What Methane Jets Can Tell Us About Enceladus – Eos

When Cassini first flew by Saturn’s icy moon Enceladus in 2005, scientists were shocked to see columns of material erupting from cracks near the south pole. The spacecraft has discovered more than 100 small fountains that spray compounds, including water vapor and methane, directly into space. After detecting the jets, Cassini skimmed the material nine times, sampling its composition despite the fact that none of the spacecraft’s instruments were designed to do so.

In the years since, scientists have tried to understand the plume’s geochemical relationship to its origin—the vast, ice-covered ocean of Enceladus below. But although previous studies have sought to understand what the elusive ocean looks like today, a team of researchers has sought to determine how those fountains changed the ocean’s chemical composition. Enceladean ocean during the 4.5 billion year lifespan of the solar system. They presented their findings at the Lunar and Planetary Science Conference (LPSC).

The mystery of the disappearance of methane

Like many astronomers, Lucas Fifer and his colleagues began with the assumption that Enceladus and the rest of Saturn’s moons formed from the icy texture of the outer solar system, like the outer solar system. like a comet. However, the amount of methane in the moon’s oceans today is about 100 times less than that provided by comets. This is Enceladus’ «missing methane».

«We’ve been trying to solve the mystery of the missing methane.»

“We were trying to solve the mystery of the missing methane,” said Fifer, a graduate student at the University of Washington and a presenter at the LPSC. «We asked, could it have erupted?»

The team collected measurements of comet abundance to estimate the initial composition of Enceladus’ ocean, as well as measurements of eruption rate and composition from Cassini data. In addition to water, the moon’s emissions of gases, including methane, carbon dioxide and ammonia, into space, and the team used that information to trace back the current ocean composition to what it might be. millions or billions of years ago.

The model shows another problem: Smoke plumes remove methane much faster than carbon dioxide or ammonia. In the time it takes to go from the original to the modern quantities of the other two gases, too much methane will be lost. Therefore, «some bio- or hydrothermally generated methane input is required to compensate for the loss through the clouds,» the researchers concluded.

Mystery of the Moon

For Hunter Waite, a former Cassini team member who has studied the composition of clouds and oceans in Enceladean, it’s a little early to try to rewind clouds. «This [plume material] Waite warned. “We don’t know exactly what happened to it, and so trying to trace its origins just from what we know about Enceladus—it’s a bit scary.”

«I’d sleep better if we had another mission to confirm Cassini’s measurements.»

Furthermore, because Cassini does not carry instruments designed to collect samples, astronomers are also concerned about the accuracy of the samples it collects.

«I would sleep much better if we had another mission that confirmed Cassini’s measurements,» said Antonin Affholder, a postdoctoral researcher at the University of Arizona who was not involved in the new study.

Waite also questioned the pre-existing assumption that Enceladus formed from comet-like matter in the first place. He says that the astronomy community is still debating how and when Saturn’s moons form. Other explanations include the moons were born in the same collision that created the rings or formed along with Saturn and the rest of the planets. Waite noted that one of those origins would radically change the moon’s «originally expected methane output.»

«It’s amazing that we found a small icy moon out there that seems to be belching out into its ocean for us to sample.»

The new model, Fifer said, «is the first and at least the first step in showing that plume loss is something that should be added to that important list.» [geochemical] processes» in the Enceladean ocean.

Affholder also emphasized the importance of this aspect in the new study. «Limiting launch losses is important for us to better understand Enceladus’ ocean geochemistry,» he said.

In the end, Waite said, “it was amazing when we found a little icy moon out there that seemed to be belching out into its ocean for us to sample.…We needed to get back to the right gear. and the right probe procedure to categorize these questions because it’s an absolutely fascinating object in the solar system.»

—Nola Taylor Tillman (@Nola_T_Tillman), Science writer

quote: Tillman, NT (2023), What can methane rays tell us about Enceladus, Eos, 104, https://doi.org/10.1029/2023EO230252. Published on July 10, 2023.
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