Alien worlds can be discovered by hunting for debris orbiting them

When it comes to finding newly born planets that are tens, if not hundreds, or even thousands of light-years away, we don’t often get lucky.

Planets form in thick clouds of dust and gas known as protoplanetary disks that orbit a star. Thus, it is very difficult to observe young planets right through all the debris. Instead, scientists must rely on clues that could indicate the presence of a protoplanet, but most of these clues are rather circumstantial at best.

But Feng Long, a researcher at the Center for Astrophysics at the Harvard and Smithsonian Institutions, has discovered a new clue that could point to the existence of a protoplanet: material in Lagrange points.

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Looking at data from the Chilean ALMA observatory relating to the protoplanetary disk LkCa 15, located about 518 light-years away, she noticed “a dusty ring with two separate and bright clumps of matter orbiting inside it,” Long said in a statement. (will open in a new tab). One of these bundles stretched out in an arc, and the other took on a lumpy shape.

“This arc and lump are separated by about 120 degrees,” she said. “This degree of separation doesn’t just happen – it’s important mathematically.”

This angle assumes that two groups of material are located at two Lagrange points. When two celestial bodies, such as a star and a planet, are gravitationally bound, there are five points in space where their gravity and orbital motion almost cancel each other out. At these Lagrange points, called L1 to L5, the material stays in place, essentially frozen into space. Based on the observed 120-degree angle between the clumps of material, Long suspects that they are located at L4 and L5, with the planet at a 60-degree angle between them.

“We’re seeing that this material isn’t just free-floating, it’s stable and has a preference for where it wants to be located based on the physics and the objects involved,” Long said.

Current astronomical technology does not allow Long to confirm her hypothesis, but she suspects that further ALMA observations of LkCa 15 may provide additional evidence to support her. Until then, Long hopes others will use her Lagrangian debris search method to find more potential protoplanets. “I hope this method will become widespread in the future,” she says.

Long’s research was published in The Astrophysical Journal Letters this week.

Follow Stefanie Waldek on Twitter @StefanieWaldek. Follow us on Twitter @Spacedotcom and on Facebook.

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