Scientist searches for stellar phosphorus to find potentially habitable exoplanets
Stellar chemical compositions used as proxy for potentially habitable
systems

Date:
September 16, 2020
Source:
Southwest Research Institute
Summary:
A scientist has identified stellar phosphorus as a probable marker
in narrowing the search for life in the cosmos. She 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.



FULL STORY ==========================================================================
A Southwest Research Institute scientist has identified stellar phosphorus
as a probable marker in narrowing the search for life in the cosmos. She
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.


========================================================================== "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 SwRI's Dr. Natalie Hinkel,
a planetary astrophysicist and lead author of a new paper about
this research in the Astrophysical Research Letters. "My coauthor,
Dr. Hilairy Hartnett, is an oceanographer and pointed out that phosphorus
is vital for all life on Earth. It is essential for the creation of
DNA, cell membranes, bones and teeth in people and animals, and even
the sea's microbiome of plankton." 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.

On Earth, the key elements for biology are carbon, hydrogen, nitrogen,
oxygen, phosphorus, and sulfur (or CHNOPS). In today's oceans, phosphorus
is considered the ultimate limiting nutrient for life as it's the least available chemical necessary for biochemical reactions.

Hinkel used the Hypatia Catalog, a publicly available stellar database
she developed, 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.

"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.

"Our Sun has relatively high phosphorus and Earth biology requires a
small, but noticeable, amount of phosphorus," Hinkel continued. "So,
on rocky planets that form around host stars with less phosphorus, it's
likely that phosphorus will be unavailable for potential life on that
planet's surface. Therefore, we urge the stellar abundance community to
make phosphorus observations a priority in future studies and telescope designs." Moving forward, these findings could revolutionize target
star selections for future research and clinch the role elements play
in exoplanet detection, formation and habitability.


========================================================================== Story Source: Materials provided by Southwest_Research_Institute. Original written by Deb Schmid. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Natalie R. Hinkel, Hilairy E. Hartnett, Patrick A. Young. The
Influence
of Stellar Phosphorus on Our Understanding of Exoplanets and
Astrobiology. The Astrophysical Journal, 2020; 900 (2): L38 DOI:
10.3847/ 2041-8213/abb3cb ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200916113519.htm

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