Launching aboard a SpaceX Falcon 9 rocket from Vandenberg Space Force Base in California, the SPHEREx observatory will scan the cosmos for water, carbon dioxide, carbon monoxide, and other life-essential compounds frozen on the surfaces of interstellar dust grains. These substances reside in vast clouds of gas and dust where stars and planets eventually take shape.

Although open bodies of water do not exist in space, scientists theorize that these icy reservoirs, attached to tiny dust particles, account for much of the universe's water. The same cosmic ice is believed to have contributed to the formation of Earth's oceans, as well as those of other celestial bodies across the galaxy.

SPHEREx will focus its observations on molecular clouds - immense regions of gas and dust where new stars and planetary systems emerge. The mission will examine these clouds, newly formed stars, and the disks of material encircling them, which serve as the raw material for planet formation.

While previous space telescopes such as NASA's James Webb Space Telescope and the now-retired Spitzer Space Telescope have identified water, carbon dioxide, and other molecules in specific regions, SPHEREx is uniquely designed for an extensive survey. Rather than capturing standard 2D images, the telescope will collect 3D spectral data, providing insights into the ice composition and its variation across different environments within molecular clouds.

SPHEREx will conduct more than 9 million observations along its line of sight, creating the most comprehensive survey of interstellar ices to date. These findings will help scientists refine their understanding of how these essential compounds form and how environmental factors influence their distribution.

Uncovering the Depths of Cosmic Ice

A previous NASA mission, the Submillimeter Wave Astronomy Satellite (SWAS), launched in 1998, aimed to detect water vapor in the galaxy, including in molecular clouds. However, it found significantly less than expected.

"This puzzled us for a while," said Gary Melnick, a senior astronomer at the Center for Astrophysics | Harvard and Smithsonian and a SPHEREx science team member. "We eventually realized that SWAS had detected gaseous water in thin layers near the surface of molecular clouds, suggesting that there might be a lot more water inside the clouds, locked up as ice."

The mission team concluded that the water, along with oxygen gas (which was also found in lower amounts than expected), was likely adhering to interstellar dust grains. There, hydrogen atoms would combine with oxygen, forming water molecules. Further research confirmed this theory, revealing that molecular clouds provide a protective environment, shielding ice-forming molecules from cosmic radiation that could otherwise destroy them.

As starlight travels through a molecular cloud, molecules such as water and carbon dioxide absorb specific wavelengths of light, leaving distinct spectral signatures. SPHEREx will leverage absorption spectroscopy to detect and analyze these signatures, complementing the work of telescopes like Webb.

A Collaborative Effort in Space Exploration

"If SPHEREx discovers a particularly intriguing location, Webb can study that target with higher spectral resolving power and in wavelengths that SPHEREx cannot detect," said Melnick. "These two telescopes could form a highly effective partnership."

Related Links
SPHEREx
Understanding Time and Space