NASA's James Webb Space Telescope (JWST), also called Webb, has found evidence of water in a comet belonging to the main asteroid belt of the solar system. The finding is intriguing because this is the first time water has been found in the main asteroid belt, which is located between Mars and Jupiter. The comet, called Comet Read, has no detectable carbon dioxide, which is unusual because all comets have this compound.
The study describing the findings was published May 15 in the journal Nature.
According to the study, main-belt comets are small solar system bodies located in the asteroid belt that repeatedly exhibit comet-like activity, which means that they show dust comae and tails, during their perihelion passages, or the points in their journey when they are closest to the Sun. These bodies show ice sublimation, which means that water ice is directly converted to water vapour.
First discovery of water in solar system’s main asteroid belt
The world's largest telescopes have intensely scrutinised the main asteroid belt, but never found any gas around the objects. Webb's discovery of water vapour around Comet Read marks the first time a gas has been found in the solar system's main asteroid belt. The finding indicates the presence of extant (existing) water ice in the asteroid belt.
Webb's observations clearly show that Comet Read has a coma, or a nebulous envelope of water vapour, but lacks a significant carbon dioxide gas coma.
Water-ice sublimation drives the activity of Comet Read, the authors noted in the study. They also said that the main-belt comets are fundamentally different from the general cometary population.
Irrespective of whether Comet Read has a unique evolutionary history or experienced different formation circumstances, the object is unlikely to be a recent asteroid belt interloper from the outer solar system, the authors noted.
The presence of water vapour around Comet Read indicates that water ice from the primordial solar system can be preserved in the main asteroid belt.
There may be a possibility of other main-belt asteroids having volatile material. However, these objects are not represented in observations of classical comets.
In a NASA statement, Stefanie Milam, one of the co-authors on the paper, said understanding the history of water distribution in the solar system will help researchers understand other planetary systems, and if they may host an Earth-like planet.
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More about comet read
Comet Read is present in the main asteroid belt, but periodically displays a halo or coma, and a tail, similar to a comet. The category of main belt comets is new, and Comet Read was one of the first comets used to establish this class. Before a separate class of main belt comets was formed, comets were understood to be present in the Kuiper Belt or Oort Cloud, beyond Neptune's orbit. The ice on the comets residing in these regions is preserved from the rays of the Sun, when they are farther away from the star.
Webb proved a long-speculated theory that water ice could be preserved in the warmer asteroid belt, inside Jupiter's orbit.
Michael Kelley, the lead author on the paper, said in the statement that in the past, astronomers have seen objects in the main asteroid belt with all the characteristics of comets, but only with the precise spectral data from Webb can they say for sure that it is definitely water ice that is creating the coma effect.
He also said that with Webb's observations of Comet Read, astronomers can now demonstrate that water ice from the early solar system can be preserved in the asteroid belt.
Carbon dioxide missing on the asteroid was a bigger mystery and surprise because this gas typically makes up about 10 per cent of the volatile material in a comet which can be easily vaporised by the Sun's heat.
Why does Comet Read lack carbon dioxide?
According to the NASA statement, there are two possible explanations for the lack of carbon dioxide on the comet. One of the possible reasons behind the comet lacking carbon dioxide is that the body may have lost the carbon dioxide it earlier had due to warm temperatures.
Another possibility, according to Kelley, is that Comet Read nat have formed in a particularly warm pocket of the solar system, where no carbon dioxide was available.
The authors concluded that main-belt comets are important for understanding the volatile inventory of the early solar system, and its subsequent evolution.