Nascent
planet seen carving a path through the disc of gas and dust surrounding the very young star PDS70
It is a moment of birth that has previously proved elusive, but astronomers say they now have the first confirmed image of the formation of a planet.
The startling snapshot shows a bright blob – the nascent planet – travelling through the dust and gas surrounding a young star, known as PDS70, thought to be about 370 light years from Earth.
The black circle in the centre of the image, to the left of the planet, is a filter to block the light from the star, enabling other features of the system to be seen.
Captured by the Sphere instrument of the European Southern Observatory’s Very Large Telescope, the planet – a gas giant with a mass greater than Jupiter – is about as far from its star as Uranus is from our sun, with further analyses revealing that it appears to have a cloudy atmosphere and a surface temperature of 1000C.
“These discs around young stars are the birthplaces of planets, but so far only a handful of observations have detected hints of baby planets in them,” said Miriam Keppler of the Max Planck Institute for Astronomy in Germany, a lead author of the research published in the journal Astronomy and Astrophysics. However, other ground-based observations have not yielded conclusive evidence.
“The problem is that until now, most of these planet candidates could just have been features in the disc,” she said. “The advantage of our detection is that we have detected [the new planet] with several different observing instruments, different filter bands and different years,” she added.
Young planets have also previously been identified using the orbiting Kepler telescope. But that method, said Keppler, also has limitations, relying on a dimming of the star’s light as a body moves in between it and the telescope
“The special thing about this new planet is that we can directly image it, so the ones by Kepler, for example, they were derived by indirect techniques,” she told the Guardian. “In this case we now have a direct image [of the planet] in its “birthplace”, which is the circumstellar disc. This is especially important because people have been wondering [for a long time], how these planets actually form and how the dust and the material in this disc forms [into] a planet, and now we can directly observe this.”
Keppler adds that the star around which the newly discovered planet orbits is just five to six million years old, noting that the planet could be even younger.
Astronomers, she says, now have a big task ahead, carrying out observations to explore how the planet develops as well as tracing its orbit around the star, a journey thought to take about 120 years for the planet to complete.
Dr Zoe Leinhardt, a computational astrophysicist specialising in planet formation at the University of Bristol and who was not involved in the research, welcomed the discovery.
“This is a relatively young star that shows all of the indications that there should be a planet there, and there is one,” she said. “For astronomers, most of the time, it is very rare that we are really able to show a picture. We just have to make an interpretation,” she said. “This is almost undeniable, so it is very exciting. It does suggest that our idea for the way planet formation works is correct.”
Leinhardt added that it is possible the planet has neighbours, or that other planets could appear over time. “The way that planets form, a large Jupiter-mass planet would be the easiest to see … and also those large planets would form more quickly,” she said. “What this does indicate is that planet formation is ongoing in that system.”
Dr Dimitris Stamatellos, leader the of the theoretical star formation and exoplanets group at the University of Central Lancashire, was also enthusiastic. “This is an impressive discovery as this is maybe the first unambiguous direct observation of a planet that is caught while still forming within a young protoplanetary disc,” he said.
But, he added, while the discovery has confirmed some theoretical predictions, it has also thrown up a conundrum. “It remains a mystery how such a massive planet can form at this unusual large distance from its parent star,” he said. “The standard planet formation theory has difficulty in explaining this planet.”