Is Triton Hiding an Underground Ocean?

Voyager 2 mosaic of Neptune’s largest moon, Triton (NASA)

At 1,680 miles (2,700 km) across, the frigid and wrinkled Triton is Neptune’s largest moon and the seventh largest in the Solar System. It orbits the planet backwards – that is, in the opposite direction that Neptune rotates – and is the only large moon to do so, leading astronomers to believe that Triton is actually a captured Kuiper Belt Object that fell into orbit around Neptune at some point in our solar system’s nearly 4.7-billion-year history.

Briefly visited by Voyager 2 in late August 1989, Triton was found to have a curiously mottled and rather reflective surface nearly half-covered with a bumpy “cantaloupe terrain” and a crust made up of mostly water ice, wrapped around a dense core of metallic rock. But researchers from the University of Maryland are suggesting that between the ice and rock may lie a hidden ocean of water, kept liquid despite estimated temperatures of  -97°C (-143°F), making Triton yet another moon that could have a subsurface sea.

How could such a chilly world maintain an ocean of liquid water for any length of time? For one thing, the presence of ammonia inside Triton would help to significantly lower the freezing point of water, making for a very cold — not to mention nasty-tasting — subsurface ocean that refrains from freezing solid.

In addition to this, Triton may have a source of internal heat — if not several. When Triton was first captured by Neptune’s gravity its orbit would have initially been highly elliptical, subjecting the new moon to intense tidal flexing that would have generated quite a bit of heat due to friction (not unlike what happens on Jupiter’s volcanic moon Io.) Although over time Triton’s orbit has become very nearly circular around Neptune due to the energy loss caused by such tidal forces, the heat could have been enough to melt a considerable amount of water ice trapped beneath Triton’s crust.

Related: Titan’s Tides Suggest a Subsurface Sea

Another possible source of heat is the decay of radioactive isotopes, an ongoing process which can heat a planet internally for billions of years. Although not alone enough to defrost an entire ocean, combine this radiogenic heating with tidal heating and Triton could very well have enough warmth to harbor a thin, ammonia-rich ocean beneath an insulating “blanket” of frozen crust for a very long time — although eventually it too will cool and freeze solid like the rest of the moon. Whether this has already happened or still has yet to happen remains to be seen, as several unknowns are still part of the equation.

“I think it is extremely likely that a subsurface ammonia-rich ocean exists in Triton,” said Saswata Hier-Majumder at the University of Maryland’s Department of Geology, whose team’s paper was recently published in the August edition of the journal Icarus. “[Yet] there are a number of uncertainties in our knowledge of Triton’s interior and past which makes it difficult to predict with absolute certainty.”

Still, any promise of liquid water existing elsewhere in large amounts should make us take notice, as it’s within such environments that scientists believe lie our best chances of locating any extraterrestrial life. Even in the farthest reaches of the Solar System, from the planets to their moons, into the Kuiper Belt and even beyond, if there’s heat, liquid water and the right elements — all of which seem to be popping up in the most surprising of places — the stage can be set for life to take hold.

Read more about this here on Astrobiology.net.

Inset image: Voyager 2 portrait of Neptune and Triton taken on August 28, 1989. (NASA)

Is Earth Alive? Scientists Seek Sulfur For An Answer

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Researchers at the University of Maryland have discovered a way to identify and track sulfuric compounds in Earth’s marine environment, opening a path to either refute or support a decades-old hypothesis that our planet can be compared to a singular, self-regulating, living organism — a.k.a. the Gaia theory.

Proposed by scientists James Lovelock and Lynn Margulis in the 70s, the Gaia theory likens Earth to a self-supporting singular life form, similar to a cell. The theory claims that, rather than being merely a stage upon which life exists, life — in all forms — works to actively construct an Earthly environment in which it can thrive.

Although named after the Greek goddess of Earth, the Gaia theory is not so much about mythology or New Age mysticism as it is about biology, chemistry and geology — and how they all interact to make our world suitable for living things.

Once called the Gaia hypothesis, enough scientific cross-disciplinary support has since been discovered that it’s now commonly referred to as a theory.

Marine phytoplankton -- like these diatoms -- may produce sulfur compounds that can be transmitted into the air, affecting climate. (NOAA image)

One facet of the Gaia theory is that sulfur compounds would be created by microscopic marine organisms — such as phytoplankton and algae — and these compounds could be transmitted into the air, and eventually (in some form) to the land, thus helping to support a sulfur cycle.

Sulfur is a key element in both organic and inorganic compounds. The tenth most abundant element in the Universe, sulfur is crucial to climate regulation — as well as life as we know it.

In particular, two sulfur compounds — dimethylsulfoniopropionate and its atmospherically-oxidized version, dimethylsulfide — are considered to be likely candidates for the products created by marine life. It’s these two compounds that UMD researcher Harry Oduro, along with geochemist and professor James Farquhar and marine biologist Kathryn Van Alstyne (of Western Washington University) have discovered a way to track across multiple environments, from sea to air to land, allowing scientists to trace which isotopes are coming from what sources.

“What Harry did in this research was to devise a way to isolate and measure the sulfur isotopic composition of these two sulfur compounds,” said Farquhar. “This was a very difficult measurement to do right, and his measurements revealed an unexpected variability in an isotopic signal that appears to be related to the way the sulfur is metabolized.”

The team’s research can be used to measure how the organisms are producing the compounds, under which circumstances and how they are ultimately affecting their — and our — environment in the process.

“The ability to do this could help us answer important climate questions, and ultimately better predict climate changes,” said Farquhar. “And it may even help us to better trace connections between dimethylsulfide emissions and sulfate aerosols, ultimately testing a coupling in the Gaia hypothesis.”

Whether or not Earth can be called a singular — or possibly even sentient — living organism of which all organisms are contributing members thereof may still be up for debate, but it is fairly well-accepted that life can shape and alter its own environment (and in the case of humans, often for the worse.) Research like this can help science determine just how far-reaching those alterations may be.

The study appears in this week’s Online Early Edition of the Proceedings of the National Academy of Sciences (PNAS).

Read more on the University of Maryland’s news page here.

Image credit: ESA ©2009 MPS for OSIRIS Team MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA. Edited by J. Major.