Moon-Forming Disk Around Exoplanet

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

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• The researchers used the ALMA observatory in Chile’s Atacama desert to detect the disc of swirling material accumulating around one of two newborn planets seen orbiting a young star called PDS 70, located a relatively close 370 light years from Earth.

Discovery

• Scientists for the first time have spotted a moon-forming region around a planet beyond our solar system – a Jupiter-like world surrounded by a disc of gas and dust massive enough that it could spawn three moons the size of the one orbiting Earth.
• It is called a circumplanetary disc, and it is from these that moons are born. The discovery offers a deeper understanding about the formation of planets and moons.
• 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.
• More than 4,400 planets have been discovered outside our solar system, called exoplanets. 
• PDS 70:
  • The orange-coloured star PDS 70
  • It is roughly the same mass as our Sun and about 5 million years old– a blink of the eye in cosmic time. 
• PDS 70c:
  • The two planets are even younger from Star. 
  • 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. 
  • PDS 70c orbits its star at 33 times the distance of the Earth from the sun, similar to the planet Neptune in our solar system. 

Exoplanet

• An exoplanet is any planet beyond our solar system. More than 4,400 planets have been discovered outside our solar system.
• Most orbit other stars, but free-floating exoplanets, called rogue planets, orbit the galactic center and are untethered to any star.

Planet Formation

• The dominant mechanism thought to underpin planet formation is called “core accretion”.
• Procedure: 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.

Birth of a Moon

• 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.

Sources: TH