One of the explanations offered at the time was that solar wind sends a steady stream of protons out in the Solar System, and these protons could interact with lunar material to produce water.

The researchers behind the finding suggest that this means many Solar System bodies are likely to be fairly water-rich—a reservoir that could have made a big contribution to Earth's oceans.

This finding is consistent with the idea that the water was produced by the interaction between protons in the solar wind and silicate-rich materials in the rocks themselves.

Based on the typical depth of the material that was transformed by the solar wind, the researchers could calculate the amount of water in particles of different sizes.

So even if something is now buried in the interior, it almost certainly was exposed to the solar wind in the past.

Total up all the rubble piles wandering the Solar System, as well as the upper surfaces of the airless bodies, and there's a remarkable amount of water held by the ostensibly dry bodies.

Over time, small bodies fell to Earth and brought water with them to create our oceans.

The solar wind, in contrast, has hydrogen isotopes that are overall lighter than what we see in our oceans.

So the researchers propose that the solar wind has indirectly helped fill our planet's oceans by producing water on dust particles that eventually fell to Earth.

And these tiny particles will have the highest amount of water per mass of anything exposed to the solar wind.