infant Saturn.

A combined NASA and ESA-funded study has found firm evidence that the nitrogen in Titan’s atmosphere originated in conditions similar to the cold birthplace of the most ancient comets from the Oort cloud — a spherical shell of icy particles that enshrouds the Solar System.

The hint comes in the form of a ratio. All elements have a certain number of known isotopes — variants of that element with the same number of protons that differ in their number of neutrons. The ratio of one isotope to another isotope is a crucial diagnostic tool.

In planetary atmospheres and surface materials, the amount of one isotope relative to another isotope is closely tied to the conditions under which materials form. Any change in the ratio will allow scientists to deduce an age for that material.

Kathleen Mandt from the Southwest Research Institute in San Antonio and colleagues analyzed the ratio of nitrogen-14 (seven protons and seven neutrons) to nitrogen-15 (seven protons and eight neutrons) in Titan’s atmosphere.

“When we looked closely at how this ratio could evolve with time, we found that it was impossible for it to change significantly,” Mandt said in a press release. “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.”

The team found that our Solar System is not old enough for this nitrogen isotope ratio to have changed as much as it has. By comparing the small change within this ratio, Mandt and colleagues found that it seemed more similar to Oort cloud comets than to Solar System bodies including planets and comets born in the Kuiper belt. The team is eager to see whether their findings are supported by data from ESA’s Rosetta mission, which will study comet 67P/Churyumov-Gerasimenko later this year.

Finally, the study also has implications for Earth. In the past, researchers assumed a connection between comets, Titan and Earth. But these results show that the nitrogen isotope ratio is different on Titan and Earth, suggesting the sources of Earth’s and Titan’s nitrogen must have been different.

It’s unclear whether Earth received nitrogen from early meteorites or if it was captured directly from the disk of gas that formed the Solar System.

“This exciting result is a key example of Cassini science informing our knowledge of the history of [the] Solar System and how Earth formed,” said Scott Edgington, Cassini deputy project scientist at NASA’s Jet Propulsion Laboratory.

The research was published this week in the Astrophysical Journal Letters.

About 

Shannon Hall is a freelance science journalist. She holds two B.A.'s from Whitman College in physics-astronomy and philosophy, and an M.S. in astronomy from the University of Wyoming. Currently, she is working toward a second M.S. from NYU's Science, Health and Environmental Reporting program.

gopher65 June 24, 2014 at 10:33 PM

This is an interesting finding. I wonder how they ruled out the possibility of a nitrogen heavy large object from the outer solar system smashing into Titan when it was young, changing the ratio. Something like Sedna or Pluto, except from further out.

Jeffrey Boerst June 25, 2014 at 2:12 AM

I’d guess that the numbers would be somewhere between the two possible isotopic ratios if that were the case. Just a guess, as I’m not at all trained. ;)

mommascientist June 25, 2014 at 4:49 PM

Hi, I’m Kathy Mandt the lead author of this study. I want to thank Shannon Hall for posting this and everyone for your interest in these results. This is a very good question about a nitrogen-heavy object possibly being the source of Titan’s nitrogen. At the present time we do not know the isotope ratio for Pluto’s nitrogen atmosphere, but we are hoping that the Alice instrument on the New Horizons spacecraft can make this measurement. We expect the isotope ratio on Pluto to be like Jupiter and the solar wind, which is VERY different from comets and Titan. For an object like Pluto or Sedna to be the source of Titan’s nitrogen, a massive change in the isotope ratio is required to take place over a very short period of time due to the collision. Our study showed that rapidly losing material from Titan’s atmosphere will not significantly change the isotope ratio because both isotopes are lost. This is why we are able to conclude that the source of Titan’s nitrogen atmosphere originated in conditions similar to comets.

Davies June 25, 2014 at 2:59 AM

Theories, theories, theories, we’ll definitely never know how the Universe works. Yes! We’re intelligent and now more advanced in technology but we have a long way to go before we truly understand. Is it really possible for the moon to be older than the Mother Planet? Or is Titan a Planet on it’s own that just love to hang around the Mother Planet Saturn?

Torbjorn Larsson OM June 25, 2014 at 12:23 PM

Theories, theories, theories, we’ll definitely never know …

Scientific theories is the best knowledge we have, “a well-substantiated explanation of some aspect of the natural world”. [ http://en.wikipedia.org/wiki/Scientific_theory ]

Analogous to how an image is worth a thousand words, a theory is better than a thousand disparate observations.

… how the Universe works.

We definitely already know how the universe works, since 2005. The first consistent theory of cosmology is now down to uncertainties smaller than percent in cases. (Say, the age of the universe.)

It is only quite a whiles into the preceding inflation that our current knowledge breaks down.

We also definitely already know how the everyday innards of the universe works, since 2013. The laws for everyday physics (the standard model in weak gravity) is now down to uncertainties way, way smaller than percents. (Say, the strength of electromagnetic interactions.)

It is only for exotic phenomena that our current knowledge breaks down. For example, if dark matter is WIMPs, a nuclei of your body will experience a minuscule heating from a direct collision once every few years. But 99.9999999 % of what we do we know all the basic laws for.

I think you are reaching not for what we already know robustly (little likelihood for revision), but for the open-ended business end of science. But that is not about how the universe works as such, it is about the very many details that low-temperature, non-exotic phenomena engender as its dynamic plays out. Small picture, not big picture.

Is it really possible for the moon to be older

Sure. A capture of a stray body would make its age unrelated to the planet. It could be older or younger down to the age of the capture if known. (But its age would not be unrelated to the planetary system in general, since captures from interstellar space are much less likely. Thus such a body would not be expected to be older than the oldest system bodies, e.g. Oort cloud bodies.)

Forty June 30, 2014 at 11:35 AM

“We definitely already know how the universe works, since 2005.”
Like dark matter and dark energy? Cold you please briefly explain what they are and how they work? Thanks

Torbjorn Larsson OM June 25, 2014 at 12:02 PM

Ah, a possible capture like Triton, albeit Triton is believed to be from the Kuiper belt.

“However, whereas Jupiter possesses four large satellites in highly regular, planet-like orbits, Titan overwhelmingly dominates Saturn’s system and possesses a high orbital eccentricity not immediately explained by co-accretion alone.” [ http://en.wikipedia.org/wiki/Titan_(moon) ]

Torbjorn Larsson OM June 25, 2014 at 12:42 PM

Speaking of which, ironic if Titan is the long sought for “planet X”.

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