In News:

NASA astronomers have confirmed the chemical fingerprint of water on the interstellar comet 3I/ATLAS using ultraviolet data from the Neil Gehrels Swift Observatory. This marks a major advance in understanding the chemistry of planetary systems beyond the Sun.

What is 3I/ATLAS?

• Designation: 3I/ATLAS
• Discovery: 1 July 2025 by the Asteroid Terrestrial-impact Last Alert System (ATLAS) in Hawaii.
• Category: Third confirmed interstellar object after 1I/‘Oumuamua (2017) and 2I/Borisov (2019).
• Origin: Formed in another planetary system, possibly 7 billion years old, older than Earth.

Trajectory & Motion

• Travels on a hyperbolic orbit—meaning it is not gravitationally bound to the Sun and will exit the Solar System permanently.
• Speed relative to Sun: 57–68 km/s.

Physical Characteristics

• An active comet with a visible coma of dust and icy particles.
• Expected to form a cometary tail as it approaches the Sun.
• Surface hue: Slightly reddish, indicating the presence of complex organics or water ice.
• Nucleus size: Estimated 10–30 km wide.
• Age: Nearly twice as old as Earth, making it one of the oldest comets ever observed.

Breakthrough Discovery: Water Signature Detected

How was it detected?

• Swift Observatory captured faint ultraviolet emissions from hydroxyl (OH).
• OH forms when sunlight breaks apart water molecules → indirect but strong evidence of water ice sublimation.

Why is it important?

• First chemical confirmation of water activity on an interstellar comet at such a large distance from the Sun.
• Indicates that protoplanetary systems outside the Solar System may share similar chemical building blocks.

Unusual Behaviour

• 3I/ATLAS was losing water at ~40 kg per second even when far beyond the usual frost line where comets become active.
• Suggests:
  • Presence of small icy grains being heated by sunlight,
  • Complex physical and chemical processes not seen in typical comets.

Scientists noted its activity “defies our models”, indicating new insights into comet evolution.

Significance for Planetary Science & Astrobiology

• Strengthens the idea that organic chemistry and water—key ingredients for life—are common across the Galaxy.
• Provides clues on:
  • Composition of ancient planetary systems,
  • How water and organics travel between stars,
  • Early stages of planet formation.

3I/ATLAS acts as a “messenger” from another star, preserving primordial material from its home system.

Interstellar Objects:

• Formed outside the Solar System and travel through it.
• Not gravitationally bound → follow open-ended hyperbolic trajectories.
• Have a perihelion (closest approach to Sun) but no aphelion.
• Often ejected from their home systems due to collisions or gravitational slingshot events.