The Cheops mission, from European Space Agency (ESA), has just revealed the existence of a strange oval-shaped planet, more like a rugby ball than a sphere. This is the first time that a similar deformation has been observed in a planetary body.
His name is WASP-103b, is located about 500 light-years away, in the constellation Hercules, and scientists studying it believe that it has been deformed by the intense tidal forces exerted by its host star, WASP-103, which is about 200 degrees warmer. hot and 1.7 times bigger than the Sun. The work has just been published in
‘Astronomy & Astrophysics’.
From Earth, we experience tides mainly because the Moon slightly ‘tugs’ on the planet as it rotates around us. The Sun also has an effect on the tides, although it is not significant because it is too far away to cause large deformations. But the same cannot be said for WASP-103b, a planet nearly twice the size of Jupiter at 1.5 times its mass, and which orbits remarkably close to its host star. So much so that each orbit takes less than a day. Astronomers suspected that such close proximity is capable of causing monumental tides, but until now they have not been able to measure them.
A gigantic rugby ball
However, using new data from ESA’s Cheops Space Telescope, combined with earlier data from the NASA / ESA Hubble Space Telescope and the Spitzer Space Telescope from NASAastronomers have finally been able to detect exactly how tidal forces act on the exoplanet. And, in fact, they are so strong that they have even managed to alter its usual spherical shape and turn it into something like a gigantic rugby ball.
Cheops obtains data from the worlds it observes using the transit method: the decrease in 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 allowed astronomers much more: to detect the tiny signal from the tidal warp of WASP-103b.
“It is incredible that Cheops was able to reveal this deformation,” says Jacques Laskar, from the Paris Observatory and co-author of the research. This is the first time such an analysis has been carried out, and we can hope that observing it for a longer time will strengthen the data and lead to a better understanding of the internal structure of the planet.
The number of Love
The researchers used the transit light curve of WASP-103b to derive a parameter, known as’the love number‘, which measures how mass is distributed within a planet. Something that also allows us to know more about its internal structure.
“The resistance of a material to deformation depends on its composition,” explains Susana Barros, from the University of Porto and main author of the research. For example, here on Earth we have tides due to the Moon and the Sun, but we can only see the tides in the oceans. The rocky part doesn’t move that much. By measuring how much the planet is deformed, we can tell how rocky it is and how much gas or water it is. ‘
The love number value for WASP-103b is similar to that of Jupiter, suggesting that its internal structure is similar, even though WASP-103b has twice the radius. “In principle,” the researcher continues, “we would expect a planet with 1.5 times the mass of Jupiter to be approximately the same size, so WASP-103b must be very inflated due to the heating of its star and perhaps other mechanisms. If we can confirm the details of its internal structure with future observations, perhaps we can better understand what it is that makes it so inflated. Knowing the size of the nucleus of this exoplanet will also be important to better understand how it formed.
However, and given that today the uncertainty in the love number is still quite high, future observations with Cheops and the James Webb Space Telescope for more details. The extremely high precision of the Webb will improve measurements of the tidal deformation of exoplanets, allowing a better comparison between the so-called ‘Hot jupiters‘and the giant planets of the Solar System.
An added mystery
There is also another mystery surrounding WASP-103b. The tidal interactions between a star and a planet that is very close and larger than Jupiter would normally make its orbit narrower and narrower, that is, it would gradually get closer to the star until it was finally devoured by it. But measurements of WASP-103b seem to indicate otherwise, and instead of decreasing, its orbital period appears to be increasing. In other words, the planet appears to be slowly moving away from its parent star. Which indicates that, apart from the tidal forces, there must be something else at stake.
Although it is still early to draw conclusions, the researchers studied several potential scenarios, such as that a companion star of the host (and not yet detected) is affecting the dynamics of the system; or that the planet’s orbit is actually slightly elliptical. With the current data, the team couldn’t confirm these scenarios, but couldn’t rule them out either. And they won’t be able to understand what’s really going on until they make new observations.
.