Astronomers have discovered evidence that small comets are breaking apart near the young star PDS 70, located 370 light-years away in the constellation Centaurus. The star is about five million years old and is surrounded by a disk of gas and dust. Earlier observations by the James Webb Space Telescope detected water vapor in this disk, even though the temperatures were high enough to prevent ice from existing. The source of this water vapor had been a mystery. A team led by Aline Novais, a postdoctoral researcher at Lund University, re-examined data from PDS 70 and found signs that might point to disintegrating comets. Between 2018 and 2020, the Harps instrument on a telescope at the European Southern Observatory captured 52 spectra of the star. These observations showed sodium absorption lines—indications of sodium gas—whose intensity changed over time. The sodium was moving at speeds between -25 and -115 kilometers per second, and the amount of sodium detected ranged from 2.4 × 10¹¹ to 7.1 × 10¹² atoms per square centimeter. Sodium is a common marker of cometary activity in our Solar System. The team ruled out the idea that the sodium came from a steady wind blowing from the disk, as that would create a consistent signal. Instead, the variable sodium levels suggest brief, transient events. The researchers propose that icy objects, ranging from 0.3 to 1.1 kilometers in size, are being thrown into highly elliptical orbits by two giant planets in the system, PDS 70 b and PDS 70 c. As these icy bodies approach the star, they release sodium clouds. The melting ice might be contributing to the water vapor detected in the disk. However, this doesn’t explain how Earth got its water, as PDS 70 is just one example of a possible transport mechanism. Other studies suggest that Earth's water might have originated from within the planet itself. Tom Barrett, a doctoral student at the University of Oxford, found that hydrogen was present in the materials that formed Earth, using synchrotron radiation analysis on enstatite chondrites. This challenges the idea that Earth's water came solely from comets or asteroids. While some comets, like 67P/Tchourioumov-Guérassimenko, have water with a different deuterium-hydrogen ratio than Earth’s oceans, it's possible that both internal processes and external delivery contributed to Earth's water. Jens Hoeijmakers, a co-author of the study, plans to use the Extremely Large Telescope in Chile to observe other objects in the PDS 70 system once it is fully operational. Sodium absorption lines are useful for detecting small amounts of gas, as sodium’s spectral lines are strong and easily identifiable. The variability of the sodium signal suggests transient events, like the passage of small bodies, rather than a continuous flow. Radial velocity measurements and column density estimates help astronomers understand the movement and mass of the gas, providing clues about the nature of these icy bodies and their role in shaping the disk around PDS 70.