Phosphates Discovered in Enceladus' Plumes

NASA Cassini Data Reveals Building Block for Life in Enceladus’ Ocean

Phosphorus, a key chemical element for many biological processes, has been found in icy grains emitted by the small moon and is likely abundant in its subsurface ocean.

Using data collected by NASA’s Cassini mission, an international team of scientists has discovered phosphorus – an essential chemical element for life – locked inside salt-rich ice grains ejected into space from Enceladus.

The small moon is known to possess a subsurface ocean, and water from that ocean erupts through cracks in Enceladus’ icy crust as geysers at its south pole, creating a plume. The plume then feeds Saturn’s E ring (a faint ring outside of the brighter main rings) with icy particles.

During its mission at the gas giant from 2004 to 2017, Cassini flew through the plume and E ring numerous times. Scientists found that Enceladus’ ice grains contain a rich array of minerals and organic compounds – including the ingredients for amino acids – associated with life as we know it.

Seen as a bright arc in this 2006 observation by Cassini, Saturn’s E ring is fed with icy particles from Enceladus’ plume, creating wispy fingers of bright material that is backlit by the Sun. The shadowed hemisphere of the moon can be seen as a dark dot inside the ring. Credit: NASA/JPL/Space Science Institute

Phosphorus, the least abundant of the essential elements necessary for biological processes, hadn’t been detected until now. The element is a building block for DNA, which forms chromosomes and carries genetic information, and is present in the bones of mammals, cell membranes, and ocean-dwelling plankton. Phosphorus is also a fundamental part of energy-carrying molecules present in all life on Earth. Life wouldn’t be possible without it.

It’s the first time this essential element has been discovered in an ocean beyond Earth.

“We previously found that Enceladus’ ocean is rich in a variety of organic compounds,” said Frank Postberg, a planetary scientist at Freie Universität Berlin, Germany, who led the new study, published on Wednesday, June 14, in the journal Nature. “But now, this new result reveals the clear chemical signature of substantial amounts of phosphorus salts inside icy particles ejected into space by the small moon’s plume. It’s the first time this essential element has been discovered in an ocean beyond Earth.”

Previous analysis of Enceladus’ ice grains revealed concentrations of sodium, potassium, chlorine, and carbonate-containing compounds, and computer modeling suggested the subsurface ocean is of moderate alkalinity – all factors that favor habitable conditions.

Enceladus and Beyond

For this latest study, the authors accessed the data through NASA’s Planetary Data System, a long-term archive of digital data products returned from the agency’s planetary missions. The archive is actively managed by planetary scientists to help ensure its usefulness and usability by the worldwide planetary science community.

The authors focused on data collected by Cassini’s Cosmic Dust Analyzer instrument when it sampled icy particles from Enceladus in Saturn’s E ring. Many more ice particles were analyzed when Cassini flew through the E ring than when it went through just the plume, so the scientists were able to examine a much larger number of compositional signals there. By doing this, they discovered high concentrations of sodium phosphates – molecules of chemically bound sodium, oxygen, hydrogen, and phosphorus – inside some of those grains.