A Visitor from Beyond: Discovery & Trajectory.

• 3I/ATLAS was first detected on 1 July 2025 by the ATLAS survey telescope in Chile.
• Its orbit is hyperbolic, which means it is not bound to the Sun and must have originated outside the Solar System (i.e. an interstellar object).
• It is the third confirmed interstellar object to traverse our Solar System (after 1I/ʻOumuamua and 2I/Borisov).
• The comet is speeding through space at tens of km/s, making its passage relatively brief as seen from Earth.

Peering In: Observational Campaigns & Key Instruments.

• The Hubble Space Telescope captured sharp images (e.g. on 21 July 2025) that helped refine estimates of its nucleus and dust coma.
• NASA’s JWST (James Webb Space Telescope) observed 3I/ATLAS in August 2025 using its NIRSpec instrument, enabling infrared spectroscopy of its coma.
• The mission SPHEREx also contributed multispectral observations (7–15 August 2025) to help characterize the comet’s composition.
• Among ground-based telescopes, Gemini, Keck, and others contributed optical, near-IR, and spectroscopic data.

Chemical Clues & Unexpected Behavior.

• WST spectroscopy revealed a coma dominated by CO₂ (carbon dioxide), with also detections of water (H₂O), CO, OCS, dust, and water ice. The CO₂ / H₂O mixing ratio is unusually high compared to typical comets.
• The ratio and relative abundances suggest 3I/ATLAS might have an intrinsically CO₂-rich nucleus, or that it formed in an environment exposed to higher radiation than typical comets in our Solar System. 
• Contrary to many standard comets, 3I/ATLAS is already releasing water at significant distances, as inferred via OH (hydroxyl) detection (a UV signature of water). This “early activity” is surprising. 
• Observers also report that its brightness has increased rapidly (much faster than expected) as it approached perihelion. That suggests dynamic changes in outgassing or dust ejection.
• There is also an oddity: some tail/dust features appear pointing in unexpected (sunward) directions, contrary to the usual away-from-Sun orientation.

The Path Forward: Perihelion, Visibility & Future Prospects.

• 3I/ATLAS reaches perihelion (closest approach to the Sun) around 29–30 October 2025 (approximately ~1.36–1.40 AU).
• After that, it will be hidden from Earth’s view (solar conjunction), but is expected to reappear in early December 2025 for renewed observations.
• NASA notes that the comet should remain visible to ground telescopes through September 2025, before slipping too close to the Sun.
• Once back in view, the comet—although faint—may be observed with telescopes (not naked eye) in morning twilight skies.
• Going forward, analysts hope to track further changes in its coma/dust, structural stability (whether it fragments), and compare its properties to known comets to deepen understanding of interstellar material.