NASA’S Hubble Space Telescope is giving astronomers a rare look at a Jupiter-sized, still-forming planet that is feeding off material surrounding a young star.
Though over 4,000 exoplanets have been cataloged so far, only about 15 have been directly imaged to date by telescopes. And the planets are so far away and small, they are simply dots in the best photos. The team’s fresh technique for using Hubble to directly image this planet paves a new route for further exoplanet research, especially during a planet’s formative years. This huge exoplanet, designated PDS 70b, orbits the orange dwarf star PDS 70, which is already known to have two actively forming planets inside a huge disk of dust and gas encircling the star. The system is located 370 light-years from Earth in the constellation Centaurus.
“This system is so exciting because we can witness the formation of a planet,” said Yifan Zhou, formerly an undergraduate at Peking University and now a postdoctoral fellow at the University of Texas at Austin. “This is the youngest bona fide planet Hubble has ever directly imaged.” At a youthful 5 million years, the planet is still gathering material and building up mass. Hubble’s ultraviolet light (UV) sensitivity offers a unique look at radiation from extremely hot gas falling onto the planet. “Hubble’s observations allowed us to estimate how fast the planet is gaining mass,” added Zhou.
The UV observations, which add to the body of research about this planet, allowed the team to directly measure the planet’s mass growth rate for the first time. The remote world has already bulked up to five times the mass of Jupiter over a period of about 5 million years. The present measured accretion rate has dwindled to the point where, if the rate remained steady for another million years, the planet would only increase by approximately and additional 1/100th of a Jupiter mass.
“We just don’t know very much about how giant planets grow,” said Brendan Bowler, a co-author and professor at the University of Texas at Austin. “This planetary system gives us the first opportunity to witness material falling onto a planet. Our results open up a new area for this research.”
The youthful PDS 70 system is filled with a primordial gas and dust disk that provides fuel to feed the growth of planets throughout the entire system. The planet PDS 70b is encircled by its own gas and dust disk that’s siphoning material from the vastly larger circumstellar disk. The researchers hypothesize that magnetic field lines extend from its circumplanetary disk down to the exoplanet’s atmosphere and are funneling material onto the planet’s surface.
“If this material follows columns from the disk onto 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 patches were found to glow fiercely in UV light.
These observations offer insights into how gas giant planets formed around our sun 4.6 billion years ago. Jupiter may have bulked up on a surrounding disk of infalling material. Its major moons would have also formed from leftovers in that disk.
A challenge to the team was overcoming the glare of the parent star. PDS 70b orbits at approximately the same distance as Uranus does from the Sun, but its star is more than 3,000 times brighter than the planet at UV wavelengths. As Zhou processed the images, he very carefully removed the star’s glare to leave behind only light emitted by the planet. In doing so, he improved the limit of how close a planet can be to its star in Hubble observations by a factor of five. “This study pushed the limits of what is possible, and so required meticulous planning and analysis,” said co-author Gregory Herczeg, professor at the Kavli Institute for Astronomy and Astrophysics at Peking University and also Zhou’s undergraduate advisor. “It’s wonderful to see our former students develop into innovative scientists.”
“While this case study is fascinating, we need a larger sample to understand planet growth and planet-disk interactions,” said Herczeg. “We know that these planets exist, left to be discovered. I am excited by the prospects of the Chinese Space Station Telescope, which should allow push the contrast limits further and expand this type of analysis to more baby planets.”
The researchers’ results were published on April 29, 2021 in The Astronomical Journal. https://iopscience.iop.org/article/10.3847/1538-3881/abeb7a
The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C. This press release is courtesy of the press released developed by STScI: https://hubblesite.org/contents/news-releases/2021/news-2021-021
Hubble Space Telescope gives astronomers a rare look at a Jupiter-sized, still-forming planet that is feeding off material surrounding a young star.