A recent article appeared in the scientific journal Nature reports the discovery of the exoplanet K2-360 b distant from Earth 764 light years in the direction of constellation of Virgo. This alien world is a so-called super-Earthor an object with a mass slightly greater than that of the Earth, approximately 7.6 times in this case. It would therefore appear to be one of the many exoplanets already discovered if it were not for the fact that this mass is concentrated in a radius that is only one and a half times the terrestrial one, thus giving the planet a extraordinary densitycomparable with that of lead. But its peculiarities do not end there, since K2-360 b orbits so close to its star that a year lasts only 21 hours. Unfortunately, given its proximity to the star, this exoplanet it is not habitable.
What is the exoplanet K2-360 b like and where is it located?
The presence of a planet around the solar-type star K2-360 was suggested by the data analysis of Kepler telescope of NASA. The latter showed how the decrease in brightness of the star was compatible with the presence of an exoplanet orbiting with a ultra-short period Of less than a day. To confirm the discovery, astronomers used data from the HARPS spectrographmounted on the ESO 3.6-metre telescope in the Chilean Andes.
HARPS confirmed the presence of K2-360 bgiving us estimates of the exoplanet’s mass and radius. In particular, K2-360 b orbits its parent star with a 21 hour periodimplying that on that planet a year lasts less than a day. Furthermore, it has a mass of approx 7.6 times that of the Earth and a radius of 1.5 times the terrestrial one. Combining these data we obtain that K2-360 b has a extraordinary density of 11 g/cm3a density comparable to that of lead and the highest ever found for a super-Earth.
Astronomers consider this planet not habitable because its surface temperature is presumably very high. The very short orbital period in fact indicates that the planet orbits very close to its star: Kepler’s third law establishes that the further a planet is from its star, the longer it takes to complete an orbit. In fact, an orbital period of only 21 hours presumes a distance from the star K2-360 so small as to ensure too high temperatures to sustain life as we know it.
The K2-360 star system
K2-360 is a solar-type star in the constellation Virgo. It is approximately 764 light-years from Earth and is in the main sequence phase where it burns hydrogen in its core, just like our Sun, with an estimated age of about 6 billion years. In addition to the planet K2-360b, this star system also appears to possess a second planet, K2-360 cfarther than the first, which orbits the star with a period very short of suns 10 days. From data analysis, scientists estimated that this second planet possesses a mass which is approximately double that of K2-360b, equal to approximately 15 times the terrestrial one. Since K2-360c does not pass in front of the stellar disk due to the inclination of its orbit, unfortunately it was not possible to exploit the combination of Kepler and HARPS data to determine the radius, and therefore the density, of this second exoplanet.
How K2-360b was discovered
The exoplanet K2-360 b was discovered thanks to combination of two techniques widely used for the discovery of planets outside the Solar System. A first clue to the existence of K2-360 b came thanks to the observations of Kepler telescope of NASA, which uses the so-called transit method. It consists of observing a star for a certain period of time in search of decreases in brightness caused by the passage of a planet in front of the stellar disk.
Once it is established that something is blocking the light coming from the star, in order to provide an accurate estimate of the mass of the object we use the radial velocity method (as shown in the video above) which consists in measuring the Doppler effect caused by the mutual gravitational attraction between the planet and the parent star. Depending on the intensity of the effect, scientists are able to derive an estimate of the mass of the exoplanet.
