Recently, astronomers have discovered a really large exoplanet, named K2-25b, in a nearby open star cluster, a discovery that could shed light on planetary evolution.
K2-25b is a planet roughly the size of Neptune, orbiting a red dwarf star smaller, dimmer and much cooler than the sun — red dwarfs are the most common stars in the universe, they are also known as M stars, comprise about 70% of the stars in the Milky Way galaxy. The planet is located in the Hyades star cluster, the nearest open star cluster to Earth — just about 150 light-years away. It is visible in the night sky in the horns of the constellation Taurus, the bull. K2-25b parent star is relatively young, so the exoplanet must be in its earlier years too.
Open clusters are powerful tools as all the stars formed with the same age and composition,
said Andrew Mann ~ who discovered K2-25b.
we can compare those to planets orbiting older stars elsewhere to see if they are different in some fundamental way — to see how planets change with time.
Compared to almost all other exoplanets discovered orbiting red dwarf, K2-25b is too big for its cool host star, its 4 times the size of Earth. Astronomers have no idea how it could possibly have formed. Mann said:
Almost all of those are less than twice the size of Earth,
K2-25b is unlikely to harbor life, astronomers says. The large size of it in relation to its host star suggests that it might have a “puffy” atmosphere of hydrogen and helium.
Radiation from the star could slowly strip away K2-25b atmosphere over time,
This could have major implications for our understanding of how planets evolve, including Earth-like planets, as we need to know how well a planet can hold an atmosphere given a certain set of conditions to tell how long it remains habitable.
Astronomers do not think hot exoplanets such as K2-25b form where they now orbit, at such close range, instead these giant planets are born far away from their stars and then migrate inward because of physical interactions with the ring of gas and dust that initially surrounds young stars.
For instance, if planets orbiting young stars are farther from their host stars than their older counterparts, it suggests that planets migrate over their lifetimes. They may form farther out and migrate inward. Many exoplanetary systems have large planets orbiting close to their stars, unlike our own solar system. This kind of research could test the theory of planetary migration.
After finding many more examples of planets orbiting young stars, we can put numbers on this,
This could even give us a glimpse into what our solar system looked like” in the past.
Further observations are needed to test such scenarios, scientists wrote. They detailed their findings in a paper recently published in the Astrophysical Journal. The paper is also available on arxiv.