Three NASA missions – STEREO, SOHO, and PUNCH – have successfully tracked interstellar comet 3I/ATLAS as it passed behind the Sun from Earth’s perspective. This rare event allowed scientists to gather unique data about the comet’s composition and behavior, enhancing our understanding of objects originating from outside our solar system.
Observing the Unseen: Challenges and Techniques
Initially, expectations were low for detecting 3I/ATLAS with STEREO’s instruments due to its anticipated faintness. However, through advanced image processing techniques – specifically, stacking multiple exposures – researchers managed to bring the comet into view using the Heliospheric Imager-1 telescope. This method combines faint signals over time, making nearly invisible objects detectable.
The SOHO spacecraft, positioned at the Sun-Earth Lagrange point 1, also captured images of the comet between October 15-26, 2025. SOHO’s Large Angle and Spectrometric Coronagraph (LASCO) spotted 3I/ATLAS from a distance exceeding twice Earth’s distance from the Sun (approximately 358 million km). The SOHO team likewise employed stacking to reveal the comet in their data.
PUNCH’s Unexpected Discovery
The PUNCH mission, designed to study the Sun’s atmosphere and solar wind, unexpectedly contributed to the observations. Despite initial doubts about its ability to detect the faint comet, the team utilized stacked observations to reveal 3I/ATLAS’s tail.
Dr. Kevin Walsh of the Southwest Research Institute, who led PUNCH’s observations, noted: “We’re really pushing the limits of the system.” This demonstrates how even instruments not specifically designed for comet detection can yield valuable data with the right techniques.
Why This Matters
The successful tracking of 3I/ATLAS by these three spacecraft is significant because it provides a rare opportunity to study an interstellar object up close. Interstellar comets originate from other star systems and hold clues about the formation and evolution of planetary systems beyond our own. By combining data from multiple missions, scientists can gain a more comprehensive understanding of the comet’s size, physical properties, and chemical makeup.
This collaborative approach highlights the power of leveraging existing space-based assets to study unexpected phenomena, expanding our knowledge of the universe beyond planned observations.
