Discovery of the planet “TOI-1420b” with a density as low as Styrofoam | sorae space portal website

The density (average density) of a planet, which is determined by its size and mass, is lower because the planet contains more light matter, and in some cases, such as Saturn, its value is less than that of water. In the case of exoplanets, which are planets outside the solar system, some have lower densities due to expansion caused by the heat of the star. So, how low is the planet’s density?

A research team including Stephanie Yoshida of the Harvard-Smithsonian Center for Astrophysics is conducting research on a NASA (National Aeronautics and Space Administration) space telescope.he-goatBased on diameter and mass values ​​observed by the Transiting Exoplanet Exploration Satellite (Transiting Exoplanet Exploration Satellite),TUI-1420B“toThe average density is 0.082 g per cubic centimeter, which is about the same as low-density Styrofoam.I figured it out. This is also an interesting result considering the age of TOI-1420b.

■Very low-density planet “puffy planet”

The densities of the planets in our solar system range from 5.513 grams per cubic centimeter for Earth, which is the highest, to 0.687 grams per cubic centimeter for Saturn, which is the lowest. The reason that Saturn’s density is less than that of water is that it is a “giant gas planet” that consists mainly of gas, and most of Saturn’s body consists of hydrogen and helium.

By expanding our field of view beyond the solar system, we have discovered several planets that appear less massive than Saturn. In addition to being gas giant planets like Jupiter and Saturn, these planets have low densities because they are “hot Jupiters.” Because the hot Jupiter orbits so close to its star, the star’s radiation heats it up, causing its atmosphere to expand and expand its diameter. As a result, it has a lower density compared to cold planets of similar mass. Among these planets is the least dense planetPuffy planet(bulge planets) (※) .

*… The phrase “puffy planets” literally translates to “thin planets” or “puffy planets.” It has not been determined how dense a celestial body must be to be called a bulge planet, and it is not an academic classification name. For this reason, Puffy Planet’s rating is like a nickname.

■TOI-1420b has been shown to have a similar density to Styrofoam.

Mr. Yoshida and his research team conducted research on the candidate planet “TOI-1420b” obtained from TESS observation data. TOI-1420b is a planet orbiting the star TOI-1420, which is about 660 light-years away in the direction of the occult constellation as seen from Earth. This study relied on observational data from the HARPS-N radial velocity spectrometer installed at the Italian National Galileo Telescope at the Roque de los Muchachos Observatory (La Palma, Canary Islands, Spain), and the mass of TOI-1420b was estimated together. By estimating the diameter from the TESS transit method, the density of TOI-1420b was estimated.

As a result, TOI-1420b was found to have a diameter of 11.89±0.33 times the diameter of Earth, but a mass of only 25.1±3.8 times. In other words,Although TOI-1420b is roughly the same size as Jupiter, it has only about 8% the mass of Jupiter.. The density of TOI-1420b calculated from this is 0.082 ± 0.015 g per cubic centimeter, which is approximately the same value as a low-density type of Styrofoam.

It is assumed that the reason for the low density of TOI-1420b is that it orbits close to the star TOI-1420. In fact, TOI-1420b orbits at a distance of about 11 million kilometers (about 0.073 AU) from TOI-1420 every 6.96 days, and its surface temperature is estimated at 680 degrees Celsius. This high temperature is thought to cause TOI-1420b to expand and become a puffy planet.

■ TOI-1420b may become the standard for Puffy Planet

at present,TOI-1420b is the largest planet with a diameter less than 50 times that of Earth.It has a record as However, simple density comparisons have also found puffy planets with low densities that are comparable to or even lower than TOI-1420b. Therefore, TOI-1420b is not the least dense planet, but from a planetary science perspective it is one of the more interesting objects to observe than the other bulge planets.

Firstly,TOI-1420b contains a lot of observational data, making it possible to conduct a more detailed investigation than other bulge planets.He is. For example, in this research, it was calculated that the proportion of gas components in the entirety of TOI-1420b is about 82%, and the center of TOI-1420b has a rocky core with a mass of about four times that of Earth. It is estimated that there is. This basic data is important for research into how Puffy Planet formed.

In addition, TOI-1420 is a G-type main sequence star like the Sun, and is estimated to be less than 10.7 billion years old. The fact that TOI-1420b, which is estimated to be the same age as the star, is a bulging planet is interesting in itself. It is thought that in the upper atmosphere of a planet experiencing such a large degree of thermal expansion, there are many gaseous components that escape gravity. Hence, the gaseous components that cause the density to decrease are gradually lost, so the planet’s density must increase.

It is currently unclear whether TOI-1420b is a puffy planet that released its atmosphere more than 10 billion years ago, or whether it recently became a puffy planet due to changes in its orbit.TOI-1420b may become a standard observation target in the investigation of how Puffy Planet was born.In addition, the atmospheric flow conditions observed during the research process can be applied to atmospheric science on other planets.

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Written by Riri Aya