A list for asteroid and comet researcher is a Public Group with 1981 members.
 A list for asteroid and comet researcher

 Public Group,
 1981 members
Re: {MPML} 2012 NJ
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 A bunch I wouldn't say, some, maybe.
In the list of NEOs (if it turns to be a NEO), it would be the 6th
largest if I am correct, quite an unexpected (and beautiful)
discovery. The last NEO larger than this one was discovered in 1990,
so 2012 NJ is the largest NEO found in 22 years... I assume some
precovery images will be found... ?
In size it is what could be called a dinosaur killer :)
Thumbs up for Spain...!
Alain
Jaime Nomen <jnomen@...> a écrit :
> Hi:
>
> data source from:
> http://www.nasa.gov/mission_pages/WISE/news/wise20110929.html
>
> "...The new data revise their total numbers from about 1,000
> down to 981, of which 911 already have been found. None of them
> represents a threat to Earth in the next few centuries.
>
> "...It is believed that all nearEarth asteroids approximately
> 6 miles (10 kilometers) across, as big as the one thought to have
> wiped out the dinosaurs, have been found... " 2011304
>
> http://www.minorplanetcenter.net/mpec/K12/K12N19.html
>
> the today observations set this new object a little bit
> under q < 1.30...
>
> Simply watching such "evasive" orbit it seems logical there
> should still be a bunch of them out there.. right?
>
> Jaime
>
>  2012 is a sort of "pathological" NEO, more of a "comet" than an
asteroid. Several other quite longperiod objects like it have been found
over the years, sometimes called "Damocloids". It turns out that the
definition of "NEO" as anything with q < 1.3 AU is a bit unfortunate. Not
only are things with q > 1.05 or so not potential PHAs (excuse the double
terminology, but here it is correct), but also it turns out that any orbit
that crosses or nearlycrosses Jupiter, such that it can be gravitationally
scattered by Jupiter by a close encounter, cannot be "scattered" inward
closer than q < 1.1 AU, unless the relative encounter velocity with Jupiter
is great enough that a "scattering" in the opposite direction will eject it
from the solar system. What all this means is that a "Damocloid" with
perihelion less than 1.1 AU, and crossing the orbit of Jupiter, will be
quickly ejected out of the solar system in a matter of thousands to tens of
thousands of years. So it's actually not a surprise to find one or a few
large objects of this sort, as Alain Maury suggests, but it would be
extraordinary to find even one that truly crosses the Earth's orbit and has
the potential for impact. With a period of around 50 years, it's not
surprising to find a new one after so many years of surveying. And others
may exist with even longer periods.
All that being said, there are objects like this that are essentially
"comets" by orbital class, but just happen not to show any coma or other
cometary features. Looking at LP comet orbits, they have periods ranging
all the way out to a million years or so  the Oort Cloud. It is highly
likely that there are thousands of objects the size of 2012 NJ out there
with perihelia 1 AU or less, come roving in every hundred years or so, and
show no cometary activity when they do. Are these NEAs? If so, then there
are thousands of them, and we've only begun to catalog them. And of course
they won't return again any time soon, so who cares? Essentially, when we
get out past Jupitercrossing, we are dealing with an impact hazard that
resembles cometary, and it really is not relevant to talk about how many
such bodies there are, but rather the flux: how many per year (decade,
century) cross the Earth's orbit? In doing my inventories, I cut off with
orbits that cross Jupiter or beyond (of which there are currently none
known that also cross the Earth's orbit). Some of the numbers you'll find
on the JPL NEO web pages are a bit mixed between "NEAs" (asteroids only)
and "NEOs" (asteroids plus comets). Trouble is, we really can't make a
meaningful estimate of how many comets or asteroids in cometlike orbits
there might be, with orbit periods going all the way out to a million years
or so.
Coming to a bottom line, nice discovery, congratulations to La Sagra group,
but don't make much of it in terms of impact risk or how many (if any)
large PHAs might be lurking out there.
Cheers,
Alan
At 11:38 AM 7/15/2012, Jaime Nomen wrote:>Hi:
*****************************************************************************
>
>data source from:
>http://www.nasa.gov/mission_pages/WISE/news/wise20110929.html
>
>"...The new data revise their total numbers from about 1,000
>down to 981, of which 911 already have been found. None of them
>represents a threat to Earth in the next few centuries.
>
>"...It is believed that all nearEarth asteroids approximately
>6 miles (10 kilometers) across, as big as the one thought to have
>wiped out the dinosaurs, have been found... " 2011304
>
>http://www.minorplanetcenter.net/mpec/K12/K12N19.html
>
>the today observations set this new object a little bit
>under q < 1.30...
>
>Simply watching such "evasive" orbit it seems logical there
>should still be a bunch of them out there.. right?
>
>Jaime
>
>
>
>
>
>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
>Posts to this list or information found within may be freely used, with
>the stipulation that MPML and the originating author are cited as the
>source of the information.Yahoo! Groups Links
>
>
>
Alan Harris Phone: 8187908291
4603 Orange Knoll Ave.
La Cañada, CA 910113364
email: harrisaw@...
***************************************************************************** > In doing my inventories, I cut off with orbits that cross Jupiter or
In what way is Halley's comet disqualified?
> beyond (of which there are currently none known that also cross the
> Earth's orbit).
What is the Earth MOID for Halley? I recall that in 1910 there was
some panic because people felt the Earth was going to be poisoned by
cyanogen from passing through Halley's tail. I guess that means the
MOID for Halley's tail can be pretty small, but off the top of my
head, I don't know what it is for Halley itself. Being quite bright and well placed on the northern skies for many nights
high resolution observations + lightcurves + spectroscopy + ?, could help to
clearly classify/define this object as a dead comet or asteroid?... Any
difference at all ?
Jaime
Mensaje original
De: Alan W Harris [mailto:harrisaw@...]
Enviado el: Sunday, July 15, 2012 23:40
Para: Jaime Nomen; mpml@yahoogroups.com
Asunto: Re: {MPML} 2012 NJ
2012 is a sort of "pathological" NEO, more of a "comet" than an asteroid.
Several other quite longperiod objects like it have been found over the years,
sometimes called "Damocloids". It turns out that the definition of "NEO" as
anything with q < 1.3 AU is a bit unfortunate. Not only are things with q >
1.05 or so not potential PHAs (excuse the double terminology, but here it is
correct), but also it turns out that any orbit that crosses or nearlycrosses
Jupiter, such that it can be gravitationally scattered by Jupiter by a close
encounter, cannot be "scattered" inward closer than q < 1.1 AU, unless the
relative encounter velocity with Jupiter is great enough that a "scattering" in
the opposite direction will eject it from the solar system. What all this means
is that a "Damocloid" with perihelion less than 1.1 AU, and crossing the orbit
of Jupiter, will be quickly ejected out of the solar system in a matter of
thousands to tens of thousands of years. So it's actually not a surprise to
find one or a few large objects of this sort, as Alain Maury suggests, but it
would be extraordinary to find even one that truly crosses the Earth's orbit and
has the potential for impact. With a period of around 50 years, it's not
surprising to find a new one after so many years of surveying. And others may
exist with even longer periods.
All that being said, there are objects like this that are essentially "comets"
by orbital class, but just happen not to show any coma or other cometary
features. Looking at LP comet orbits, they have periods ranging all the way out
to a million years or so  the Oort Cloud. It is highly likely that there are
thousands of objects the size of 2012 NJ out there with perihelia 1 AU or less,
come roving in every hundred years or so, and show no cometary activity when
they do. Are these NEAs? If so, then there are thousands of them, and we've
only begun to catalog them. And of course they won't return again any time
soon, so who cares? Essentially, when we get out past Jupitercrossing, we are
dealing with an impact hazard that resembles cometary, and it really is not
relevant to talk about how many such bodies there are, but rather the flux: how
many per year (decade,
century) cross the Earth's orbit? In doing my inventories, I cut off with
orbits that cross Jupiter or beyond (of which there are currently none known
that also cross the Earth's orbit). Some of the numbers you'll find on the JPL
NEO web pages are a bit mixed between "NEAs" (asteroids only) and "NEOs"
(asteroids plus comets). Trouble is, we really can't make a meaningful estimate
of how many comets or asteroids in cometlike orbits there might be, with orbit
periods going all the way out to a million years or so.
Coming to a bottom line, nice discovery, congratulations to La Sagra group, but
don't make much of it in terms of impact risk or how many (if any) large PHAs
might be lurking out there.
Cheers,
Alan
At 11:38 AM 7/15/2012, Jaime Nomen wrote:>Hi:
*****************************************************************************
>
>data source from:
>http://www.nasa.gov/mission_pages/WISE/news/wise20110929.html
>
>"...The new data revise their total numbers from about 1,000 down to
>981, of which 911 already have been found. None of them represents a
>threat to Earth in the next few centuries.
>
>"...It is believed that all nearEarth asteroids approximately
>6 miles (10 kilometers) across, as big as the one thought to have wiped
>out the dinosaurs, have been found... " 2011304
>
>http://www.minorplanetcenter.net/mpec/K12/K12N19.html
>
>the today observations set this new object a little bit under q <
>1.30...
>
>Simply watching such "evasive" orbit it seems logical there should
>still be a bunch of them out there.. right?
>
>Jaime
>
>
>
>
>
>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
>Posts to this list or information found within may be freely used, with
>the stipulation that MPML and the originating author are cited as the
>source of the information.Yahoo! Groups Links
>
>
>
Alan Harris Phone: 8187908291
4603 Orange Knoll Ave.
La Cañada, CA 910113364
email: harrisaw@...
*****************************************************************************  At 05:01 PM 7/15/2012, Dave Tholen wrote:
> > In doing my inventories, I cut off with orbits that cross Jupiter or
Yes, there are any number of comets that cross both the Earth's and
> > beyond (of which there are currently none known that also cross the
> > Earth's orbit).
>
>In what way is Halley's comet disqualified?
Jupiter's orbits, but not, as far as I recall, asteroids. Part of my
little essay was to point out that once you adopt "NEO", defined to include
comets as well as asteroids, then the concept of "total population" becomes
close to meaningless, and of course there are many, almost arbitrarily
large (consider C/HaleBopp) objects that cross the Earths orbit. The
sensible question becomes "how often?" not "how many?" For me, I cut off
at Jupitercrossing; anything that crosses the orbit of Jupiter is part of
the "O" of NEO, not "A" of NEA. I'm not saying they don't exist, they just
aren't part of a meaningful number inventory.
*****************************************************************************
Alan Harris Phone: 8187908291
4603 Orange Knoll Ave.
La Cañada, CA 910113364
email: harrisaw@...
*****************************************************************************  Dave Tholen wrote:
> What is the Earth MOID for Halley? I recall that in 1910 there was
I get Earth MOID = 0.0659 AU, Jupiter MOID = 0.8116, Venus = 0.0487,
> some panic because people felt the Earth was going to be poisoned by
> cyanogen from passing through Halley's tail. I guess that means the
> MOID for Halley's tail can be pretty small, but off the top of my
> head, I don't know what it is for Halley itself.
Mars = 0.0679. Small MOIDs, but not small enough to be interesting or
terrifying. (Except, perhaps, to numerous people in 1910.)
This did remind me that after 109P/SwiftTuttle was recovered in
1992, Brian Marsden suggested that it might hit the earth in something
like 2126, so I checked the MOID of that object as well and got an
Earth MOID of 0.0009 AU for the last apparition, increasing to 0.0048 for
the 2126 apparition.
 Bill  Bill J. Gray wrote:
> I get Earth MOID = 0.0659 AU
Just wanted to note that comet Halley passes the Earth in
a distance of just 0.034 AU on April 10, 837, i.e., about
one third of the current MOID. Unless the two are actualley
met a the closest intersection distance of their orbits, the
MOID at that time might have been even smaller. (I don't have
the elements for that return of the comet here right now, so
I can't check...)
Cheers,
Herbert  Herbert Raab wrote:
> a distance of just 0.034 AU on April 10, 837, i.e., about
Sorry  about half of the current MOID, actually... :)
> one third of the current MOID.
But about 1/3 of the distance of C/1996 B2 (Hyakutake) at
it's closes approach.
Herbert  Congrats to La Sagra team for the discovery of this interesting object!!
On our blog our confirmation image and an animation of 2012 NJ:
http://bit.ly/Mcmfgn
Ciao,
Ernesto Guido, Giovanni Sostero & Nick Howes
http://remanzacco.blogspot.com
http://twitter.com/comets77  Herbert Raab wrote:
> Just wanted to note that comet Halley passes the Earth in
I can get an orbit based on observations since 1835, using
> a distance of just 0.034 AU on April 10, 837, i.e., about
> one third of the current MOID. Unless the two are actually
> met a the closest intersection distance of their orbits, the
> MOID at that time might have been even smaller. (I don't have
> the elements for that return of the comet here right now, so
> I can't check...)
astrometry available at
http://www.minorplanetcenter.net/iau/ECS/MPCATOBS/MPCATOBS.html
But with this, I get a closest approach of 0.018 AU, on 837
April 11. Presumably, I need astrometry from previous apparitions.
(And yes, nongravs are included. Without them, residuals are
horrible. Elements shown below, for what they're worth. The
MOID is probably still about right, even if the details of the
approach have gotten fuzzy when extrapolated backward that far.)
I've hunted occasionally for "older" comet astrometry (the MPC
comet data mostly starts in 1870, with a few exceptions)
without success.
JPL's SmallBody Database Browser, at
http://ssd.jpl.nasa.gov/sbdb.cgi
gives various orbits. The currentepoch one is based on JPL's
solution, which also uses 1835present data. Also provided is an
837epoch orbit from observations made from 1607 to 1759, from
the 2008 SAO Comet Catalog.
 Bill
Orbital elements:
P/1
Perihelion 837 Mar 2.470518 TT; A1=7.76e10, A2=1.64e10
Epoch 837 Apr 10.0 TT = JDT 2026871.5 Earth MOID: 0.0100 Ju: 0.9985
M 0.49227 (2000.0) Ve: 0.0785 Ma: 0.0203
n 0.01277665 Peri. 100.11344 0.54236911 0.81565100
a 18.1213781 Node 44.94877 0.83816698 0.50890469
e 0.9678618 Incl. 163.43919 0.05754866 0.27518984
P 77.14 M(N) 9.1 K 10.0 q 0.58238762 Q 35.6603687
From 8147 observations 1835 Aug. 212003 Mar. 8; mean residual 1".979.  In 1984, at the occasion of the return of Comet Halley of 1986,
I calculated the least distance between the orbit of the Earth
and that of the comet, for several apparitions of the comet. The
comet's orbital elements were taken from the work of Yeomans and
Kiang, "The longterm motion of comet Halley", Monthly Notices of
the Royal Astronomical Soc., Vol. 197, pages 633646 (1981).Here
are some of the values I found. They were published on page 91 of
the "Hemelkalender 1985" that I wrote for our Belgian, Dutchlanguage
astronomical society VVS :
Year Least distance
296 0.0124 a.u.
374 0.0069
451 0.0025
530 0.0008
607 0.0023
684 0.0048
760 0.0077
837 0.0080
912 0.0126
Important : these are the least distances between the two orbits,
*not* between the Earth and the comet!
From these values, it appears that about the year 530 the two orbits
exactly crosses, so a collision with the Earth was possible!
Jean Meeus
[Nontext portions of this message have been removed]  The persistent close MOID is why we get _two_ annual meteor showers
from Comet Halley debris, yes? So this isn't such big news, que no?
\Brian
On Mon, 20120716 at 18:08 +0200, Jean Meeus wrote:
> In 1984, at the occasion of the return of Comet Halley of 1986,
> I calculated the least distance between the orbit of the Earth
> and that of the comet, for several apparitions of the comet. The
> comet's orbital elements were taken from the work of Yeomans and
> Kiang, "The longterm motion of comet Halley", Monthly Notices of
> the Royal Astronomical Soc., Vol. 197, pages 633646 (1981).Here
> are some of the values I found. They were published on page 91 of
> the "Hemelkalender 1985" that I wrote for our Belgian, Dutchlanguage
> astronomical society VVS :
>
> Year Least distance
> 296 0.0124 a.u.
> 374 0.0069
> 451 0.0025
> 530 0.0008
> 607 0.0023
> 684 0.0048
> 760 0.0077
> 837 0.0080
> 912 0.0126
>
> Important : these are the least distances between the two orbits,
> *not* between the Earth and the comet!
> From these values, it appears that about the year 530 the two orbits
> exactly crosses, so a collision with the Earth was possible!
>
> Jean Meeus  Hi Jean,
Thanks both for the table and for the reference to the paper
of Yeomans and Kiang. My immediate thought was that they wouldn't
have data from the last (1986) apparition. However, they also
used historical Chinese observations to constrain the time of
perihelion at apparitions going back to 141... a pretty interesting
technique. So you should definitely trust their results (and your
MOIDs based on them) and ignore mine.
 Bill
Jean Meeus wrote:> In 1984, at the occasion of the return of Comet Halley of 1986,
> I calculated the least distance between the orbit of the Earth
> and that of the comet, for several apparitions of the comet. The
> comet's orbital elements were taken from the work of Yeomans and
> Kiang, "The longterm motion of comet Halley", Monthly Notices of
> the Royal Astronomical Soc., Vol. 197, pages 633646 (1981).Here
> are some of the values I found. They were published on page 91 of
> the "Hemelkalender 1985" that I wrote for our Belgian, Dutchlanguage
> astronomical society VVS :
>
> Year Least distance
> 296 0.0124 a.u.
> 374 0.0069
> 451 0.0025
> 530 0.0008
> 607 0.0023
> 684 0.0048
> 760 0.0077
> 837 0.0080
> 912 0.0126
>
> Important : these are the least distances between the two orbits,
> *not* between the Earth and the comet!
> From these values, it appears that about the year 530 the two orbits
> exactly crosses, so a collision with the Earth was possible!
>
> Jean Meeus
>  Brian Skiff wrote:
> The persistent close MOID is why we get _two_ annual meteor showers
I think the reason we get two (Eta Aquarids in May, Orionids in
> from Comet Halley debris, yes? So this isn't such big news, que no?
October) has more to do with the fact that there are two places where
the orbits come close to each other. If you look at (*)
http://www.projectpluto.com/mpec.htm
and click on "Show Orbit in OrbitViewer", you can see this pretty
clearly. Pull the slider so that you're looking from above the solar
system, set the date to May 7, and the earth will pass very close to
the orbit of Halley. Set it to October 23, and it passes near another
point on Halley's orbit... though if you move the slider back, you'll
see that it's not nearly as close as the May point.
 Bill
(*) Ignore almost everything else in the pseudoMPEC. I chopped out
about 7000 lines of astrometry and residuals just to bring it down to
a reasonable size. Also note that the applet doesn't numerically
integrate, so don't use it for other apparitions.
 Bill  I wasn't being so serious, of course, but perhaps the main point,
relative to the discussion about 2012 NJ, is that you can have a body
with "Damocloid"/Comet Halleytype motion that intersects Earth's orbit
quite often, but odds are still extremely low that you'll get hit.
Well, we plow through Comet Halley's dust twice a year (and similarly
for bunches of other comets), but the big stuff (nearly) always misses.
\Brian
On Mon, 20120716 at 14:37 0400, Bill J Gray wrote:
> Brian Skiff wrote:
> > The persistent close MOID is why we get _two_ annual meteor showers
> > from Comet Halley debris, yes? So this isn't such big news, que no?
>
> I think the reason we get two (Eta Aquarids in May, Orionids in
> October) has more to do with the fact that there are two places where
> the orbits come close to each other. If you look at (*)
>
> http://www.projectpluto.com/mpec.htm
>
> and click on "Show Orbit in OrbitViewer", you can see this pretty
> clearly.  The probability can generally be modeled by considering that a comet or a Damocloid that crosses the orbit of the earth will penetrate in two places a one AU sphere centered on the sun. Each point of penetration has a circular region around it equal to the radius of the earth. The probability that the object will strike the earth is then the ratio of the areas of these two circular regions to the entire surface area of the one AU sphere or about one in 5.4 x 10^16. Admittedly, an object like a Damocloid will tend to concentrate more towards the ecliptic and the probability will be a bit higher. However, longperiod comets tend to be more isotropically distributed and the probability will be similar to the above result. The total annual risk of a random impact is then the above number times the total number of earthcrossing longperiod comets (many millions? many unobserved during perihelion passage) times the inverse of their period. There are statistics regarding the average periods of longperiod comets but the estimates of the total population are not so well constrained.
Did I do that right or did I make a mistake somewhere? Bottom line: I don't lose sleep over the threat.
 Roy
Original Message>From: Brian Skiff <bas@...>
>Sent: Jul 16, 2012 12:08 PM
>To: Bill J Gray <pluto@...>
>Cc: MPML <mpml@yahoogroups.com>
>Subject: Re: {MPML} Halley MOID
>
> I wasn't being so serious, of course, but perhaps the main point,
>relative to the discussion about 2012 NJ, is that you can have a body
>with "Damocloid"/Comet Halleytype motion that intersects Earth's orbit
>quite often, but odds are still extremely low that you'll get hit.
>Well, we plow through Comet Halley's dust twice a year (and similarly
>for bunches of other comets), but the big stuff (nearly) always misses.
>
>
>\Brian
>
>
>On Mon, 20120716 at 14:37 0400, Bill J Gray wrote:
>> Brian Skiff wrote:
>> > The persistent close MOID is why we get _two_ annual meteor showers
>> > from Comet Halley debris, yes? So this isn't such big news, que no?
>>
>> I think the reason we get two (Eta Aquarids in May, Orionids in
>> October) has more to do with the fact that there are two places where
>> the orbits come close to each other. If you look at (*)
>>
>> http://www.projectpluto.com/mpec.htm
>>
>> and click on "Show Orbit in OrbitViewer", you can see this pretty
>> clearly.
>
>  Again over definitions of NEO Groups, according
http://neo.jpl.nasa.gov/neo/groups.html
NECs > Near Earth Comets q<1.3 AU "and" P<200 years
So a comet with a bit longer period than that, even crossing here beside
shouldn`t be included in this group (same sort of "arbitrary" number of
period of years as the minimum perihelium distance is considered)
* but at least we have a maximum P for the upper limit on this group
NEAs > Near Earth Asteroids. with q<1.3 AU
* no upper P, a, or Q limit stablished
Therefore, it seems there isn`t a well defined NEA group on the upper end
and no particular NEO group has been created for objects as 2012 NJ, apparenly
asteroidal so far and Amor type orbit..¿?, better said "cometlike orbit" with
longer P than most NEA
Splitting them in some sort of pathological" NEO list
as Alan stressed, :) limiting when they have Q > Jupiter, could clarify all
that
although the reason for that iit seems only a matter of impact probability,
which should be meaningless for these objects with longer periods, even though
what really
means short and long period?...for instance, others as the big NEO (3552) Don
Quixote seems to share a similar situation but with a significant shorter
period.
Jaime > Did I do that right or did I make a mistake somewhere?
It does seem like a very small threat. Can't say I've worried
> Bottom line: I don't lose sleep over the threat.
about it, or seen anything here to cause worry.
"...The probability that the object will strike the earth is
then the ratio of the areas of these two circular regions to the
entire surface area of the one AU sphere or about one in 5.4 x 10^16."
Seems a reasonable analysis, but that end result seems off.
With an earth radius of 6378 km and an AU of 150 million km, and
earth crosssectional area = pi * 6378^2 = 1.3e+8 km^2
oneAU radius sphere area = 4 * pi * (1.5e+8)^2 = 2.8e+17 km^2
area of _both_ earth crosssections = 2.6e+8 km^2
...I get odds of about 1.1 billion to one. Slightly worse than
this because the comet doesn't hit that sphere headon, but at an angle.
Your point remains, though: it's not much of a threat.
 Bill Oh, I am such a twit! I got distracted and did the volume of the sphere,
not the surface area. Oh, well...
 Original Message 
From: "Bill J Gray" <pluto@...>
To: "gpobs" <gpobs@...>
Cc: "Brian Skiff" <bas@...>; "MPML" <mpml@yahoogroups.com>
Sent: Monday, July 16, 2012 4:05 PM
Subject: Re: {MPML} Halley MOID
>> Did I do that right or did I make a mistake somewhere? Bottom line:
>> I don't lose sleep over the threat.
>
> It does seem like a very small threat. Can't say I've worried
> about it, or seen anything here to cause worry.
>
> "...The probability that the object will strike the earth is
> then the ratio of the areas of these two circular regions to the
> entire surface area of the one AU sphere or about one in 5.4 x 10^16."
>
> Seems a reasonable analysis, but that end result seems off.
> With an earth radius of 6378 km and an AU of 150 million km, and
>
> earth crosssectional area = pi * 6378^2 = 1.3e+8 km^2
> oneAU radius sphere area = 4 * pi * (1.5e+8)^2 = 2.8e+17 km^2
> area of _both_ earth crosssections = 2.6e+8 km^2
>
> ...I get odds of about 1.1 billion to one. Slightly worse than
> this because the comet doesn't hit that sphere headon, but at an angle.
>
> Your point remains, though: it's not much of a threat.
>
>  Bill
>  Hello all,
Just to clarify:
Very small impact probability, the vast majority of impacts are by
asteroids, but on average, much higher impact velocity therefore much
more energy, and more destruction.
Alain
Bill J Gray <pluto@...> a écrit :
>> Did I do that right or did I make a mistake somewhere?
>> Bottom line: I don't lose sleep over the threat.
>
> It does seem like a very small threat. Can't say I've worried
> about it, or seen anything here to cause worry.
>
> "...The probability that the object will strike the earth is
> then the ratio of the areas of these two circular regions to the
> entire surface area of the one AU sphere or about one in 5.4 x 10^16."
>
> Seems a reasonable analysis, but that end result seems off.
> With an earth radius of 6378 km and an AU of 150 million km, and
>
> earth crosssectional area = pi * 6378^2 = 1.3e+8 km^2
> oneAU radius sphere area = 4 * pi * (1.5e+8)^2 = 2.8e+17 km^2
> area of _both_ earth crosssections = 2.6e+8 km^2
>
> ...I get odds of about 1.1 billion to one. Slightly worse than
> this because the comet doesn't hit that sphere headon, but at an angle.
>
> Your point remains, though: it's not much of a threat.
>
>  Bill
>  Hello all,
Just to clarify:
Very small impact probability, the vast majority of impacts are by
asteroids, but on average, much higher impact velocity therefore much
more energy, and more destruction.
Alain
Bill J Gray <pluto@...> a écrit :
>> Did I do that right or did I make a mistake somewhere?
>> Bottom line: I don't lose sleep over the threat.
>
> It does seem like a very small threat. Can't say I've worried
> about it, or seen anything here to cause worry.
>
> "...The probability that the object will strike the earth is
> then the ratio of the areas of these two circular regions to the
> entire surface area of the one AU sphere or about one in 5.4 x 10^16."
>
> Seems a reasonable analysis, but that end result seems off.
> With an earth radius of 6378 km and an AU of 150 million km, and
>
> earth crosssectional area = pi * 6378^2 = 1.3e+8 km^2
> oneAU radius sphere area = 4 * pi * (1.5e+8)^2 = 2.8e+17 km^2
> area of _both_ earth crosssections = 2.6e+8 km^2
>
> ...I get odds of about 1.1 billion to one. Slightly worse than
> this because the comet doesn't hit that sphere headon, but at an angle.
>
> Your point remains, though: it's not much of a threat.
>
>  Bill
>  Hello all,
Just to clarify:
Very small impact probability, the vast majority of impacts are by
asteroids, but on average, much higher impact velocity therefore much
more energy, and more destruction.
Alain
Bill J Gray <pluto@...> a écrit :
>> Did I do that right or did I make a mistake somewhere?
>> Bottom line: I don't lose sleep over the threat.
>
> It does seem like a very small threat. Can't say I've worried
> about it, or seen anything here to cause worry.
>
> "...The probability that the object will strike the earth is
> then the ratio of the areas of these two circular regions to the
> entire surface area of the one AU sphere or about one in 5.4 x 10^16."
>
> Seems a reasonable analysis, but that end result seems off.
> With an earth radius of 6378 km and an AU of 150 million km, and
>
> earth crosssectional area = pi * 6378^2 = 1.3e+8 km^2
> oneAU radius sphere area = 4 * pi * (1.5e+8)^2 = 2.8e+17 km^2
> area of _both_ earth crosssections = 2.6e+8 km^2
>
> ...I get odds of about 1.1 billion to one. Slightly worse than
> this because the comet doesn't hit that sphere headon, but at an angle.
>
> Your point remains, though: it's not much of a threat.
>
>  Bill
>  Hello all,
Just to clarify:
Very small impact probability, the vast majority of impacts are by
asteroids, but on average, much higher impact velocity therefore much
more energy, and more destruction.
Alain
Bill J Gray <pluto@...> a écrit :
>> Did I do that right or did I make a mistake somewhere?
>> Bottom line: I don't lose sleep over the threat.
>
> It does seem like a very small threat. Can't say I've worried
> about it, or seen anything here to cause worry.
>
> "...The probability that the object will strike the earth is
> then the ratio of the areas of these two circular regions to the
> entire surface area of the one AU sphere or about one in 5.4 x 10^16."
>
> Seems a reasonable analysis, but that end result seems off.
> With an earth radius of 6378 km and an AU of 150 million km, and
>
> earth crosssectional area = pi * 6378^2 = 1.3e+8 km^2
> oneAU radius sphere area = 4 * pi * (1.5e+8)^2 = 2.8e+17 km^2
> area of _both_ earth crosssections = 2.6e+8 km^2
>
> ...I get odds of about 1.1 billion to one. Slightly worse than
> this because the comet doesn't hit that sphere headon, but at an angle.
>
> Your point remains, though: it's not much of a threat.
>
>  Bill
>  Hello all,
Just to clarify:
Very small impact probability, the vast majority of impacts are by
asteroids, but on average, much higher impact velocity therefore much
more energy, and more destruction.
Alain
Bill J Gray <pluto@...> a écrit :
>> Did I do that right or did I make a mistake somewhere?
>> Bottom line: I don't lose sleep over the threat.
>
> It does seem like a very small threat. Can't say I've worried
> about it, or seen anything here to cause worry.
>
> "...The probability that the object will strike the earth is
> then the ratio of the areas of these two circular regions to the
> entire surface area of the one AU sphere or about one in 5.4 x 10^16."
>
> Seems a reasonable analysis, but that end result seems off.
> With an earth radius of 6378 km and an AU of 150 million km, and
>
> earth crosssectional area = pi * 6378^2 = 1.3e+8 km^2
> oneAU radius sphere area = 4 * pi * (1.5e+8)^2 = 2.8e+17 km^2
> area of _both_ earth crosssections = 2.6e+8 km^2
>
> ...I get odds of about 1.1 billion to one. Slightly worse than
> this because the comet doesn't hit that sphere headon, but at an angle.
>
> Your point remains, though: it's not much of a threat.
>
>  Bill
>  Damned webmail... sorry to all.
Alain
amaury@... a écrit :
>
> Hello all,
> Just to clarify:
> Very small impact probability, the vast majority of impacts are by
> asteroids, but on average, much higher impact velocity therefore much
> more energy, and more destruction.
> Alain
>
>
> Bill J Gray <pluto@...> a écrit :
>
>>> Did I do that right or did I make a mistake somewhere?
>>> Bottom line: I don't lose sleep over the threat.
>>
>> It does seem like a very small threat. Can't say I've worried
>> about it, or seen anything here to cause worry.
>>
>> "...The probability that the object will strike the earth is
>> then the ratio of the areas of these two circular regions to the
>> entire surface area of the one AU sphere or about one in 5.4 x 10^16."
>>
>> Seems a reasonable analysis, but that end result seems off.
>> With an earth radius of 6378 km and an AU of 150 million km, and
>>
>> earth crosssectional area = pi * 6378^2 = 1.3e+8 km^2
>> oneAU radius sphere area = 4 * pi * (1.5e+8)^2 = 2.8e+17 km^2
>> area of _both_ earth crosssections = 2.6e+8 km^2
>>
>> ...I get odds of about 1.1 billion to one. Slightly worse than
>> this because the comet doesn't hit that sphere headon, but at an angle.
>>
>> Your point remains, though: it's not much of a threat.
>>
>>  Bill
>>
>
>
>  Hi all,
Now this object is designated as a comet  P/2012 NJ (La Sagra). Quite an interesting object deserves all sorts of followup observations and studies. Many congratulations to the team!
Cheers, ManTo
*******************************************************
ManTo Hui (Cantonese)
("Wentao Xu", "WenTao Hsu" in Mandarin)
+23deg09m12s, +113deg18m54s
Canton, China Mainland
Undergraduate, School of Physics, WHU (20082012)
Astrowebsite: http://comethunter.lamost.org
Blog: http://pachacoti.wordpress.com  According to Cbet 3178, 2012 NJ is now COMET P/2012 NJ (LA SAGRA):
http://www.cbat.eps.harvard.edu/iau/cbet/003100/CBET003178.txt
a 35" tail has been reported by observers using the 1.23m telescope
on Calar Alto on July 16, 17, and 18 UT.
Ciao,
Ernesto
http://remanzacco.blogspot.com
http://twitter.com/comets77  Yes, "all sorts", including rotational lightcurves and "nucleus"
spectrophotometry. These marginally active barelycomets are amenable to
the usual asteroidtype observations (as well as "comet" type observations,
if you can see enough activity to measure).
At 10:55 AM 7/18/2012, M.T. Hui wrote:>Hi all,
*****************************************************************************
>
>Now this object is designated as a comet  P/2012 NJ (La Sagra). Quite an
>interesting object deserves all sorts of followup observations and
>studies. Many congratulations to the team!
>
>
>Cheers, ManTo
>
>*******************************************************
>ManTo Hui (Cantonese)
>("Wentao Xu", "WenTao Hsu" in Mandarin)
>+23deg09m12s, +113deg18m54s
>Canton, China Mainland
>Undergraduate, School of Physics, WHU (20082012)
>Astrowebsite: http://comethunter.lamost.org
>Blog: http://pachacoti.wordpress.com
>
>
>
>
>
>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
>Posts to this list or information found within may be freely used, with
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>source of the information.Yahoo! Groups Links
>
>
>
Alan Harris Phone: 8187908291
4603 Orange Knoll Ave.
La Cañada, CA 910113364
email: harrisaw@...
*****************************************************************************
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