NASA spacecraft reveal interstellar comet 3I/ATLAS brightened rapidly as it swooped behind the sun

Tracking 3I/ATLAS Behind the Sun

As 3I/ATLAS approached perihelion—the point in its orbit closest to the sun—it became hidden from Earth-based telescopes, passing directly behind our star. However, this did not prevent astronomers from monitoring its progress. Amateur astronomer Worachate Boonplod utilized data from the National Oceanic and Atmospheric Administration’s GOES-19 weather satellite, which is equipped with the CCOR-1 instrument designed to observe the sun’s corona. Boonplod detected the comet in these images starting October 18, noting that it remained visible to the satellite until October 24.

The comet’s brightness at this time was comparable to stars of magnitude 11, which is beyond naked-eye visibility but detectable with sensitive instruments. Boonplod tracked the comet’s movement across the satellite’s field of view, confirming its trajectory as it moved from left to right relative to background stars. This observation was significant because it demonstrated the value of repurposing space weather monitoring satellites for comet tracking during periods when Earth-based observation is impossible.

In addition to GOES-19, NASA’s PUNCH mission—comprising four small satellites focused on solar observation—and the joint NASA-European Space Agency Solar and Heliospheric Observatory (SOHO) also tracked 3I/ATLAS. SOHO’s LASCO C3 coronagraph instrument followed the comet until October 26, using a technique that blocks the sun’s bright disk to reveal surrounding features like the solar corona and nearby objects such as comets.

Rapid Brightening and Cometary Activity Near Perihelion

On October 28, researchers published a study on the preprint server arXiv detailing the comet’s rapid brightening as it neared perihelion on October 29. The team estimated that the comet’s brightness would reach magnitude 9 at its closest approach to the sun. While still too faint for unaided human eyes, this brightness level makes 3I/ATLAS accessible to amateur astronomers equipped with good backyard telescopes.

The study’s findings were based on data from space-based solar instruments like GOES-19 and SOHO. One notable observation was that the comet appeared distinctly bluer than the sun. This color difference aligns with the presence of gas emissions, which contribute significantly to the comet’s increased brightness. As comets approach the sun, solar heat causes surface ices to sublimate, releasing gases that form a glowing coma and tail around the nucleus.

Solar radiation further ionizes these gases, enhancing the comet’s brightness. This process explains the observed rapid brightening of 3I/ATLAS as it swung close to the sun. Such behavior is typical of comets, but observing it in an interstellar visitor provides valuable data on how these objects react to intense solar radiation.

The Unique Nature of Interstellar Comet 3I/ATLAS

Discovered in July 2023, 3I/ATLAS is only the third interstellar comet ever identified, joining the ranks of rare visitors from beyond our solar system. Its trajectory is unusually flat and straight, and it is traveling at speeds exceeding 130,000 miles per hour (210,000 kilometers per hour)—the highest velocity ever recorded for a solar system object. This rapid motion suggests it originated from a distant star system and has been traveling through interstellar space for billions of years.

Scientists estimate that 3I/ATLAS could be the oldest comet ever observed, potentially predating our solar system by about 3 billion years. Its age and velocity imply it has undergone gravitational interactions with stars and nebulas, gaining momentum through slingshot effects. This journey has made it a valuable subject for studying the composition and dynamics of material from other star systems.

In terms of size, data from the Hubble Space Telescope indicate that the comet’s nucleus could be up to 3.5 miles (5.6 kilometers) wide, making it potentially the largest interstellar object detected to date. Despite some sensational speculation about its nature, the scientific consensus is that 3I/ATLAS is a natural space rock rather than an artificial spacecraft.

Future Visibility and Scientific Opportunities

After its perihelion passage and period behind the sun, 3I/ATLAS is expected to become visible again from Earth-based telescopes by early December 2023. This renewed visibility will allow astronomers to continue monitoring its behavior as it moves away from the sun and exits the inner solar system.

Moreover, the comet’s trajectory will bring it close to Jupiter in March 2026, offering a rare chance for spacecraft orbiting the gas giant to observe it up close. Such observations could provide further insights into the comet’s composition, structure, and interaction with the solar environment.

The continued study of 3I/ATLAS not only enhances our understanding of cometary physics but also contributes to knowledge about the materials and conditions present in other star systems. Each interstellar visitor carries clues about the formation and evolution of planetary systems beyond our own.

What this means

The passage of interstellar comet 3I/ATLAS through our solar system has provided a rare and valuable opportunity to study a visitor from beyond our stellar neighborhood. Thanks to innovative use of solar observation satellites and dedicated astronomers, the comet’s rapid brightening and unique characteristics have been closely monitored even when hidden behind the sun. As it re-emerges into view, continued observations promise to deepen our understanding of cometary behavior under extreme conditions and offer insights into the nature of material traveling through interstellar space. This event underscores the importance of versatile space-based instruments and international collaboration in expanding our knowledge of the cosmos.