Where the sky hits the Sun

via Astronomy Now.

The exoplanet WASP 12b, orbiting the sun like star WASP 12, 600 light years away in the area of the constellation of Auriga, is seemingly unremarkable as exoplanets go. It is a hot Jupiter type object, about 1.4 times the size of Jupiter but seventy five times closer in to its star than the Earth, and completes an orbit of its star in around twenty-six hours.

Such objects dominate our league tables of exoplanet discovery. Their sizes and closeness to the star, plus their fast years make them ideal for spotting via the photometric method, where the dip in light as the planet transits its star is measured. Their masses and the velocity of their orbits also mean the Doppler shift method (and the astrometry one where the physical motion of a star is observed) where the star, pulled one way and another by the planet, like a ball on a string whirled around it, causes the star to wobble significantly enough for its spectrum to be red and blue shifted measurably. Even in the gravitational lensing arena, the masses of these objects cause the greatest and therefore most distinct flaring.

However, WASP 12b is a little separated from the pack by its orbital characteristics. Whereas the other hot Jupiters tend to lie in near circular orbits, 12b has a more eccentric one – more elliptical. This means the tidal forces on the planet, ie the difference in gravitational pull from the star on the front of the planet compared with the back, change dramatically over the course of its 26 hour orbit. This in turn means that as well as the roasting from the direct radiation of the star, the inside of the planet is heated by it continuously getting squashed and stretched.

This heating has led to an expansion of the planet’s atmosphere beyond the point at which the planet’s gravity is stronger than that of the star. 190 million, billion tonnes of material (a tiny ten millionth of a mass of Jupiter) gets stripped from 12b in every one of our years. Furthermore, with an estimated ten million years before the planet finally spirals to a fiery death within the star itself, there’s a chance that WASP 12b will lose its entire atmosphere and be left as a planetary core remnant in orbit of the star (if the planet has a solid core, it will be left as a highly dense rocky planet).

The atmosphere is believed to have formed a gaseous disk around the star and it has been suggested that within this disk lurks at least one large rocky planet, potentially the object whose interactions left 12b in its peculiar orbit.

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