(meteorobs) Upcoming Leonid returns

[Mikhail Maslov]

Hello, Jure and all,

JA> with the Meteor Winter in full strength now, I though I'd ask a few questions
JA> on the Leonids. With 8 years having passed since the parent comet's return, 
JA> the time of very strong Leonid returns and certainly storms is over. :(

JA> However, several fairly strong returns are predicted for the next 4 or 5 
JA> years. My question: how certain are these predictions, especially their peak 
JA> ZHRs?

These predictions are less certain than say predictions of 1999-2002
storms. The main problem is accuracy of 55P orbital elements for
perihelions in 15 century. If they are correct the Leonids in 2008 and
2009 can give ZHRs above hundred meteors. Say my current estimation
for 1466 trail in 2008 shows ZHR=115 with quite bright meteors (I took into
consideration activity in 2003 and 2004).
Due to the uncertainty in the comet orbital elements in future I'm going to
elaborate alternative element sets for 15-16 centuries and make
predictions with them. The doubt in these elements is based on the
computations which show that these trails (1400-1567) give good
activity not only in 2008 and 2009, but also in some past years, say
in 1907 and 1977. But we have no reports of strong activity for these
years. Alternative set of predictions can give a good comparison.
The real activity in 2008 and 2009 will allow to conclude, what
elements are more accurate.


JA>And furthermore, does any of the experts of Leonid simulations think
JA> that a very strong return, perhaps even approaching storm strength, is 
JA> possible at any time?

Principally yes for any Leonids return. Although in "usual" years even
returns with ZHR above 100 would be very exceptional, as in the past (at
least in 19-20 centuries) such cases were unknown. For any shower even
if predictions show absense of or low activity, there is always a
chance, that a cloud from very old trails encounters the Earth. The
comet 55P is on its current orbit at least for 10000 years and
computations consider only a very small part of trails ejected during
this time. But practically this chance is very small. The more old is
a trail, the more it is diffused in general.


JA>  The reason I'm asking this is that, again IIRC, one of 
JA> the trails encountered in 2003 was 15 revolutions old, yet it only made 14 
JA> (!!) revolutions around the Sun!

The reason is that this part of trail consists of particles with
quite high ejections velocities - 25-30 m/s. They are ejected in the
direction of the comet movement at a perihelion, so their orbital
periods are notably higher than the comet's one. Therefore, as the comet
made 15 revolutions, these particles had time to make only 14
revoluions.

JA> In one of the articles, by Esko I think, it 
JA> was stated that we missed a very dense part of the trail, dense enough to 
JA> cause a very significant meteor storm. (Esko, please correct me if I'm wrong)

The picture I attached to the message shows 1433, 1466 and 1499 trails
in the vicinity oh the Earth orbit around 2003 Leonid return. We can
see, that very dense trails intersected out planet orbit on September
14. On 13 November when the Earth passed closest to the node of these
trails, very dence parts of 1499 trail were a little outside the Earth
orbit. In case of closer enclounter they would produce something
stormy.

JA> Assuming that the trail didn't just stop somewhere along the way, waited for
JA> the comet to make another revolution and then proceeded, it had to have slowly 
JA> increased its lag behind the comet. Could it have, under favourable encounter 
JA> geometry, caused a meteor storm in the 'off years'?

Again principally yes, but in the Leonids case such particles with high ejection
velocities show a tendency to form compact clouds (possibly resonant)
and move away from the Earth orbit to 0.02-0.06 AU. Some of them can be
again pulled close to it, but as they are compact chances that the
Earth will pass their nodes exactly when they are there are small.
Also, nodes of such clouds are usually significantly differ from the
current comet node. Say, 1499 trail in 2003 gave activity on 13
November, whereas traditional Leonid peak was on 17 November. In past
it lowered the chances of such activity obsevation.
Here are some non-zero encounters of 1433,1466,1499 trails with the
Earth on 2003

2003
rev. Year  rd-re   ej. Vel. fM(fNP) sol.long max. Time       ZHR ex.
            AU       m/s              deg       UT
14   1499 -0,00219  26,67  -0,029   230,602 13.11.2003 11:07   1
14   1499 -0,00216  26,66   0,049   230,602 13.11.2003 11:08   2
14   1499  0,00120  26,50   0,211   230,736 13.11.2003 14:19   13
14   1499  0,00130  26,27  -0,249   230,745 13.11.2003 14:32   16
15   1466 -0,00209  26,88  -0,080   230,864 13.11.2003 17:22   3
14   1499  0,00324  24,30   0,662   231,034 13.11.2003 21:25   20
16   1433  0,00498  19,84   0,256   231,612 14.11.2003 11:12   5
16   1433  0,00437  19,64  -0,793   231,716 14.11.2003 13:41   20
16   1433  0,00414  19,58   1,037   231,734 14.11.2003 14:07   30
14   1499 -0,00573  19,07  -0,149   233,710 16.11.2003 13:12   2


JA> Off topic, the weather's been awful here for the past 6 months! I think the 
JA> number of clear nights with no moon could be counted on the fingers of both 
JA> hands...
JA> Clear skies!
JA> Jure A.

Don't forget that this year we have also predictions for Leonids
enhancemnt from 1932 trail. It is very certain.

Best regards, Mikhail