NASA’s Hubble Space Telescope gives astronomers a rare look at a still-forming Jupiter-sized planet that feeds on matter surrounding a young star.
“We just don’t know much about the growth of giant planets,” said Brendan Bowler of the University of Texas at Austin. “This planetary system gives us the first opportunity to see material fall on a planet. Our results open a new area for this research.”
Although more than 4000 exoplanets have been cataloged to date, only about 15 have been directly imaged by telescopes to date. And the planets are so far away and small, these are just dots on the best photos. The team’s new technique for using Hubble to directly image this planet opens a new avenue for further research on exoplanets, especially during a planet’s formative years.
This huge exoplanet, designated PDS 70b, revolves around the orange dwarf star PDS 70, which is already known to have two actively forming planets inside a huge disk of dust and gas circling the star. The system is located 370 light years from Earth in the constellation Centauri.
“This system is so exciting because we can witness the formation of a planet,” said Yifan Zhou, also of the University of Texas at Austin. “This is the youngest authentic planet that Hubble has ever directly imagined.” At five million years of youth, the planet is still gathering materials and building mass.
Hubble’s ultraviolet (UV) sensitivity offers a unique look at the radiation from extremely hot gases falling on the planet. “The Hubble observations have allowed us to estimate how quickly the planet is gaining mass,” Zhou added.
UV observations, which add to the body of research on this planet, allowed the team to directly measure the rate of mass growth of the planet for the first time. The distant world has already accumulated up to five times the mass of Jupiter over a period of about five million years. The current measured accretion rate has declined to the point where, if the rate remained stable for another million years, the planet would only increase by about 1 / 100th of Jupiter’s mass.
Zhou and Bowler point out that these observations are a single snapshot in time – more data is needed to determine whether the rate at which the planet is adding mass is increasing or decreasing. “Our measurements suggest that the planet is at the end of its forming process.”
The young PDS 70 system is filled with a disk of primordial gas and dust that provides fuel to fuel the growth of planets throughout the system. Planet PDS 70b is surrounded by its own disk of gas and dust that siphons material from the much larger circumstellar disk. The researchers hypothesize that the magnetic field lines extend from its circumplanetary disk to the exoplanet’s atmosphere and carry material across the planet’s surface.
“If this material follows the columns of the disk on the planet, it would cause local hot spots,” Zhou explained. “These hot spots could be at least 10 times hotter than the temperature of the planet.” These hot plates were found to glow violently in UV light.
These observations offer insight into how the gas giant planets formed around our Sun 4.6 billion years ago. Jupiter may have accumulated on a surrounding disc of infallible matter. Its main moons would also have formed from the remains of this disc.
A challenge for the team was to overcome the star’s glare from the parents. PDS 70b orbits roughly the same distance as Uranus from the Sun, but its star is more than 3,000 times brighter than the planet at UV wavelengths. While Zhou was processing the images, he very carefully removed the glare from the star to leave only the light emitted by the planet. In doing so, he improved the limit of how far a planet can be from its star in Hubble observations by a factor of five.
“Thirty-one years after launch, we’re still finding new ways to use Hubble,” Bowler added. “Yifan’s observation strategy and post-processing technique will open new windows to study similar systems, if not the same system, over and over with Hubble. it does it at a constant rate. “
The researchers’ results were published in April 2021 in The astronomical journal.