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Here’s a plain-English summary of what Avi Loeb is saying in that passage about the interstellar object 3I/ATLAS:
1. Starting assumption
He begins with the most conservative idea: suppose 3I/ATLAS is an ordinary natural comet made of ice and dust, not a spacecraft or something artificial. He then checks whether the numbers we can observe actually fit that assumption.
2. What the latest image shows
The newest post-perihelion (after closest approach to the Sun) images show huge jets of gas and dust:
- about 1 million km long in the direction of the Sun,
- about 3 million km long pointing away.
If these are normal comet jets, their gas should be streaming out at about 0.4 km/s—roughly the speed of sound in such conditions.
At that speed, it would take the jets one to three months to grow to that size, meaning they’ve been active for that long.
3. Mass loss and density estimates
That level of mass loss actually fits the small non-gravitational acceleration that was observed earlier—so the numbers appear self-consistent so far.
4. Energy from the Sun vs. what’s required
Now comes the key test: does the Sun provide enough energy to vaporize that much material?
- Turning CO₂ ice into gas requires about 600 J per gram (five times less than for water ice).
- Spectra from the JWST showed that the comet’s gas is about 87 % CO₂, so that’s the relevant value.
- To sublimate 5 billion tons of CO₂ in a month, you need roughly 3 × 10¹⁸ joules of energy.
- At perihelion, the Sun shines on it with about 700 J / m² / s.
For the Sun to deliver that much total energy, 3I/ATLAS would need to absorb sunlight over at least 1,600 km² of surface area—the same as a sphere 23 km wide.
But Hubble data limit its diameter to no more than 5.6 km.
That’s a huge mismatch. If the jets were driven by sunlight, the comet would need to be 16 times larger than it appears to be. For water-ice sublimation the mismatch would be even worse—equivalent to 51 km diameter.
5. “Houston, we have a problem.”
In short, the natural-comet model doesn’t add up: the observed mass loss is far too high for the energy it could receive from the Sun given its measured size.
6. Possible explanation 1 – the comet blew apart
Maybe the comet simply broke up near the Sun.
If it fragmented into many pieces, the total surface area exposed to sunlight would multiply.
To get 16 times more area, it would need at least 16 fragments, maybe many more—essentially an explosion at perihelion.
If that happened, the pieces will slowly drift apart under the Sun’s tidal forces, eventually forming a string of fragments like Comet Shoemaker–Levy 9 did before hitting Jupiter in 1994.
Upcoming observations will check for that pattern.
7. Possible explanation 2 – it didn’t break up → something else
But if observations in December 2025 show that 3I/ATLAS is still intact, then the natural-comet idea really fails.
We’d have to consider that it’s not a typical comet at all—perhaps something artificial or exotic.
8. Statistical oddities
Even before this, there was a major anomaly:
- 3I/ATLAS seems a million times more massive than the earlier interstellar visitor ‘Oumuamua.
- Given what we know about how much solid material exists in interstellar space, it’s incredibly unlikely that such a giant object would wander into our solar system now—roughly once every ten thousand years at best.
- Combine that with its unusually aligned retrograde orbit, and the chance of it being an ordinary interstellar rock drops to about one in a hundred million.
9. Alternative: engineered propulsion
If, instead of natural jets, the outflows were controlled thrusters, the picture changes completely.
A rocket exhaust speed of 3–5 km/s (chemical) or 10–50 km/s (ion propulsion) could produce the same visible jets with far less mass loss—orders of magnitude less material.
That would neatly explain the energy discrepancy: the Sun wouldn’t need to vaporize the material; the object would be propelling itself.
10. What happens next
Future spectroscopic data (measuring jet velocity, mass, and composition) will tell whether the jets behave like natural gas outflows or engineered exhaust.
If 3I/ATLAS didn’t break apart and shows jet speeds far beyond what sunlight can drive, then the “natural comet” idea may have to give way to something more intriguing.
In short:
If 3I/ATLAS really is just a comet, it should have disintegrated when the Sun heated it.
If it’s still intact and still showing jets, the numbers force us to consider that it may be artificially propelled—a kind of interstellar spacecraft rather than an ordinary chunk of ice and dust.
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