JWST observations reveal water vapor in the atmosphere of young planet V1298 Tauri c

Star system: V1298 Tauri A | Distance from the Sun: 352 light years

V1298 Tauri c is a young super-Earth progenitor — an infant version of a planet like those commonly found in our galaxy — orbiting a star about 23 million years old. These young, inflated planets are crucial for understanding how planetary atmospheres form and change over time, unlike older planets whose atmospheres may have already settled. As part of the KRONOS research program, space telescope observations have now analyzed the light passing through this planet's atmosphere to identify its composition.

Using the NIRISS instrument on the James Webb Space Telescope, researchers obtained a transmission spectrum, which is a method of splitting light to identify chemical signatures. The analysis successfully detected water vapor in the atmosphere of V1298 Tau c. While no other specific molecules were identified in this set of data, the presence of water provides a clear starting point for characterizing this young world.

The findings show that the atmospheric metallicity, a measure of how many elements heavier than hydrogen and helium are present, is roughly 15 times higher than the solar value. This level of metallicity is similar to that of other young planets but systematically lower than what is typically observed in older, mature planets of a similar mass. This suggests that the relationship between a planet's mass and its atmospheric metallicity likely changes as the planet ages.

Key findings
- Water vapor was detected in the atmosphere of the young super-Earth progenitor V1298 Tau c.
- The planetary atmosphere shows an atmospheric metallicity approximately 15 times the solar value.
- The results provide evidence that the relationship between planet mass and metallicity evolves over time.
- V1298 Tau c has an atmospheric composition similar to its massive companion planet, V1298 Tau b.

Scientific study

KRONOS I: The 1{-}2.8μm JWST Transmission Spectrum of the 23 Myr V1298 Tau c (external link)