Baby planet reveals its hiding place – Sky & Telescope

A new analysis of archival data reveals the presence of gas in the protoplanetary disk surrounding the young star TW Hydrae. This discovery suggests the presence of a planet with a mass four times that of Earth and offers researchers a unique opportunity to study the early stages of planetary formation.

Outflows of planetary offspring

Baby planets form in disks surrounding young stars, but the details of this process remain unclear, especially because planets are often shrouded in dusty gas, obscuring them from view. Massive gas planets like Jupiter and Saturn are thought to form by gas accreting onto rocky cores that gradually carve out lanes in the disk.

How can we tell if accretion is occurring in a protoplanetary disk? As growing planets accumulate gas and dust, they also eject material into their surroundings in the form of eruptions. As the outgoing gas hits its surroundings, shocks form, triggering the formation of molecules such as sulfur monoxide (SO). This gives researchers a clue: the planet may be hidden, but the emission of these shock-formed molecules can give away its position.

A search in archives

This tells us as Potential baby planets will be found in the future, but where to look? One of the best places to look for signs of planet formation is around TW Hydrae, an 8-million-year-old star less than 200 light-years away. TW Hydrae possesses the closest known protoplanetary disk, which appears almost face-on from our vantage point, with concentric rings of light and dark like a bull’s-eye. Researchers previously found two gaps in this disk, at 26 and 42 AU, that could be explained by two planets of about 4 Earth masses. In addition, a cluster of emission at 52 AU hinted at the presence of a circumplanetary disk feeding gas to a growing planet.

Tomohiro Yoshida (National Astronomical Observatory of Japan) and collaborators analyzed archival data from the Atacama Large Millimeter/submillimeter Array (ALMA) to search for signs of outflow from a baby planet in TW Hydrae’s disk. The team detected an arc of SO2 molecules originating in a gap 42 AU from the star, exactly where a planet is expected to be.

Shocking evidence

What does the modeling say about the origin of this emission? The authors used ballistic flow modeling to show that the SO2 flux could be explained by a growing planet with a mass of 4 Earth masses. Combining estimates of the accretion and mass loss rates, the team finds an overall rate for the planet's growth that matches theoretical expectations for a planet with a mass of 4 Earth masses.

With evidence of the outflows already in hand, Yoshida’s team plans to continue the search, conducting further observations to look for evidence of the outflow in the emission of other promising molecules, such as silicon monosulfide. Overall, this work cements another line of evidence for the presence of a planet in the 42 AU space of TW Hydrae, and we can expect future observations to further illuminate this growing planetary family!

Citation

“Outflow driven by a protoplanet embedded in the TW Hya disk”, Tomohiro C. Yoshida et al 2024 ApJL 971 L15. document:10.3847/2041-8213/ad654c

This post originally appeared on AAS Newfeaturing highlights of research from the journals of the American Astronomical Society.