Dust Trail of a Dead Comet Phaethon

Japanese version
Home page
Updated on June 12, 2005



* Call for observation campaign

Asteroid (3200) Phaethon, discovered in 1983, is a source of Geminids meteor shower occured in December. It is probably a dead comet, which had been showing cometary activity before. However, no coma or tail is confirmed on Phaethon recently.

There is a dust trail, source of Geminids meteor shower, along the orbit of Phaethon. Although the dust trail is extremely faint, it becomes rich due to overlap and easier to detect when the view direction from the Earth and the direction of Phaethon's orbit coincide.

When the view direction from the Earth to Phaethon and the direction of Phaeton's orbit coincide, the dust trail around the nucleus of Phaethon may look like the coma or tail.

There have been only three chances to detect such a dust trail since its discovery in 1983. And the fourth chance will come in 2004 December.

Table: Chances to detect the Phaethon's dust trail, when Phaethon is not too faint, and observational condition is good.

Period             Mag.  θ  Ph   r     d    TrM1  TrM2
1984 Dec. 14 - 16  13.1   3  29  1.21  0.27  17.5  18.7
1991 Dec. 22 -  2  16.9   3  28  1.76  1.04  18.3  19.5
1994 Dec. 14 - 19  14.5   0  27  1.36  0.45  16.2  17.5
2004 Dec. 15 - 22  15.3   0  26  1.49  0.62  16.3  17.5

Period: When the angle between the view direction from the Earth to
        Phaethon and the direction of Phaeton's orbit (θ) becomes
        smaller than 5 degree.
Mag.  : Phaethon's magnitude at the minimum angle.
θ    : The minimum angle during the period.
Ph    : Phase angle at the minimum angle.
r     : Heliocentric distance at the minimum angle.
d     : Geocentric distance at the minimum angle.
TrM1  : Surface brightness of dust trail.
TrM2  : Surface brightness of dust trail, including phase angle effect.

The surface brightness of dust trail in the table is calculated assuming the dust trail looks 20 mag at 1 AU from the Sun in the direction of θ = 90 degree.

In 1984 December, no observations were reported. In 1991 December, only one observation was reported on Jan. 1. In 1994 December, 4 nights observations from 3 observatories were reported.

The dust trail became brightest in 1994 December. But there was a full moon at that time, so the condition was bad to detect the faint dust trail. The dust trail in 2004 will be as bright as in 1994. Although there is a crescent moon in 2004, the condition is better than in 1994.

The observational condition in 2004 December is as follows. The sets of the best time of observation and the altitude of Phaethon at latitude 35 degree in the Northern/Sothern Hemisphere are displayed.

Date       R.A.      Dec.    Mag.  TrM1  TrM2 Lat.35N deg Lat.35S deg
Dec. 15   2 45.35   31 46.4  15.3  18.2  19.3  21:05 (86)  21:05 (24)
     16   2 40.28   31  9.2  15.3  17.8  19.0  20:56 (86)  20:57 (24)
     17   2 35.30   30 31.1  15.3  17.2  18.4  20:47 (85)  20:57 (25)
     18   2 30.42   29 52.0  15.3  16.3  17.5  20:38 (85)  20:58 (25)
     19   2 25.65   29 12.2  15.3  16.8  18.1  20:30 (84)  20:59 (26)
     20   2 20.98   28 31.6  15.4  17.5  18.8  20:21 (83)  20:59 (26)
     21   2 16.43   27 50.5  15.4  18.0  19.3  20:13 (83)  21:00 (26)
     22   2 12.00   27  8.9  15.4  18.3  19.6  20:04 (82)  21:01 (27)


* Result of observation campaign

Many people kindly participated in the Phaethon's dust trail observation campaign from December 15 to 22 in 2004. I appreciate to all of the contributors very much.

When I called for observations of this campaign in October, I received many comments. John Bortle pointed out that there would not be any particularly strong concentration of dust particles in its immediate vicinity because it has been inactive for a considerable period of time. However, despite of the little expectation of success, Alan W. Harris, P. Clay Sherrod, and many people supported the challenge and encouraged the campaign.

It was unclear which kind of instruments are best to detect the dust trail of Phaethon. We had two dying comets in 2003. A small wide field telescopes was better to detect the faint large coma of comet Encke. However, the faint tail of comet LINEAR (C/2002 CE10) was only detectable with a 8-m Subaru telescope. Therefore, any sorts of observation tries were encouraged.

Many contributors observed Phaethon, took the images and reported the results for the campaign. Here I introduced their results.

Unfortunately, nobody succeeded to detect the dust trail of Phaethon in this campaign. The dust tube to be the source of Geminids meteor shower has not confirmed yet in the history.

o Stefano Sposetti

Stefano Sposetti took the images of Phaethon on Dec. 14, 18 and 20 using the 40cm f/4 newtonian and CCD. Here are the integrated images: 89 images of 60s integration time on Dec. 14, 130 images of 60s integration time on Dec. 18, and 120 images of 60s integration time on Dec. 20.

o Vishnu Reddy and Ron Dyvig

Although clouded out most of the campaign period from Dec. 15 to 22, they had observed it for the couple of weeks until Dec. 12 doing lightcurve work using a 26-inch F/4.8 Newtonian and Apogee 1kx1k CCD camera SITe chip at Badlands Observatory.

Vishnu Reddy commented that they did not find any signs of a tail development or the dust trail on their images of 180 seconds exposure.

o Hisao Hori

Hisao Hori observed it on Dec. 15 between 15:53 and 16:06 (UT) using 1.13-m reflector and took 5 images of two minute exposures and integrated them.

Hisao Hori commented that a very faint something like a tail may be visible towards north, but it can be highly blurs because the image was not corrected with a flat field.

o Masayuki Suzuki

Masayuki Suzuki observed it on Dec. 16 using a 0.20-m telescope and took 30 images of 60 second exposures and integrated them.

Masayuki Suzuki commented that nothing unusual was found.


o Oribe Takaaki

Oribe Takaaki observed it on Dec. 17 for about one hour from 11:20 (UT) using a 1.03-m telescope at Saji Observatory and took 30 images of 2 minute exposures and integrated 27 images among them.

Oribe Takaaki commented that nothing unusual was found.

o Isao Ootsuki

Isao Ootsuki observed it on Dec. 17.

o David Higgins

David Higgins observed it on Dec. 18 using a 0.36-m Schmidt-Cassegrain telescope and took 40 x 1 minute integrations and stacked them.

David Higgins commented that he could see no evidence of a tail.

o Pepe Manteca

Pepe Manteca observed it on Dec. 18 using a 14" f/6.3 Schmidt-Cassegrain telescope with ST9 + AO7, and commented no tail was visible.

o Sergio Foglia

Sergio Foglia observed it on Dec. 18 and 20 at 21 o'clock (UT) at Osservatorio Astronomico di Suno, Italy, and commented that no dust and tail was found.

Sergio Foglia also observed it on Dec. 19.




o Kamil Hornoch and Peter Kusnirak

Peter Kusnirak observed it at Dec. 18.785 UT using 0.65-m RL + AP7p CCD. Kamil Hornoch commented that no coma, tail nor dust trail was observed on the coadded R-band image of total exposure time of 1575-sec.

Kamil Hornoch also investigated profiles of 4 same field stars with almost same brightness as Phaethon, and commented that they are quite similar with profile of Phaethon.

Profile of Phaethon

Profile of same field star 1

Profile of same field star 2

Profile of same field star 3

Profile of same field star 4

o Claudine Rinner

Claudine Rinner observed it on Dec. 19 using a T400 F1346mm with a ST10XME and took 60x1min images and integrated them.

o Arto Oksanen

Arto Oksanen observed it on Dec. 21 from 20:08 to 21:03 (UT) using a 0.40-m Meade LX200 telescope of Nyrola observatory and took 50 one minute Rc-exposures and averaged them.

Arto Oksanen commented that no apparent coma or dust trail was visible.


* Related papers

H. Hsieh and D. Jewitt (2005). Search for Activity in (3200) Phaethon. Ap. J., 624, 1093-1096.

They observed Phaethon on 2003 December 19 using a Tektronix 2048x2048 pixel CCD and a standard Kron-Cousins R-band filter at the f/10 focus of the University of Hawaii (UH) 2.2-m telescope on Mauna Kea. However, no coma was found. No dust trail was present.

It was just one year before the Phaethon's dust trail observation campaign in 2004 December.


Copyright(C) Seiichi Yoshida (comet@aerith.net). All rights reserved.