Phosphorus-Rich Stars Critical in Search for Extraterrestrial Life

Multi-star system


“Our Sun has relatively high phosphorus and Earth biology requires a small, but noticeable, amount of the element. So, on rocky planets that form around host stars with less phosphorus, it’s likely that it will be unavailable for potential life on that planet’s surface,” said planetary astrophysicist, Natalie Hinkel, a Southwest Research Institute scientist who has identified stellar phosphorus — essential on Earth for the creation of DNA, cell membranes, bones and teeth in people and animals, and even the microbiome of ocean-dwelling plankton–as a probable marker in narrowing the search for life in the cosmos.

“Therefore,” Hinkel added, “we urge the stellar abundance community to make phosphorus observations a priority in future studies and telescope designs.” Hinkel has developed techniques to identify stars likely to host exoplanets, based on the composition of stars known to have planets, and proposes that upcoming studies target stellar phosphorus to find systems with the greatest probability for hosting life as we know it. On Earth, the key elements for biology are carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur. In today’s oceans, phosphorus is considered the ultimate limiting nutrient for life as it’s the least available chemical necessary for biochemical reactions.

The Hypatia Catalog

“When searching for exoplanets and trying to see whether they are habitable, it’s important that a planet be alive with active cycles, volcanoes and plate tectonics,” said Hinkel, who used the Hypatia Catalog, a database she developed of 9,434 stars, 1,309 of which host planets and 1,829 of which are in multistar systems, to assess and compare the carbon, nitrogen, silicon, and phosphorus abundance ratios of nearby stars with those in average marine plankton, the Earth’s crust, as well as bulk silicate on Earth and Mars.

Star Composition –A Proxy for Exoplanetary Ecosystems 

Determining the elemental ratios for exoplanetary ecosystems is not yet possible, but it’s generally assumed that planets have compositions similar to those of their host stars. Scientists can measure the abundance of elements in a star spectroscopically, studying how light interacts with the elements in a star’s upper layers. Using these data, scientists can infer what a star’s orbiting planets are made of, using stellar composition as a proxy for its planets.

“But there’s so little phosphorus stellar abundance data,” Hinkel said. “Phosphorus data exists for only about 1% of stars. That makes it really difficult to figure out any clear trends in between the stars, let alone the role of phosphorus in the evolution of an exoplanet.”

It’s not that the stars are necessarily lacking phosphorus, but it’s difficult to measure the element because it’s detected in a region of the light spectrum not typically observed: at the edge of the optical (or visual) wavelengths of light and infrared light. Most spectroscopic studies are not tuned to find elements in that narrow range.

Moving forward, these findings could revolutionize target star selections for future research and clinch the role elements play in exoplanet detection, formation and habitability.

Source: Astrophysical Journal Letters

The Daily Galaxy, Max Goldberg via Southwest Research Institute 

Image credit: Multi-star system,

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