3I/ATLAS — The Interstellar Visitor Through Our Solar System

Comet 3I/ATLAS is not just any comet. It is a rare interstellar object, traveling from beyond our Solar System, offering scientists a once-in-a-lifetime opportunity to study material from another star system. First spotted in July 2025, 3I/ATLAS has already caught the attention of astronomers worldwide, and ESA and NASA missions have turned their instruments to track this cosmic visitor.

A Rare Interstellar Object

Only two interstellar objects had been observed before 3I/ATLAS: ʻOumuamua in 2017 and 2I/Borisov in 2019. With its discovery, 3i atlas interstellar object became the third confirmed interstellar object entering our Solar System.

What sets 3I/ATLAS apart is its hyperbolic orbit, meaning it cannot stay in orbit around the Sun. This confirms that the comet comes from outside our Solar System. Its trajectory and speed also suggest it could be older than our Solar System, possibly around 7.6 billion years old, which makes it a treasure trove for studying the history of other star systems.

Discovery of 3I/ATLAS

The Asteroid Terrestrial-impact Last Alert System (ATLAS) telescope in Chile first detected the comet on 1 July 2025. Archival images from other ATLAS observatories and the Zwicky Transient Facility in California confirmed observations going back to 14 June 2025.

The comet’s name, 3i/atlas, stands for:

• 3 — the third known interstellar object
• I — interstellar
• ATLAS — the survey telescope that discovered it

The 3i/atlas arrival date at its closest point to the Sun is 30 October 2025, just inside Mars’ orbit, about 1.4 AU (210 million km) from the Sun. Its closest approach to Earth will still be safe at 1.8 AU (270 million km).

Observing 3I/ATLAS from Mars

When 3I/ATLAS approached Mars on 3 October 2025, ESA’s Mars orbiters — ExoMars Trace Gas Orbiter (TGO) and Mars Express — captured the comet’s closest view. The comet was about 30 million km from the Red Planet.

The Observation Challenge

Both orbiters are designed to photograph Mars, not distant, faint objects. Nonetheless, scientists adapted their instruments. ExoMars TGO used its Colour and Stereo Surface Imaging System (CaSSIS) to take a series of images. The comet appeared as a small, fuzzy white dot — the coma, a cloud of gas and dust surrounding the icy nucleus.

Nick Thomas, principal investigator of CaSSIS, noted that the comet was 10,000 to 100,000 times fainter than typical Martian targets. Despite this, TGO successfully detected the comet’s glow.

The coma forms as the Sun’s heat vaporizes the comet’s ice, releasing gas and dust. Although CaSSIS could not resolve the nucleus, it confirmed that 3I/ATLAS is active and releasing material.

Case Study: ExoMars TGO Observing 3I/ATLAS

Objective:

To capture an interstellar comet using instruments meant for planetary imaging.

Method:

ExoMars TGO’s CaSSIS camera captured multiple images of 3I/ATLAS using long exposures, while Mars Express attempted imaging with shorter 0.5-second exposures.

Findings:

• Coma detected, nucleus unresolved
• Tail not visible yet, but may appear as the comet nears the Sun
• Demonstrated that Mars orbiters can contribute to interstellar object science

Conclusion:

This case shows that planetary missions can be flexible. Even instruments built for Mars can study objects millions of km away, providing valuable data for scientists.

NASA’s Observations and Updates

NASA has been observing 3I/ATLAS with a range of assets:

• Hubble Space Telescope captured images of the comet on 21 July 2025, showing a teardrop-shaped dust cocoon.
• Observations as of 20 August 2025 estimated the nucleus size to be between 440 meters and 5.6 km.

NASA continues to monitor the comet using Hubble, Webb, TESS, Swift, SPHEREx, the Perseverance rover, Mars Reconnaissance Orbiter, and more. These observations provide essential data on 3i atlas size interstellar object and behavior as it approaches the Sun.

What Makes 3I/ATLAS Special

Interstellar comets like interstellar comet are unique because they carry material from other star systems. Studying them helps scientists understand:

• How other planetary systems form
• What types of ice and dust exist beyond our Solar System
• The chemical history of objects far older than our Sun

These interstellar visitors are like messengers from distant galaxies, giving a glimpse of worlds we might never directly explore.

Future Observations

ESA’s Jupiter Icy Moons Explorer (Juice) will observe 3I/ATLAS after its closest approach to the Sun. Although Juice will be farther than the Mars orbiters, it will see the comet in a more active and brighter state. Data from Juice is expected in February 2026.

Meanwhile, ESA’s Comet Interceptor mission, launching in 2029, is designed to wait in space for pristine comets or interstellar objects like 3I/ATLAS. This mission aims to study them in unprecedented detail and could revolutionize our understanding of interstellar visitors.

Michael Kueppers, project scientist for Comet Interceptor, said:

“Discovering multiple interstellar objects shows their diversity. Visiting one could completely change our knowledge of the Universe.”

Emotional Insight: Why We Care About 3I/ATLAS

Seeing interstellar comet pass through our Solar System reminds us that space is vast and full of surprises. Unlike planets or moons, this object comes from an entirely different star system, carrying ancient materials that could predate our Sun.

Even without a telescope in hand, knowing that we can detect and study objects from other star systems is exciting. It connects humanity to the galaxy in a tangible way, showing that science is capable of bridging light-years of space with technology and curiosity.

FAQs About 3I/ATLAS

Q1: What is interstellar comet
It is a rare interstellar object, the third confirmed comet from outside our Solar System.

Q2: When is interstellar comet closest to the Sun?
The 3i/atlas arrival date at perihelion is 30 October 2025, just inside Mars’ orbit.

Q3: How far will it come from Earth?
It will remain 1.8 AU (270 million km) away — completely safe.

Q4: Can it be seen with a telescope?
Yes, ground-based telescopes may see it until September 2025 and again in December 2025 after it passes behind the Sun.

Q5: Where can I find updates on 3I/ATLAS?
You can follow detailed updates at YAS Space, which covers interstellar objects and space science news.

Conclusion

interstellar comet is more than a comet; it is a cosmic messenger traveling across the galaxy. Its hyperbolic orbit, interstellar origin, and potential age make it a rare object for scientific study. ESA’s Mars orbiters, NASA telescopes, and future missions like Juice and Comet Interceptor provide us with an unprecedented chance to understand interstellar objects and the early universe.

Watching 3I/ATLAS reminds us of the immensity of space, the age of the Universe, and our growing ability to explore it. Every observation is a small but meaningful step toward understanding where we come from and what exists beyond our solar neighborhood.