Evidence · 3I/ATLAS

No acceleration in the early arc

Fitting positions from 15 May to 23 September 2025, Cloete, Loeb and Vereš found no acceleration above about 3 × 10^-10 au per day squared, which with JWST's mass-loss rate implies a diameter above 5 km.

Speculative0

What it means

Key questionHow big is the nucleus of 3I/ATLAS?

2 answers, none ahead yet

Openunchanged

Answer this evidence bears onMore than 5 km across

Supports1 for, 2 against

Disputedunchanged

What it implies

Holds only if the acceleration was truly absent; far from the Sun a small push is expected to be undetectable.For the key question: How big is the nucleus of 3I/ATLAS?

Next steps 1

Fit the last Hubble DD 18152 visits for nucleus size

Could decideFair odds~40 h

On: How big is the nucleus of 3I/ATLAS?

10score

Details

The final visits (March to April 2026, beyond 5 au) had the faintest coma. A radius fit with coma subtraction that lands inside 0.35-1.8 km would settle the size; one outside would reopen it. The data are public in MAST.

Ranked by how likely each is to move the key question, for the time it takes

Sources 1

Upper Limit on the Non-Gravitational Acceleration and Lower Limits on the Nucleus Mass and Diameter of 3I/ATLAS

Cloete et al. 2025

SRC

Cite it

Mysteries Department. (2026). No acceleration in the early arc [Evidence EVD0DFQ48WD5C4Z]. https://mysteriesdept.com/r/EVD0DFQ48WD5C4Z

@misc{mysteriesdept_evd0dfq48wd5c4z,
  title     = {No acceleration in the early arc},
  author    = {{Mysteries Department}},
  year      = {2026},
  note      = {Evidence, catalog key EVD0DFQ48WD5C4Z},
  url       = {https://mysteriesdept.com/r/EVD0DFQ48WD5C4Z}
}