Interstellar object facts for kids
An interstellar object is a space object, like an asteroid or a comet, that travels through the vast space between stars. The word "interstellar" means "between stars." These objects are not attached by gravity to any star, so they wander freely through the galaxy.
Sometimes, these cosmic travelers pass through our Solar System. When they do, we call them interstellar interlopers or visitors. Because they are moving so incredibly fast, the Sun's gravity can't trap them into an orbit. They just fly by and then head back out into deep space.
The very first interstellar visitor we ever saw in our Solar System was named 1I/ʻOumuamua, which was spotted in 2017. Before that, astronomers had found rogue planets, which are planets that were kicked out of their own star systems and now drift through space alone.
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How Are Interstellar Objects Named?
When astronomers find a new visitor from another star system, it needs a special name. The International Astronomical Union (IAU), the group in charge of naming space objects, created a new system just for them.
These objects get a name that starts with the letter I, which stands for "interstellar." So, the first one found was named 1I, the second was 2I, and so on. This helps everyone know that this object is not from around here! Before they are confirmed to be interstellar, they might get a temporary name starting with C/ (for comet) or A/ (for asteroid).
How We Study Interstellar Visitors
How Fast Do They Travel?
| Object | Speed |
|---|---|
| C/2012 S1 (ISON) (A comet from our own Oort Cloud) |
0.2 km/s 0.04 au/yr |
| Voyager 1 (A human-made spacecraft leaving the Solar System) |
16.9 km/s 3.57 au/yr |
| 1I/ʻOumuamua | 26.33 km/s 5.55 au/yr |
| 2I/Borisov | 32.1 km/s 6.77 au/yr |
| 2014Jan08 bolide (Possible interstellar meteor, still being studied) |
43.8 km/s 9.24 au/yr |
)One of the biggest clues that an object is from another star system is its incredible speed. These objects are moving much faster than anything in our Solar System. The table on the right shows the "interstellar velocity" of some objects. This is the speed they have when they are very far from our Sun's gravity.
As you can see, ʻOumuamua and Borisov were moving much faster than even our fastest spacecraft, Voyager 1. Their high speed proves they are not bound by the Sun's gravity and are just passing through.
How Many Visitors Are There?
Scientists believe that interstellar objects are very common. They estimate that several objects like ʻOumuamua pass inside Earth's orbit every year. On any given day, there could be as many as 10,000 of them flying around inside the orbit of Neptune!
Most of these objects are too small and dark for us to see with our current telescopes. But as our technology gets better, like with the new Vera C. Rubin Observatory, we expect to find many more.
Where Do They Come From?
Interstellar objects begin their journey in other star systems. Most scientists think they are pieces of rock and ice, like asteroids and comets, that were "kicked out" from their home. This can happen when a small object passes too close to a giant planet, like Jupiter. The planet's powerful gravity can fling the object out of its star system at very high speed.
This has happened in our own Solar System! In the 1980s, a comet named C/1980 E1 flew close to Jupiter. Jupiter's gravity accelerated it so much that it was thrown onto a path that will take it out of the Solar System forever. Scientists believe this happens in most star systems, filling the galaxy with these wandering objects.
Can We Capture a Visitor?
Just as planets can eject objects, they can also sometimes capture them. It's very rare, but computer models show that a huge planet like Jupiter could grab a passing interstellar object and pull it into an orbit around our Sun. This might happen once every 60 million years.
Some scientists think that comets like Machholz 1 and Comet Hyakutake might be captured interstellar objects because their chemical makeup is different from other comets in our Solar System. Another object, an asteroid named 514107 Kaʻepaokaʻawela, orbits the Sun backwards and might have been captured billions of years ago.
Confirmed Interstellar Visitors
So far, astronomers have confirmed a few objects that have traveled from other stars into our Solar System.
1I/ʻOumuamua: The First Messenger
Discovered on October 19, 2017, by the Pan-STARRS telescope, 1I/ʻOumuamua was the first interstellar object ever detected in our Solar System. Its name, ʻOumuamua, is a Hawaiian word that means "a messenger from afar arriving first."
ʻOumuamua was very strange. It was dim, reddish, and appeared to be shaped like a cigar or a flat pancake. Unlike a comet, it didn't have a fuzzy cloud or tail of gas and dust around it. This suggested it might be a rocky object from the inner part of its home star system. It flew through our system at an amazing speed and is now heading back out into interstellar space, never to return.
2I/Borisov: A More Familiar Comet
The second visitor, 2I/Borisov, was discovered on August 30, 2019, by an astronomer named Gennadiy Borisov in Crimea.
Unlike the mysterious ʻOumuamua, 2I/Borisov looked much more like a typical comet. It had a fuzzy cloud (a coma) and a tail, which told astronomers it was made of ice and dust that was turning to gas as it got closer to the Sun. Its composition was very similar to comets from our own Oort Cloud. In 2020, astronomers even saw its core breaking into pieces.
3I/ATLAS: The Third Visitor
A third interstellar object was discovered on July 1, 2025. It was found by the ATLAS survey. Named 3I/ATLAS, it is expected to make its closest approach to the Sun in October 2025. Scientists are excited to study this new visitor to learn more about where it came from.
Possible Interstellar Visitors
Besides the confirmed objects, scientists are studying other objects that might also be from interstellar space.
Mysterious Meteors
A meteor is what we see when a small piece of space rock burns up in Earth's atmosphere, creating a "shooting star." Scientists at Harvard University believe that two meteors, one from 2014 and another from 2017, were moving so fast that they must have come from outside our Solar System.
The first one, called IM1 (CNEOS 2014-01-08), exploded over Papua New Guinea in 2014. The second, IM2, arrived in 2017. Both seemed to be made of unusually strong material.
This is a very exciting idea, but it is still being debated. Other scientists are carefully checking the data because measuring a meteor's speed so precisely is very difficult. It's possible that errors in the measurements made the meteors seem faster than they really were. Science often works this way, with new ideas being tested and checked by many different experts.
Can We Visit an Interstellar Object?
Studying these visitors up close would be amazing, but it's very hard because they move so fast. Even so, scientists and engineers are already designing missions that could one day chase after one.
- Project Lyra: This is a plan from the Initiative for Interstellar Studies to send a spacecraft to an object like ʻOumuamua. One idea is to use a "gravity assist" from Jupiter and then fly very close to the Sun. The Sun's immense gravity would act like a slingshot, flinging the probe at incredible speeds to catch up with the interstellar object.
- Comet Interceptor: This is a real mission being built by the ESA and JAXA, planned to launch in 2029. The spacecraft will wait in space for a new comet to be discovered. If a suitable interstellar object flies by and is within reach, the mission could be redirected to fly past it and take the first-ever close-up pictures of a visitor from another star.
Images for kids
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Comet Machholz 1 (96P/Machholz) as viewed by STEREO-A (April 2007). Some scientists think it could be a captured interstellar object.
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Interstellar visitors can be any size, from large objects like comets to tiny dust particles. Finding them all is a challenge for scientists.
See also
In Spanish: Objeto interestelar para niños
- Global catastrophic risk
- Hyperbolic asteroid
- List of artificial objects leaving the Solar System
- List of hyperbolic comets
- List of Solar System objects by greatest aphelion
- Rogue black hole
