Astronomers have made some new observations using Earth’s most powerful set of radio telescopes of a circumplanetary disk of gas and dust, similar to the one that is thought to have created the moons of Jupiter.
Rice University astronomer Andrea Isella and his team used the gigantic 66-antenna Atacama Large Millimeter/Submillimeter Array (ALMA) to collect millimeter-wave signals that unveiled the existence of dust particles spread throughout the star system where planet PDS 70 c and PDS 70 b are developing.
“Planets form from disks of gas and dust around newly forming stars, and if a planet is large enough, it can form its own disk as it gathers material in its orbit around the star,” Isella said. “Jupiter and its moons are a little planetary system within our solar system, for example, and it’s believed Jupiter’s moons formed from a circumplanetary disk when Jupiter was very young.”
Looking for New Leads
The curious thing about them is that the circumplanetary disks are disappearing from the system within about 10 million years, meaning that they haven’t existed in our solar system for more than 4 billion years. Isella and her colleagues are starting to look for them in different regions of the system so they can observe young star systems and theorize and directly observe the planets taking shape inside of them. In 2017, observations made by ALMA were analyzed and researched by Isella and his team.
“There are a handful of candidate planets that have been detected in disks, but this is a very new field, and they are all still debated,” Isella said. “(PDS 70 b and PDS 70 c) are among the most robust because there have been independent observations with different instruments and techniques.”
ALMA Observations Look Promising
PDS 70 is a dwarf star and has roughly three-quarters the mass of the sun. Its planets are 5 to 10 times bigger than Jupiter. The distance that PDS 70 b is orbiting from the star is 1.8 billion miles, about the distance from the sun and Uranus. In an orbit that has the size of Neptune lies PDS 70c.
A planet-hunting tool called the SPHERE displayed infrared light images of the PDS 70 b in 2018 at the European Southern Observatory’s Very Large Telescope (VLT). A visible wavelength of light dubbed H-alpha was also spotted by a VLT tool called MUSE, which is discharged when hydrogen particles collapse onto a planet or a star and become ionized.
Isella said: “H-alpha gives us more confidence that these are planets because it suggests they are still drawing in gas and dust and growing,”
The observations made with ALMA offer more information.
“It’s complimentary to the optical data and provides completely independent confirmation that there is something there,” he said.
“There’s much that we don’t understand about how planets form, and we now finally have the instruments to make direct observations and begin answering questions about how our solar system formed and how other planets might form.”
Isella is an assistant professor of astronomy and physics and Earth, environmental and planetary sciences at Rice. He’s also a co-investigator at the NASA-funded CLEVER Planets project.