Why in the News?
Astronomers discovered 3I/ATLAS, a 7-billion-year-old interstellar comet, using the NASA-funded ATLAS telescope in Chile. It is now nearing its closest approach to the Sun.
About 3I/ATLAS:
- Discovery: It was detected on July 1, 2025, by the ATLAS telescope in RÃo Hurtado, Chile; confirmed interstellar due to its hyperbolic orbit and high speed (57–68 km/s).
- Significance: It is likely the oldest comet ever observed, possibly 7.6–14 billion years old, older than our 4.5-billion-year-old solar system.
- Nature: It appeared like an interstellar comet, showing signs of activity, including a coma (cloud of dust/ice) and likely a tail as it nears the Sun.
- Composition: Rich in water ice and complex organic compounds; has a reddish hue indicating ancient, primordial material.
- Size: Estimated nucleus diameter is 10–30 km, larger than previous interstellar objects like 1I/ʻOumuamua and 2I/Borisov.
- Trajectory:
- Closest to Earth: ~270 million km (no threat).
- Closest to Sun: ~210 million km (Oct 29–30, 2025).
- Will exit the solar system permanently after perihelion.
- Scientific Importance:
- It offers rare opportunity to study materials from another star system.
- It can reveal clues about the formation of the Milky Way, other solar systems, and early star formation processes.
Back2Basics: ATLAS Telescope
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What are Interstellar Objects?
- Overview: Celestial bodies that originate outside the solar system and travel through it on open-ended (hyperbolic) orbits.
- Key Characteristics:
- Not gravitationally bound to the Sun.
- Travel at very high speeds, often unaffected by solar gravity.
- Do not return once they pass through the inner solar system.
- Known Interstellar Visitors:
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- 1I/ʻOumuamua (2017) – Asteroid-like, no coma or tail.
- 2I/Borisov (2019) – Active comet with typical cometary features.
- 3I/ATLAS (2025) – Discussed above.
- How are they Identified:
- Hyperbolic trajectory confirmed via orbital calculations.
- Speed at great distances exceeds gravitational escape velocity.
- Scientific Value:
- Provide direct clues about planetary formation beyond our solar system.
- Can reveal chemical signatures from other star systems.
- Allow us to study primordial matter from distant parts of the galaxy.
- Act as natural probes from unknown regions of the Milky Way.
How is 3I/ATLAS different from ordinary Comets?
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3I/ATLAS |
Ordinary Comets |
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| Origin | Formed outside the Solar System; interstellar in nature | Formed within the Solar System — Kuiper Belt or Oort Cloud |
| Orbital Type | Hyperbolic (eccentricity ≈ 6); unbound from the Sun | Elliptical or parabolic; bound by the Sun’s gravity |
| Velocity | Very high,~57 km/s (too fast to be captured by Sun) | Moderate, typically 10–40 km/s within solar orbit |
| Trajectory | Enters and exits Solar System once; non-repeating | Periodic or long-period; returns after fixed intervals |
| Tail Direction | Exhibited a rare sunward (anti-tail) due to COâ‚‚-driven ice scattering | Always points away from the Sun due to radiation pressure and solar wind |
| Composition | High COâ‚‚/Hâ‚‚O ratio, nickel-rich, iron-poor, chemically distinct | Dominated by Hâ‚‚O, CO, COâ‚‚, silicates, and dust in solar proportions |
| Activity Pattern | Displays phase shift: anti-tail → normal tail as it nears the Sun | Predictable increase in activity and sublimation near perihelion |
| Spectral Signature | Strong COâ‚‚ emission lines; unusual metallic features | Typical cometary spectra, OH, CN, Câ‚‚, CO, NHâ‚‚ bands |
| Size of Nucleus | Estimated 0.44–5.6 km in diameter | Varies widely; many are a few kilometres across |
| Scientific Significance | Provides insight into exoplanetary system composition and interstellar chemistry | Preserves a record of early Solar System formation and evolution |
| Speculative Aspects | Some hypotheses suggest a possible artificial or exotic origin (no evidence) | Fully natural and well-understood in origin and dynamics |
| [UPSC 2011] What is the difference between asteroids and comets?
1. Asteroids are small rocky planetoids, while comets are formed of frozen gases held together by rocky and metallic material. 2. Asteroids are found mostly between the orbits of Jupiter and Mars, while comets are found mostly between Venus and mercury. 3. Comets show a perceptible glowing tail, while asteroids do not. Which of the statements given above is/are correct? Options: (a) 1 and 2 only (b) 1 and 3 only* (c) 3 only (d) 1, 2 and 3 |
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