Forum der Vereinigung der Sternfreunde

21 mag am 1.8.2021

Orbital elements:
    C/2021 O3 (PANSTARRS)                                                       
T 2022 Apr. 20.49806 TT                                 Rudenko                 
q   0.2888063            (2000.0)            P               Q                  
                   Peri.  299.88349     -0.56671024     -0.81340873             
                   Node   189.02692     +0.64769077     -0.53821683             
e   1.0            Incl.   56.72241     -0.50925059     +0.22065558             
From 61 observations 2021 July 26-Aug. 1.

https://minorplanetcenter.net/mpec/K21/K21P05.html
(CBET 5009)

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Uwe Pilz, Fachgruppen Kometen und Astrophysik/Algorithmen.
Oft benutzte Instrumente: Fujinon 16x70 FMT-SX-2, TMB Apo 105/650, Skywatcher Evostar 120/900 ED, Ninja Dobson 320/1440, Smartscope Dwarf-3

David Seargent spekuliert in der Mailingliste, dass dieser Komet im nächsten Jahr freisichtig werden könnte. Dazu müsste er dynamisch alt sein, also schon ein paar Vorübergänge an der Sonne hinter sich haben.

Ich habe das mal nachgerechnet. Mit n=3,5 (dynamisch neu) ist die Maximalhelligkeit 5 mag, mit n=6 (dynamisch alt) wird die Magnitude negativ. Alles rechnerisch freilich, und vor allem aus der jetzigen Gasentwicklung extrapoliert. Da sich der Komet mit r~4 AE noch jenseits der Eisgrenze befindet, ist diese durch leichtflüchtige Gase geprägt. Die Eisgrenze (knapp 3 AE) durchläuft er erst im November.

Ich habe weiter die Bahngeometrie vom 1. April bis 11. Mai dargestellt, die Querstriche gibt es für jeden Tag – ihr könnt also abzählen, wenn ihr ein konkretes Datum wissen wollt.

Vor dem Perihel ist er praktisch unsichtbar, nach dem Perihel steigt er steil nach Norden. Am dem 5. Mai wird er zirkumpolar, diese Position ist in der Karte dargestellt. Der Komet kulminiert gegen 13 Uhr MEZ, ist also sowohl am Abend- als auch am Morgenhimmel zu finden.

So weit nicht schlecht. Spekulativ ist wie immer die Helligkeitsentwicklung.

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Uwe Pilz, Fachgruppen Kometen und Astrophysik/Algorithmen.
Oft benutzte Instrumente: Fujinon 16x70 FMT-SX-2, TMB Apo 105/650, Skywatcher Evostar 120/900 ED, Ninja Dobson 320/1440, Smartscope Dwarf-3

Zu sehen nicht, aber für die CCD-Kamera war der Komet am 2.8. mit 19.2 mag "leichte" Beute. Mal sehen, was uns dieser Komet für Überraschungen bereitet.

Gruß

Werner

Hello Uwe,

Could you explain a little bit about how a dynamically new comet will be fainter than a dynamically old comet? I would have expected the opposite but I am just an old farm boy who has inhaled to much dust.

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Cheers, Mike
Arizona

Dear Mike and all,

dynamical new comets have a fresh surface. That means gas evolutions may occur nearly everywhere. What we expect to see is the evolution far away and this increases with closer solar distances to n=4 that means r^4: r^2 come form the illumination and another r^2 come from increased gas evolution.

Dynamical odl comest are covered by a dust layer. The comets need to free parts of the surface, centres of activity. What we see is gas evolution only from a few such centres. We may expect that with closer solar distanced we get more of them. So (with unsharp glasses) we have n=6: n=2 come form illumination, another n=2 come from increased gas evolution and additional n=2 come form more cnetres of activity.

Dynamical new comets are not fainter, but they have more activity far outwards. If the comes is old, and we could replace it with the same comet but fresh, it would be much brighter. But with icoming closer to sun the curve is steeper.

Last year we had a comet with incredible n=17 which normally occurs only for a few days (outburst). But here we had weeks. I illustrated what may be happened. Our situation here is covered too. The article is in German, but may be the illustraions are useful:

http://fg-astrophysik.vdsastro.de/algAktivitaetKometen

For short: we don't know what we see at the moment. A dynamical fresh comet, rather small. Or a giant dynamical old one.

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Uwe Pilz, Fachgruppen Kometen und Astrophysik/Algorithmen.
Oft benutzte Instrumente: Fujinon 16x70 FMT-SX-2, TMB Apo 105/650, Skywatcher Evostar 120/900 ED, Ninja Dobson 320/1440, Smartscope Dwarf-3

Hello Uwe,

Thank you for your reply.

So in old farm boy language a new comet that has never ventured any closer to the Sun than say Pluto should have an abundance of volatile gases and water near the surface that will boil away and create a coma farther from the Sun than an older comet which has to get more solar radiation to boil away gases and water farther below it's surface. Thus a new comet will initially make us think that it may become very bright but once the easy stuff has boiled away it may not brighten as expected whereas an old comet is more likely to follow a brightening curve since it will probably follow a known radiation/out-gassing curve observed by similar old comets.

So can one assume that unless a new comet gets a lot closer to the Earth or Sun in a future perihelion passage that the initial trip into the inner solar system will probably be it's brightest or will future passages be brighter since gasses boiling away much deeper under the crust will blow a lot more stuff off the comet than the easy stuff that boiled away near the surface in it's first visit?

Thank you for your patience with my questions Uwe, I appreciate your thoughts and the thoughts of everyone in this group.

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Cheers, Mike
Arizona

> thus a new comet will initially make us think that it may become very bright but once the easy stuff has boiled away it may not brighten as expected whereas an old comet is more likely to follow a brightening curve since it will probably follow a known radiation/out-gassing curve observed by similar old comets

Dear Mike, I don't think it is correct this way.

You described deskriptive what young and old comets are, all ok.

But the reason for the different brightness variation is slightly different.

When we see a comet far away we may have
1) A smaller body outgassing at all the surface (fresh)
2) A lager body outgassing only at parts of its surface (old)

If the smaller body comes closer to sun it increases outgassing to a certain degree
If the larger body comes closer to the sun the outgassing increases to the same degree AND more of the surface gets active. This is not possible for fresh comet, because all is already active

Therewith, the brightness curve of an old comet is steeper.

_________________
Uwe Pilz, Fachgruppen Kometen und Astrophysik/Algorithmen.
Oft benutzte Instrumente: Fujinon 16x70 FMT-SX-2, TMB Apo 105/650, Skywatcher Evostar 120/900 ED, Ninja Dobson 320/1440, Smartscope Dwarf-3