NEW YORK – Comet 3I/ATLAS’s unusual trajectory and unprecedented size have ignited debates and theories as to what the object could be. A controversial theory put forward by Avi Loeb, a Harvard astrophysicist and his team is that the interstellar object might be some form of “alien technology.”

The colossal interstellar object was first spotted in Chile by NASA’s ATLAS survey telescope on 1 July, 2025. When astronomers initially saw it, they were not entirely sure exactly what they were looking at. Barrelling at 61 km per second relative to the Sun, the object appeared as a faint blip against the crowded star fields near the galactic center. Within hours, follow-up observations revealed its hyperbolic trajectory, meaning the origins of our cosmic guest may be from another star system altogether.

The discovery itself was almost accidental. Earlier images before the discovery show that 3I/ATLAS had been visible as early as June 14, 2025. The chances are that it was likely overlooked due to the interstellar object passing through a dense cluster of stars in the backdrop of the Milky Way’s centre. The observations were first submitted to the Minor Planet Center (MPC) when the NASA-funded Asteroid Terrestrial-impact Last Alert System (ATLAS) first discovered the comet in July. Amateur astronomers and professional observatories across the globe provided observations to the effort, with the MPC collecting 122 observations from 31 different observatories within days of the official announcement.

This Manhattan-size interstellar wanderer is the third confirmed interstellar object to ever visit our solar system, following ‘Oumuamua in 2017 and comet 2I/Borisov in 2019. What makes 3I/ATLAS particularly special is its incredible magnitude and physical properties. It could potentially be thousands of times more massive than its 2 predecessors and is a “major anomaly” that could give us new insight into interstellar space.

What particularly surprised astronomers is the comets’ bizarre orbits. Unlike average comets that follow elliptical orbits around the Sun, 3I/ATLAS travels on an unbound, hyperbolic path with an eccentricity of 1.2. This means that it will pass through our solar system once, never to return. Its hyperbolic excess velocity of approximately 36 miles (58 km) per second validates its deep space origins, as no gravitational displacement caused by other solar system planets could account for such extreme speed.

A Giant Among Cosmic Pebbles

The size disparity between 3I/ATLAS and its predecessors is tremendous. The first interstellar object, ‘Oumuamua, discovered in 2017, measured roughly 400 meters in length, which is about the size of several city blocks. Comet 2I/Borisov, discovered in 2019, has an estimated diameter of approximately 0.6 miles (1 km). By contrast, 3I/ATLAS dwarfs both with a nucleus potentially spanning roughly 1 to 3 miles across, with recent estimates suggesting it could be even larger.

Oumuamua and 2I/Borisov remain small, while 3I/ATLAS allegedly exceeds 33 billion tons. This makes 3I/ATLAS 3 to 5 orders of magnitude more massive than its predecessors. To put this in perspective, that is roughly equivalent to 33 billion compact cars compressed into a single cosmic snowball.

The mass estimate comes from trajectory analysis conducted by Harvard astrophysicist Avi Loeb and his team. By measuring how little the comet’s path deviated from pure gravitational motion despite its active loss of gas. They determined that 3I/ATLAS must be incredibly massive to resist the subtle pushes from its own gas emissions. The comet is shedding material at a rate of up to 60 kgs per second which is enough to erode a millimeter-thick layer from its surface over 6 months.

An Unusual Path Through the Cosmos

3I/ATLAS’s trajectory makes the comet come into close vicinity of 3 planets in our solar system. The comet is predicted to make its way close to Venus, into the orbit of and close to Mars. Finally, it will have a close brush with Jupiter on its way out back into deep space. On October 3, 2025, it approached within 17.4 million miles (28 million kms) of Mars which made it close enough for spacecraft orbiting the Red Planet to capture detailed observations. The European Space Agency’s Mars Express and ExoMars Trace Gas Orbiter successfully photographed the comet during this encounter, providing some of the closest views yet obtained.

Following its Mars encounter, 3I/ATLAS will reach its closest point to the Sun on October 29, 2025, passing just inside Mars’ orbit at a distance of 210 million kilometers. During this perihelion approach, the comet will be moving faster than 150,000 miles per hour as solar heating increases. It will then continue outward, making a relatively close pass by Jupiter in March 2026 before heading back into interstellar space forever.

A Chemical Fingerprint from Another World

The James Webb Space Telescope sent the first images back to astronomers and they discovered something bizarre. NASA’s James Webb Space Telescope detected an unusually high ratio of carbon dioxide to water in the comet’s coma (envelope surrounding the comet’s nucleus). These ratios are the highest ever recorded for any comet. The unusual carbon dioxide-to-water ratio measured at 7.6 to 1, could give us insight into the comet’s mysterious origins.

The comet may have formed in the outer reaches of its birth system, where carbon dioxide naturally freezes out of the gas. Alternatively, billions of years of exposure to cosmic radiation during its interstellar journey may have created a “cooked shell” on the surface where carbon dioxide ices accumulated.

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