HomeScience and ResearchSpaceScientists discover, for the first time, an oval-shape planet

Scientists discover, for the first time, an oval-shape planet

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Astronomers believe its distortion is caused by the tremendous tidal forces of its host star.

The European Space Agency’s (ESA) Cheops mission has just discovered the existence of a weird oval-shaped planet that looks more like a rugby ball than a sphere. Notably, this is the first time a planetary body has been seen deformed.

WASP-103b is around 500 light-years away in the constellation Hercules, and scientists investigating it believe it has been distorted by the enormous tidal forces generated by its host star, WASP-103, which is about 200 degrees hotter and 1.7 times larger than the Sun.

The research was recently published in the journal ‘Astronomy & Astrophysics’.

Tides occur in the waters on Earth mostly due to the Moon’s small ‘pull’ on the earth as it circles around us. The Sun has an effect on the tides as well, however it is minor because it is too far away to induce substantial deformations. However, WASP-103b, a planet nearly twice the size of Jupiter with 1.5 times its mass and orbiting extremely close to its host star, cannot be considered to be the same. So fast that each orbit takes under a day. Astronomers had suspected that such close proximity may cause massive tides, but they hadn’t been able to measure them until now.

A giant rugby ball

However, by combining fresh data from the ESA’s Cheops Space Telescope with previously acquired data from the NASA/ESA Hubble Space Telescope and NASA’s Spitzer Space Telescope, astronomers have been able to determine the precise nature of tidal forces.

In fact, they are so powerful that they have managed to transform their regular spherical shape into something resembling a massive rugby ball.

Cheops obtains data from the worlds it observes using the transit method: the dimming of light that occurs when a planet passes in front of its star from our point of view. Usually studying the shape of that light curve reveals details like size. But Cheops’ high precision has enabled astronomers to do much more: detect the tiny signal of WASP-103b’s tidal warp.

“It’s incredible that Cheops was actually able to reveal this tiny deformation,” said Jacques Laskar, co-author of the research. “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 better knowledge of the planet’s internal structure.”

The Love number

The astronomers used the transit light curve of WASP-103b to establish a parameter called ‘the love number’ that quantifies the distribution of mass within a planet. Something that also enables us to gain a better understanding of its internal structure.

“The resistance of a material to being deformed depends on its composition,” explained Susana Barros, lead author of the research. “For example, here on Earth we have tides due to the Moon and the sun but we can only see tides in the oceans. The rocky part doesn’t move that much. By measuring how much the planet is deformed we can tell how much of it is rocky, gaseous or water.”

WASP-103b’s love number is close to Jupiter’s, implying that its internal structure is similar, despite the fact that WASP-103b has twice the radius.

“In principle we would expect a planet with 1.5 times the mass of the Jupiter to be roughly the same size, so WASP-103b must be very inflated due to heating from its star and maybe other mechanisms,” added Susana.

“If we can confirm the details of its internal structure with future observations maybe we could better understand what makes it so inflated. Knowing the size of the core of this exoplanet will also be important to better understand how it formed.”

Given the current level of uncertainty in the number of loves, more observations with Cheops and the James Webb Space Telescope will be necessary to get more information. Webb’s exceptional precision will improve planetary tidal warping studies, allowing for a more accurate comparison between so-called “hot Jupiters” and the Solar System’s large planets.

An added mystery

WASP-103b is also shrouded in a cloud of mystery. Tidal interactions between a star and a planet very close to and larger than Jupiter would generally force the planet’s orbit to shorten, causing it to approach the star more closely until it was consumed.

However, measurements of WASP-103b appear to show that, rather than declining, its orbital period is rising. To put it another way, the planet looks to be drifting away from its parent star. This suggests that, in addition to tidal forces, something else is at work.

Although it is too early to draw any conclusions, the researchers looked into numerous possibilities, including the possibility that the host star’s companion star (which has yet to be discovered) is influencing the system’s dynamics, or that the planet’s orbit is slightly elliptical.

The scientists couldn’t validate these scenarios based on the present data, but they couldn’t rule them out either.

And until they make new observations, they won’t be able to figure out what’s actually going on.

Source: 10.1051/0004-6361/202142196

Image Credit: ESA

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