Scientists studying the interstellar comet 3I/ATLAS have found something remarkable: it carries unusually high levels of deuterium, the heavy form of hydrogen found in “heavy water”.

3I/ATLAS is only the third known object to visit our solar system from another star. Because it formed around a different sun, its chemistry gives scientists a rare look at how planetary building blocks differ across the galaxy.

The high deuterium levels are exciting because they relate to one of science’s big questions: where did Earth’s water come from? Comets have long been suspects, and each new measurement helps refine the answer.

The comet is currently passing through our solar system on a one-way trip. Telescopes around the world are tracking it closely, and researchers expect more findings in the coming months as it nears the Sun. The findings were based on observations from ground-based telescopes and space observatories working together during the comet’s approach.