With its wide field of view, the TESS space observatory continuously monitors large swathes of the sky and records the faintest fluctuations in light. Its mission is to discover worlds orbiting stars other than our Sun, but it was recently repurposed to observe a much closer object, an interstellar visitor passing through our own system.
You guessed it if you regularly read Techno-Science.net: it's 3I/ATLAS.
NASA's TESS spacecraft recently spotted the interstellar comet 3I/ATLAS, illustrated here against a starry background.
Credit: TESS insert by NASA/comet background by Enrico Bellodi from Pexels/assembled by Kenna Hughes-Castleberry via Canva pro
Between January 15 and 22, a dedicated series of observations was devoted to comet 3I/ATLAS as it is now in its departure phase. The images taken during this interval show a bright point moving swiftly against a starry background, leaving behind a faint trail. This data subsequently allowed astronomers to reconstruct its trajectory with great accuracy, providing a rare portrait of its behavior.
A scientist from
MIT assembled these images into a video sequence covering 28 hours, tracing the comet's path. A time jump appears in the sequence, however, caused by an interruption due to a satellite safe mode. Despite this gap, this visualization facilitates the examination of the comet's activity, such as the ejection of dust and gas, or the rotation speed of its nucleus.
The measurements indicate an apparent magnitude of about 11.5 for this object, making it a hundred times less perceptible than the naked eye limit. Observing it therefore requires the use of telescopes. This faint brightness also explains why the comet remained invisible until July 2025, during its approach to the Solar System.
The interstellar comet 3I/ATLAS appears as a bright spot with a tail in this animation from TESS images, showing its motion over 28 hours.
Credit: NASA/Daniel Muthukrishna, MIT
One surprising detail is that TESS had recorded the comet's passage several months before its official identification. By exploring the archives, astronomers were able to spot this interstellar traveler and reconstruct its route. While its precise origin remains undetermined, this data nevertheless provides clues about its composition and its long space journey.
Now publicly accessible via repositories such as the
Mikulski Archive for Space Telescopes, the January observations offer several hours of data to analyze. Researchers hope to find recurring patterns in brightness changes, which could provide additional information about the properties of 3I/ATLAS.
What is an interstellar comet?
These celestial objects are not bound by gravity to our Sun or any other star. They traverse the galaxy on open trajectories and at very high speeds. Unlike the resident comets of our Solar System, these visitors come from other stellar systems, carrying with them primordial materials from distant regions.
Their identification is a recent phenomenon, with only a few confirmed examples like 3I/ATLAS. These comets represent a unique opportunity to analyze the composition and physical mechanisms of objects formed in extrasolar environments. Their nuclei, made of ice, dust, and gas, sublimate when approaching a star like our Sun, generating the bright tails we observe.
By studying their activity, such as the emission of dust and gas, scientists can deduce information about their internal structure and past. For example, the rotation of the nucleus can indicate previous collisions or gravitational influences.
These comets act as natural messengers, also carrying chemical signatures that could indicate differences or similarities between stellar systems.