Talk of the "International Workshop on Paolo Farinella (1953-2000): the Scientists, the man", Pisa, 14-16 June 2010

1. Objects in Encke-like orbits
G. B. Valsecchi
IASF-Roma, INAF, Roma (Italy)

2. The orbit of 2P/Encke
The orbit of 2P/Encke is unusual in several respects:
• its Q is so low that encounters with Jupiter are not possible;
• numerical integrations show that it has a high probability of
falling into the Sun (LD94).
Table: Orbital elements and related quantities for 2P/Encke.
a(AU) e i ω Ω P(yr) q(AU) Q(AU) T
2.21 0.85 12◦ 186◦ 334◦ 3.28 0.33 4.09 3.027

3. 2P/Encke and the Taurids
2P/Encke is the presumed parent body of a very large meteoroid
complex; the main meteor stream of this complex is that of the
Taurids, a populous near-ecliptical stream.
Table: Orbital elements of the Taurids.
q(AU) e i ω Ω
0.32 0.85 3◦ 299◦ 213◦
0.34 0.82 6◦ 118◦ 27◦

4. The “Taurid asteroids”
ACS93 pointed out that there are many small NEAs residing in the
Taurid complex.
Their “Taurid asteroids” are identified with a reduced version of
the D-criterion (SH63), involving only a, e and i:
2 2
a − 2.1 i − 4◦
D= + (e − 0.82)2 + 2 sin .
3 2

5. The “Taurid asteroids”
It turns out that the distribution of the longitudes of perihelion
of asteroids with D < 0.25 is significantly non-random, and that
this is mostly due to the existence of two groups whose apse lines
are approximately aligned with those of 2P/Encke and of (2212)
Hephaistos.
ACS93 suggested that this finding supports the scenario according
to which a giant comet of the Jupiter family could have ended in
an Encke-like orbit and suffered a hierarchical fragmentation in the
last 20 000 yr, the concentrations being the signature of this
process.