Astronomers using a mountain covered in 66 radio telescopes have revealed a “domino effect” or chain reaction mechanism where the formation of one planet around a star can trigger the creation of others farther out.
It comes from a new study of the only star system astronomers know that has a rotating disk of gas and dust around it containing already-formed planets. The micron-sized dust grains in a protoplanetary disk like this around a young star are thought to be the building blocks of planets and moons in all star systems.
However, exactly how that happens for a multi-planet star system — like our solar system — is unknown.
Birthplace Of Planets
The paper, published today in The Astrophysical Journal Letters, details observations of young star PDS 70, 367 light-years from the solar system in the constellation Centaurus. PDS 70 is the only known system where already-formed planets have been observed within a protoplanetary disk. Two planets are known to exist around the star.
Previous studies with the ALMA telescope revealed a ring of dust grains surrounding the two known planets in this system but lacked the resolution to detail the activity within the dust ring. Observing at longer wavelengths using ALMA, the researchers could penetrate dust clouds and reveal a clump of dust at the outer edge of the two planets’ orbits.
Domino Effect
The paper concludes that the clump is being shepherded into place by the gravitational influence of the two existing planets, providing the material for forming a new planet.
That suggests, according to scientists, that planets may form in sequence around stars, with the development of one planet influencing the formation of the next. This ‘domino effect’ or chain reaction could explain how multi-planet systems form.
However, whether or not the solar system formed this way is unclear. Although the planets formed from a protoplanetary disk — the inner planets (including Earth) in the hot region close to the sun and the outer gas planets farther out — it’s thought that the giant planet Jupiter may have acted as the “shepherd.” Any domino effect was likely complicated by gravitational forces, the giant planets migrating, and collisions of young planets. In other words, chaos.
First-Born Planet
PDS 70 is famous among astronomers and exoplanet hunters. It’s where, in 2018, the European Southern Observatory’s Very Large Telescope captured the first confirmed image of a planet forming in the protoplanetary disk surrounding a young star. It was seen to be carving a path through the gas and dust, about the same distance from its star as Uranus is from the sun. The planet, PDS 70b, was revealed to be a giant gas planet with a mass a few times that of Jupiter and a surface temperature of around 1,800 degrees Fahrenheit (1,000 degrees Celsius).
Atacama Desert
The new observations come from the Atacama Large Millimeter/submillimeter Array radio astronomy site on the Chajnantor plateau in Chile’s Atacama desert. One of the driest and highest places on Earth, its altitude of 16,500 feet (5,000 meters) allows observations to be made under exceptionally clear skies and through less of Earth’s dense atmosphere.
Just a few miles from ALMA is the University of Tokyo Atacama Observatory, the world’s highest astronomical observatory at 5,640 meters atop Cerro Chajnantor in Chile, which opened in May. TAO is a 6.5-meter aperture telescope specializing in infrared observations — just as the James Webb Space Telescope does. It’s able to study the environments around stars — including planet-forming regions such as found around PDS 70 — and see through cosmic dust. It’s expected to revolutionize ground-based astronomy and alleviate demand for observing time on both JWST and the Hubble Space Telescope.
Wishing you clear skies and wide eyes.
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