If you want to ask which planet in the solar system is the smallest, Mercury with a diameter of less than 4,800 kilometers, it is definitely the best choice.
But do you know who will win this laurel among the more than 5,000 exoplanets discovered so far?
Hello and welcome aboard the Puzzler. Let's leave the solar system today and go in search of the smallest exoplanet!
Of all the exoplanets discovered so far, the smallest is probably this rocky planet called Kepler-37b in the constellation Lyra.
Similar to the eight planets of the solar system, it is also orbiting a G-shaped star that is about the same size and temperature as the Sun. It only takes about 13 days to complete a revolution. With the Kepler Space Telescope, scientists calculated that Kepler-37b has a 35% occlusion rate to the Earth based on the transit method. It is 27% larger than the Moon and slightly smaller than 38% of Mercury. As a result, its radius is slightly larger than that of the Moon, but smaller than that of Mercury. For its part, its smaller size suggests that it is likely to be composed mainly of rock and metal, similar in composition to rocky planets in the solar system.
Its main-sequence stars have about 6% of the mass of the Sun and less than 10% of the Sun's temperature. Despite the low temperatures, Kepler-37b orbits only 15 million kilometers from its parent star. It is more than 3 times closer than Mercury to the Sun.
Such a close distance results in a surface temperature, most likely as high as 400 degrees Celsius. Given its size and surface temperature, astronomers believe that Kepler-37b may not be a place to live. To a large extent, it will be a barren planet with no atmosphere and no liquid water.
Of course, it's not the only planet around. In addition to him, there are at least two confirmed exoplanets that are also orbiting their parent stars.
It's just that the orbits of these three exoplanets are too close to the main star. As a result, none of them are located in the habitable zone. So, although there is one of them, it is twice the size of the Earth. But it's probably not the super-Earth we're looking forward to!