From UPSC perspective, the following things are important :
Prelims level : Exoplanets
Mains level : Core accretion
Scientists for the first time have spotted a Moon-forming region around an exo-planet beyond our solar system.
What are Exoplanets?
- More than 4,400 planets have been discovered outside our solar system, called exoplanets.
- Most orbit other stars, but free-floating exoplanets, called rogue planets, orbit the galactic center and are untethered to any star.
- No circumplanetary discs had been found until now because all the known exoplanets resided in “mature” – fully developed – solar systems, except the two infant gas planets orbiting PDS 70.
What is the new finding?
- The researchers have detected a disc of swirling material accumulating around one of two newborn planets.
- They were seen orbiting a young star called PDS 70, located a relatively close 370 light-years from Earth.
- It is called a circumplanetary disc, and it is from these those moons are born.
- The discovery offers a deeper understanding of the formation of planets and moons.
Focus of the finding: Formation of disc
- In our solar system, the impressive rings of Saturn, a planet around which more than 80 moons orbit, represent a relic of a primordial moon-forming disc.
- The orange-colored star PDS 70, roughly the same mass as our Sun, is about 5 million years old– a blink of the eye in cosmic time.
- The two planets are even younger. Both planets are similar (although larger) to Jupiter, a gas giant.
- It was around one of the two planets, called PDS 70c, that a Moon-forming disc was observed.
Observing birth of a moon: Core Accretion
- Stars burst to life within clouds of interstellar gas and dust scattered throughout galaxies.
- Leftover material spinning around a new star then coalesces into planets, and circumplanetary discs surrounding some planets similarly yield moons.
- The dominant mechanism thought to underpin planet formation is called “core accretion”.
- In this scenario, small dust grains, coated in ice, gradually grow to larger and larger sizes through successive collisions with other grains.
- This continues until the grains have grown to a size of a planetary core, at which point the young planet has a strong enough gravitational potential to accrete gas which will form its atmosphere.
- Some nascent planets attract a disc of material around them, with the same process that gives rise to planets around a star leading to the formation of moons around planets.
- The disc around PDS 70c, with a diameter about equal to the distance of the Earth to the sun, possesses enough mass to produce up to three moons the size of Earth’s moon.