Moon research reinforces impact theory

Scientists can now confirm the moon is not made of Swiss cheese, but instead was formed from the same stuff the Earth was.

New research answers most of the questions relating to the giant smash-up that ultimately created the moon.

Astronomers have known for ages that emmentaler cheese was not the main constituent of the moon, despite what their children had persistently told them.

Rather, most scientists focused on astronomy believed a massive collision between the Earth and another large planet in the early days of the solar system knocked out the material from which the moon ultimately coalesced.

The problem with this theory was the many unanswered questions, such as why the moon is basically an Earth twin, given its composition. Or, how the collision could have thrown off enough material to deliver the moon.

Two groups of scientists have come up with answers to these questions, in the process adding considerable weight to the collision model for the formation of the moon. Both papers were released online yesterday in the journal Science.

The original collision theory held that a small planet called Theia hit the Earth, flinging Theia debris into orbit to shape the moon. Moon rocks showed, however, that the moon and earth are made of similar stuff - and so this theory could not be correct.

Instead, the Harvard/Seti group described a similar collision where the Earth was spinning much faster, completing a revolution in only two hours. In this case the debris from the collision would in fact have come from the Earth.

They showed that the Earth and moon have matching chemical isotopes. They also explained how the spin of the Earth gradually slowed due to gravitational interaction between the sun and moon.

A team from the Southwest Research Institute in Texas answered the questions in a similar way. In their scenario, the Earth and its impactor have about the same mass, four to five times the mass of present day Mars.

They collide, spraying out a disc of material that gradually forms an orbiting moon. The two colliders merge into one, with the new planet's outer layer made of much the same material as the moon's debris disc.

They calculated the newly formed Earth would be spinning too fast, but gravitational drag would eventually serve to slow the Earth to its current clip.

No doubt the new findings will come as a blow to those still supporting the Swiss cheese lunar theory. They will, however, be able to keep their theory alive, advertising their cheese during children's TV programming.