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PDS 70

PDS 70

The protoplanetary disk of PDS 70 with new planet PDS 70b (right)
Observation data
Epoch J2000      Equinox J2000
Constellation Centaurus
Right ascension 14h 08m 10.15455s[1]
Declination −41° 23′ 52.5733″[1]
Apparent magnitude (V) 12[2]
Characteristics
Evolutionary stage Pre-main-sequence
(T Tauri)
Spectral type K7[3]
U−B color index 0.71[4]
B−V color index 1.06[4]
Astrometry
Radial velocity (Rv)0.74±3.22[1] km/s
Proper motion (μ) RA: -29.697 mas/yr[1]
Dec.: -24.041 mas/yr[1]
Parallax (π)8.8975 ± 0.0191 mas[1]
Distance366.6 ± 0.8 ly
(112.4 ± 0.2 pc)
Details
Mass0.76 ± 0.02[3] M☉
Radius1.26 ± 0.15[3] R☉
Luminosity0.35 ± 0.09[3] L☉
Temperature3972 ± 36[3] K
Rotation~50 days[5]
Rotational velocity (v sin i)~10[5] km/s
Age5.4 ± 1[3] Myr
Other designations
V1032 Cen, 2MASS J14081015-4123525, IRAS 14050−4109
Database references
SIMBADdata

PDS 70 (V1032 Centauri) is a very young T Tauri star in the constellation Centaurus. Located 370 light-years (110 parsecs) from Earth, it has a mass of 0.76 M☉ and is approximately 5.4 million years old.[3] The star has a protoplanetary disk containing two nascent exoplanets, named PDS 70b and PDS 70c, which have been directly imaged by the European Southern Observatory's Very Large Telescope. PDS 70b was the first confirmed protoplanet to be directly imaged.[6][7][3]

Discovery and naming

A light curve for PDS 70 (aka V1032 Centauri), plotted from TESS data[8]

The "PDS" in this star's name stands for Pico dos Dias Survey, a survey that looked for pre-main-sequence stars based on the star's infrared colors measured by the IRAS satellite.[9] PDS 70 was identified as a T Tauri variable star in 1992, from these infrared colors.[10] PDS 70's brightness varies quasi-periodically with an amplitude of a few hundredths of a magnitude in visible light.[11] Measurements of the star's period in the astronomical literature are inconsistent, ranging from 3.007 days to 5.1 or 5.6 days.[12][13]

Protoplanetary disk

The protoplanetary disk around PDS 70 was first hypothesized in 1992[14] and fully imaged in 2006 with phase-mask coronagraph on the VLT.[2] The disk has a radius of approximately 140 au. In 2012 a large gap (~65 au) in the disk was discovered, which was thought to be caused by planetary formation.[5][15]

The gap was later found to have multiple regions: large dust grains were absent out to 80 au, while small dust grains were only absent out to the previously-observed 65 au. There is an asymmetry in the overall shape of the gap; these factors indicate that there are likely multiple planets affecting the shape of the gap and the dust distribution.[16]

The James Webb Space Telescope has been used to detect water vapor in the inner part of the disk, where terrestrial planets may be forming.[17][18]

Planetary system

The PDS 70 planetary system[19]
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(years) 		Eccentricity Inclination Radius
b 3.2+3.3
−1.6 MJ 		20.8+0.6
−0.7 		123.5+9.8
−4.9[20] 		0.17±0.06 131.0+2.9
−2.6° 		2.72+0.39
−0.34[21] RJ
c 7.5+4.7
−4.2 MJ 		34.3+2.2
−1.8 		191.5+15.8
−31.5[20] 		0.037+0.041
−0.025 		130.5+2.5
−2.4° 		2.04+1.22
−0.89[21] RJ
Protoplanetary disk ~65–140 AU ~130° —

In results published in 2018, a planet in the disk, named PDS 70 b, was imaged with SPHERE planet imager at the Very Large Telescope (VLT).[3][7] With a mass estimated to be a few times greater than Jupiter,[19] the planet is thought to have a temperature of around 1,200 K (930 °C; 1,700 °F)[21] and an atmosphere with clouds;[7] its orbit has an approximate radius of 20.8 AU (3.11 billion kilometres),[19] taking around 120 years for a revolution.[20]

The emission spectrum of the planet PDS 70 b is gray and featureless, and no molecular species were detected by 2021.[22]

A second planet, named PDS 70 c, was discovered in 2019 using the VLT's MUSE integral field spectrograph.[23] The planet orbits its host star at a distance of 34.3 AU (5.13 billion kilometres), farther away than PDS 70 b.[19] PDS 70 c is in a near 1:2 orbital resonance with PDS 70 b, meaning that PDS 70 c completes nearly one revolution once every time PDS 70 b completes nearly two.[23]

Circumplanetary disks

Modelling predicts that PDS 70 b has acquired its own accretion disk.[6][24] The accretion disk was at first observationally supported in 2019,[25] however, in 2020 evidence was presented that the current data favors a model with a single blackbody component of the planet.[26] The accretion rate was measured to be at least 5*10−7 Jupiter masses per year.[27] A 2021 study with newer methods and data suggested a lower accretion rate of 1.4±0.2*10−8 MJ/year.[28] It is not clear how to reconcile these results with each other and with existing planetary accretion models; future research in accretion mechanisms and Hα emissions production should offer clarity.[29]

The photospheric blackbody radius of the planet is 3.0±0.2 RJ. Its bolometric temperature is 1193±20 K, while only upper limits on these quantities can be derived for the optically thick accretion disk, significantly larger than the planet itself. However, weak evidence that the current data favors a model with a single blackbody component is found.[26]

In July 2019, astronomers using the Atacama Large Millimeter Array (ALMA) reported the first-ever detection of a moon-forming circumplanetary disk. The disk was detected around PDS 70 c, with a potential disk observed around PDS 70 b.[30][31][32] The two planets and the superposition of PDS 70 c and the protoplanetary disk was confirmed by Caltech-led researchers using the W. M. Keck Observatory in Mauna Kea, whose research was published in May 2020.[33] An image of the circumplanetary disk around PDS 70 c separated from the protoplanetary disk was finally confirming the circumplanetary disk and was published in November 2021.[34]

Possible planet d

VLT/SPHERE observations showed a third object 0.12 arcseconds from the star. Its spectrum is very blue, possibly due to star light reflected in dust. It could be a feature of the inner disk. The possibility does still exist that this object is a planetary mass object enshrouded by a dust envelope. For this second scenario the mass of the planet would be on the order of a few tens ME.[20] JWST NIRCam observations also detected this object. It is located at around 13.5 AU and if it is a planet, it would be in a 1:2:4 mean-motion resonance with the other protoplanets.[35]

Possible co-orbital body

In July 2023, the likely detection of a cloud of debris co-orbital with the planet PDS 70 b was announced. This debris is thought to have a mass 0.03-2 times that of the Moon, and could be evidence of a Trojan planet or one in the process of forming.[36][37]

  • ALMA image of a resolved circumplanetary disk around exoplanet PDS 70c
    ALMA image of a resolved circumplanetary disk around exoplanet PDS 70c
  • Hubble image of PDS 70. This is only the second multi-planet system to be directly imaged.
    Hubble image of PDS 70. This is only the second multi-planet system to be directly imaged.
  • James Webb Space Telescope spectrum of PDS 70, detecting water in the terrestrial region of the protoplanetary disk
    James Webb Space Telescope spectrum of PDS 70, detecting water in the terrestrial region of the protoplanetary disk

See also

References

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  29. ^ Gebhardt, Chris; Warren, Haygen (2021-05-13). "With Hubble, astronomers use UV light for first time to measure a still-forming planet's growth rate". NSF (NASASpaceflight). ...and that's lower than super-Jupiter gas giant planet formation models predict. Zhou et al. are quick to caution that their calculations are a snapshot in time. Additional observation, multi-decade, multi-century observations will reveal if accretion rates fluctuate greatly over time as planets go through growth spurts, so to speak, followed by periods of less active formation or if "Hα production in planetary accretion shocks is more efficient than [previous] models predicted, or [if] we underestimated the accretion luminosity/rate," noted Zhou et al. in their paper published in April 2021 issue of The Astronomical Journal. The team further noted, "By combining our observations with planetary accretion shock models that predict both UV and Hα flux, we can improve the accretion rate measurement and advance our understanding of the accretion mechanisms of gas giant planets."
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