Interstellar Comet 3I/ATLAS Encounters Solar Eruption

The interstellar comet 3I/ATLAS, discovered in July 2025, has been struck by a coronal mass ejection (CME) from the Sun. This event offers scientists a rare opportunity to observe the interaction between a CME and an interstellar object.

3I/ATLAS is the third confirmed interstellar object to pass through our solar system, following 'Oumuamua in 2017 and 2I/Borisov in 2019. It is traveling at approximately 137,000 miles per hour and is expected to make a close approach to Mars in the coming week.

The CME, a significant release of plasma and magnetic fields from the Sun, impacted 3I/ATLAS earlier this week. Similar events have been observed before; for instance, in April 2007, NASA's STEREO A spacecraft recorded Comet Encke losing its tail after being hit by a CME. The tail reformed within minutes.

Observations of 3I/ATLAS have revealed a higher ratio of carbon dioxide to water than typically seen in comets, suggesting it may have formed near the CO₂ ice line in a distant protoplanetary disk. Its nucleus is estimated to be about 3.5 miles in diameter, making it potentially the largest and oldest interstellar object observed, possibly 3 billion years older than our solar system.

As 3I/ATLAS approaches the Sun, it has exhibited increased brightness, particularly in the green part of the visible spectrum. This green coloration may be due to the release of diatomic carbon (C₂), which glows emerald when energized by solar ultraviolet radiation.

The impact of the recent CME on 3I/ATLAS remains under study. Scientists are eager to observe the comet as it passes near Mars next week to assess any changes resulting from this solar event.