Astronomers have discovered water vapor while observing a rare comet in the Solar System using the James Webb Space Telescope.
This is the first time water vapor has been detected around a comet located in the asteroid belt, situated between the orbits of Mars and Jupiter around the Sun. This discovery comes after 15 years of effort by astronomers observing rare comets using various observational methods.
Illustration showing ice vaporizing into gas from comet 238P/Read as it approaches the Sun. (Image: NASA/ESA).
A detailed study of the discovery was published on May 15 in the journal Nature.
Comets typically exist in the Kuiper Belt and the Oort Cloud, icy regions beyond Neptune’s orbit, where temperatures are cold enough to preserve some materials left over from the formation of the Solar System.
However, a rare subclass of comets known as main-belt comets are objects in the asteroid belt with nearly circular orbits around the Sun. Unlike ordinary comets, which release icy material through sublimation (where solids convert directly into gas), main-belt comets appear to emit only dust.
Due to their proximity to the Sun compared to regular comets, main-belt comets are not expected to retain much ice.
Thus, the discovery of water vapor around a main-belt comet might add further evidence to theories regarding how water came to be present on Earth. Water-rich comets and asteroids could have collided with early Earth, delivering water to our planet.
The James Webb Space Telescope captured an image of comet 238P/Read using its NIRCam instrument on September 8, 2022. (Image: NASA/ESA/CSA/M. Kelley/H. Hsieh/A. Pagan).
Main-belt comets were co-discovered by Henry Hsieh, a senior scientist at the Planetary Science Institute in Tucson, Arizona, initially in 2006. The comet Read, where water vapor was discovered, was originally just a minor subject in the study.
The precise data collected by the James Webb’s near-infrared spectrograph enabled astronomers to identify signs of water vapor around comet Read shortly after it approached the Sun.
Michael Kelley, an astronomer and lead research scientist at the University of Maryland in College Park, stated: “With the James Webb observations of comet Read, we can now demonstrate that frozen water from the early Solar System can be preserved in the asteroid belt.”
