Why in News?
The interstellar comet 3I/ATLAS is in the news because a groundbreaking study published in Nature confirmed it is one of the oldest objects ever detected in our solar system, estimated to be between 10 and 12 billion years old.
Discovery & Nomenclature
- Data collected by the James Webb Space Telescope (JWST) and the ALMA radio telescope array revealed that this cosmic time capsule formed during the universe's "cosmic noon"—long before our own Sun and Solar System existed.
- Meaning of Name: The "3I" indicates it is the third confirmed Interstellar Object ever discovered passing through our solar system, following 1I/สปOumuamua (2017) and 2I/Borisov (2019).
- Discovery Date: It was first detected on July 1, 2025.
- The Discoverer: It was spotted by the NASA-funded ATLAS (Asteroid Terrestrial-impact Last Alert System) survey station located in Rio Hurtado, Chile.
- Scientific Designation: Officially catalogued by astronomers as C/2025 N1 (ATLAS).
Trajectory & Speed
- Hyperbolic Path: Unlike local comets, it travels on an unbound, hyperbolic trajectory, proving it is a temporary visitor that will eventually leave our solar system permanently.
- Record Velocity: It sped through the inner solar system at roughly 2,50,000 km/h (over 60 km/s), marking one of the highest speeds ever recorded for a solar system visitor.
- Earth Proximity: It posed no threat to Earth, making its closest approach on December 19, 2025, at a safe distance of 1.8 Astronomical Units (approx. 270 million kilometers).
- Mars Flyby: It passed within 29 million kilometers of Mars in October 2025, where it was photographed as a fuzzy white coma by NASA’s Perseverance Mars Rover.
- Future Departure: The comet is currently passing the orbit of Saturn; it will exit Pluto's boundary by 2029 and leave our solar system entirely around 2035.
Physical & Chemical Anomalies
- Core Size: The comet's icy heart (nucleus) is relatively small, measured at just over 700 metres in diameter.
- Frigid Birthplace: The massive abundance of heavy water ice indicates it spent its formative years in a deeply frozen, dense star-forming cloud that was vastly colder than our own pre-solar nebula.
- Volatile Outgassing: When warmed by the Sun, it experienced dramatic "cryovolcanic" activity, creating a 40-fold surge in water and methane emissions, blasting out powerful chemical jets.
- Wobbling Behaviour: Observations of its sunward jets revealed a precession (wobble), allowing astronomers to calculate that the comet nucleus rotates once every 15.5 hours.
- Chameleon Colour Change: As it emerged from behind the Sun, its outer dust crust shed to expose pristine volatile ice, causing its visible colour to shift dramatically from red to a vibrant green and blue hue.
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