Should We Message 3I/ATLAS?

Unfortunately, there is no way to launch a chemical rocket from Earth that would intercept the new interstellar object 3I/ATLAS before it reaches perihelion on October 29, 2025, since its retrograde motion will bring it up to a velocity of 98 kilometers relative to Earth — a few times faster than our fastest rockets.

Nevertheless, this relative speed is still 3,000 times lower than the speed of light, allowing us to easily reach 3I/ATLAS with a light beam.

Should we send a message to 3I/ATLAS from one of the radio telescopes on Earth?

This would have made sense if we knew that 3I/ATLAS is a technological spacecraft carrying some form of intelligence, be it natural or artificial. We could consider this radio signal as a way to start a conversation on a blind date with an interstellar visitor to our backyard.

Whether we take advantage of this opportunity depends on the answers we give to two follow-up questions:

(i) First, is there intelligence on 3I/ATLAS that might comprehend our message? Speaking to an icy rock makes little sense.

(ii) Second, if 3I/ATLAS harbors alien intelligence, that entity might perceive our artificial light beam as a threat and respond violently as if we were predators.

On November 16, 1974, the Arecibo radio telescope broadcasted an interstellar radio message, carrying basic information about humanity and Earth, towards the globular cluster of stars Messier 13 which is located 22.2 thousand light years away. Sending a radio signal to a civilization that might be located so far away is far less risky, as it would take that civilization a long time to respond to us even at the speed of light. But a visitor to our backyard, like 3I/ATLAS, can easily enter our home planet, Earth, within a travel time of less than a few months, by Christmas 2025.

As of now, we cannot assess with great confidence whether 3I/ATLAS is a natural dust-rich comet with no gaseous tail on an extremely rare trajectory, or perhaps a technological object on a path that was designed to align with the ecliptic plane of the planets around the Sun. All we know is that 3I/ATLAS exhibits a rare (0.2% probability) alignment of its retrograde path with the ecliptic plane, and that its arrival time is perfectly matched for a close encounter with Mars, Venus and Jupiter (with a 0.0005% probability, as discussed here). On the “Loeb scale,” recently defined with explicit criteria in a paper that I co-authored with Omer Eldadi and Gershon Tenenbaum (accessible here), we gave 3I/ATLAS a rank of `4’, where `0’ is the default value for a natural object and `10’ refers to an artificial object. If humanity were to message 3I/ATLAS and receive a response, its rank would immediately jump from `4’ to `10’.

During an exchange with 3I/ATLAS, we could use the Turing Test as a measure of the intelligence with which we communicate, as long as the two sides develop a common language for communication. Our side of the communication channel can be assisted by our most advanced artificial intelligence systems to decode the messages we receive. But as anyone who went on a blind date knows, exchanging text messages could be a very different experience than an actual encounter “in person.”

Physical measures of interstellar visitors are as ambiguous as they are in blind dates among humans. For example, recent imaging of 3I/ATLAS by the Hubble Space Telescope revealed a glow ahead of the object but no bright tail of gas and dust behind it — as often observed for comets (see details here). In addition, spectroscopic measurements show no evidence for molecular or atomic gas accompanying this glow (see related papers here, here and here, as well as the discussion about water ice here). But even if 3I/ATLAS showed a large non-gravitational acceleration without a cometary tail — as observed for the first interstellar object 1I/`Oumuamua (see data here and here), astronomers would argue that it is a “dark comet, ” an oxymoron used to describe an object that shows non-gravitational acceleration without a corresponding cometary tail (see a related discussion here).

This brings us back to the question: should we message 3I/ATLAS to find out, once and for all, whether it carries intelligence?

It would be prudent to wait until 3I/ATLAS reaches perihelion with the expectation that if it is a natural comet, it will erupt in enhanced outgassing as a result of its intensified illumination by the Sun. This could inform us beyond any reasonable doubt that 3I/ATLAS is natural, bringing its rank to `0’ on the “Loeb scale.” On the other hand, if 3I/ATLAS will execute an unexpected maneuver at the time of its closest approach to the Sun — when the Solar gravitational assist can amplify the thrust of its engine, we would still have time to engage with 3I/ATLAS long before it, or any mini-probes it releases, will reach Earth.

On blind dates, it is wise to observe the other side before starting a conversation. Here’s hoping that our encounter with 3I/ATLAS will be as boring as dating an icy rock or as uplifting as meeting the smartest student in our Galactic class of intelligent civilizations.

ABOUT THE AUTHOR

Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024.