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K2-33 is an extremely young pre-main-sequence star located about 472 light-years (145 pc) away from the Earth in the constellation of Scorpius. It is known to host one planet, a super-Neptune, named K2-33b. It is also notable for its young age.
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Nomenclature and history
K2-33 also has the 2MASS catalogue number J16101473-1919095 and EPIC designation 205117205.
Planetary candidates were detected around the star by NASA's Kepler Mission on its K2 mission, a mission tasked with discovering planets in transit around their stars. The transit method that Kepler uses involves detecting dips in brightness in stars. These dips in brightness can be interpreted as planets whose orbits pass in front of their stars from the perspective of Earth, although other phenomenon can also be responsible which is why the term planetary candidate is used.
Following the acceptance of the discovery paper, the Kepler team provided an additional moniker for the system of "K2-33". The discoverers referred to the star as K2-33, which is the normal procedure for naming the exoplanets discovered by the spacecraft. Hence, this is the name used by the public to refer to the star and its planet.
Candidate planets that are associated with stars studied by the Kepler Mission are assigned the designations ".01" etc. after the star's name, in the order of discovery. If planet candidates are detected simultaneously, then the ordering follows the order of orbital periods from shortest to longest. Following these rules, there was only one candidate planet were detected, with an orbital period of 5.424865 days.
The designation of b is given to the first planet orbiting a given star, followed by the other letters of the alphabet. In the case of K2-33, there was only one planet, so only the letter b are used. The name K2-33 derives directly from the fact that the star is the catalogued 33rd star discovered by K2 to have confirmed planets.
Stellar characteristics
K2-33 is a pre-main-sequence star that is approximately 54% the mass of and 105% the radius of the Sun. It has a temperature of 3540 K and is about 9.2 million years old. In comparison, the Sun is about 4.6 billion years old and has a temperature of 5778 K. It has about the same amount of metals as the Sun, with a metallicity ([Fe/H]) of 0. The star's luminosity is 15% that of the Sun.
The star's apparent magnitude, or how bright it appears from Earth's perspective, is 14.3. It is too dim to be seen with the naked eye.
Planetary system
The only known planet transits the star; this means that the planet's orbit appear to cross in front of their star as viewed from the Earth's perspective. Its inclination relative to Earth's line of sight, or how far above or below the plane of sight it is, vary by less than one degree. This allows direct measurements of the planet's periods and relative diameters (compared to the host star) by monitoring the planet's transit of the star.
K2-33b is known remarkably for its extremely young age, only one other planet is younger (V830 Tau b), with an age of around 2 million years, while K2-33b is only 9.3 million years old. Nonetheless, it is quite a discovery in the search of exoplanets.
Infrared measurements by the Spitzer Space Telescope show that there is still a disk of planetary debris, indicating that planet formation may not be finished yet.