The star around which astronomers got their first-ever sighting of a fledgling planet has been shown to have another world and possibly even a giant moon-forming disc.
This swirling mass of dust and cloud is orbiting the first of the newborn planets, which researchers directly imaged back in June 2018.
The findings are helping validate previously untested theories of planetary formation and suggest that giant moons like Enceladus and Europa may be commonplace.
In our solar system, such moons are considered prime candidates in the search for extraterrestrial life.
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PDS 70, the star around which astronomers got their first-ever sighting of a fledgling planet has been shown to have another world and possibly even a giant moon-forming disc, pictured in this artist’s impression
PDS 70 is a low-mass star, smaller and a thousand times younger than our Sun, located 370 light years from Earth in the constellation of Centaurus.
Astronomers revealed a picture last June showing that the star is being orbited by a young giant planet, dubbed PDS 70b, one that further study confirmed is still growing out the material in the disc of dust and gas surrounding PDS 70.
It turns out, however, that this fledgling planet is not alone, with astronomers led from Leiden University in the Netherlands having announced the detection of a second body in orbit around the star.
The second planet is still sucking up hydrogen from around it, which allowed it to be detected using the new hydrogen emission detecting MUSE instrument at the Very Large Telescope facility, on the mountain of Cerro Paranal, in Chile’s Atacama Desert.
‘What makes PDS 70 superlative is that it’s absolutely unambiguous that there’s at least one planet there,’ astronomer Kate Follette of Amherst College, Massachusetts, told Quanta Magazine.
In addition, she noted, ‘the evidence for a second planet is very convincing.’
This is not the only revelation from the system, however, with a second team of researchers having found evidence that the first planet, PDS 70b, may be surrounded by its very own disc of rotating dust and gas.
It is from these circumplanetary discs that large moons are thought to form, much like the Galilean moons that orbit around Jupiter in our solar system.
Astronomer Valentin Christiaens of Monash University in Melbourne, Australia and colleagues studied PDS 70b using a near-infrared light detecting instrument called Sinfoni, which is also based at the Very Large Telescope.
‘When we eventually saw the blob, I got very excited,’ he said.
Dr Christiaens’ analysis showed that the light coming from the planet was redder than expected for a planet alone — which the researchers argue is caused by the planet-encircling disc.
This dusty material, they explain, would absorb heat and then re-emit the energy as infrared light.
Astronomers revealed a picture last June showing that PDS 70 is being orbited by a young giant planet, dubbed PDS 70b, one that further study confirmed is still growing out the material in the disc of dust and gas surrounding the star
The first signs that there might be planets in orbit around PDS 70 came back in 2012.
In the star’s surrounding disc, astronomers noticed a dust-free band, one that begins at around where Uranus’ orbit lies in our solar system and that extended out to three times the starting distance.
The first of the two planets to be detected, PDS 70b, orbits just within the inner edge of the gap in the disc.
One planet alone, however, is not enough to explain why the gap is so large — but two planets might, as they would be able to open up a much larger gap in the disc as they both grow by attracting material our of the protoplanetary disc.
In fact, the second planet, PDS 70c — which goes around the star once for every two orbits of PDS 70b — was found lying just within the outer edge of the gap in the disc.
With the finding of PDS 70c said University of Nevada, Las Vegas, astrophysicist Zhaohuan Zhu, ‘everything seems to start to connect.’
Two studies using the Very Large Telescope facility (pictured) in Chile’s Atacama Desert have revealed that the distant star PDS 70 has not one but two newborn planets – and one may have a moon-forming disc
The fact that the planets are both bright and orbit so far out from their star makes the PDS 70 system ideal for astronomers to analyse, as well as allowing for previously untested theories of planetary formation to be validated.
‘PDS 70 is really becoming a benchmark system,’ said Space Telescope Science Institute astronomer Julien Girard, who helped to discover both the second planet and its potentially moon-forming disc.
In our solar system, Professor Zhu noted, Enceladus and Europa — two of the most promising targets in the search for extraterrestrial life — both orbit giant planets.
If young gas giants often have discs that can form moons, he added, ‘maybe [moons like] Europa or Enceladus could be common in our galaxy.’
The full findings of the research revealing the second planet orbiting PDS 70 were published in the journal Nature Astronomy.
A pre-print version of the second study that suggests that PDS 70b has its own circumplanetary disc may be read on the arXiv repository.
