On July 1st, 2025, astronomers at NASA's Asteroid Terrestrial-impact Last Alert System (ALERT) detected the third interstellar object (ISO) to enter our Solar System - 3I/ATLAS. Shortly thereafter, an international team led by researchers from Michigan State University (MSU) published the first scientific paper detailing the early scientific findings on this ISO. Hundreds of hours of observations have since been dedicated to measuring the astrometry, photometry, rotation period, and spectroscopy of this object to determine its trajectory, composition, and where it came from.
In a recent study, a team from MSU analyzed the images taken by NASA's Transiting Exoplanet Survey Satellite (TESS), which revealed evidence of 3I/ATLAS as early as May. These images suggest that the object may have been active ("outgassing") longer than scientists previously thought, meaning that spectra from its tail could yield additional insight into its composition. They further provide additional information about 3I/ATLAS, which will only be visible in the sky for a few more months before it leaves the Solar System and is out of range for even our most powerful instruments.
The research was led by Adina D. Feinstein, an Assistant Professor and NASA Sagan Fellow with MSU's Department of Physics and Astronomy. She was joined by John W. Noonan, an Assistant Research Professor and former Postdoctoral Fellow from the Edmund C. Leach Science Center at Auburn University, and Darryl Z. Seligman, an Assistant Professor and an NSF Astronomy and Astrophysics Postdoctoral Fellow at MSU. The paper detailing their findings appeared on September 11th in the Astrophysical Journal Letters.
Thanks to the Gemini North telescope, a group of astronomers managed to capture images of the recently discovered comet 3I/ATLAS, the third such object ever discovered. Credit: NOIRLab
Since it was first detected, scientists worldwide have worked tirelessly to observe and study this ISO while they still can, and papers are being released on a near-daily basis. Ordinarily, Feinstein and her colleagues are involved in exoplanet research, where they consult TESS data to look for transiting exoplanets. However, TESS observations often cross the orbital plane of our Solar System, which is where 3I/ATLAS has been traveling since it entered the Solar System. For their study, Feinstein and her colleagues used TESS data to contribute to research on the third ISO ever detected.
This consisted of filtering out light from the background stars, then combining multiple images to create a clear picture. The additional two months of images revealed that before the ISO was releasing clouds of gas that were mostly water, it was likely outgassing other volatiles prior. This could include carbon monoxide and carbon dioxide, two potential biosignatures astrobiologists look for when characterizing exoplanet atmospheres. Said Feinstein:
There are so few interstellar objects that we've detected in our solar system, and they each seem to be unique. 3I/ATLAS gives us an opportunity to study other solar systems up close and personal, without actually needing to visit them. As soon as I realized 3I/ATLAS should be in these TESS images, I downloaded them as quickly as I could. That gives us an idea of what comets and asteroids could be made of in systems beyond our own Sun. It's always been assumed that other systems are different from ours, but now we have evidence of how different they might be.
Researchers expect 3I/ATLAS to be visible for several more months and will use that time to try and learn more about this cosmic interloper. This will include data obtained by the James Webb Space Telescope's (JWST) sophisticated infrared optics and spectrometers. These observations will reveal more about 3I/ATLAS' composition, which could yield additional clues about where it came from and how it has evolved since. "Learning about other solar systems places humanity into context," said Feinstein. "One of life's greatest questions is 'are we alone in the universe?' Each NASA mission gets us a little bit closer to answering this big, overarching question."
In the meantime, this study highlights the importance of all-sky surveys and shows how they can conduct science operations beyond their primary mission and purpose. Said Noonan:
Capturing as many observations from this prediscovery period, where 3I/ATLAS may be in telescope images but wasn't previously identified, is essential to our understanding of how these objects 'turn on' as they approach our sun. These interstellar objects have likely not been warmed significantly in millions, if not billions, of years, and any opportunity to see how they responded to that early heating is of interest.
Further Reading: MSU, The Astrophysical Journal Letters
