A dramatic plume sprays water ice and vapor from the south polar region of Saturn's moon Enceladus. Cassini's first hint of this plume came during the spacecraft's first close flyby of the icy moon on February 17, 2005.NASA/JPL/Space Science Institute
A new NASA-supported study shows that the waters of icy ocean moons are likely to contain enough phosphorus (P) to support life as we know it. Phosphorus is one of six elements that are thought to be absolutely necessary for life as we know. The others include carbon, hydrogen, nitrogen, oxygen, and sulfur. Collectively, these six elements are often referred to as CHNOPS.
Apart from phosphorus, the rest of this set of elements (C, H, N, O, and S) have been identified on at least one of the icy ocean moons in our solar system. Identifying P to complete the set is important because, on Earth, phosphorus plays a particularly important role in the biosphere.
An artist depiction of the interior structure of Saturn’s moon Enceladus, showing an ocean trapped between an icy ceiling and a rocky bed at the ocean floor.Image credit: NASA/JPL–Caltech.
The abundance of life in many habitats on Earth is limited by the amount of phosphorus available. The availability of phosphorus could also have been an important control for the amount of life on our planet over the course of Earth’s history. On Earth, rocks above sea level wear down releasing phosphorus that washes into the ocean. This phosphorus then disappears when living organisms that consumed the phosphorus die and are buried or due to chemical reactions in deep sea hot springs.
When thinking about the habitability of icy ocean worlds, such as Jupiter’s moon Europa or Saturn’s moon Enceladus, this process for delivering phosphorus to the ocean doesn’t exist. There are no continents on these worlds where rock is exposed. This means that any phosphorus for life must come from the chemical reactions occurring on the deep seafloor. Additionally, there are thought to be hot springs on these moons which might also consume phosphorus. Because of this, scientists hypothesized that phosphorus could be very limited in oceans hidden by ice shells. However, new research shows that this might not be the case.
Artist's concept of the ice shell that covers the ocean of Jupiter's moon Europa.Image credit: NASA/JPL-CalTech.
A team of scientists at the NASA Ames Research Center used millions of computer simulations to understand the behavior of phosphorus when water reacts with rocks under the seafloor. These simulations examined a wide range of temperatures and many different rocks that might exist on the bottom of icy world oceans. They found that the reaction between water and rock could result in enough phosphorus to support cell populations larger than those found in the deep ocean of Earth in almost all conditions likely to exist on ice covered moons in the solar system. In fact, in these simulations hot springs, which consume phosphorus on Earth, produce phosphorus on ocean moons because of the different ocean chemistry. These simulations provide a framework to interpret future satellite observations of phosphorus from ocean moons.
NASA's digital Europa Clipper poster is available at: https://europa.nasa.gov/resources/173/europa-clipper-journey-to-an-ocean-world-poster/Image credit: NASA/ Jet Propulsion Laboratory-Caltech.
“It seems like these alien oceans are not that alien,” says lead author Noah Randolph-Flagg, a NASA Astrobiology Postdoctoral Program (NPP) Fellow at the NASA Ames Research Center. “The saltiness, acidity, nutrients, etc. seem very similar to what we think Earth looked like when life arose.”
This means that, contrary to previous thought, the availability of phosphorus is unlikely to be a limiting factor for life on icy ocean worlds if that life is similar to the types of marine microorganisms found on Earth.
Noah Randolph-Flagg, NASA Astrobiology Postdoctoral Program (NPP) Fellow at the NASA Ames Research Center.Image credit: Courtesy Noah Randolph-Flagg.
“It seems likely that these moons have many of the ingredients required for Earth-like life’,” continued Randolph-Flagg. “The question then becomes if that life exists and which environments are the best candidates in which to search for life. Just because an ocean would be a nice place for a microbe to live, doesn’t mean that there are microbes to live in it.”
The study, “Phosphate availability and implications for life on ocean worlds,” was published in the journal Nature Communications.