Portuguese-led team discovers
rugby ball-shaped exoplanet

Wasp-103b is an exoplanet of several particularities. It orbits a star 1.7 times larger and about 200 degrees hotter than the Sun. In addition, it is extremely close to its star — so much so that it takes just one day to complete one orbit. Scientists have suspected that the excessive forces caused by the star “would result in a huge deformation of the planet” for a long time, as the Institute of Astrophysics and Space Sciences (IA) indicates in a press release, but it had not yet been possible to confirm it. At least until now.

Astronomer’s assumptions were right, as the extreme accuracy of CHEOPS (Characterising Exoplanet Satellite) confirmed them. The observations made by the European Space Agency (ESA) mission formed the basis for the study of an international team led by researcher Susana Barros, from IA, which, for the first time, detected the deformed figure of an exoplanet.

One more peculiarity of Wasp-103b: this exoplanet is roughly shaped like a rugby ball. Using the “exoplanet transit observations made by CHEOPS”, combined with data from the Hubble and Spitzer space telescopes, the team concluded that the planet in question is “wider at the equator than at the poles” — hence the similar shape to the planet in question of a rugby ball.

“This result is the result of several years of our work at IAstro, to develop models of planet deformation and extremely accurate data analysis models. This allowed us to lead this study within the CHEOPS consortium, whose extreme precision allowed us to detect for the first time the deformed shape of an exoplanet”, explains Susana Barros, quoted in a press release from IAstro. The study was published in Astronomy & Astrophysics.

A satellite with Portuguese Technology

This ESA mission involves three other Portuguese companies in addition to the Institute of Astrophysics. Deimos Engenharia leads the scientific component of CHEOPS, along with the IA. 

Nuno Ávila, the Country Manager in Portugal of Deimos Engenharia, explained to Agência Espacial Portuguesa in 2019 that Deimos had developed “two of the most important components of the CHEOPS scientific centre, the main one being the planning system, which will collect all observation requests from the scientific community throughout the useful life of the satellites”. 

For its part, Portuguese company FHP ensures that the internal temperature remains constant, which allows the equipment to withstand the extreme temperature range of space. The company has designed and produced the protections known as multi-layer insulation (MLI), which allow the telescope’s structure, the radiator and the optical table to withstand the extreme thermal amplitude of space, which varies between high temperatures coming from the Sun or absolute zero (around -273ºC) on the opposite side of the Sun. Finally, LusoSpace was responsible for supplying two magnetometers – a system used to measure the strength and direction of the Earth’s magnetic field – which will be used in satellite navigation.

Bigger, heavier and hotter than Jupiter

Observations from CHEOPS may also reveal information about the exoplanet’s internal structure. They may indicate how much of the planet is made up of rock, water or gaseous parts, “as a material’s resistance to being deformed depends on its composition”.

In the case of Wasp-103b, the calculations suggest “an internal composition similar” to Jupiter’s, “although the planets are in very different environments”, according to the AI statement. “One would expect an exoplanet with 1.5 times the mass of Jupiter to be roughly the same size”, says the statement, but this exoplanet’s diameter is twice that of Jupiter, which is the largest planet in our solar system.

The work of the IA researchers seems to be just beginning, however. New observations with CHEOPS, complemented with data collected by the James Webb space telescope, will be necessary to unravel other mysteries of this exoplanet. The team has already confronted a new question: “the tidal forces on a planet so close to its star would normally slow down its orbit, causing the planet’s orbit to decay until it is eventually swallowed by the star. However, the orbital velocity of WASP-103b appears to be increasing, with the planet moving away from the star.” The scientists will need additional data to clarify whether such an increase in speed is possible and, if so, what might cause it.

CHEOPS is carrying out the first of a series of three missions, which also include Plato and Ariel (in which there is also significant Portuguese participation). They plan to execute the missions within the present decade, aiming to advance the state of research regarding various aspects of exoplanets.