Moons like ours are a rarity in the universe

New observations from NASAs Spitzer Space Telescope suggest that moons like Earths, that have been formed out of tremendous collisions, are uncommon in the universe.

Washington, Nov 21 : New observations from NASA's Spitzer Space Telescope suggest that moons like Earth's, that have been formed out of tremendous collisions, are uncommon in the universe.

"When a moon forms from a violent collision, dust should be blasted everywhere," said Nadya Gorlova of the University of Florida, who is also the lead author of a new study on the topic. "If there were lots of moons forming, we would have seen dust around lots of stars, which we didn't," she added.

Scientists believe that the moon formed after a planetary body as big as Mars smacked into our infant Earth. This impact had probably broken off a piece of the planet's mantle. Some of the resulting debris fell into orbit around Earth, eventually forming into the moon we see today.

As for the other moons in our solar system, they either formed simultaneously with their planet or were captured by their planet's gravity.

The new observations by the research team looked for the dusty signs of similar smash-ups around 400 stars that are all about 30 million years old, roughly the age of our sun when Earth's moon formed.

What they found was that only 1 out of the 400 stars is immersed in the telltale dust. Taking into consideration the amount of time the dust should stick around, and the age range at which moon-forming collisions can occur, the scientists then calculated the probability of a solar system making a moon like Earth's to be at most 5 to 10 percent. "We don't know that the collision we witnessed around the one star is definitely going to produce a moon, so moon-forming events could be much less frequent than our calculation suggests," said George Rieke of the University of Arizona, Tucson, who's a co-author of the study.

In addition, the observations tell astronomers that the planet-building process itself winds down by 30 million years after a star is born. Like our moon, rocky planets are also built up through messy collisions that spray dust all around.

Though current thinking holds that this process lasts from about 10 to 50 million years after a star forms, the research team found only 1 star out of 400 with collision-generated dust. This indicates that the 30-million-year-old stars in the study have, for the most part, finished making their planets. "Astronomers have observed young stars with dust swirling around them for more than 20 years now," said Gorlova.

"But those stars are usually so young that their dust could be left over from the planet-formation process. The star we have found is older, at the same age our sun was when it had finished making planets and the Earth-moon system had just formed in a collision."

ANI