Astronomers using the NASA/ESA/CSA James Webb Space Telescope have detected water ice as well as frozen forms of carbonyl sulfide, ammonia, methane, and methanol in a dark molecular cloud called Chamaeleon I.
This Webb image features the central region of the Chameleon I dark molecular cloud, which resides 630 light-years away in the constellation of Chamaeleon; the cold, wispy cloud material (blue, center) is illuminated in the infrared by the glow of the young, outflowing protostar Ced 110 IRS 4 (orange, upper left); the light from numerous background stars, seen as orange dots behind the cloud, can be used to detect ices in the cloud, which absorb the starlight passing through them. Image credit: NASA / ESA / CSA / M. Zamani, ESA & Webb / F. Sun, Steward Observatory / Z. Smith, Open University / Ice Age ERS Team.
“Our results provide insights into the initial, dark chemistry stage of the formation of ice on the interstellar dust grains that will grow into the centimeter-sized pebbles from which planets form in disks,” said lead author Dr. Melissa McClure, an astronomer at Leiden Observatory.
“These observations open a new window on the formation pathways for the simple and complex molecules that are needed to make the building blocks of life.”
“Webb allowed us to study ices that exist on dust grains within the darkest regions of interstellar molecular clouds,” added Dr. Danna Qasim, an astronomer at the Southwest Research Institute.
“The clouds are so dense that these ices have been mostly protected from the harsh radiation of nearby stars, so they are quite pristine.”
“These are the first ices to be formed and also contain biogenic elements, which are important to life.”
Webb has a 6.5-m-wide mirror providing remarkable spatial resolution and sensitivity, optimized for infrared light.
As a result, the telescope has been able to image Chamaeleon I, one of the densest, darkest clouds in the Universe.
“These observations provide new insights into the chemical processes in one of the coldest, darkest places in the Universe to better understand the molecular origins of protoplanetary disks, planetary atmospheres, and other solar system objects,” Dr. Qasim said.
Most interstellar ices contain very small amounts of elements like oxygen and sulfur. The study authors seek to understand the lack of sulfur in interstellar ices.
“The ices we observed only contain 1% of the sulfur we’re expecting,” Dr. Qasim said.
“99% of that sulfur is locked-up somewhere else, and we need to figure out where in order to understand how sulfur will eventually be incorporated into the planets that may host life.”
The astronomers propose that the sulfur may be locked in reactive minerals like iron sulfide, which may react with ices to form the sulfur-bearing ices observed.
“Iron sulfide is a highly reactive mineral that has been detected in the accretion disks of young stars and in samples returned from comets. It’s also the most common sulfide mineral in lunar rocks,” Dr. Qasim said.
“If sulfur is locked-up in these minerals, that could explain the low amount of sulfur in interstellar ices, which has implications for where sulfur is stored in our Solar System.”
“For example, the atmosphere of Venus has sulfur-containing molecules, in which the sulfur could have partially come from interstellar-inherited minerals.”
“Our identification of complex organic molecules, like methanol and potentially ethanol, also suggests that the many star and planetary systems developing in this particular cloud will inherit molecules in a fairly advanced chemical state,” said Dr. Will Rocha, an astronomer at Leiden Observatory.
“This could mean that the presence of precursors to prebiotic molecules in planetary systems is a common result of star formation, rather than a unique feature of our own Solar System.”
The research is a part of the Ice Age project, one of Webb’s 13 Early Release Science programs.
“We simply couldn’t have observed these ices without Webb,” said Webb project scientist Dr. Klaus Pontoppidan, an astronomer at the Space Telescope Science Institute.
“The ices show up as dips against a continuum of background starlight.”
“In regions that are this cold and dense, much of the light from the background star is blocked and Webb’s exquisite sensitivity was necessary to detect the starlight and therefore identify the ices in the molecular cloud.”
The findings appear in the journal Nature Astronomy.
_____
M.K. McClure et al. An Ice Age JWST inventory of dense molecular cloud ices. Nat Astron, published online January 23, 2023; doi: 10.1038/s41550-022-01875-w
