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With Very Large Telescope, astronomers spy a planet being born around a young star

Astronomers have captured the first clear image of a planet caught in the act of being born. It is carving a path through the primordial disc of gas and dust around the very young star PDS 70.

An international team of astronomers using the Very Large Telescope in the Atacama Desert in Chile has captured a snapshot of a planet forming in the middle of the disc of gas and dust around its young star.

The system of dwarf star PDS 70, described in two papers published in the journal Astronomy & Astrophysics, offers an unprecedented glimpse at these early stages of planetary formation.

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PDS 70 lies around 114 parsecs (or about 372 light-years) away in the direction of the constellation Centaurus. Astronomers had taken notice of it back in the 1980s and 1990s because infrared emissions from the system seemed to indicate it was very young, around 3 million to 10 million years old, said Michael Meyer, an astronomer at the University of Michigan in Ann Arbor who co-wrote both papers.

As a star is born, planets begin coalescing out of the disc of gas and dust that spins around their stellar host. Astronomers want to study the dusty discs around nascent stars to learn more about planetary formation, but it’s extremely difficult because the light from the star itself outshines its dimmer surroundings.

For these papers, a German-led team of scientists managed to capture images of the disc and the planet around PDS 70 thanks to a coronagraph on the European Southern Observatory’s Very Large Telescope. A coronagraph uses a mask to block out the bright light from the star, the way you might use your hand to block out the sun when looking for something overhead. This allowed astronomers to study the disc and discover a planet in its midst.

This chart shows the southern constellation of Centaurus and marks most of the stars visible to the unaided eye on a clear dark night. The dwarf star PDS 70 is marked with a red circle.
This chart shows the southern constellation of Centaurus and marks most of the stars visible to the unaided eye on a clear dark night. The dwarf star PDS 70 is marked with a red circle. (ESO, IAU and Sky & Telescope)

Researchers had long known about large gaps in the disc that they speculated might be the product of a planet forming and moving through it, but they could not tell for sure until now.

“This is perhaps the best case to date for seeing a true protoplanet still embedded in the disk of gas and dust from which such gas giant planets form,” Meyer said in an email. “There have been a handful of other cases and those are still under study, but this is perhaps the ‘cleanest’ result to date.”

The planet PDS 70b sits about 1.86 billion miles away from its host star, roughly as far as Uranus is from our sun. It appears to be a gas giant planet a few times more massive than Jupiter, the king of our solar system. But unlike Jupiter, whose temperature is a chilly minus-163 degrees Fahrenheit or so, this planet is far hotter than any planet in our solar system, Meyer said, with a temperature of around 1,340 to 2,420 degrees.

“This planet is so hot because it is very young,” he said. “It is still converting potential energy of contraction into heat at its surface. Jupiter has been doing this for billions of years, and radiating that energy away as it cools over time.”

The discovery of this planet, coalescing out of and carving through its dusty cradle, offers a tantalizing target for astronomers and planetary scientists looking to study this early epoch in stellar formation, the scientists said.

“The ability to relate its physical properties to the impact it is having on its circumstellar disk is unique at the moment,” Meyer said. “We will also begin to study whether the protoplanet is surrounded by a circumplanetary disk (such as one out of which the large satellites of Jupiter are thought to have formed), and we will study whether the protoplanet is still growing in mass.”

This is the first clear image of a planet caught in the very act of formation. The planet is visible as a bright point to the right of the center of the image. The star itself is blacked out to make the rest of the system visible.
This is the first clear image of a planet caught in the very act of formation. The planet is visible as a bright point to the right of the center of the image. The star itself is blacked out to make the rest of the system visible. (ESO/A. Muller et al.)

Ultimately, he added, the scientists want to understand the physical processes that determine how massive planets will be and what orbits they will take.

“Both are important to understand the demographics of forming planetary systems,” Meyer said. “It may be that the formation of gas giant planets like this, might have an important impact on the nature of forming terrestrial planets like Earth, perhaps impacting their habitability.”

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