Have you ever made a complete mess in your kitchen while baking? At times, the flour may appear to be floating in the air, but once you have added a lot of water and shaped your dough, the bread becomes more like a ball. A similar process works in a distant solar system known as the PDS 70, except that flour and water are exchanged for gas and dust. In the case of the planet PDS 70b, gas and dust are slowly absorbed as this distant world accumulates mass over millions of years.
Researchers using Hubble directly measured the growth rate of mass of the PDS 70b for the first time, using the observatory’s unique ultraviolet sensitivity to capture radiation from extremely hot gas entering the planet. The massive, Jupiter-sized world orbits about the same distance as Uranus from the Sun – although it moves through a mess of gas and dust as it moves through the solar system. The planet, which began to form about 5 million years ago, may be at the end of its formation. The researchers’ findings reveal a new way to study emerging planets that could help other astronomers who want to learn more about how giant planets grow in distant solar systems.
NASA’s Hubble Space Telescope gives astronomers a rare look at a still-forming Jupiter-sized planet that feeds on material surrounding a young star.
“We just don’t know much about how giant planets grow,” said Brendan Bowler of the University of Texas at Austin. “This planetary system gives us the first opportunity to witness material fall on the planet. The results reveal a new area for this study.”
Although more than 4,000 exoplanets have been cataloged so far, only about 15 have been made directly by telescopes to date. And the planets are so far away and small, they are just points of the best pictures. The team’s fresh technique of using Hubble to directly image this planet paves a new route for further exploration of exoplanets, especially during the planet’s emerging 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 surrounding 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, also of the University of Texas at Austin. “This is the youngest conscientious planet Hubble has ever depicted directly.” At the age of 5 million, the planet is still collecting material and accumulating mass.
Hubble’s ultraviolet (UV) sensitivity offers a unique look at the radiation from extremely hot gas falling on the planet. “Hubble’s observations have allowed us to judge how fast the planet is gaining mass,” Zhou added.
Ultraviolet observations, which complement the object of study for this planet, allowed the team for the first time to directly measure the mass growth rate of the planet. The distant world has already increased Jupiter’s mass to fivefold in a period of about 5 million years. The current measured rate of growth has decreased to the point where, if the rate remains stable for another million years, the planet will increase by only approximately an additional 1/100 of Jupiter’s mass.
Zhou and Bowler emphasize that these observations are a snapshot of time – more data is needed to determine whether the rate at which the planet is gaining mass is increasing or decreasing. “Our measurements show that the planet is at the end of the formation process.”
The PDS 70 youth system is complete with a primary gas-powder disk that provides fuel to power planetary growth throughout the system. The planet PDS 70b is surrounded by its own disk for dust and gas and dust, which extracts material from the much larger orbital disk. Researchers suggest that the lines of the magnetic field extend from its orbital disk to the atmosphere of the exoplanet and direct material to the planet’s surface.
“If this material follows columns from the planet’s disk, it will lead to local hotspots,” Zhou explained. “These hot spots can be at least 10 times hotter than the planet’s temperature.” These hot spots have been found to glow brightly in UV light.
These observations give an idea of how the gas giant planets formed around our sun 4.6 billion years ago. Jupiter may have accumulated on the surrounding disk of falling material. Its main moons would also be formed from the remnants of this disk.
The challenge for the team was to overcome the reflections of the mother star. PDS 70b orbits at approximately the same distance as Uranus does from the Sun, but its star is over 3,000 times brighter than the planet in UV waves. As Joe processed the images, he very carefully removed the star’s glare, leaving behind only light emitted from the planet. In this way, he improved the limit of how close a planet could be to its star in Hubble’s observations by five times.
“Thirty-one years after launch, we’re still finding new ways to use Hubble,” Bowler added. “Yifan’s monitoring strategy and post-processing technique will open new windows for multiple studies of similar systems or even the same system with Hubble. With future observations, we could potentially find out when most of the gas and dust falls on their planets and does so at a constant rate. “
The researchers’ results were published in April 2021 in The Astronomical Journal.
A giant planet at a great distance from sun-like stars puzzles astronomers
Yifan Zhou et al. Hubble Space Telescope UV and Hα measurements of excess accretion from Young Giant Planet PDS 70 b, The Astronomical Journal (2021). DOI: 10.3847 / 1538-3881 / abeb7a
Provided by the ESA / Hubble Information Center
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