17 years ago, scientists were the first to calculate the size of the first extra-solar planet. Then the question arose: “Why are they so big?”. The recent discovery of twin planets will help come closer to the answer.
Gas giants are filled with hydrogen and helium, and also exceed the earth's diameter by at least 4 times. If such objects are close to their stars, then they are called “hot Jupiter”. By mass, they resemble Jupiter and Saturn, but more often they become large and almost reach stellar parameters.
Most likely, their incredible dimensions are related to the heat flow in the atmosphere, which is explained by several theories. But we do not have millions of years to follow the development of a particular planetary system.
To solve this problem, the researchers decided to revise the data of the K2 mission in order to find the hot Jupiters around the giant stars. These stars arrive in the later stages of life, therefore they influence the planets more. Scientists believe that hot Jupiter near such stars should increase due to the direct flow of energy. During the search, we found two planets at intervals of 9 days. It turned out that both are 30% larger than the size of Jupiter. A survey from the Keck Observatory showed that despite the scale, they still reach only half of Jupiter’s massiveness. Surprisingly, the characteristics are very similar, so they were called "twins".
Using the tracking models of planetary evolution, the researchers determined the growth of the planets while absorbing heat from the star and transferring it to the depth of the interior, because of which the entire planet began to expand in size, but decrease in terms of density.
Of course, it is risky to rely on data confirmed by only two objects. But these explanations exclude inflationary moments and are consistent with observations. In the end, the Sun will also become a red giant and will affect the entire system. Therefore, studying the influence of stars in other systems will help to understand what will happen to life on Earth.