- This topic has 3 replies, 2 voices, and was last updated 1 day, 10 hours ago by
.
-
Posts
-
Hello all, In my talk to the BAA Comet Section in Edinburgh I wondered if interstellar comet 3i would display an anti-tail. It seems it has, looking at recent images, such as, 3i Atlas with tail 9th…Michael Buechner, posted on the BAA Gallery that indeed an anti-tail does seem to be present. There are also indications of a rather chaotic conventional tail to been seen in the same image. This comet keeps to offer suprise upon suprise. Shame it did come close to Sun and Earth during it one off visit to the inner Solar System. We will have a good chance to continue observing this comet for the next couple of months.
Denis,
This is worth a read:
https://sites.psu.edu/astrowright/2025/09/29/3i-atlass-anti-tail-isnt-unique/
After debunking a load of Loeb junk it explains that the anti-tail in this case is related to relatively massive dust grains that don’t get accelerated backwards into the tail. It references the famous LSST paper that has a zillion (I exaggerate slightly) authors:
Nick,I realised that the 3i anti-tail we are seeing is not the “usual” type of comet anti-tail that we see in LP comets which lay a trial of dust along the orbit, which we can then see edge on as we cross the orbital plane of the comet.In 3i we are seeing dust that is being released at present but remaining in the direction of ejection.
Is that correct?
I am here to learn that is why I am in the BAA.Conventional modelling of the dust tail of a comet assumes that the dust grains are small and emitted from the nucleus in all directions at low velocity. Solar radiation pressure is then sufficient to accelerate the grains in the anti-Sun direction to form the dust tail. In the case of 3I one explanation for the “anti-tail” is that some of the dust grains are large and that they are emitted preferentially in the sunward direction at a higher velocity. It then takes more time for the solar radiation pressure to turn them around and push them back in the anti-solar direction.
This mechanism was postulated for the anti-tail of C/2014 UN271 in this paper by Farnham et al:
https://iopscience.iop.org/article/10.3847/PSJ/ac323d
The attached graphic is figure 7 of that paper. It shows modelled dust tail syndynes for different particle sizes and emission velocities and it demonstrates how an anti-tail can form in these circumstances.
Attachments:
- You must be logged in to reply to this topic.