PDS 70

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. 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, as well as a third unconfirmed protoplanet. PDS 70b was the first confirmed protoplanet to be directly imaged.

Discovery and naming

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. PDS 70 was identified as a T Tauri variable star in 1992, from these infrared colors. PDS 70's brightness varies quasi-periodically with an amplitude of a few hundredths of a magnitude in visible light. Measurements of the star's period in the astronomical literature are inconsistent, ranging from 3.007 days to 5.1 or 5.6 days.

Protoplanetary disk

The protoplanetary disk around PDS 70 was first hypothesized in 1992 and fully imaged in 2006 with phase-mask coronagraph on the VLT. 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. 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. 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.

Planetary system

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). With a mass estimated to be a few times greater than Jupiter, the planet is thought to have a temperature of around 1,200 K (930 °C; 1,700 °F) and an atmosphere with clouds; its orbit has an approximate radius of 20.8 AU (3.11 billion kilometres), taking around 120 years for a revolution. The emission spectrum of the planet PDS 70 b is gray and featureless, and no molecular species were detected by 2021. A second planet, designated PDS 70 c, was discovered in 2019 using the VLT's MUSE integral field spectrograph. The planet orbits its host star at a distance of 34.3 AU (5.13 billion kilometres), farther away than PDS 70 b. 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.

Circumplanetary disks Modelling predicts that PDS 70 b has acquired its own circumplanetary disk (CPD). The CPD was at first observationally supported in 2019, however, in 2020 evidence was presented that the current data favor a model with a single component of the planet. The accretion rate was measured to be at least 5 • 10−7 Jupiter masses per year. A 2021 study with newer methods and data suggested a lower accretion rate of (1.4±0.2)×10−8 MJ per year. 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. 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. 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. 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. In 2025 two studies found variable accretion from the variable H-alpha emission line for both planet b and c. One work used Magellan/MagAO-X and the other used Hubble. Planet b did show a general fading trend, with a decrease in brightness by a factor of 4.6. Planet c did increase in brightness by a factor of 2.3 between 2023 and 2024. The MagAO-X observations also suggest in reasonably good agreement with a predicted scattered light model of a CPD that both planets are surrounded by a compact disk with a radius of about 3 astronomical units.

… excerpt ends here. Continue reading the full article.