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Alignment of a Star and a Planet

29 Jun 2020, 16:00 UTC
Alignment of a Star and a Planet
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The planets in our solar system all orbit in roughly the same direction as the Sun spins — but this isn’t true for all planetary systems! Recent measurements of the spin angle of a nearby, planet-hosting star provide new insight into how solar systems form.
The Birth of a Solar System
If planets form from the same rotating material that created their host star, why don’t all planets have orbits that are aligned with their stars’ spins? [NASA/JPL-Caltech]In a widely accepted theory for solar system formation, a star and its planets are born from the same swirling nebula of gas and dust. As the nebula collapses, it forms a spinning star at its center, with the remaining matter flattening into a rotating disk around the newborn star. Planets later form within this disk.
In this picture, conservation of angular momentum suggests that the spin axis of a star should be aligned with the orbital angular momentum vectors of its planets — a state known as spin–orbit alignment.
This is true in our solar system: our planets’ orbits are aligned to within 7° of the Sun’s spin. But roughly a third of the planets we’ve measured in other systems have significant ...

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