"Long-ago collisions between clouds of gas and dust could explain why many alien solar systems have planets with strange, highly tilted orbits — and why habitable worlds may be rare in the universe, a new study suggests.

Newly forming solar systems may be jostled by interactions with nearby clumps of matter, leading to systems in which alien planets have dramatically tilted orbits and the smaller (and potentially habitable) worlds are ejected, according to the study.

"We may be on the cusp of solving the mystery of why some planetary systems are tilted so much and lack places where life could thrive," said study lead author Pavel Kroupa, of the University of Bonn in Germany, in a statement. "Our work should help other scientists refine their search for life elsewhere in the universe."

Tilting a planet nursery

Most of the planets in our own solar system, including Earth, have relatively circular orbits and are lined up along a plane that isn't tilted much from the sun's equator. They also orbit in the same direction around the sun as our star spins.

But many other solar systems are not so neatly ordered, harboring planets that move in the opposite direction of their stars' spin on highly tilted orbits. The new study offers a possible explanation for these seemingly irregular traits..."

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