Citizen Science in Astronomy (Part 7): Comet 3I/ATLAS and a Disintegrating Exoplanet

In a recent SETI Live, SETI Institute astronomers, Dr. Franck Marchis and Dr. Lauren Sgro, discussed two rare and compelling discoveries: a newly identified interstellar comet, Comet 3I/ATLAS (C/2025 N1), and BD+05 4868 b, one of only four known disintegrating exoplanets. Both objects are being studied with the help of Unistellar’s global citizen science network, which consists of thousands of distributed backyard telescopes capable of capturing high-precision astronomical data.

Expanding the Reach of Citizen Science

Dr. Franck Marchis, SETI Institute astronomer, Director of Citizen Science, and Chief Scientific Officer at Unistellar, along with Dr. Lauren Sgro, SETI Institute exoplanet astronomer, discussed how Unistellar’s decentralized telescope network enables large-scale observational campaigns, capturing even faint and transient phenomena across the sky.

The discussion underscored how citizen scientists, by contributing thousands of data points from around the world, are playing a direct role in advancing planetary science, exoplanetary studies, and interstellar object research.

Comet 3I/ATLAS: An Interstellar Visitor

Comet 3I/ATLAS, officially designated C/2025 N1, was discovered on July 1, 2025, using the Asteroid Terrestrial-impact Last Alert System (ATLAS) in Chile. Its hyperbolic orbit (an open trajectory that does not loop back into the Solar System) confirmed its interstellar origin. This makes it only the third known interstellar object, following 1I/‘Oumuamua (2017) and Comet 2I/Borisov (2019).

Because Comet 3I/ATLAS was discovered early in its approach, astronomers have a unique opportunity to study its composition and activity in detail. Citizen astronomers using Unistellar telescopes have already collected more than 50 independent observations. These data reveal:

• A gradual increase in brightness, consistent with cometary activity as solar heating sublimates volatile ices
• Refinement of the comet’s orbital parameters by tracking its precise motion against background stars
• Evidence of dust and gas emissions, confirmed by complementary spectroscopic observations

Early Unistellar observations pushed the detection limits of the network, identifying the comet at magnitude 17.8, making it the faintest object ever captured by this citizen science community. The comet is expected to brighten to around magnitude 14 later this year, though its proximity to the Sun will make direct observation challenging during its closest approach.

BD+05 4868 b: A Rare Disintegrating Exoplanet

In May 2025, astronomers identified a new disintegrating exoplanet: BD+05 4868 b. This Mercury-sized rocky world orbits its parent star at just 0.02 astronomical units (AU) – 20 times closer than Earth is to the Sun. At such extreme proximity, stellar radiation is stripping away planetary material, creating a trailing dust tail similar in appearance to a comet.

Unlike typical planetary transits, which produce a symmetrical dip in stellar brightness as the planet passes in front of its star, the light curve of BD+05 4868 b shows an extended dimming after the planet’s passage. This asymmetry results from the trailing dust tail crossing the star’s disk.

To study this rare system, SETI Institute astronomers coordinated a campaign with Unistellar observers worldwide. With 26 observers contributing data across 22 hours, the network achieved an unprecedented 26 hours of continuous coverage of a single exoplanet transit, an accomplishment impossible for a single ground-based observatory.

This extensive dataset is now being analyzed in tandem with Keck Observatory spectroscopy, which will reveal the chemical composition of the disintegrated material. Such measurements could provide the first direct insights into the interior makeup of an exoplanet.

Looking Ahead: Asteroid Occultations and Beyond

The discussion also previewed upcoming opportunities for citizen scientists. On August 26, 2025, the main-belt asteroid Pulcova, a 100-kilometer-wide body with a small moon, will occult an 11th magnitude star along a path stretching across the United States. Observations of this event will refine the asteroid’s size, shape, and confirm the orbital parameters of its moon. The Unistellar community will also have two final chances to observe the disintegrating planet, BD+05 4868 Ab, from August 22 to 24.

Why These Discoveries Matter

Interstellar comets like 3I/ATLAS offer a rare opportunity to directly sample material from other planetary systems, improving our understanding of planet formation in diverse environments. Disintegrating exoplanets reveal the extreme evolutionary pathways of small rocky worlds, bridging planetary geology with stellar astrophysics.

Citizen science continues to amplify the capacity of professional astronomers, enabling discoveries that would otherwise be impossible with limited telescope time.

Learn More

Explore ongoing citizen science projects at the SETI Institute.

Watch the full SETI Live episode here.