Kinematic study reveals older age for PDS 70 and its protoplanets

The star PDS 70 is significantly older than previously estimated, according to new kinematic measurements. By tracking the motion of surrounding stars, researchers determined PDS 70 is between 12 and 16 million years old. This adjustment challenges existing theories on how its two protoplanets formed, suggesting that at least one of these giant worlds may have developed long after the central star itself.

Star system: PDS 70 | Distance from the Sun: 370 light years

The PDS 70 star system is a vital target for understanding how giant planets form within the swirling disks of dust and gas surrounding young stars. It is the only known system where two protoplanets, PDS 70 b and PDS 70 c, have been directly observed still embedded in their original material. For years, the system was estimated to be about 5.4 million years old, a figure based on models of how stars brighten and dim over time. However, this estimate conflicted with the age of the wider stellar group to which PDS 70 belongs.

To resolve this, investigators measured the precise movements of 405 stars in the Scorpius-Centaurus region using the Wide Field Spectrograph. By combining these radial velocity measurements—which track how fast stars move toward or away from us—with position data from the Gaia mission, they mapped the history of the stellar group. This kinematic approach, which looks at how groups of stars drift through space together over time, allowed for a much more accurate estimate of the system's age than previous methods.

The findings indicate that PDS 70 is actually between 12 and 16 million years old, making it roughly three times older than earlier models suggested. This new age creates a puzzle regarding the protoplanets, as their observed brightness does not align with the standard theory that they formed at the same time as their host star. The data suggest that PDS 70 b likely formed more than 7 million years after the star first ignited, implying a delayed formation process for these massive worlds.

Key findings
PDS 70 is estimated to be 12 to 16 million years old based on its motion through space.
The previous age estimate of 5.4 million years is no longer considered accurate.
The brightness of the planet PDS 70 b is inconsistent with it being as young as the star.
The planet PDS 70 b likely formed at least 7.7 million years after the host star.

Scientific study

Kinematic structure and age of a Scorpius--Centaurus subcomponent: implications for PDS 70 planetary system (external link)