The planet Kepler-37b is slightly bigger than the Moon

A comparison of the size of the planets of the Kepler-37 system with the Moon, Mercury, Mars and the Earth (Image NASA/Ames/JPL-Caltech)

A comparison of the size of the planets of the Kepler-37 system with the Moon, Mercury, Mars and the Earth (Image NASA/Ames/JPL-Caltech)

A group of scientists working at the mission of the Kepler space telescope announced that they discovered a new planetary system orbiting the star Kepler-37. So far nothing new considering that this kind of news is coming on a daily basis but this time they discovered a very small planet because Kepler-37b is slightly larger than the Moon.

The star Kepler-37 is a yellow dwarf of spectral class G about 210 light years away from Earth. It’s a little smaller than the Sun, therefore a little less hot and bright but the two stars are certainly similar. Kepler-37 is older than the Sun since it’s about 6 billion years old.

Three planets have been discovered in the system of the star Kepler-37, which has been studied using asteroseismology. In essence, its internal structure has been studied through the interpretation of its pulsations and its spectrum. Different oscillation modes penetrate differently in the depths of the star providing information similar to those obtained by seismologists studying the Earth’s interior.

The star Kepler-37 is the smallest so far studied using asteroseismology and this was possible thanks to the precision of the Kepler space telescope instruments. Knowing its characteristics helped the search for planets, which are small and the distance of all of them from their star is less than Mercury from the Sun. Considering the similarities between the two stars, it’s easy to see that the temperature on the surface of these planets must be very high.

The largest planet, Kepler-37d, has a radius estimated at about twice the Earth’s and its year lasts about 40 days. The planet Kepler-37c has a radius estimated at about three quarters of the Earth’s and its year lasts about 21 days. The planet Kepler-37b is the most interesting because it has a radius that is less than one third of the Earth’s, meaning less than 2,000 kilometers (1,200 miles), the smallest planet yet found in another solar system.

The planet Kepler-37b is the closest to its star so its year lasts only about 13 days and the average temperature on the surface is estimated to be around 425 degrees Celsius (about 800 degrees Fahrenheit). Astronomers think that it’s a rocky planet but because of its small size and its proximity to its star it’s very unlikely to have an atmosphere. In short, the conditions aren’t exactly hospitable for life.

The planet Kepler-37b is smaller Mercury but far bigger than Pluto. This has triggered a debate about its real nature because if it were in our solar system it could be considered a dwarf planet. It’s important to remember that the definition of dwarf planet isn’t only about the size but also the fact that it hasn’t cleared its orbital region of other objects of comparable size.

At the moment, it’s impossible to ascertain whether the characteristics of a celestial body in another star system make it a planet or a dwarf planet so astronomers speak generically of exoplanets. Maybe it’s just a matter of time before scientists can investigateĀ  exoplanets in a more thorough way as it’s becoming normal to find planets smaller than the Earth. Kepler-37b is very small and is likely to remain the center of attention.



About Massimo Luciani


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