Moon had a dramatic, explosive history, study says

The super moon appears in the sky in Cairo, Egypt, October 17, 2016. (REUTERS/Amr Abdallah Dalsh)

The super moon appears in the sky in Cairo, Egypt, October 17, 2016. (REUTERS/Amr Abdallah Dalsh)

A new model for how the moon formed in the distant past suggests a dramatic, violent collision that altered the Earth’s tilt and spin rate.

Today, the Earth is tilted just over 23 degrees compared to its orbital plane around the sun. According to the new research, scientists think that one possibility is that that angle was much different a very long time ago.

"Evidence suggests a giant impact blasted off a huge amount of material that formed the moon," Douglas Hamilton, a professor of astronomy at the University of Maryland and a co-author of the new study, said in a statement. "This material would have formed a ring of debris first, then the ring would have aggregated to form the moon. But this scenario does not quite work if Earth's spin axis was tilted at the 23.5 degree angle we see today."


Instead, the researchers think that the impact might have knocked the Earth’s tilt off by as much as 60 to 80 degrees, and also set our planet spinning very fast. Eventually, the system dynamics became what they are today.

Hamilton added that their model is just one way the moon’s orbit could have been born.

"There are many potential paths from the moon's formation to the Earth-moon system we see today,” he said in the statement. “We've identified a few of them, but there are sure to be other possibilities."


The scientists also think the moon moved away from the Earth after the impact.

“As the moon moved outward, the Earth’s steep tilt made for a more chaotic transition as the sun became a bigger influence,” Matija Cuk of the SETI institute said in the statement. “Subsequently, and over billions of years, the moon’s tilt slowly decayed down to the five degrees we see today.” (The moon's orbit is presently angled about five degrees compared to the Earth's orbit around the sun.) 

In other words, the system as it is now is the result of an explosive past that eventually became more stable.

The new research was published in the journal Nature.

Follow Rob Verger on Twitter: @robverger