This image of the newly formed exoplanet PDS 70b shows how material can fall onto the gigantic world as it builds up mass. Using Hubble’s UV sensitivity, researchers gained unique insight into the radiation from extremely hot gas falling on the planet, allowing them, for the first time, to directly measure the planet’s rate of mass growth. SCIENCE: McDonald Observatory – University of Texas, Yifan Zhou (UT) ILLUSTRATION: NASA, ESA, STScI, Joseph Olmsted (STScI)
Planets come in many compositions and sizes, and they can grow significantly larger than even the gas giants in our solar system. One such giant planet, PDS 70b, has two to three times the radius of Jupiter and about three times its mass. Now Hubble has made a rare direct observation of this planet to learn how planets so large are growing.
The planet’s host star, the orange dwarf PDS 70, is 370 light years away in the constellation Centaurus. This is one of the relatively few systems in which a planet has been mapped directly. Most of the time, exoplanets are recognized by seeing how the light coming from their host star changes, from which the presence of planets can be inferred. But occasionally a planet is big enough to be seen directly, like the clunky PDS 70b.
In addition to observing the planet, Hubble could see how fast it was growing by watching the radiation from hot gas falling on it. The planet moves around the star through a cloud of dust and gas and collects material on its journey. The researchers believe that while the planet is still growing, it will soon reach the end of its growth phase.
“We just don’t know much about how giant planets grow,” one of the researchers, Brendan Bowler of the University of Texas at Austin, said in a statement. “This planetary system gives us the first opportunity to see material fall on a planet. Our results open up a new area for this research. “
“This system is so exciting because we can watch a planet form,” said another researcher, Yifan Zhou, also from the University of Texas at Austin. “This is the youngest real planet Hubble has ever mapped directly.”
If we learn how this planet grows, we can also learn how planets like Jupiter were formed in our solar system. It can also have grown by scooping up material from a disk of dust and gas.
“Thirty-one years after launch, we’re still finding new ways to use Hubble,” said Bowler. “Yifan’s observation strategy and post-processing technique open new windows to examine similar systems or even the same system repeatedly with Hubble. With future observations, we could possibly find out when most of the gas and dust falls on their planets, and if it does so at a constant rate. “