Donuts of dust: An artist’s impression of the PDS 70 system with protoplanets, each surrounded by dust rings illuminated by starlight. The planets themselves (not to scale) have thin rings of plasma heated to around 14,000 degrees Fahrenheit, which glow at the red emission line of H-alpha light. Credit: Emmeline Close and Laird Close.

New observations have been made of very young planets through the use of a sophisticated adaptive optics instrument.

The unprecedented observations of newborn planets have revealed rings of dust, which will likely give rise to moons, as well as startling changes in the planets’ brightness, which are telltale signs of their turbulent youth.

With a sun more than 4.5 billion years old, our solar system is considered ‘middle-aged’, and the pictures of what it might have looked like in its infancy are lost to time.

Taking advantage of a sophisticated adaptive optics instrument, a team of astronomers at the University of Arizona made observations that reveal unprecedented details of planets when they are very young. 

The instrument, dubbed Magellan Adaptive Optics Xtreme, or MagAO-X, observed two young planets orbiting PDS 70, a very young five-million-year-old star in the constellation Centaurus, 370 light-years from Earth. 

With a deformable mirror that changes its shape quickly, MagAO-X corrects for atmospheric distortion in a way that is reminiscent of how noise-cancelling headphones filter out noise. 

“This is a really great breakthrough in technology,” said Laird Close, a professor of astronomy at Steward Observatory, in the U of A College of Science, adding that the images surpass the resolution of space telescopes, including the 2.4-meter Hubble Space Telescope and the James Webb Space Telescope.

Correcting for turbulence

Paired with the 6.5-metre Magellan Telescope at Las Campanas Observatory in Chile, the instrument works as an ‘adaptive optics system’, meaning it corrects for turbulence in the atmosphere that hampers astronomical observations.

Effectively, the system eliminates the ‘twinkle’ of stars, enabling the telescope to make images rivalling those from an optical space telescope.  

Close said: “The mirror shape-shifts at a rate comparable to adjusting an eyeglasses prescription 2,000 times per second.

“Because our technology removes disturbances from the atmosphere, it’s a bit like taking a 6-1/2-metre telescope mirror and putting it in outer space by clicking a computer mouse button.”

He added: “This level of resolution revealed features around these planets in incredible detail.”

Astronomers believe that during its infancy, our solar system might have resembled a smaller version of the PSD 70 planetary system.

The star is surrounded by a giant, pancake-shaped disk of gas and dust. Intriguingly, the disk is marked by a large dust-free gap, hinting at planets.

Close said: “Multiple massive planets act kind of like brooms or vacuum cleaners; they basically scatter the dust away and clear the large gap that we observe in this great big disk of gas and dust that surrounds the star.”

Protoplanets

Infant planets, known as protoplanets, are very rare, and the PDS 70 planets b and c are the only such planets well-known to astronomers out of 5,000 confirmed exoplanets.

Developing sharper images of protoplanets and the dust around them is key to understanding how planets and their moons form, according to the research team.

Although the planets in PSD 70 already contain several times the mass of Jupiter, they are only about five million years old – which means that they are still growing.

As the planets gain mass from their ‘birth cloud’, ‘waterfalls’ of hydrogen gas fall onto them, Close explained.  

When that happens, the planets glow in what astronomers call H-alpha, a wavelength of light emitted by hydrogen gas when in a certain excited state from the shock heating of the gas hitting the planet’s surface. 

Close explained: “Targeting that special wavelength of light allows MagAO-X to effectively limit noise and distinguish between protoplanets and their surrounding features or imaging artifacts.”

Co-author Jialin Li, a doctoral student in astronomy, added: “We can see, for the first time, rings of dust surrounding protoplanets made visible by the bright starlight reflecting off of them.”

Moons

Over the next few million years, the dust likely will collapse to form moons around each of these young planets.

MagAO-X’s sharp images revealed the first observation of young planets dramatically changing in brightness.

The researchers saw one of the planets (PDS 70 b) fade to one-fifth its original brightness over just three years while the other (PDS 70 c) doubled in brightness.

Close explained that the rapid change in brightness at H-alpha could be due to changes in the amount of hydrogen gas that is flowing onto the planets: “Essentially, one of the planets abruptly went on a diet while the other was feasting on hydrogen.”

Still, scientists are not yet sure what exactly causes such dramatic changes. 

Close advised: “Our team will continue to utilize MagAO-X to search for more protoplanets around other young stars.

“While discovering these protoplanets is right at the edge of what is technically possible today, as technology improves we should discover more such systems in the near future.”

MagAO-X principal investigator Jared Males, an associate astronomer at Steward Observatory, said: “One of our main goals is to demonstrate just how well these observations can be done with telescopes on the ground.

“We can always build larger telescopes on the ground than in space, and this result shows how important it is to build the next generation of even larger telescopes and equip them with instruments like MagAO-X.”

The research is published in The Astronomical Journal.