Astronomers using the NASA/ESA Hubble Space Telescope have imaged a Jupiter-sized, still-forming planet around the orange dwarf star PDS 70. This is the first time that an exoplanet has been directly imaged in the ultraviolet (UV).
This Hubble image shows the young exoplanet PDS 70b. Image credit: Joseph DePasquale, STScI.
PDS 70 is a K7-type pre-main sequence star located 370 light-years away in the constellation of Centaurus.
Also known as V* V1032 Cen and IRAS 14050-4109, the star is only 5.4 million years old.
It hosts two actively forming planets, PDS 70b and c, and a huge circumstellar disk of dust and gas in which a large region from 20 to 40 AU is cleared of dust.
PDS 70b is located within the disk gap at a distance of about 21 AU from the star, similar to the orbit of Uranus in our Solar System.
PDS 70c is located near the outer edge of the disk gap at 34.5 AU from the star, similar to Neptune’s distance from our Sun.
“PDS 70 is so exciting because we can witness the formation of a planet. This is the youngest bona fide planet Hubble has ever directly imaged,” said Dr. Yifan Zhou, an astronomer at the University of Texas at Austin.
Dr. Zhou and colleagues used the near-UV/visible (UVIS) channel of Hubble’s Wide Field Camera 3 (WFC3) instrument to observe PDS 70b.
“Hubble’s UV observations allowed us to estimate how fast the planet is gaining mass,” Dr. Zhou noted.
According to the team, PDS 70b has already bulked up to five times the mass of Jupiter over a period of 5.4 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 an additional 1/100th of a Jupiter-mass.
“These observations are a single snapshot in time — more data are required to determine if the rate at which the planet is adding mass is increasing or decreasing,” the astronomers said.
“Our measurements suggest that the planet is in the tail end of its formation process.”
PDS 70b is encircled by its own gas-and-dust disk that’s siphoning material from the PDS 70 system’s 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,” Dr. Zhou said.
“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.”
The findings appear in the Astronomical Journal.
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Yifan Zhou et al. 2021. Hubble Space Telescope UV and Hα Measurements of the Accretion Excess Emission from the Young Giant Planet PDS 70b. AJ 161, 244; doi: 10.3847/1538-3881/abeb7a
