Okay, you're right, I forgot about relativistic proper time being different from "Newtonian" time and handling that brings efficiency up to 1 despite the otherwise identical effective potentials.
Stronger outgassing also corresponds to less of a tail, because it ejects dust faster = makes the tail puffier => a very puffy tail is essentially just a diffuse coma, basically what we see now. Thin dust tails correspond to dust ejected at low speeds = relatively little outgassing.
Nothing about his claim is sensible. The nongravs are most likely far smaller than the current measurements, due to the astrometry being biased by the asymmetric coma (comet was ~4 sigma away in the JWST obs). Observations (especially in the radio) also show strong outgassing.
That may be true, but if 3I/ATLAS were instead an Oort cloud with the same properties, it may still stand out in some aspects, but I'd argue (based on the published data so far) would be distinctly less weird than at least of couple of other comets we know of.
The thing above it is just a star that saturated the detector.
Yes, it's very close to the JPL ephemeris position.
Depends a lot on your sky conditions, horizon, and telescope. The first two need to be just about perfect right now to catch it with a typical amateur-class telescope, but it's rapidly becoming easier.
I think it's bright enough now that even small telescopes should be able to get it, especially with how quickly the comet is moving out from the Sun angularly.
We already recovered it with the Lowell Discovery Telescope this morning: cometary.org/@qicheng/sta...
October 29 data is likely from these ALMA observations: almascience.nrao.edu/aq/?project_... They need highly accurate orbits for their narrow fields of view, so will often bypass the MPC (at least initially) to get their astrometry incorporated into the JPL orbit faster.
The thought is that if you have some CO2 mixed with H2O ice near the surface, the cooling from CO2 sublimation will stop efficient H2O sublimation. After enough CO2 goes away, some H2O might get warm enough to do so. May or may not be anywhere close to what's happening, but that's the speculation.
Yes, that range is still valid. A comet of its brightness would usually be on the upper side of that range, but at the moment, there's no evidence/need for it to be bigger than 5 km, as far as I can tell.
This is also a very weak bound, because comet astrometry tends to have large systematic errors due to coma asymmetry biasing the fitting of the nucleus position, which is hard for orbit fitting software to handle. In practice, comet positions/orbital parameters being 10+ sigma off is not uncommon.
The easy way to do the calculation would be to put the astrometry into an orbit fitting program with nongravitational parameters, like find_orb. I just did that, and the 3-sigma upper bound on A1 (radial nongrav at 1 au) is ~5e-7 au/d^2 (~2x that of `Oumuamua), so it's bigger than... ~50 m.
That sounds about right to me. All the iron/nickel comet papers basically came out together in big bunch once they noticed that.
That's because even though it was recorded on those earlier comets, it wasn't actually noticed apart from on sungrazing comets until that paper.
C/2025 K1 was >10 deg to the west of C/2025 R2 at the time of this image, whereas 3I looks to be at about the right spot ~4 deg away.
It may be at least a little weird, but hard to say by how much as there's only been 1 comet where the ratio has been measured at greater distances from the Sun.
Fig. 2 of this paper shows the ratio is generally on the order of ~1 for solar system comets not super close to the Sun: www.nature.com/articles/s41... Fig. 3 also suggests the actual line strengths of the two tend to be somewhat similar.
The thing is, one could say the same about any of the thousands of known comet or asteroids, or even about birds. Perhaps one day, all the penguins will just suddenly fly themselves to Mars. But until then, there's no good reason to seriously consider how they might all be aliens in disguise.
The problem is by this logic, we can *never* rule out anything as being aliens. Birds? Could be aliens spying on us. Clouds? Might be their nanobot formations. Lightning? Could be their communications. There's just as much evidence for those claims as there is of 3I/ATLAS being from aliens.
I'd forgotten about SPHEREx, but this new paper seems to support that the Swift OH detection is probably not real, with a far lower upper limit on water: arxiv.org/abs/2508.15469 Pretty convincing CO2 though. But obviously alien spaceships are gas powered. Or breathing. Or something...
Going by this article (payloadspace.com/reflect-orbi...), it sounds like their plan is based off having "thousands" of 55-m mirrors. From some quick math, they'd need ~10^4 of those pointed at one spot to match the Sun.
This Oort cloud comet has pretty much exactly the same kind of coma profile: iopscience.iop.org/article/10.3...
The previous figure in the exact same paper (arxiv.org/pdf/2508.02934) clearly shows the inner coma closely following a 1/rho profile just like a normal comet with steady dust loss. It rolls off farther out as normal, usually from activity beginning recently + radiation pressure + dust evolution.
I'd expect no less. It's the broken clock / monkey-on-typewriter strategy of being right; send out enough nonsense, and eventually some of it'll accidentally turn out to be correct.
Also not particularly convincing to me. It looks to me like it just assumes the rock/non-water component is a certain color matching a particular meteorite, and then attributes the entire observed color difference to water (vs. any of the many other differences that could affect the color).
Honestly, I'm very skeptical of the claimed OH detection as it doesn't really look the way OH should (i.e., a very diffuse fuzz, not a point). Also a huge jump from an upper limit from just weeks earlier. There's since been JWST observations that'll give better numbers, whenever that's published.
If the coma were made of very small grains, it might be possible to tell in MIR as dust grains don't thermally radiate efficiently at wavelengths more than an order of magnitude or so larger than their size. However, many distant comets have ~0.1 mm grains, which emit MIR just like a big nucleus.
Better to get to writing those before he scoops you!
