Space

They came from other stars! [COMIC]

Meet the only three interstellar objects astronomers have ever spotted

Three objects from the stars, illustrated with arms, legs and faces, seem to be heading towards the viewer. On the outer edge of the image are various planetary shapes.

Astronomers have only ever found three objects from other stars. Here’s what we know about these interstellar objects — and why they’re so cool.

Maki Naro

By Matthew R. Francis and Maki Naro

Text (above image): On July 1, 2025, the ATLAS* telescope in Chile spotted an unusual comet — one that came from another star! Image: An observatory on a hill is silhouetted against a night sky. Overhead, a bright blue object is streaking through the sky. Text (below image): *Asteroid Terrestrial-impact Last Alert System
Text (above image): Scientists call this interstellar visitor Comet 3I/ATLAS (or just Atlas), because it’s only the third interstellar (3I) object ever found. Image: Three rock-shaped characters charge toward the planets of our solar system. Text (below image): THEY CAME FROM OTHER STARS.
Text (above first image): Our first visitor, 1I/`Oumuamua, had features of both an asteroid and a comet. First image: An oblong rock-like character wearing sneakers and pulling a suitcase smiles and waves. Text (above second image): Meanwhile, 2I/Borisov was definitely a comet. A rounded rock-like character is surrounded by a blue cloud. Also smiling, it wears sneakers and carries a suitcase in each hand.
Text (above image): Comets and asteroids are the remains from the very early formation of a solar system. Each one is billions of years old. Image: A white woman with short brown hair and wearing a green jacket smiles and holds up an ammolite fossil shell. She says, “An interstellar object is a fossil from another system coming to visit us!” Her nametag reads: Cyrielle Opitom, planetary scientist, University of Edinburgh.
Text (above image): Astronomers know these visitors came from outside the solar system by the paths they take. Local comets follow elliptical orbits around the sun, like planets do. Image: The sun is surrounded by concentric circles showing the orbits of planets in our solar system. One comet follows an oval-shaped path around the sun, labeled “elliptical.” Another follows a boomerang-shaped path past the sun, labeled “hyperbolic.” Text (below image): Interstellar comets follow hyperbolic orbits, so they whiz past but don’t go around the sun.
Text (above image): Some people have suggested that interstellar objects might be spaceships. But scientists know they aren’t, because interstellar objects look more like comets, which are cloaked in a haze of gas. Image: The icy, rocky heart of a comet is surrounded by a hazy tail of gas as it streaks through space. Nearby, a picture of aliens driving a spaceship is crossed out with a big red “X.” Cyrielle Opitom floats in space wearing an astronaut suit. She says, “A comet is basically a big block of rock and ice. It comes close to the sun, and ice vaporizes and creates an atmosphere.”
Text (above image): Ice doesn’t just mean water! It can be carbon dioxide (“dry ice”), carbon monoxide, cyanogen, methane and other molecules. Image: A hazy cloud of different colored bits drifts in space. Bluish-green bits are labeled as “cyanogen (CN)2.” Purple bits are labeled as “carbon monoxide (CO).” Whitish bits are labeled as “methane (CH4)." Yellow bits are labeled “carbon dioxide (CO2).” Text (below image: Researchers can tell what is in a comet’s atmosphere — or “coma” — by the spectrum of light it emits.
Text (above image): The types and amounts of ice in interstellar comets might teach us about where they formed. Image: Concentric circles show the paths of orbits increasingly distant from a central star. On one path, an icy comet is labeled “H2O.” On the next path farther from the star, a colder comet is labeled “H2O + CO2.” On the next path out, an even colder, icier comet is labeled as “H2O + CO2 + CH4.” And on the most distant path, a comet inside an ice cube is labeled “H2O + CO2 + CH4 + CO.” Text (below image): The farther from its star a comet forms, the colder things are, and the more types of ice it can contain.
Text (above image): Everything astronomers see in interstellar visitors is familiar from our solar system, but the proportions are strange! First image: An oblong rock-like character smiles and holds a camera. It is labeled: `Oumuamua: A bit mysterious (didn’t have a coma), but maybe iron, nickel and organic gunk (like Pluto). Second image: A rounded rock-like character wearing sunglasses is smiling. It is labeled: Borisov: Extra carbon monoxide (like Comet Hale-Bopp). Third image: A circular rock-like character wearing a safari hat smiles. It is labeled: Atlas: extra carbon dioxide, extra nickel.
Text (above image): A still-unsolved mystery: We don’t know where these visitors come from! Interstellar space is big and empty, so we can’t trace their paths back to their original star. Image: The three rock-shaped interstellar object characters walk past in a line, toting their luggage and smiling. Below, Cyrielle Opitom floats in her space suit. She says, “We aren't certain even where comets in our solar system formed.”
Text (above image): Because comets are generally born on the outer edges of star systems, it’s easy for them to get bumped out of orbit. So the Milky Way probably has lots of these wanderers roaming interstellar space. The new Vera C. Rubin Observatory in Chile could see more than three new visitors each year! Image: An observatory aims its telescope at the night sky. Overhead, the outlines of imagined interstellar objects stroll around, wandering space.
The planets of our solar system huddle around the three interstellar objects, smiling at them. Cyrielle Opitom looks upward at the celestial objects. She says, “What we learn from interstellar objects might help us understand our own solar system. And what we learn about our own solar system will help us understand these interstellar objects.”
All: Maki Naro

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Power Words

More About Power Words

alien: A non-native organism. (in astronomy) Life on or from a distant world.

asteroid: A rocky object in orbit around the sun. Most asteroids orbit in a region that falls between the orbits of Mars and Jupiter. Astronomers refer to this region as the asteroid belt.

astronaut: Someone trained to travel into space for research and exploration.

astronomer: A scientist who works in the field of research that deals with celestial objects, space and the physical universe.

atmosphere: The envelope of gases surrounding Earth, another planet or a moon.

carbon dioxide: (or CO2) A colorless, odorless gas produced by all animals when the oxygen they inhale reacts with the carbon-rich foods that they’ve eaten. Carbon dioxide also is released when organic matter burns (including fossil fuels like oil or gas). Carbon dioxide acts as a greenhouse gas, trapping heat in Earth’s atmosphere. Plants convert carbon dioxide into oxygen during photosynthesis, the process they use to make their own food.

carbon monoxide: A toxic gas whose molecules include one carbon atom and one oxygen atom. (The “mono” in “monoxide” is a prefix from Greek that means “one”.) One common source: fossil-fuel burning.

celestial: (in astronomy) Of or relating to the sky, or outer space.

celestial object: Any naturally formed objects of substantial size in space. Examples include comets, asteroids, planets, moons, stars and galaxies.

cloud: A plume of molecules or particles, such as water droplets, that move under the action of an outside force, such as wind, radiation or water currents.

comet: A celestial object consisting of a nucleus of ice and dust. When a comet passes near the sun, gas and dust vaporize off the comet’s surface, creating its trailing “tail.”

dry ice: The common term for frozen carbon dioxide. Much colder than water ice, dry ice changes from a solid directly into a gas — a process known as sublimation — at temperatures warmer than −78.5° Celsius (−109.3° Fahrenheit).

elliptical: Having the shape of an ellipse, which is an oval shape.

fossil: Any preserved remains or traces of ancient life. There are many different types of fossils: The bones and other body parts of dinosaurs are called “body fossils.” Things like footprints are called “trace fossils.” Even specimens of dinosaur poop are fossils. The process of forming fossils is called fossilization.

haze: Fine liquid or solid particles scattered through the atmosphere that make it hard to see. Haze can be caused by harmful substances such as air pollutants or by water vapor.

interstellar: Between stars.

iron: A metallic element that is common within minerals in Earth’s crust and in its hot core. This metal also is found in cosmic dust and in many meteorites.

methane: A hydrocarbon with the chemical formula CH4 (meaning there are four hydrogen atoms bound to one carbon atom). It’s a natural constituent of what’s known as natural gas. It’s also emitted by decomposing plant material in wetlands and is belched out by cows and other ruminant livestock. From a climate perspective, methane is 80 times more potent than carbon dioxide is in trapping heat in Earth’s atmosphere, making it a very important greenhouse gas.

Milky Way: The galaxy in which Earth’s solar system resides.

molecule: A group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in air is made of two bound oxygen atoms (O2). Water is made of two hydrogen atoms and one oxygen atom (H2O).

nickel: Number 28 on the periodic table of elements, this hard, silvery element resists oxidation and corrosion. That makes it a good coating for many other elements or for use in multi-metal alloys.

observatory: (in astronomy) The building or structure (such as a satellite) that houses one or more telescopes. Or it can be a system of structures that make up a telescope complex.

orbit: The curved path of a celestial object or spacecraft around a galaxy, star, planet or moon. One complete circuit around a celestial body.

organic: (in chemistry) An adjective that indicates something is carbon-containing; also a term that relates to the basic chemicals that make up living organisms.

planet: A large celestial object that orbits a star but unlike a star does not generate any visible light.

Pluto: A distant world that is located in the Kuiper Belt, just beyond Neptune. Known as a dwarf planet, Pluto is the ninth largest object orbiting our sun.

proportion: The amount of a certain component of a mixture relative to other components. For example, if a bag contains 2 apples and 3 oranges, the proportion of apples to oranges in the bag is 2 to 3. Or it could be the relative size of some element of a whole (such as the proportion of the head to the rest of the body was unusually small).

solar system: The eight major planets and their moons in orbit around our sun, together with smaller bodies in the form of dwarf planets, asteroids, meteoroids and comets.

spectrum: (plural: spectra) A range of related things that appear in some order. (in light and energy) The range of electromagnetic radiation types; they span from gamma rays to X rays, ultraviolet light, visible light, infrared energy, microwaves and radio waves.

star: The basic building block from which galaxies are made. Stars develop when gravity compacts clouds of gas. When they become hot enough, stars will emit light and other forms of electromagnetic radiation. The sun is our closest star.

sun: The star at the center of Earth’s solar system. It is about 27,000 light-years from the center of the Milky Way galaxy. Also a term for any sunlike star.

telescope: Usually a light-collecting instrument that makes distant objects appear nearer through the use of lenses or a combination of curved mirrors and lenses. Some, however, collect radio emissions (energy from a different portion of the electromagnetic spectrum) through a network of antennas.

vaporize: To convert from a liquid to a gas (or vapor) through the application of heat.

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