Analyze This: Ice around baby stars may hint at origins of Earth’s water

Distant baby stars might be able to shed new light on the origins of Earth’s water.

One clue to where water came from is how much of it is “semi-heavy.” In semi-heavy water molecules, one hydrogen is replaced with a hefty form of the element called deuterium. Deuterium contains a neutron in its nucleus along with a single proton. Instead of H2O, semi-heavy water is HDO.

Water with a high ratio of HDO to H2O likely formed in a very cold place. Say, a frigid, star-forming cloud of gas, dust and ice. Earth’s oceans have a higher ratio of HDO to H2O than our sun does. That has led astronomers to suspect that some of our water came from ice in the dark cloud where the sun was born.

To find out, scientists need to know more about the ratio of HDO to H2O ice in the chilly nurseries where sunlike stars form. They also want to know how that ratio may change over a star’s lifetime.  

Astronomers can spot semi-heavy water ice in space by its interactions with light. But it’s hard to see these signs from Earth. So researchers used data from when the James Webb Space Telescope (JWST) peered at the star L1527.

At just 100,000 years old, L1527 is an infant compared with our 4.5-billion-year-old sun. But its size and surroundings suggest it could grow up to look a lot like the sun. The dust and gas around this star are forming a disk. L1527 is gobbling up some of this material. What’s left behind could someday form planets — as happened in our solar system.

JWST saw a fairly high ratio of HDO to H2O ice in the stuff swaddling L1527. The researchers compared that ratio with the ice and gas around other baby stars, including slightly older ones. That suggested that the HDO to H2O ratio around a star might not change much as the star evolves. The team also compared L1527’s HDO to H2O ratio with that of the ice seen on comets and meteorites in our solar system.

The team shared its findings in the June 20 Astrophysical Journal Letters.

These observations offer new details about what happens to water as stars mature. This may help scientists figure out where Earth’s water came from. And that, in turn, could help pin down what it takes to make a planet habitable. But first, astronomers will need to observe the water around more baby stars — in both ice and gas forms.

Data Dive:

Look at the HDO to H2O ratio for the interstellar medium. That’s the space between stars, which has a similar value as our sun. How does its HDO to H2O ratio compare with that of Earth’s oceans? How does the HDO to H2O ratio of Earth’s oceans compare with that of carbonaceous meteorites? What about with the two families of comets? How does the ratio of HDO to H2O ice around L1527 compare with that of the more massive stars viewed by JWST? What might researchers find if they keep looking at more stars with JWST?