Our planets circles just one star, but Kevin
Wagner and his team have found a planet that orbits a whacking three stars! How
have they found this planet? They just looked.
Spotting planets
Most of the
time, exoplanets, planets that are outside of our solar system, are discovered
with the transit method. This method uses the brightness of a star to determine
if a planet moves in front of it, because if that happens, the star gets a
little bit dimmer, and with that, scientists can find out the size, orbit time
and other things about that exoplanet. Discovering an exoplanet through
directly looking at it with a telescope is really hard. Because the light from
the star is so much brighter than the light that comes from the planet, it’s
hard to see the thing, particularly because it’s also very close to the star.
So scientists use some smart tricks to block out the starlight, and they can
observe the planet. With this particular exoplanet, it was even harder than
normal to block out the starlight, since there wasn’t just one star, but three.
But there’s also a large advantage of directly observing an exoplanet compared
to using the transit method; when they directly look at it, scientists can find
out what kind of atmosphere the planet has. And Kevin Wagner and his team have
found out that this new exoplanet is a bit like Jupiter.
That’s an odd size
Planets
like Jupiter aren’t very rare, in fact, it’s one of the most common types of
exoplanets. And planets in star systems with more than one star aren’t that
rare, but what makes this particular star system special is its size. This star
system, which is called HD 131399, is way bigger than ours, which is quite
weird, since planets usually don’t orbit that far away from the centre of a
system with more than one star. This is because the gravity of ‘outer’ stars (B
and C) make it impossible for a planet to form so close to those outer stars.
How did it end up there?
Kevin
Wagner and his team have two theories about how the planet ended up in its orbit.
One theory is that the planet used to orbit the centre star or the outer stars
and was kicked out of orbit by another planet. Another states that the planet already
existed before the three-star system formed and the planet accidentally ended
up in its odd orbit when the three-star system came into existence. The problem
with the first theory is that it requires another large planet to hang around
in the star system, the planet that kicked our Jupiter-like planet out of
orbit, and scientists haven’t found this planet yet. It could, however, be the
case that we simply can’t detect this planet. But for now, this strange
star-system remains a mystery.
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