Everything We Know About 3I/ATLAS, the New ‘Oumuamua

Understanding the vastness of space is a challenge for us humans. We are comfortable in our own cosmic neighborhood—the solar system—where familiar faces like Jupiter, Mars, and, of course, Earth reside. However, beyond this familiar territory, over 18 billion kilometers away from the Sun, lies the cold, desolate expanse of interstellar space. To date, only two human-made objects, the Voyager probes, have crossed this boundary. Until recently, only two known objects had ventured into our solar system from interstellar space: the famous ‘Oumuamua in 2017 and Borisov in 2019. These encounters stirred excitement and perhaps even fear, as they represented visitors from the depths of space that humanity cannot hope to reach in our lifetimes.

In the six years since these visits, we have enjoyed a period of calm, but recent observations have once again captured our attention. I’m Alex McColgan, and you’re watching Astrum. Join me as we explore everything we know about NASA’s latest observations of comet 3I/ATLAS, the third interstellar object ever observed, which will make its closest approach to the Sun before the end of the year.

3I/ATLAS has gone through several names in the short time since its discovery. However, recent revelations about its origin and trajectory have turned this otherwise unremarkable space rock into something noteworthy. On July 1st of this year, the NASA-funded ATLAS survey telescope was performing its routine task of scanning the skies for moving objects. The ATLAS project, or Asteroid Terrestrial-impact Last Alert System, consists of four telescopes located in Chile, South Africa, and Hawaii. These telescopes capture around 800 images each night, and as of now, they have recorded 1,212 Near-Earth Objects that will pass within 1.3 AU of our planet. But on that particular night, the telescope in Rio Hurtado, Chile, reported some significant findings.

The ATLAS telescopes are unique in their ability to survey the Galactic plane—the bright, disk-shaped region of our galaxy where most of its mass resides. Other surveys, like Pan-STARRS and the Catalina Sky Survey, often avoid this area due to sensitivity issues that lead to overexposure. However, the ATLAS telescope took four 30-second survey images from the direction of the Sagittarius constellation and discovered an object making a beeline towards our solar system. Initially named A11pl3Z, this object quickly caught the attention of the Minor Planet Centre (MPC) in Cambridge, Massachusetts.

As the designated authority for labeling and tracking minor bodies in the solar system, the MPC promptly issued an electronic circular about this new visitor, detailing all previous observations and providing information about its trajectory. Through this analysis, astronomers realized that this object was no stranger to us. The Zwicky Transient Facility in California and the other ATLAS telescopes had made “pre-discovery” observations of it, dating back to June 14th! With this data, the MPC deduced that the object has a hyperbolic and highly eccentric orbit, indicating that it originated from interstellar space. This recognition earned it the name 3I/ATLAS, as it is the third interstellar object to infiltrate our solar system.

Initially, the MPC could not determine whether this object was an asteroid or a comet until combined data revealed that it had a coma—a diffuse halo of dust and gas produced when ice is exposed to solar radiation and sublimates. This feature is more typical of comets, leading to another name: C/2025 N1. The MPC has called for additional observations of this comet to help refine its trajectory, so we can expect a flurry of new data in the coming months, and astronomers are naturally very excited. Michele Bannister, an astronomer at the University of Canterbury in New Zealand, explained that working on the previous interstellar visits was a “transformational opportunity” for science, so it’s likely this visitor will inspire similar excitement.

But what do we already know about this latest interstellar visitor? And what do scientists hope it can teach us in the near future? Firstly, there is no need to worry, as this comet poses no threat to Earth. At its closest approach, it will still be around 1.6 astronomical units away—over 600 times farther than the Moon is from Earth! So, since we can observe from a safe distance, what kind of journey will this comet take?

As mentioned earlier, 3I/ATLAS has a highly eccentric orbit, currently measuring an eccentricity value of around 6. For reference, an eccentricity of 0 represents a perfect circle, while anything above 1 indicates that the object has enough velocity to escape the gravitational pull of the body it orbits. With an eccentricity of 6, this comet has one of the most extreme hyperbolic orbits ever measured, which may explain how it can travel such vast distances through space to reach us.

Even more surprising is the speed at which this comet is traveling. Its current incoming velocity is a staggering 58 km per second! That’s like running the length of 580 football fields every second! This incredible speed makes 3I/ATLAS the fastest interstellar comet we have ever observed—‘Oumuamua and Borisov had velocities of just 26 and 32 km per second, respectively, due to their different orbital shapes.

With such a rapid approach, astronomers were eager to determine exactly where 3I/ATLAS was headed. The current orbit is heliocentric, meaning it is centered around our Sun, allowing astronomers to infer its incoming trajectory before it reaches us. At its closest approach to the Sun on October 30, the comet will be at a distance of 1.4 AU, placing it just inside the orbit of Mars.

Once the interstellar nature of this comet became clear, astronomers utilized other globally distributed telescopes to gather more data. In particular, the Las Cumbres Observatory (LCO) telescopes are designed to observe transient astronomical events, which can include comet outbursts and changes in brightness. Using two 0.36-meter LCO telescopes based in Hawaii, astronomers scheduled a one-hour observation sequence for 3I/ATLAS, aiming to identify a light curve for the comet and observe any rotational variability.

Rotational variability refers to changes in brightness caused by the comet spinning on its axis. It may have an irregular shape or active regions that appear brighter when facing Earth. By monitoring brightness changes over time, astronomers can identify repeating patterns that indicate a complete rotation cycle.

Using the LCO telescopes, astronomers determined that the comet has a rotation period of approximately 29 hours, though further observations are needed to refine this estimate. Surprisingly, 3I/ATLAS exhibited a much flatter light curve than ‘Oumuamua, with only 0.2 magnitudes of brightness variation during the 29-hour period. Despite this minimal variation, 3I/ATLAS is exceptionally bright, currently being the brightest interstellar object observed to date. The comet remained relatively faint until late May this year, when it reached a magnitude of around 20. Since then, it has increased in brightness to between 17 and 18 magnitudes as it approaches the Sun.

As we continue to gather more data on 3I/ATLAS, astronomers are hopeful that this interstellar visitor will provide valuable insights into the nature of comets and the conditions in other star systems. The excitement surrounding this discovery underscores the importance of ongoing astronomical research and observation, reminding us that the universe is full of surprises waiting to be uncovered.