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 5 million-year-old star in the constellation Centaurus, 370 light-years from Earth. 

Published in The Astronomical Journal, the observations show for the first time compact rings of dust surrounding the "baby planets," which will likely give rise to moons. The team also observed startling changes in planet brightness, telltale signs of the system's turbulent youth. 

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.

Paired with the 6.5-meter 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 rivaling those from an optical space telescope.  

"The mirror shape-shifts at a rate comparable to adjusting an eyeglasses prescription 2,000 times per second," Close said. "Because our technology removes disturbances from the atmosphere, it's a bit like taking a 6-1/2-meter telescope mirror and putting it in outer space by clicking a computer mouse button.

"This level of resolution revealed features around these planets in incredible detail," he added. "To give you an idea of the resolution, picture me standing in Phoenix, and you standing in Tucson. With MagAO-X, you'd be able to see whether I'm holding up one quarter-dollar coin or two from 125 miles away."

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.

"Multiple massive planets act kind of like brooms or vacuum cleaners," Close said. "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."

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 5 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. 

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

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

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 said, explaining 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," he said.

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

"Our team will continue to utilize MagAO-X to search for more protoplanets around other young stars," Close said. "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."

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

Funding for this work was provided by NASA Exoplanet Research Program. MagAO-X is supported by the National Science Foundation and the Heising-Simons Foundation.