Astronomers have long wondered how Earth became water-rich—bountiful with abyssal oceans, frigid glaciers and rain that pours from the sky into lakes, rivers and wetlands. Water, which is composed of the first and third most common elements in the universe, is a deceptively simple molecule to form. Yet while the details of its delivery to rocky planets like our own may be essential for understanding life’s cosmic prevalence, they remain mostly unknown.
Water is a potent medium for the assembly of complex organic molecules and offers havens for the emergence and subsequent evolution of life as we know it. Deep within Earth it ensures the lithic lubrication that keeps climate-stabilizing plate tectonics from grinding to a halt—another mechanism that just might be crucial for life. And when frozen as ice it plays a key role in planet formation by providing the glue that helps young worlds grow. As such, scientists are anxious to better understand water’s planetary peregrinations—the pathways it takes to transform planets from desiccated rocks into worlds as soaked as Earth.
To gain more insight, astronomers are utilizing the James Webb Space Telescope (JWST) to peer into protoplanetary disks: the swirls of gas and dust around young stars where planets are actively forming today. Although astronomers have glimpsed water within such disks before, their view has been hazy. For example, water vapor is visible to the Atacama Large Millimeter/submillimeter Array (ALMA)—in many respects the most powerful radio observatory on Earth—but the facility largely cannot detect water ice. This blocks a protoplanetary disk’s outer regions from ALMA’s scrutiny. The array also cannot deeply probe the hot, inner regions of disks where terrestrial bodies form. JWST, on the other hand, was designed with such studies in mind and has—quite literally—opened the floodgates. The new space observatory is delivering unprecedented looks at how water passes from star-forming…
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