The enigmatic comet 3I/ATLAS has captured the attention of astronomers worldwide, emerging as a significant discovery due to its extraordinary size and mass. According to a new study, 3I/ATLAS appears to be substantially larger and more massive than the two previously confirmed interstellar objects, ʻOumuamua and Borisov. This revelation sheds light on our understanding of interstellar objects that periodically traverse our solar system.
The findings surrounding comet 3I/ATLAS were detailed in a study authored by Richard Cloete, Peter Vere, and Harvard astronomer Avi Loeb. Their analysis utilized the most precise tracking data collected since the comet's discovery in July, revealing that 3I/ATLAS exhibits characteristics of being “anomalously massive.” This significant discovery raises fundamental questions regarding our expectations for the composition and behavior of interstellar objects.
Recent observations suggest that 3I/ATLAS might measure up to three miles in length, positioning it as a remarkable entity in the cosmos. The team's research focused on over four months of optical measurements compiled by the Minor Planet Center, comparing the comet's trajectory against predictions based solely on gravitational forces.
The comprehensive analysis of 3I/ATLAS indicated minimal deviation from the expected gravitational path, suggesting a negligible degree of non-gravitational acceleration. This finding implies that the comet’s nucleus must be at least five kilometers (a little over three miles) in diameter. Such dimensions make it substantially more massive than its interstellar predecessors, ʻOumuamua and Borisov.
Between May and September, more than 4,000 astrometric measurements related to 3I/ATLAS’s motion were gathered from 227 observatories around the globe. The team was able to calculate an upper limit on the comet's non-gravitational acceleration, which was found to be less than 15 meters per day squared. This measurement, in conjunction with momentum conservation principles, implies that the gas jets produced on the comet’s surface, due to solar heating, should yield a detectable push. However, the absence of observable deviation suggests that 3I/ATLAS is indeed quite massive.
In early August, data from the James Webb Space Telescope revealed that 3I/ATLAS experiences a significant mass loss of approximately 150 kilograms per second, with a gas outflow velocity of around 440 meters per second. When this data is incorporated into momentum-balance equations, it indicates that the nucleus of the comet likely has a minimum mass of 33 billion tons. If composed of solid, ice-rich material, this further reinforces estimates that the diameter of 3I/ATLAS is around five kilometers.
The latest findings align with previous estimates derived from images captured by the Hubble Space Telescope, suggesting that 3I/ATLAS is indeed larger than both ʻOumuamua and Borisov. Additionally, imagery from Gemini South, taken in late August, confirmed the presence of a conventional cometary tail, further supporting the notion of its significant mass.
Avi Loeb emphasized the unusual nature of 3I/ATLAS, noting that its mass surpasses expectations for interstellar objects. "We should have detected around 100,000 ʻOumuamua before discovering an object as large as 3I/ATLAS," he stated, referencing a paper he published in July that suggested the rarity of such large interstellar bodies.
Despite the constraints on the object’s size, the recent observations have provided limited insights into its composition. The only indications stem from spectroscopy conducted by the JWST and SPHEREx, which revealed mass fractions of CO2 (87%), CO (9%), and H2O (4%). Additionally, traces of cyanide and nickel were detected without the presence of iron, raising intriguing questions about the nature of 3I/ATLAS.
Loeb has proposed a controversial hypothesis that 3I/ATLAS might be more than just a typical comet. He cites its unusual mass, trajectory, and unique spectral data as potential indicators of a more complex origin. "The detection of nickel without iron is typically associated with industrially produced alloys," he noted, suggesting the possibility that 3I/ATLAS could be something entirely novel.
However, many experts maintain that the evidence overwhelmingly supports the view that 3I/ATLAS is a natural comet. Tom Statler, NASA’s Lead Scientist for Solar System Small Bodies, affirmed, "It behaves like a comet." This debate continues as astronomers await further observations.
As 3I/ATLAS approaches Mars on October 3, astronomers are eager to gather more data about this fascinating interstellar object. The discovery of such a large nucleus presents challenges to current models of interstellar object populations, leading researchers to reconsider the frequency and characteristics of objects like ʻOumuamua.
Upcoming observations using the HiRISE camera on NASA’s Mars Reconnaissance Orbiter and the Juno spacecraft as 3I/ATLAS nears Jupiter next March are anticipated to provide critical information regarding the comet’s surface and overall characteristics. Avi Loeb expressed excitement for the forthcoming data, stating, "I can’t wait for this data!"
In conclusion, while the debate surrounding 3I/ATLAS continues, its discovery challenges our existing paradigms about interstellar objects. The findings from this study prompt a reevaluation of how we understand the composition and behavior of these celestial wanderers and the number that may exist throughout the vast expanses of interstellar space.
The recent study titled “Upper Limit on the Non-Gravitational Acceleration and Lower Limits on the Nucleus Mass and Diameter of 3I/ATLAS” is available online at the Harvard & Smithsonian Center for Astrophysics.
