PLANETS ARE ALL GLOBES, right? Wrong. If they are like WASP-103b, then they are far from the perfect orbs we see in our mind’s eyes — rather, a new discovery reveals some planets might look more like a potato.
THE DISCOVERY — The planet, WASP-103b, is located
around an F-type star 1500 light-years away from Earth. This star is larger and
more massive than the Sun, and
the planet is also large, about one-and-a-half times the size of Jupiter. An
international team of astronomers published fresh findings in Astronomy &
Astrophysics on Tuesday that detail the world’s weird
shape for the first time.
It seems that because of its close proximity to its home
star — less than 20,000 miles — tidal stresses pull WASP-103b into an
unlikely shape, which astronomers have compared to a rugby ball. It also looks
a bit like an egg or a potato.
HERE’S THE BACKGROUND — Planets in our Solar System
exist millions of miles from our host star, and they take at least a few
months, a year (Earth!), or many years to make one full orbit of the Sun. But a
group of exoplanets known as Hot Jupiters orbit their home stars in a matter of
days, sometimes just hours. Hot Jupiters which orbit their star in less than a
day are known as ultra-short-period planets.
Astronomers initially discovered WASP-103b in 2014, and noted at
the time that the planet must experience severe tidal stresses due to its
proximity to its home star — it orbits WASP-103 in 22 hours. This is not the
shortest known orbital period — some exoplanets have been found with periods
less than 10 hours — but it is short enough to make WASP-103b a pretty extreme world.
When it was discovered, scientists suspected it might have an unusual shape
based on modeling, though it was unconfirmed — until now.
HOW THEY DID IT — Using the European Space Agency’s
CHEOPS mission and data from NASA’s Hubble and Spitzer space telescopes, the
team pieced together the weird shape of WASP-103b. The planet transits WASP-103
from our point of view — that is, passes in front of its home star.
This is one of the primary planet-hunting methods, wherein a
telescope waits for an exoplanet to pass in front of a distant star and notes
how much the star seems to dim. The dimming can give a lot of info about the
planet, including its size. But this study takes a different approach by also
analyzing the light curves coming from WASP-103 to determine the shape of its
planet.
The combined approach suggests the planet stretches at its
equator, yanked by tidal forces into an oblong shape — something unseen in our
Solar System as our planets are all too far away from the Sun for such a
dramatic effect. Even Jupiter’s moon Io, which is stretched and pulled by
Jupiter over the course of its 42-hour orbital period, stays roughly spherical.
Finding a planet like this is rare — another planet, WASP-12b is a similar size, oblong shape, and has a
similar orbital period, but it is being ripped apart by its home star and isn’t
so well-detailed in observations.
“It’s incredible that Cheops was actually able to reveal this tiny deformation,” Jacques Laskar, a Paris Observatory at Université Paris Sciences et Lettres astronomer and co-author of the research, says in a press statement. “This is the first time such analysis has been made, and we can hope that observing over a longer time interval will strengthen this observation and lead to a better knowledge of the planet's internal structure.”
WHY IT MATTERS — To date, astronomers have discovered
4,884 planets — and have around 8,400 candidates they’re working their way
through confirming. These planets all come in different shapes, sizes, and
configurations. Such a vast amount of data helps astronomers refine how planets
form, and how systems like our own come to be — as well as challenging our
assumptions.
This includes understanding the tidal stresses stars put on
their planets. Most ultra-short period planets are doomed as their star siphons
off material or otherwise rip them apart. But in a weird twist, astronomers
believe that WASP-103b is moving away from, rather than toward, WASP-103,
potentially sparing it this nefarious fate.
WHAT’S NEXT — Further studies of WASP-103b will help
astronomers understand the internal structure of the planet and how it affects
the atmosphere of the world, which is puffed out in comparison to Jupiter.
These investigations will also help confirm if the planet is, indeed, moving
away from the star, and what could be causing that.
The recently-launched James Webb Space
Telescope could look at WASP-103b and similar tidally-stressed planets
to better understand them, the ESA says. We can’t wait to see what other
strange worlds the telescope might turn up.