New solar composition ratios that could reconcile longstanding questions

A paper about this research, which addresses the long-standing "solar abundances" problem, appears in the AAS Astrophysical Journal.

"This is the first time this kind of interdisciplinary analysis has been done, and our broad data set suggests more abundant levels of solar carbon, nitrogen and oxygen than previously thought," said Dr. Ngoc Truong, an SwRI postdoctoral researcher. "Solar system formation models using the new solar composition successfully reproduce the compositions of large Kuiper Belt objects (KBOs) and carbonaceous chondrite meteorites, in light of the newly returned Ryugu and Bennu asteroid samples from JAXA's Hayabusa-2 and NASA's OSIRIS-REx missions."

To make this discovery, the team combined new measurements of solar neutrinos and data about the solar wind composition from NASA's Genesis mission, together with the abundance of water found in primitive meteorites that originated in the outer solar system. They also used the densities of large KBOs such as Pluto and its moon Charon, as determined by NASA's New Horizons mission.

"This work provides testable predictions for future helioseismology, solar neutrino and cosmochemical measurements, including future comet sample return missions," Truong said. "The solar composition is used to calibrate other stars and understand the composition and formation of solar system objects. These breakthroughs will enhance our understanding of the primordial solar nebula's chemistry and the formation of numerous solar system bodies."

The team examined the role of refractory, tar-like organic compounds as a major carrier of carbon in the protosolar nebula. Solar system formation models using measurements of organics from comet 67P/Churyumov-Gerasimenko and the most widely adopted solar composition ratios did not produce the dense, rocky Pluto-Charon system.

"With this research, we think we finally understand the mix of chemical elements that made the solar system," said SwRI's Dr. Christopher Glein, an expert in planetary geochemistry. "It has more carbon, nitrogen and oxygen than what is currently assumed. This new knowledge gives us a firmer basis for understanding what element abundances in giant planet atmospheres can tell us about the formation of planets. We already have our eyes on Uranus -- NASA's next target destination -- and beyond."

In the search for habitable exoplanets, scientists measure the abundances of elements in stars spectroscopically to infer what a star's orbiting planets are made of, using stellar composition as a proxy for its planets.

"Our findings will significantly affect our understanding about the formation and evolution of other stars and planetary systems, and even further, they enable a broader perspective of galactic chemical evolution," said Truong.

A Cornell University-affiliated scientist contributed to the research, which was supported by SwRI's Internal Research and Development program and the Heising-Simons Foundation.