Advances in Space Research 40 (2007) 215–219
www.elsevier.com/locate/asr

Creating an artificial Geminid meteor shower: Correlation
between ejecta velocity and observability
T. Kasuga a,b,*, M. Sato b, J. Watanabe bbaInstitute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822-1897, USA
National Astronomical Observatory of Japan (NAOJ), National Institutes of Natural Sciences (NINS), 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan

Received 31 October 2006; received in revised form 29 March 2007; accepted 6 April 2007

Abstract
One of the interesting arguments for a space impact mission to asteroid 3200 Phaethon is to create an artificial Geminid meteor
shower. In this work we investigate the artificial shower’s dates of observability and dependence on ejecta velocity using dust trail theory.
We find that when the dust ejecta velocities are 200 m/s the artificial meteor showers start to be visible in 2204 and continue for about 30
years. If the dust ejecta velocity is 20 m/s they only last 10 years from 2215 to 2225. Thus, the onset of artificial shower activity begins
sooner and lasts longer with higher ejecta velocities. To produce an artificial meteor shower with 3200 Phaethon as the parent will require
higher impact energy than the Deep Impact spacecraft delivered to 9P/Tempel 1.
! 2007 COSPAR. Published by Elsevier Ltd. All rights reserved.
Keywords: Artificial meteor shower; Deep Impact

1. Introduction
Ground-based observations suggest that the surfaces ofprimitive objects such as comets, asteroids, and dormant
comets have probably been modified physically and compositionally by solar heating and/or space weathering(e.g. Jewitt, 2004). However, their interiors have probably
been unaffected by these processes. Therefore, Belton andA’Hearn (1999) proposed a scientific mission to explore
the sub-surface region using excavation in a hypervelocity
impact. The existence of relatively pristine materials is
expected at depths of about 20 m.
The Deep Impact (DI) mission revealed differences
between the surface and interior comet 9P/Tempel 1(A’Hearn et al., 2005). The DI collision excavated relatively unprocessed cometary material from tens of meters
below the comet’s surface. A world-wide observational*
Corresponding author. Address: National Astronomical Observatoryof Japan (NAOJ), National Institutes of Natural Sciences (NINS), 2-21-1
Osawa, Mitaka, Tokyo 181-8588, Japan.
E-mail address: kasugats@ifa.hawaii.edu (T. Kasuga).

campaign using ground and space-based telescopes (Meech
et al., 2005) monitored the comet before and after the
impact. Sugita et al. (2005) carried out mid-IR spectroscopic observations and derived a crystalline-to-amorphous ratio of silicates for the ejected dust. The ratio issimilar to those of Oort-cloud comets (e.g. Hale-Bopp)and suggest that Jupiter-family comets and Oort-cloudcomets have a similar origin.
Kasuga et al. (2006b) proposed the DI concept for aspace mission to a meteor shower parent body. The target is asteroid 3200 Phaethon which has been recognized
as the parent of the Geminid meteor stream and it has
been suggested that the asteroid is actually a dormant
comet. On the basis of dust trail theory (e.g. McNaught
and Asher, 2002) a DI-like collision on 3200 Phaethon
will be able to cause an artificial meteor shower a couple
hundreds years after the impact event if we took ejecta
velocities of 20 m/s, which are almost consistent withthe orbital evolution of that parent. The onset of activity
for the artificial meteor shower will depend on thevelocity of ejected dust.

0273-1177/$30 ! 2007 COSPAR. Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.asr.2007.04.026

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T. Kasuga et al. / Advances in Space Research 40 (2007) 215–219

Table 1
Derived ejecta velocities due to the DI Impactor’s collision with 9P/Tempel 1 as determined from ground-based telescopes
Observation

Ejecta velocity (m/s)

Reference

Optical (mid-IR)
Optical (orange filter 648 ± 43 nm)
Optical (orange filter 648 ± 43 nm)
Spectroscopy (mid-IR)
Optical (VR–BV filters)
Polarimetry"200 ± 20>160
110–300
125 ± 10230
158–270

Meech et al. (2005)
Keller et al. (2005)
Küppers et al. (2005)
Sugita et al. (2005)
Schleicher et al. (2006)
Furusho et al. (submitted for publication)

In this paper we model a DI-like collision on 3200 Phaethon on 2022 April 12. The selected impact date was chosen because the object passes through the ecliptic plane on
the Earth side and a new mission program can be carriedout in Japan (Kasuga et al., 2006b) after 2020. We use
the derived ejected velocities of dust plume during DI
impact on 9P/Tempel 1 from ground-based observations
in our simulations. We calculate the distributions of a tubeof the dust trail for artificial meteor showers activated in
the impact and discuss the observable duration of artificial
meteor shower.

A’Hearn et al. (2005) reported the fastest ejecta velocity of "5 km/s immediately after the impact flash using
the in situ flyby camera on the DI spacecraft. That material was accompanied by a gas-driven expansion so thevelocity value deduced by A’Hearn is appropriate toactive comets in the production of artificial meteor
showers.

2. Simulation of the artificial meteor shower
Table 1 compiles several observational methods using
ground-based telescopes during the DI collision on
9P/Tempel 1 along with derived velocities of the ejected
dust plume (Meech et al., 2005; Keller et al., 2005; Küppers
et al., 2005; Sugita et al., 2005; Schleicher et al., 2006;
Furusho et al., submitted for publication). They wereobtained 6–23 h later or throughout the impact time on
UT 4 July 2005. The derived velocities of ejected dust range
from about 100 to 300 m/s.
We simulated the evolution of a tube of the dust trail
associated with a DI-like collision on 3200 Phaethon using
the most simple dust trail theory (Sato, 2003). Radiationpressure can be neglected because Kasuga et al. (2006a)
clarified that meteoroids in showers are large and compact:
blackbody-like particles rather than sub-micron and fluff
balls (Kimura et al., 2002). The meteoroids must be large
because of their small b values1 of 10!5 to 10!3, which
are obtained from observations of cometary dust trails(Ishiguro et al., 2002, 2003).
We selected the impact day on 3200 Phaethon as 2022
April 12 and assume that the ejected dust particles aremoderately large and compact. We assumed the ejecta
velocity to be 200 m/s – almost averaged value from Table
1 and it would have stable dust ejecta with the negligible
gas ejection force. The 200 m/s ejection velocity used in
the simulation is roughly at the upper limit for micron sized
dust particles because the DI results for 9P/Tempel 1 wereobtained with optical to mid-IR telescopes (e.g. Meech
et al., 2005). We expect that larger dust particles will haveslower ejection velocities.

1b – the ratio of solar radiation pressure to solar gravity.

2.1. Results: fast ejecta velocity of 200 m/s
Details of the simulation process are described in Sato
(2003) and Kasuga et al. (2006b). In general, we consider
the short term evolution of Phaethon’s orbital elements(for about hundred years). Then we determine the distribution of a tube of the dust trail formed at the collisionepoch using test meteoroids ejected in the direction of
Phaethon’s motion (which we define as positive ejection
velocities) and in the opposite direction (negative ejection
velocities). The orbital evolution of Phaethon and thetest meteoroids are roughly constant because their orbits
are far from Jupiter.
Fig. 1 shows the evolution of a tube of the dust trail
after the impact event on 2022 April 12 where the ejecta
velocities ranged from !200 to +200 m/s. The artificial
meteor shower would be observable on the Earth for about
30 years from about 2204 to 2236. The earliest showers arethose caused by dust trails formed of mainly +200 m/sejecta while for the latest showers the !200 m/s ejecta willbe the main source. Phaethon itself crosses the Earth’s
orbit around 2224.
Prior to 2202 the trails are more than 0.002 AU from the
Earth’s orbit – too far to produce active meteor showers.
High activity meteor showers are expected in 2203, 2206,
2207, 2209 and from 2211 to 2236 because in these years
the trails approach to within 0.001 AU of the Earth. After
2237 the artificial meteor shower activity will tail off
because of the increasing distance of the trails from the
Earth’s orbit.
2.2. Results: slow ejecta velocity of 20 m/s
Fig. 2 shows the evolution of a tube of the dust trail after
the simulated impact event on 2022 April 12 (Kasuga et al.,2006b) when the ejecta velocity is an order of magnitude lessthan that studied in the previous section. Generally, trails’
evolution are associated with the parent moving. Therefore,

T. Kasuga et al. / Advances in Space Research 40 (2007) 215–219

217

Fig. 1. Evolution of a tube of the dust trail after the impact event on 2022 April 12. ‘+200’ (or ‘!200’) is the ejection velocity (m/s) at impact. Artificial
meteor showers would be seen between 2204 and 2236.

Fig. 2. Distribution of a tube of the dust trail after the simulated impact event on 2022 April 12. ‘+20’ s(or ‘!20’) is the ejection velocity (m/s) at impact.
Meteor showers would be seen between 2215 and 2225.

ejecta velocities of meteoroids are applied to be ±20 m/s inFig. 2. In this case, artificial meteor showers will occur overthe 10 years from 2215 to 2225.
Prior to 2214 the trails are more than 0.002 AU from
Earth’s orbit. In 2218, 2219, 2222 and 2223, the trails

approach within 0.001 AU of the Earth which implies
particularly active meteor showers. After 2224 meteor
shower activity will decrease due to the increasing distance of the trail from the Earth’s orbit (above
0.002 AU).

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T. Kasuga et al. / Advances in Space Research 40 (2007) 215–219

3. Discussion
We investigated the production of artificial meteor
shower and their dependence on the ejecta velocity at the
impact for simulated impacts on 3200 Phaethon on 2022
April 12. If the ejecta velocities are of 200 m/s artificial
meteor showers begin in 2204 and continue for about 30
years. If the ejecta velocities are only 20 m/s the artificial
meteor showers last for only 10 years from 2215 to 2225.
We conclude that the active period for artificial meteor
shower tends to be sooner and last longer as the ejecta
velocity gets faster.
If dust trails are to be the source of artificial meteor
showers the size of ejected meteoroids needs to be larger
than about a micron. During the DI collision on 9P/Tempel 1, micron sized dust particles were ejected and theirreleased speed was relatively high (ranging from 100 to
300 m/s). Artificial activity triggered by the DI collision
on 9P/Tempel 1 was small and did not last longer than normal activity level (Küppers et al., 2005).
Belton and A’Hearn (1999) suggested that the velocity
and mass of an impactor should be above 33 km/s and500 kg in order to penetrate the mantle of 3200 Phaethon
and activate it like comet. To create a 33 km/s impact on
3200 Phaethon it is advantageous to select impact dates
when 3200 Phaethon passes through the ecliptic planeon the Earth side for delivering substantial science payload with limited fuels. The DI collision on 9P/Tempel
1 would be expected to eject faster and larger meteoroids
if the impactor had higher speed and mass (10 km/s and
370 kg, respectively) (A’Hearn et al., 2005). The production of an artificial meteor shower will require higher
impact energy than that of DI on 9P/Tempel 1 (19GJ) to artificially activate the target and produce higher
speed ejecta and larger size meteoroids. In the future wewill constrain the impact energy which relates the meteor
shower activity rate and the period of artificially derived
meteor showers.
Artificial Geminid meteors may be due to either evolvedor fresh meteoroids liberated from surface or interior,respectively of 3200 Phaethon. Its surface appears to be
rocky with an asteroidal, not comet-like, appearance(Green et al., 1985; Birkett et al., 1987) but it seems to havethe evidence of once-cometary activity (Gustafson, 1989).
Due to its small perihelion distance (q " 0.14 AU) thermal
alteration of its surface is likely.
Kasuga et al. (2006a) investigated the thermal desorption of Na in meteoroids and its dependence on perihelion distance of meteor showers. Na is a relatively
volatile and abundant element in meteoroids in meteor
showers. Thus, Na is a good indicator for the effect ofsolar heating on meteoroids. Spectroscopic studies ofGeminid meteors confirm a diversity of Na abundance,from extreme Na depletion to almost the solar abundance (e.g. Kasuga et al., 2005; Trigo-Rodrı̀guez et al.,2003). The wide range of Na abundance in Geminid
meteors may be due to their history and position on

the parent body before the meteoroids were ejected.
Thermal desorption of Na in Geminid meteoroids while
they are independently undergoing orbital evolution ininterplanetary space is difficult because the temperatureof meteoroids at q " 0.14 AU is lower than the sublimation temperature of alkali silicates ("900 K) (Kasuga
et al., 2006a). Therefore, the diversity of Na abundancesin Geminid meteors can only originate in the thermal
evolution of 3200 Phaethon itself.
A DI-like collision on 3200 Phaethon would reveal thenature of dormant comets from both below and on the surface. Among other useful scientific studies, We may be able
to better understand the puzzling variety of Na abundancesin Geminid meteors.
Acknowledgements
T.Kasuga thanks Dr. Robert Jedicke (IfA, UH) and the
JSPS Research Fellowships for young scientists.
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