Shedding lights on the mechanism responsible for the formation of Hot Jupiters. The study: “Gas, not dust: Migration of TESS/Gaia hot Jupiters possibly halted by the magnetospheres of protoplanetary disks” of I. Mendigutia (CAB) appeared on A&A
Hot Jupiters are gas giants that orbit at distances less than 0.1 AU from their host star. But what determines the final orbital radius of these planets? In intermediate-mass stars, it seems to be the dispersion of gas in their protoplanetary disks.
Hot Jupiters are a class of exoplanets that are not found in our Solar System. They are gas giants orbiting their star at distances smaller than 0.1 Astronomical Units (AU; 1 AU is the average distance between Earth and the Sun, approximately 150 million km). Due to the intense irradiation received from the central star, the atmospheres of these planets reach equilibrium temperatures above 1500 K.
The formation of these planets certainly takes place within protoplanetary disks—disk-shaped structures composed of gas and dust (mainly solid grains of silicate and other elements) that surround young stars during the first few million years of their evolution. Planets form within these disks and may later migrate toward closer orbits due to interactions with the disk itself. The final orbits of hot Jupiters can thus correspond to the minimum distance reached by the planet at the end of their migration, when the protoplanetary disk has dispersed
What determines this minimum distance? The authors of the study “Gas, not dust: Migration of TESS/Gaia hot Jupiters possibly halted by the magnetospheres of protoplanetary disks“, led by astrophysicist I. Mendigutía from the Centro de Astrobiología in Madrid, propose two hypotheses:
- The sublimation of dust in the inner region of the protoplanetary disk.
- The disruption of the gas disk near the star, caused by the stellar magnetic field.
In short, the temperature in the disk increases as one gets closer to the star. When it reaches about 1500 K, the dust particles in the disk sublimate, turning into gas and effectively destroying the dust component of the disk. The gas can move closer to the star, but the high temperatures lead to a strong degree of ionization, which enhances the interaction between the gas and the stellar magnetic field. At certain distances—depending on factors such as the strength of the magnetic field—this interaction also leads to the disruption of the gas disk.
The research team analyzed hot Jupiters orbiting 47 intermediate-mass stars (between 1.3 and 3 solar masses) and concluded that the planets orbital distances were most likely set by the disruption of the gas disk. This conclusion is supported by two main pieces of evidence:
- If dust sublimation had determined the final planetary orbit, a correlation between the star luminosity and the planet orbital distance would be expected. However, no such correlation is observed.
- The orbits
of hot Jupiters around low-mass stars tend to be larger than those around intermediate-mass stars, which usually have weaker magnetic fields and thus smaller gas disruption radii
The study was published as a Letter in the journal Astronomy & Astrophysics. Among the co-authors is astrophysicist J. Maldonado of INAF – Osservatorio Astronomico di Palermo.
In the cover illustration (click here to view it in full), a graphical representation of a protoplanetary disk around an intermediate-mass star is shown, indicating the locations of the dust sublimation front (“dust barrier”) and the gas disk truncation radius (“gas barrier”) for both a low-mass star and an intermediate-mass star.
Mario Giuseppe Guarcello
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