The Mysterious Interstellar Object
Interstellar objects are a rare and intriguing phenomenon. The most recent among them, 3I/ATLAS, brings with it significant scientific challenges, particularly when it comes to measuring its mass. One of the most pressing questions regarding this interstellar body is centered around the **diameter** of its solid-density nucleus. The SPHEREx space observatory detected a flux from 3I/ATLAS that suggests a substantial nucleus, potentially up to 46 kilometers in diameter. This is an astonishing size that might indicate a solid core or merely a cloud of opaque dust scattering sunlight.
The collective limitations of various observational technologies, including Hubble Space Telescope, do not offer the resolution required to accurately estimate the amount of sunlight reflected by this nucleus. Consequently, the theoretical inferences drawn from the data are highly model-dependent, adding another layer of uncertainty regarding the actual size of 3I/ATLAS.
The Importance of Mass Measurement
Why measure the mass of 3I/ATLAS? As the mass of a nucleus is related to its diameter cubed, determining the mass could effectively constrain the size of this intriguing object. The implications of understanding its mass scale are astronomical—literally. For instance, if 3I/ATLAS does possess a solid core of 46 kilometers, its mass would be roughly **1020 grams**, which is an order of magnitude greater than the previous interstellar comet, **2I/Borisov**.
Measuring Techniques: The Rocket Equation
One efficient way to gauge the mass of 3I/ATLAS involves employing the **rocket equation**. The basic principle states that the force acting on the object is equal to the excess of its mass loss rate directed toward the Sun, multiplied by the outflow speed relative to its surface. Specifically, the equation can be represented as:
Force = Mass Loss Rate × Outflow Speed
By dividing this non-gravitational force by the object’s non-gravitational acceleration, we can compute its mass.
According to recent findings from the Webb telescope, the mass loss rate of CO2 from 3I/ATLAS was estimated at **129 kilograms per second**, with an outflow velocity of **0.44 kilometers per second**. When both factors are multiplied, they yield a non-gravitational acceleration of about **6×10-11 centimeters per second squared**. However, this level is significantly lower than the minimum measured for objects within our solar system, indicating that more research is needed.
The Quest for Clarity
To clarify the existing uncertainties, it is essential to consider the possibility that the non-gravitational acceleration could become more detectable as 3I/ATLAS approaches the Sun. Alternatively, a smaller nucleus diameter would require a reassessment of the estimated high mass of 3I/ATLAS compared to the likely rocky material present in interstellar space.
As indicated in earlier studies, a sub-kilometer nucleus diamond would imply a nucleus mass below **1015 grams**, suggesting a non-gravitational acceleration significantly higher than previously assumed.
The Influence of Gravity
In situations involving larger objects, gravity may provide a more effective method for gauging mass. **3I/ATLAS** is expected to pass within **29 million kilometers** of *Mars* on **October 3, 2025**. At this distance, its gravitational influence could impart a velocity change to Mars, akin to two fuzzy billiard balls colliding.
This velocity kick can be calculated using the gravitational acceleration formula: **GM/b²**, where G is Newton’s constant and b is the distance of closest approach to Mars. However, for a mass estimation that yields a mass kick of about **3×10-7 centimeters per second**, the uncertainty in the orbit of Mars makes this observation unreliable.
Future Opportunities for Measurement
The intriguing aspect of 3I/ATLAS is its potential as a technological object. If it were to maneuver and get closer to Mars or the Earth, we might be able to release a mini-probe that could be sent to collect critical data. The **Minimum Orbit Intersection Distance (MOID)** of **3I/ATLAS** from Mars is strikingly short—just **0.018 AU or 2.7 million kilometers**. This close proximity allows for various exciting possibilities.
Calls for Collaboration: A NASA Challenge
As noted by **Avi Loeb**, there is an urgent need for collaboration among scientific institutions. A suggestion made was for NASA to utilize the available fuel of the **Juno spacecraft** and bring it as close to 3I/ATLAS as possible when it approaches **34 million kilometers** from **Jupiter** on **March 16, 2026**. This could enable measuring gravitational deflection and contribute to a precise mass measurement of 3I/ATLAS.
A Collective Look Ahead
The future of understanding the nature and characteristics of 3I/ATLAS may hinge on innovative approaches and new data. Following the advice of seasoned basketball coaches—to focus on the ball rather than the audience—we must prioritize high-quality data collection and analysis over social media chatter.
Data-driven measurements will ultimately elucidate the mysteries surrounding 3I/ATLAS and may even redefine our understanding of interstellar objects in general.
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