Not every day scientists can observe an interstellar object, that is, an asteroid or a comet coming from outside our solar system. In fact, it has only happened three times: with the asteroid 1I/Oumuamua, discovered in 2017, with the comet 2I/Borisov, spotted in 2019, and with the comet 3I/ATLAS, detected on July 1st.
Since this new interstellar visitor was discovered with a Chilean telescope that is part of the 'Asteroid Terrestrial-impact Last Alert System (ATLAS),' observatories worldwide have pointed their instruments towards it to calculate its orbit, discover its characteristics, and observe material coming from another stellar system, as they have only a few months to study it.
Space agencies assure that it does not pose a threat as it will remain at a safe distance from Earth at all times. When it makes its closest approach to our planet on December 19, it will be situated 270 million kilometers away. Yesterday, Thursday, October 30, it made its closest approach to the Sun, passing at about 200 million kilometers from our star. Despite scientists confirming that it behaves like a comet and follows a trajectory that rules out a collision with Earth, hoaxes about the danger it poses and theories suggesting it could be a spaceship are spreading.
"This comet poses no risk to Earth," affirms Michael Kueppers, a scientist at the European Space Astronomy Centre (ESAC) of the European Space Agency (ESA), in a phone conversation. Kueppers denies that the UN's Planetary Defense protocols have been activated upon the arrival of 3I/ATLAS, as reported in some media. "What has been done by the International Asteroid Warning Network (IAWN) is an observation campaign to practice tracking these objects and be able to predict their trajectory accurately. The goal is to be prepared for when an asteroid or comet that poses a risk to Earth is detected. It has been done several times already and is a routine procedure," he assures.
As explained by this ESA scientist, asteroids are not the only threat to our planet, as a comet could also impact: "And if that happens, it will be critical that we are able to quickly track that object, as they are detected with less advance notice. We would have fewer opportunities to observe and study it, so we would have to act very quickly."
"The IAWN is a network that is activated whenever observations of an interesting object are needed, but there does not necessarily have to be a risk of collision with Earth. And that is what NASA has done now. They have told us: 'Let's take advantage of this already established network to observe this super interesting object, even though it has been said that the agency has secretly activated the Planetary Defense protocols," clarifies Julia de León, head of the Solar System group at the Institute of Astrophysics of the Canary Islands (IAC), one of the centers that has been studying this comet.
According to this astronomer, they are constantly training to be more efficient in sharing information: "Every year we do exercises and campaigns. And for those of us who are dedicated to this, having a comet from another planetary system come is a great gift. We have been very attentive since it was classified as an interstellar object at the beginning of July," says De León, who laments that "so much misinformation about this object is being spread through the internet."
"All we can do is refute these false pieces of information and explain the real situation when we talk to the media," states Michael Kueppers.
The case of comet 3I/ATLAS, compares the ESA scientist, is different from that of asteroid 2024 YR4, discovered in late December 2024: "With this object, the Planetary Defense protocols were indeed activated." For two months, there was an estimated small probability of it colliding with Earth during its approach on December 22, 2032.
Faced with that risk, the UN's Planetary Defense protocols were activated for the first time, activating the two reaction groups created to address the threat of these space rocks: the International Asteroid Warning Network (IAWN) and the Space Mission Planning Advisory Group (SMPAG). In the following weeks, the probability of impact exceeded 3%, but as more observations were made, the risk of impact against Earth was ruled out. Currently, the probability of this rock impacting the Moon on that day is 4%.
Avi Loeb, the scientist from Harvard University who gained fame when he suggested that the interstellar object Oumuamua was an alien spacecraft, is also attracting media attention these weeks, defending the hypothesis that 3I/ATLAS could have a non-natural origin, meaning that it may not be a comet but a technological object created by another civilization. He argues that it exhibits "several anomalous characteristics" and believes that this week, as it has approached the Sun, is crucial to determine its true nature.
However, both Michael Kueppers and Julia de León maintain that they have not observed any evidence to support that hypothesis: "All we see is the normal behavior of a comet, like those we have in the Solar System. Apart from coming from another star, it is not particularly different. As it approaches the Sun, it becomes more active, and we are seeing the same gases and dust tail. I honestly do not believe that theory about a supposed spaceship has any basis," affirms Kueppers.
Thus, he considers that the elements being mentioned to support its possible technological origin have scientific explanations. Regarding its composition, he states that the James Webb has found in 3I/ATLAS a composition similar to that of other comets: mainly water and carbon dioxide. "The proportion of carbon dioxide is higher than in comets from our solar system, indicating that it has formed in a colder environment," he points out. Julia de León agrees: "As it happened with comet Borisov, we are seeing that it has a slightly higher percentage of carbon dioxide ice than what we usually find in comets from the Solar System."
Additionally, Kueppers states that this comet, traveling at 60 kilometers per second, has entered the Solar System with a higher speed than other objects "because it has spent a long time traveling through space and has accelerated."
Otro aspecto que ha dado lugar a comentarios, según expone Julia de León, es que se ha visto emisión de jets (chorros) de gas concentrados en algunas del cometa: "Es algo bastante normal. Si hay volátiles concentrados en ciertas zonas del objeto, cuando comienza a salir el chorro de partículas no es uniforme por toda la superficie, pero tienden a homogeneizarse", señala. "Es un objeto natural, no hay ningún indicio que apunte a que no lo sea", subraya esta astrónoma, que admite su malestar ante la proliferación de esas teorías. "Desconozco por qué Avi Loeb las propicia, cuando, además, él no es un científico planetario y, por tanto, no es especialista en este tipo de objetos. Ya está bien de teorías locas", reclama.
El tamaño del cometa
A medida que recaban más datos están pudiendo afinar algunas de sus características, como su posible tamaño. Aunque al principio se llegó a estimar un núcleo de entre 10 y 30 kilómetros, Michael Kueppers explica que ahora creen que es mucho más pequeño: "Las estimaciones que se han hecho con los datos del telescopio espacial Hubble apuntan a que mide entre 220 metros y dos kilómetros pero no sabemos con seguridad qué tamaño tiene", admite.
"Como es un cometa, emite gases y polvo, y el brillo que vemos es la luz del Sol reflejada en esas partículas de polvo, que van dejando la forma típica de un cometa. Esto hace que parezca más grande de lo que realmente es. Cuando observas un cometa ya está activo, por lo que definir el tamaño del núcleo de un cometa es muy difícil dado que el polvo impide que veamos su interior", explica Julia de León, que también considera que el tamaño más fiable es inferior a tres kilómetros.
Aunque actualmente 3I/ATLAS no es visible desde la Tierra, sí pueden observarlo varias naves espaciales, como JUICE, de la ESA, y otras misiones de NASA. "En el caso de nuestra sonda JUICE, que se dirige hacia el sistema de Júpiter, va a poder observar el cometa hasta mediados de noviembre. Los datos no llegarán hasta febrero pues debido a que ahora está muy cerca del Sol, las comunicaciones con la Tierra de nuestra nave están muy limitadas", afirma Kueppers.
A medida que se aleje del Sol podrá divisarse de nuevo con los instrumentos terrestres, tal y como adelanta Julia de León: "A finales de noviembre podrá ser visible al amanecer, y estará en mejores condiciones para observarlo en diciembre desde la Tierra. Podremos verlo durante unos meses más, cada vez la señal será más débil. Por eso, hemos activado esa campaña de observaciones coordinadas, para aprovechar al máximo ese tiempo".