Wednesday, June 29, 2022

Toi-1807b, the planet where a year lasts only 13 hours

Toi-1807b is an extrasolar planet discovered in 2020 and is one of the few known planets that completes an orbit around its star in less than a day. The interesting aspects of Toi-1807b do not stop there: the planet is in fact very young, with an age not exceeding 300 million years, and this makes it one of the youngest planets ever observed.

Astronomers have been able to observe the planet both by the radial velocity method and by the transit method. However, the observations were not at all trivial. As the Toi-1807b system is so young, the central star, an orange dwarf slightly colder than the Sun, is very active and its stellar activity has masked the presence of the planet for a long time. Only very high-resolution observational techniques have succeeded in separating the planet from stellar activity.

Having measurements with both radial velocities and the transit method is essential to derive information about the structure of the planet. The first method provides the mass of the planet, while the second gives the radius. Having these two values we can deduce the density, which gives us information both on the internal structure and on the possible presence of the atmosphere.

In the case of Toi-1807b the researchers found that this is a Earth-like planet with a mass 2.5 times that of our planet and a radius 1.5 times that of Earth.

Young planets such as Toi-1807b are expected to be surrounded by a primordial atmosphere, formed by gas acquired from the circumstellar disc from which the planets formed. Toi-1807b has no atmosphere, but this should not surprise us: being so close to its star (its orbital distance is less than 1/100 of the distance of the Earth-Sun) Its atmosphere has already been photoevaporated from the star’s intense stellar activity.

Credit: D. Nardiello/Nasa - Eyes-on-exoplanets.

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