NASA highlights studies linking Sun’s ancient behavior to Earth’s radiation and early warming

NASA on Monday highlighted two recent NASA-funded studies that link the Sun’s ancient behavior to Earth in very different ways: one proposes that collapses of the solar system’s protective bubble may have exposed Earth to unusually high radiation in the geologically recent past, while the other suggests energetic particles from the young Sun could have helped warm early Earth and spur prebiotic chemistry.

The new item on NASA’s science website, published Aug. 24, 2026, is a summary of earlier peer-reviewed papers, not a report of discoveries made Monday. One study, published in February, used simulations to argue that encounters between the Sun and dense, cold interstellar clouds could have dramatically compressed the heliosphere and increased radiation reaching Earth. The other, published in May, combined laboratory experiments and climate modeling to suggest proton activity from the young Sun may have produced greenhouse nitrous oxide and amino-acid precursors in Earth’s primitive atmosphere. Both papers add to active scientific debates, but neither settles them.

The first paper, “Increased and varied radiation during the Sun’s encounters with cold clouds in the last 10 million years,” was published Feb. 11 in Scientific Reports by Merav Opher and colleagues. Opher leads SHIELD, a NASA-funded heliophysics research center headquartered at Boston University.

Using magnetohydrodynamic and particle simulations, the team modeled what could happen if the Sun moved through very dense, cold interstellar clouds. In those scenarios, the heliosphere — the bubble created by the solar wind around the solar system — could shrink to about 0.22 plus or minus 0.01 astronomical unit. Earth orbits at 1 astronomical unit, so that modeled collapse would place Earth outside the heliosphere’s main shielding region.

The paper linked such encounters to geological isotope peaks around 13 million to 14 million years ago, 6 million to 7 million years ago, and 2 million to 3 million years ago. It pointed to measured deposits of iron-60 and plutonium-244 in Earth and lunar records as evidence that something unusual happened during those periods. Those isotope deposits are real observations; the dispute is over what produced them and what they meant for Earth.

Opher’s team proposed that these episodes could have raised Earth’s exposure to heliospheric energetic particles and galactic cosmic rays, with possible climate effects. The Scientific Reports abstract said the “intensity of < 10 MeV protons was at least an order of magnitude more intense than today’s most extreme solar energetic particle (SEP) events.” But the paper presents a mechanism, not proof that radiation changes drove particular climate shifts.

That distinction matters because the heliosphere normally extends far beyond Earth’s orbit. In many models today, it reaches roughly 100 to 150 astronomical units toward the incoming interstellar medium. Against that backdrop, a compression to 0.22 astronomical unit would be extraordinary.

The second paper, “Proton Irradiation of Primitive Atmospheres of Young Exoplanets and Early Earth: N2O Greenhouse Warming and Prebiotic Synthesis,” was published in Astrophysical Journal Letters in May after first appearing on arXiv on March 18. Co-author Vladimir Airapetian is a scientist at NASA’s Goddard Space Flight Center.

In laboratory proton-irradiation experiments, the researchers exposed nitrogen- and carbon-dioxide-rich gas mixtures meant to resemble primitive atmospheres. They reported producing nitrous oxide, or N2O, “at mixing ratios up to ∼10^3 ppmv,” according to the abstract, along with amino-acid precursors including glycine.

The team then used photochemical modeling and NASA’s ROCKE-3D climate model to test Archean-like conditions on early Earth. In the paper’s reported runs, an atmosphere made of 90% nitrogen and 10% carbon dioxide produced a modeled global mean surface temperature of about 18 degrees Celsius without N2O, about 30 C with 100 parts per million by volume of N2O, and about 34 C with 400 ppmv N2O. The authors framed that as one possible contribution to the faint young Sun paradox, the longstanding question of how early Earth maintained liquid water when the Sun was only about 70% to 75% as bright as it is today.

That paradox is a standard problem in Earth science because geological evidence indicates early Earth had liquid water despite the weaker young Sun. The new paper does not claim to solve the puzzle on its own, but argues that solar proton events may have been part of the mix by generating a greenhouse gas and molecules relevant to prebiotic chemistry.

The first study, meanwhile, has already drawn published criticism. On April 14, Nature Astronomy published a Matters Arising piece by Dominik Koll and colleagues arguing there was “No indication of a strong increase in galactic cosmic ray intensity 2-3 Myr ago from cosmogenic nuclides.” Opher and co-authors published a same-day reply defending their interpretation. Taken together, the two NASA-highlighted studies broaden the discussion over how the Sun may have influenced Earth’s climate and chemistry across deep time, but they remain proposals built on modeling, experiments and contested interpretation, not settled explanations.