SPHEREx survey reveals rapid disappearance of molecular ice around young stars

A new survey of over 20,000 young stars has mapped the presence of water, carbon dioxide, and carbon monoxide ice in the regions where planets form. The findings show a sharp decrease in these ice signatures as stars age beyond three million years, indicating that the building blocks for future planetary systems are depleted rapidly during the earliest stages of stellar development.

Star system: HK Tauri A | Distance from the Sun: 428 light years

Molecular ices are vital components of star-forming environments, acting as reservoirs for elements like carbon, oxygen, and nitrogen. These ices trace the chemical path from dusty molecular clouds to the flat disks of gas and dust that surround young stars. As planets form within these disks, the availability of such chemical building blocks plays a critical role in the composition of emerging worlds.

To better understand these processes, researchers analyzed spectra from the SPHEREx mission, which provides a detailed light signature for a vast sample of over 20,000 young stellar objects younger than 20 million years. By comparing these observations against laboratory templates for water, carbon dioxide, and carbon monoxide, the team identified hundreds of stars containing these ices. This broad approach allows for a population-level view of how ice mantles evolve throughout the early life of a star.

The analysis reveals that the presence of ice changes significantly as stars mature. Specifically, the rate of detecting combined water and carbon dioxide ice drops by a factor of ten between three million and five million years of age. This decline suggests that physical processes, such as the dispersal of the surrounding dusty envelope or the light-driven stripping of ices known as photodesorption, effectively clear out these ice reserves early in the star's pre-main-sequence evolution. These results establish a new baseline for understanding the timeline of chemical change in developing planetary systems.

Key findings
Identification of 746 water ice candidates across a large population of young stars.
Detection of 131 stars with both water and carbon dioxide signatures.
A tenfold decrease in ice detection rates between three and five million years of age.
Strong correlation between ice presence and highly obscured environments, indicating early-stage retention.
Confirmation that ice depletion occurs rapidly during the first few million years of stellar evolution.

Scientific study

Evolutionary Demographics of Molecular Ice Mantles in Young Stars with SPHEREx (external link)