6. ---------------------------- (from Comet Papers)
Title - Comet 108P/Ciffreo: The Blob
By - Yoonyoung Kim, David Jewitt et al, Feb 2023
Extracts - Short-period comet 108P / Ciffreo was discovered in 1985 & is a Jupiter family comet (i.e. a likely escapee from the Kuiper Belt). Orbital period : 7 years. Most recent perihelion : Oct 2021 at 1.66 AU. A peculiar morphology was reported in late 2021, with the emerging appearance of a double object, consisting of a centrally condensed nucleus with a co-moving diffuse structure (the “blob”) located to its east. It is inferred that there was zero nucleus-blob separation in Aug 2021. This feature was observed in Dec 1985 also, with a “detached dust tail” persisting to at least 1986 March. Archived images taken in 2014 show a morphology soon after perihelion, similar to that in early 2022, while a single post-perihelion image from 2007 does not. In other comets, a double appearance normally indicates a nearly co-moving, secondary source displaced from, and independent of, the outgassing activity from the main nucleus. However, this interpretation raises the question of how the double morphology could persist in successive orbits. The blob was clearly apparent in Dec 2021, and a slight extension in the nucleus was observed in Nov 2021. Except for the emergence of the blob, the shape of the extended envelope in the background is stable, suggesting that the diffuse coma is not related to the blob.
Nucleus diameter is calculated to be 1 km. Lamy et al. (2004) cite a larger diameter of 2.8 km, which might be due to larger dust contamination of the near-nucleus region. The separation between the nucleus and the centroid of the blob increases slowly over 6 months, reminiscent of the separation speeds of some fragmenting comets and asteroids (Boehnhardt 2004). Though Figure 6 does not rule out a splitting event, the re-appearance of the double morphology in successive 7 year orbits argues strongly against this possibility. We further rule out that a fragment could be co-moving with the main nucleus by being gravitationally bound. The 6,000 km separation between the nucleus & the blob is far larger than the Hill radius of the nucleus. The ratio of the blob mass to nucleus mass is 10^(−6). This measurement shows how an almost inconsequential mass of material can substantially affect the morphology of the comet.
We used a Monte-Carlo model of coma particle dynamics to show that the blob is an artifact of the turn-around of particles ejected sunward in a narrow jet and repelled by solar radiation pressure. This interpretation is also puzzling since it raises the question of why it would apply only to 108P out of the hundreds of comets that have been imaged in the modern era. We suggest that topography (most likely a pit) present near the pole of a high-obliquity nucleus may be responsible for the collimation of the jet and the formation of the observed blob. A nearly co-moving coma structure in the Centaur 174P/Echeclus is potentially of similar origin.
My Feedback - "As a rough approximation, we take the thermal speed Vs = (8kT/πµmH)^1/2, where T is 200 K (-73 C) is the temperature of the sublimating surface ..." -- Crackpot science ! There is no ice at - 73 C & hence, nothing to sublimate away. These pseudo-scientists are weak in temperature physics. The entire Pit Source section of the paper is nonsense.
. ----------------------------
No comments:
Post a Comment