31/ Atlas Interstellar Object
Here is a distilled “cheat-sheet” of the new, peer-reviewed SPHEREx data Loeb just published, plus what it really means.

1. The headline numbers

- CO₂ coma detected – 70 kg s⁻¹ outflow, visible to > 348 000 km radius.

- H₂O upper limit – < 4.5 kg s⁻¹ (an order of magnitude below earlier, unconfirmed claims).

- Radius dilemma – 1 µm flux implies 46 km nucleus; that would make the mass 10⁶ × 2I/Borisov, wildly inconsistent with population statistics.

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2. What the data favor (mainstream view)

- CO₂-driven activity is common for long-period comets and Centaurs; no exotic physics required.

- Steep brightness profile is naturally produced by CO₂ sublimation at 3.2 AU, where water is still mostly frozen.

- Reddened surface matches radiation-processed KBO-like organics, not polished metal.

3. What still doesn’t add up (Loeb’s talking points)

- 46 km radius conflicts with comet population statistics by × 10⁴.

- Planar alignment (within 5° of Earth’s orbit) has 0.2 % random probability—statistically odd, but not impossible.

- No H₂O is puzzling, yet not unprecedented for CO₂-dominated bodies.

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4. Next real test

- JWST data (taken 6 Aug 2025) still unreleased.

- Mars HiRISE campaign on 3 Oct 2025 will resolve 30 km px⁻¹—good enough to see geometry, solar panels, or thermal hot-spots.

Bottom line

The SPHEREx results strengthen the CO₂-comet model, but do not erase the statistical oddities Loeb highlights.

The definitive call will come from HiRISE in 4 weeks, not from SPHEREx.

Read:

3I/ATLAS is Large and Releases Carbon Dioxide (CO2) | by Avi Loeb | Aug, 2025 | Medium https://lnkd.in/gh24QyVT

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