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No Place Like Home

Watch Alien Worlds Whirl Around a Distant Star

Scientists turned years of images into a spellbinding movie of a faraway stellar system in action.

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"The images were initially captured by Dr. Christian Marois of the National Research Council of Canada’s Herzberg Institute of Astrophysics. The movie animation was put together by Wang, who is part of the Berkeley arm of the Nexus for Exoplanet System Science (NExSS), a NASA-sponsored group formed to encourage interdisciplinary exoplanet science."

Not too far away, four worlds are orbiting a young, bright star—and now, after staring at the alien stellar system for seven years, we can watch as the planets quietly trace their cosmic loops.

There’s something indescribably majestic about watching these whirling worlds, each obeying the same laws of planetary motion that Johannes Kepler derived four centuries ago. After all, though we can see moons orbiting our planetary neighbors, it’s improbable that we’ll ever observe our own solar system perform this dance from afar.

The blotted-out star in the center of the video is called HR 8799, and it’s in the constellation Pegasus, about 129 light-years from Earth. About five times brighter than the sun, HR 8799 is just 30 million years old, the equivalent of a stellar newborn.

Its four visible planets are bloated and large, each more massive than Jupiter, and take between 40 and 400 Earth-years to complete one orbit. It’s possible that undetected smaller, rocky planets live closer to the star—and that a fifth large world is hiding among a dusty debris disk on the outskirts of the system.

This system of exoplanets is one of the first scientists have directly imaged. The star is near enough—and the planets are big enough—that one of the Keck telescopes atop Hawaii’s Mauna Kea could see it. UC Berkeley graduate student Jason Wang made the video by compiling seven images of the system taken from August 2009 until the summer of 2016. He then interpolated the motion of the planets between the still frames.

The result is a magical celestial sight, one that earthly eyes have been waiting centuries to see.

“It's just really cool that we can watch planets orbit other stars, and awesome to see by eye Keplerian motion in action,” says Wang.

By studying young stellar systems such as HR 8799, scientists are hoping to learn more about how planets grow and evolve, and perhaps even get a glimpse of what the beginning of our own planetary neighborhood was like.

“It's just hard to go back billions and billions of years and rewind time in our own solar system,” Wang says. “We rather find it easier to study young star systems like this to understand planet formation.”

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