Most of the water inside the Moon was delivered via asteroids over four billion years ago, according to a study published online Tuesday in the journal Nature Communications.
The Moon is believed to have formed from the debris generated by the collision of a Mars-sized planet with the Earth about 4.5 billion years ago. Soon after its formation, an ocean of magma was present on the Moon. Water is also known to have been present in the interior of the Moon.
However, until now, the timing and nature of the delivery of water to the Moon, and the relative contributions of asteroidal and cometary sources, have not been clear.
Using a combination of numerical models and measured isotopic compositions of lunar samples from a range of previous studies, a team of researchers from the UK, the United States, and France have found that water was delivered to the interior of the Moon during a period of ten to 200 million years, while the lunar magma ocean was also present.
A water-rich class of asteroids known as carbonaceous chondrites were responsible for most of the water in the lunar interior, with comets accounting for less than 20 percent of the total water budget of the Moon, according to the study.
Since comets were not major players in the first few hundred million years of inner solar system history, they only delivered a small part of the Moon's water, said Jessica Barnes from the Open University in the UK, who is one of the authors of the study.
The study reveals that comets and asteroids collided with the magma ocean on the Moon, and a thermal lid, which formed at the surface of the magma ocean, prevented loss of volatiles such as water through degassing to space, allowing water to be retained in the Moon's interior.
In addition to asteroids and comets, it is also likely that some of the water inside the Moon may be derived from the early Earth during the Moon-forming impact event, note the authors. (Xinhua)
