Astronomers have discovered another puzzling interstellar object—this third one is big, bright and fast

Astronomers who try an asteroid alert system saw a large brilliant object crossing the solar system late on July 1, 2025.

The potentially interstellar origins of the object have aroused scientists around the world, and the next morning, the European space agency confirmed that this object, named A11PL3Z then designated 3i / Atlas, is the third never found from the outside of our solar system.

Current measures estimate that 3i / Atlas measures approximately 12 miles (20 kilometers) wide, and although its path does not take it near the earth, it could contain indices on the nature of a previous interstellar object and on the formation of the planet in solar systems beyond ours.

On July 2 at 3 p.m., Mary Magnuson, associate editor of the US conversation, spoke to Darryl Z. Seligman, astrophysicist at Michigan State University which has been studying 3i / Atlas since its discovery.

What makes 3i / Atlas different from its predecessors?

We have discovered two interstellar objects so far, “Oumuamua and Comète 2i / Borisov. “Oumaumua did not have a dust tail and a significant unruck acceleration, which led to a wide variety of hypotheses concerning its origin. 2i / Borisov was very clearly a comet, although it has a somewhat unique composition compared to the comets of our solar system.

All our preparation for the next interstellar object was preparing for something that looked like a ‘Oumamua, or something that looked like Borisov. And this thing is unlike any of them, which is crazy and exciting.

This object is shocking brilliant and it is very far from the earth. It is much greater than the two interstellar objects that we have seen – it is orders of magnitude larger than ‘Oumamua.

For a certain context, ‘Oumaumua was discovered when it was very close to the earth, but this new object is so large and brilliant that our telescopes can see it, even if it is still much more distant. This means that observatories and telescopes can observe it much longer than for the two previous objects.

It’s huge and it’s much further, but it is also much faster.

When I went to bed last night, I saw an alert on this object, but no one knew what was going on. I have some collaborators who discover the orbits of things in the solar system, and I expected to wake up by saying something like “yeah, it is not really interstellar.” Because several times, you think you may have found something interesting, but as more data happens, it becomes less interesting.

Then, when I woke up at 1 am, my colleagues who are experts on the orbits said things like “no, it’s definitely interstellar. It is for real”.

How can astronomers know if something is an interstellar object?

The eccentricity of the orbit of the object is the way you know that it is interstellar. The eccentricity refers to the way in which a non -circular orbit is non -circular. Thus, an eccentricity of zero is a pure circle, and as eccentricity increases, it becomes what is called an ellipse – an stretched circle.

And then once you have exceeded eccentricity, you go from an ellipse to a hyperbolic orbit, and it is unrelated. Thus, while an elliptical orbit is extended, it is still in orbit and returns. An object with a hyperbolic orbit passes and it leaves, but it never comes back. This type of orbit indicates that it does not come from this solar system.

When the researchers collect data, they obtain points of light on the sky and they do not know how far they are. It is not as if they saw them and could simply say: “Oh, it’s eccentric.” What they see is how far the object is compared to the other stars in the background, what is its position and how fast it moves. And then from this data, they try to adjust the orbit.

This object moves quickly for the distance to which it is, and that is what tells us that it could be hyperbolic. If something moves quickly enough, it will escape from the solar system. Thus, a hyperbolic and unrelated object must intrinsically move more quickly.

It is a real time process. My employees have pre -existing software, which, every night, will obtain new observations from all small bodies and objects of the solar system. It will determine and update what the orbits are in real time. We get data points, and with more data, we can refine which orbit best corresponds to points.

What can scientists learn from an interstellar object?

Objects like this are virgin essential remains of the planet’s training process in other planetary systems. The small bodies of our solar system have taught us a lot about how the planets of the solar system have formed and have evolved. This could be a new window on understanding planet’s formation throughout the galaxy.

While we examine the incoming data, we try to determine if it is a comet. Over the next two weeks, there will probably be much more information to say that if it has a cometary tail like Borisov, or if it has an acceleration which is not due to a gravitational traction, like ‘Oumamua.

If it is a comet, the researchers really want to know if he is frozen. If it contains ICEs, it tells you a ton. The chemistry of these small bodies is the most important aspect when it comes to understanding the planet formation, because the chemical composition tells you about the conditions under which the solar system of the object was found when the object was formed.

For example, if the object contains a lot of ice, you will know that, wherever it comes from, it has not spent a lot of time near a star, because these ice cream would have melted. If it contains a lot of ice, it could tell you that it was formed very far from a star and was then ejected by something widening, like a planet of the size of Jupiter or Neptune.

Basically, this object could say more about astronomers of a population of objects that we do not fully understand or on the conditions of another solar system.

We had a few hours to obtain preliminary observations. I suspect that practically each telescope will look at this object for the next two nights, so we will get much more information on this subject very soon.

This article is republished from the conversation under a Creative Commons license. Read the original article.