An interstellar comet, designated 3I/ATLAS, has just completed its closest pass to the Sun, coming within approximately 126 million miles (203 million kilometers) of our star. This recent maneuver positions the comet on an outgoing trajectory, although it will remain in our solar system for some time. Astronomers expect to observe 3I/ATLAS again in the coming weeks, despite it currently being obscured by the Sun from the perspective of Earth-based telescopes.
According to Darryl Seligman, an assistant professor in the Department of Physics and Astronomy at Michigan State University, stargazers using telescopes should first glimpse the comet in the predawn sky around November 11, 2023. Observations will continue for several months before the comet begins its exit from our solar system. It is anticipated to make its closest approach to Earth on December 19, 2023, passing within about 168 million miles (270 million kilometers). The European Space Agency has confirmed that there is no threat posed by the comet to our planet.
3I/ATLAS is notable for being only the third known interstellar object to traverse our solar system. Since its discovery on July 1, 2023, astronomers have been collecting data to understand its unique characteristics compared to comets formed within our solar system. Each observation provides insight into the comet’s composition and its origins from beyond our cosmic neighborhood.
Understanding Interstellar Comets
Comets are often described as “dirty snowballs,” containing a mix of ice, dust, and rock. Their nuclei, or solid cores, release gas and dust when they come close to a star, forming the distinctive tails we associate with them. As 3I/ATLAS approaches the Sun, astronomers hope to learn more about its material composition, which may provide clues about the star system it originated from.
Seligman noted, “When it gets closest to the Sun, you get the most holistic view of the nucleus possible.” He highlighted the significance of understanding the composition of volatiles released during this period, which can reveal the primordial materials from which the comet formed. Advanced tools, such as the Hubble Space Telescope and the James Webb Space Telescope, have been employed alongside missions like SPHEREx to study this enigmatic object.
Preliminary studies indicate that 3I/ATLAS is estimated to be between 3 billion and 11 billion years old, significantly older than our solar system, which is about 4.6 billion years old. Seligman explained that the comet’s ability to transition carbon dioxide directly from solid to gas suggests it has likely never encountered another star before its recent approach to the Sun.
Ongoing Observations and Future Prospects
Despite fading from the view of ground-based telescopes in October, 3I/ATLAS remained observable for space missions such as PUNCH (Polarimeter to Unify the Corona and Heliosphere) and SOHO (Solar and Heliospheric Observatory). On October 3, 2023, the comet made its closest approach to Mars, coming within 18.6 million miles (30 million kilometers) of the planet.
While a government shutdown has hampered data sharing from NASA missions observing the comet since October 1, the ESA’s Mars Express and ExoMars Trace Gas Orbiter attempted to capture images of 3I/ATLAS. Although these instruments are primarily designed for studying Mars, the ExoMars orbiter succeeded in capturing the comet as a faint dot. Nick Thomas, principal investigator of the orbiter’s camera, described this observation as “very challenging,” noting the comet’s brightness was 10,000 to 100,000 times fainter than typical targets.
Looking ahead, the ESA’s Jupiter Icy Moons Explorer, or Juice, plans to observe 3I/ATLAS in November using various instruments. However, scientists do not expect to receive the data until February due to the spacecraft’s data transmission rate.
As astronomers prepare for several more months of observation, Seligman emphasized the potential for significant scientific discoveries, stating, “There’s going to be amazing science that comes out.” The ongoing study of 3I/ATLAS not only enhances our understanding of interstellar objects but also contributes to the broader knowledge of the universe and its formation.
