Comets and asteroids were not the only delivery options for seeding Earth -- and potentially other planets -- with water and organic materials for life.
New research shows hydrogen ions in the solar wind, a ubiquitous stream of particles flowing from the sun, react with oxygen in interplanetary dust grains to form little packets of water.
PHOTOS: Simmering Solar Views from SDO
Scientists have known for some time that interplanetary dust grains, like the comets and asteroids from which they came, contain organic carbon, considered a key building block for life.
But the mechanism for making water in the dust grains' radiation-beaten edges was unproven until a team of researchers analyzed some samples retrieved from high up in Earth's atmosphere.
The grains were collected during high-altitude research flights and analyzed in laboratories with an advanced electron microscope that can pick out extremely tiny details. For example, the rims of the interplanetary dust grains where the water was found are about 100 nanometers thick, roughly one-thousandths the width of a human hair.
NEWS: Moon Made Water From Solar Wind
Researchers are not sure how much solar wind-produced water could have arrived -- and still be arriving -- on Earth.
"There is an enormous number of factors that can play a role," physicist Hope Ishii, with the University of Hawaii, told Discovery News.
For starters, the amount of radiation coming from the sun has changed over time, as has the amount and sizes of interplanetary dust grains in the solar system.
ANALYSIS: Watching the Sun Rip into Planets' Atmospheres
Heating also plays a role. For example, suspected solar wind-produced water on the surface of the moon varies depending on whether measurements are made in lunar day or night. The water could be escaping into space as temperatures climb, or it could be migrating to colder areas, such as inside permanently shadowed craters in the lunar polar regions.
Though carried out on a much smaller scale, similar solar wind water production in dust grains has some advantages for longevity.