International Space Agencies – Missions and Discoveries

Moon-forming region seen around an exoplanet for the first time


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.

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