WASP-33b is an extrasolar planet orbiting the

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

HD 15082 HD 15082 (also known as WASP-33) is a star located roughly 399 light years away in the northern constellation of Andromeda (constellation), Andromeda. The star is a Delta Scuti variable and a planetary transit variable. A hot Jupiter typ ...

. It was the first planet discovered to orbit a Delta Scuti variable star. With a semimajor axis of and a mass likely greater than Jupiter's, it belongs to the hot Jupiter class of planets.

Discovery

In 2010, the SuperWASP project announced the discovery of an extrasolar planet orbiting the star

. The discovery was made by detecting the transit of the planet as it passes in front of its star, an event that occurs every 1.22 days.

Orbit

A study in 2012, utilizing the Rossiter–McLaughlin effect, determined the planetary orbit is strongly misaligned with the equatorial plane of the star, misalignment equal to −107.7°, making the orbit of WASP-33b retrograde. The periastron node is precessing with the period of 709 years.

Physical characteristics

Limits from radial velocity measurements imply it has less than 4.1 times the mass of Jupiter. The

exoplanet An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...

orbits so close to its star that its surface temperature is about . The transit was later recovered in

Hipparcos ''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial obj ...

data.

Atmosphere

In June 2015, NASA reported the exoplanet has a

stratosphere The stratosphere () is the second layer of the atmosphere of the Earth, located above the troposphere and below the mesosphere. The stratosphere is an atmospheric layer composed of stratified temperature layers, with the warm layers of air ...

, and the

atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...

contains titanium monoxide, which creates the stratosphere. Titanium oxide is one of only a few compounds that is a strong absorber of visible and ultraviolet radiation, which heats the atmosphere, and is able to exist in a gas state in a hot atmosphere. The detection of temperature inversion (stratosphere), water and titanium oxide was disproved with the higher quality data obtained by 2020. Only upper limit of titanium oxide volume mixing rate equal to 1 ppb can be obtained. Later research reconfirmed the existence of titanium oxide in the atmosphere of WASP-33b, although in concentrations not detectable by HARPS-N. The neutral iron and silicon were also detected. 15-121a-HubbleDetectsStratosphereOnWASP33b-20150611

15-121a-HubbleDetectsStratosphereOnWASP33b-20150611

In 2020, with the detection of secondary eclipses (when the planet is blocked by its star), the mass of the planet along with temperature profile across its surface was measured. ''WASP-33b'' has strong winds in its atmosphere, similar to Venus, shifting the hottest spot 28.7±7.1 degrees to the west. The averaged wind speed is 8.5 km/s in the thermosphere. The illuminated side brightness temperature is , while the nightside brightness temperature is . The atmospheric escape driven by hydrogen Balmer line absorption is relatively modest, totaling about one to ten Earth masses per billion years. The water in dayside atmosphere of WASP-33b is mostly dissociated to hydroxyl radicals due to high temperature, as planetary emission spectra indicated.

Non-Keplerian features of motion for WASP-33b

In view of the high rotational speed of its parent star, the orbital motion of WASP-33b may be affected in a measurable way by the huge

oblateness Flattening is a measure of the compression of a circle or sphere along a diameter to form an ellipse or an ellipsoid of revolution (spheroid) respectively. Other terms used are ellipticity, or oblateness. The usual notation for flattening is ...

of the star and effects of general relativity. First, the distorted shape of the star makes its

gravitational field In physics, a gravitational field is a model used to explain the influences that a massive body extends into the space around itself, producing a force on another massive body. Thus, a gravitational field is used to explain gravitational phenome ...

deviate from the usual Newtonian inverse-square law. The same is true for the Sun, and part of the precession of the orbit of Mercury is due to this effect. However, it is estimated to be

9 \times 10^9

greater for WASP-33b. Other effects will also be greater for WASP-33b. In particular, precession due to general relativistic frame-dragging should be

3 \times 10^5

greater for WASP-33b than for

Mercury Mercury commonly refers to: * Mercury (planet), the nearest planet to the Sun * Mercury (element), a metallic chemical element with the symbol Hg * Mercury (mythology), a Roman god Mercury or The Mercury may also refer to: Companies * Merc ...

, where it is so far too small to have been observed. It has been argued that the oblateness of HD 15082 could be measured at a percent accuracy from a 10-year analysis of the time variations of the planet's transits. Effects due to the planet's oblateness are smaller by at least one order of magnitude, and they depend on the unknown angle between the planet's equator and the orbital plane, perhaps making them undetectable. The effects of frame-dragging are slightly too small to be measured by such an experiment. Nodal precession of WASP-33b, caused by oblateness of the parent star, was measured by 2021. The gravitational quadrupole moment of the HD 15082 was found to be equal to 6.73×10⁻⁵. The non-Keplerian precession is expected to be 500 times smaller, yet to be detected.

References