Moon-forming region seen around exoplanet for the first time

Synopsis:

Scientists for the first time have spotted a Moon-forming region around a planet beyond our solar system. The research offers a deeper understanding of the formation of planets and moons.

Background:

• A study published in the Astrophysical Journal Letters has for the first time spotted a Moon-forming region around a planet beyond our solar system.
• More than 4,400 planets have been discovered outside our solar system, called exoplanets. 
• However, no circumplanetary discs had been found until now as all known exoplanets resided in “mature” (fully developed) solar systems, except the two infant gas planets orbiting PDS 70.

Findings of the study:

• The researchers used the ALMA observatory in Chile’s Atacama Desert to detect the disc of swirling material accumulating around one of two infant planets seen orbiting a young star called PDS 70.
• The disc around PDS 70c possesses enough mass to produce up to three moons, of the size of Earth’s moon.
• It is called a circumplanetary disc, and it is from these that moons are born. The discovery offers a deeper understanding of the formation of planets and moons.

About PDS 70:

• The orange-coloured star PDS 70, roughly the same mass as our Sun, is about 5 million years old.  The star is approximately 370 light-years from Earth. 
  • A light-year is the distance light travels in a year, about 9.5 trillion km.
• The system has two planets (PDS 70b and PDS 70c) around it which 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.

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 combines to form 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 the size of a planetary core. Once the core is formed, the young planet develops a strong enough gravitational potential to accrete gas which will form its atmosphere.
• Some nascent planets attract a disc of material around them and the process of core accretion begins which eventually leads to the formation of moons around planets.