Astronomers have found signs that comets may be streaking past PDS 70, a star roughly 5.4 million years old and about 370 light-years from Earth, and they propose that those comets could be carrying water into the region where rocky planets can form. The study, led by Aline Novais of Lund University in Sweden, was published Aug. 24 in Nature Communications.

The evidence is indirect but specific. In archival observations from 2018, the team found neutral sodium gas in front of the star that appeared, vanished, and changed speed from night to night. They conclude that the likely source is icy bodies vaporizing as they pass close to the star, a process known as sublimation.

That matters beyond one distant system because the origin of Earth's water is still debated. PDS 70 lets scientists look for a comparable process in a system where planets are still forming, rather than reconstructing events from billions of years ago.

Signals Hidden in Starlight

The researchers reanalyzed 52 archival spectra taken between 2018 and 2020 with the HARPS instrument on the European Southern Observatory's 3.6-meter telescope at La Silla, Chile. In the 2018 data, they identified 43 variable sodium absorption features moving toward Earth at roughly 25 to 115 kilometers per second, or about 56,000 to 257,000 miles per hour.

Those features came and went on daily timescales and covered only part of the star's disk, which points to compact clouds of gas rather than a smooth, steady flow. The team weighed other explanations, including winds blowing off the disk of gas and dust around the star, and found them harder to reconcile with the data, though the authors note they cannot definitively rule out a disk wind.

The activity largely faded in the 2020 spectra. But new observations from early 2026 with the UVES spectrograph in Chile show the variability continuing, including some features moving away from Earth. The authors say those receding signals add support for the comet interpretation, and they plan to analyze that dataset in a separate study.

Using the sodium measurements, the team estimated that bodies roughly 0.3 to 1.1 kilometers across, or about 0.2 to 0.7 miles, could account for the minimum amount of sodium observed if they vaporized completely.

A Young System Built for This Test

PDS 70 has become a benchmark because two young giant planets, PDS 70 b and PDS 70 c, have been directly imaged inside a gap in the disk around the star. The James Webb Space Telescope later detected water vapor in the innermost part of that disk, close to the star, but the source of that water was unclear.

The Lund team ran computer simulations to test whether the giant planets could fling icy bodies from the outer disk inward. According to the models, they can. In the final million years of the simulations, an average of about 0.5% to 2.9% of the test particles crossed the gap toward the inner disk, depending on whether a third, still-unconfirmed planet was included.

Novais said in a Lund University release that comets "may be responsible for transporting water to the inner parts" of the system. Co-author Alexandra Stockwell Murphy called it "reminiscent of a possible process in the early Solar System."

If confirmed, PDS 70 would be the youngest system in which exocomet activity has been observed, the coolest star known to host it, and only the second system with both exocomets and confirmed planets, after Beta Pictoris, according to the paper.

The Evidence Check

This is an observational study paired with computer modeling, published in a peer-reviewed journal. It found variable sodium gas consistent with exocomets, along with simulations showing that inward scattering of icy bodies is plausible. It did not detect water in any comet, did not image a comet, and did not show that the water Webb saw came from comets.

The authors are direct about those limits. They write that unambiguously confirming exocomets will require more work, including time-series spectra to track individual objects, attempts to catch dust tails crossing the star, measurements of elemental ratios, and better estimates of the planets' masses, which currently carry uncertainties of several Jupiter masses.

Other explanations for PDS 70's inner water remain on the table. Water could form in place through chemistry in the inner disk, or icy dust could drift inward with gas across the gap carved by the planets. The comet pathway adds to that list rather than replacing it.

The study's scope is narrow: one star, sporadic observations spanning 46 days in 2018, and a 2026 dataset still under analysis. Nature World News did not obtain comment from an astronomer outside the study team, and readers should treat the result as a strong candidate rather than a confirmed detection.

Why the System Matters for Earth's Water Debate

Debates over whether comets, water-rich asteroids, or Earth's own interior supplied the oceans have relied largely on chemical fingerprints in meteorites and comet measurements, and the results have pointed in more than one direction.

A system like PDS 70 offers something different: a chance to see a possible delivery mechanism at work while planets are still being built. As Universe Today's coverage of the study noted, researchers still debate whether Earth's water came from gases released by the young planet itself, was delivered by asteroids and comets, or both.

Lund astronomer Jens Hoeijmakers said the Extremely Large Telescope, now under construction in Chile, should help reveal whether more planets orbit PDS 70 and clarify how water and other planet-building materials move through the system. Additional planets would change the simulations, because their gravity shapes where icy bodies end up.

Nothing about this finding changes conditions on Earth or any scientific consensus about the planet's history. It adds a new observational test to one of planetary science's longest-running debates, one that astronomers can revisit with each new round of observations.

The next steps are the analysis of the 2026 UVES data and future observations that could confirm or rule out the comet explanation. Until then, the most accurate description of PDS 70's comets is promising evidence, not proof.

What Readers Want to Know

What did astronomers find around PDS 70?

They found neutral sodium gas that changed from night to night in front of the star, a pattern the researchers say is most likely caused by comets vaporizing as they pass close to it.

Did the study detect water in the comets?

No. The James Webb Space Telescope detected water vapor near the star in earlier work. The new study proposes that comets could help explain that water but did not measure water in any comet.

How far away is PDS 70?

About 370 light-years from Earth. The star is roughly 5.4 million years old, very young compared with the Sun's age of about 4.6 billion years.

Why does this matter for Earth?

Scientists still debate where Earth's water came from. PDS 70 offers a chance to study a possible water-delivery process in a system that is still forming planets.

Is the finding confirmed?

Not yet. The authors say more observations are needed, including tracking individual comets over time and pinning down the masses of the system's planets.

What happens next?

The team plans a separate analysis of observations made this year, and future telescopes such as the Extremely Large Telescope in Chile could reveal more planets and clarify how water moves through the system.