[meteorite-list] Asteroid Gets Initial Elevated Risk Rating, But Impact Unlikely (Asteroid 2004 MN4)

From: Charles Viau <cviau_at_meteoritecentral.com>
Date: Fri Dec 24 04:48:30 2004
Message-ID: <20041224094827.AE6F326555_at_ns4.beld.net>

Thanks to Ron (original article) and comments by Herbert and Sterling.

Fantastic facts, and one of the greatest reasons to be on this list.

I sure hope that our technology can get a handle on these errant missiles
before something happens that makes our collections irrelevant.

Regards,
CharlyV

-----Original Message-----
From: Sterling K. Webb [mailto:kelly_at_bhil.com]
Sent: Friday, December 24, 2004 2:19 AM
To: Meteorite List
Cc: Herbert Raab; Charles Viau
Subject: Re: [meteorite-list] Asteroid Gets Initial Elevated Risk Rating,But
Impact Unlikely (Asteroid 2004 MN4)

Hi,

    The best chance of refining the orbit of 2004 MN4 lies in a search
for sky photos of the times and places in the past when this object
should have been visible.

    In the case of the last object with a chance of hitting the Earth
in the future (in 2018), the successful search for what are called
"pre-discovery" images from years previous to its official "discovery"
refined the orbit enough to eliminate that future collision
probability.

    If such images could be found for 2004 MN4's previous approaches,
the further back the better, the orbit could be determined with much
greater precision than observations over the next six months. The
object is certainly large enough (and hence bright enough) to have
shown up in past sky plates.

    The chief difficulty in finding such images is that the object's
orbit lies mostly inside the Earth's orbit, to Sunward, where
observation is difficult if not impossible for most of the year. The
search would have to be for the periods each year after April 13, when
the object is exterior to the Earth's orbit.

    You'll recall there was a very, very close approach just earlier
this week by a very small object (16 feet) which also approached from
the Sunward (blind) side.

    Often forgot in these discussions is the fact that while the
probability of an impact is often low or negligible at any one crossing
of the Earth's orbit, in the long run, the chance of eventually
impacting with a low-inclination Earth-crossing object is virtually
100%.

    It takes the Earth approximately 432 seconds for its entire
diameter to pass a specific point on its orbital path, creating 200
chances to be impacted at a specific point every day. In the case of an
object with exactly the same inclination as the Earth which crossed the
Earth's orbit on the same day at the same point every year, a collision
would be inevitable at some point in that 73,050 year cycle (365.25
times 200).

    And objects with very low inclinations will always be perturbed,
repeatedly, into and out of a matching inclination with the Earth's
orbit. In other words, sooner or later, they're gonna get ya!

    While we are busily cataloging the easy-to-observe exterior
objects, very little is being done to discover the hard-to-observe
Sunward objects because the strategies are hard (i.e., expensive) to
implement, like photographing the western horizon just before dawn to
catch objects that have just crossed the Earth's orbit.

    Yet Aten class Earth crossers --- whose numbers are not well known
nor even well-estimated --- are vastly more dangerous than the better
cataloged Apollos and Amors, for just that reason.


Sterling K. Webb
-----------------------------------------
Herbert Raab wrote:

> Charles Viau wrote:
>
> > Are our orbital calculating capabilities really good enough to
> > project out 25 years on such a small object?
>
> Yes and no. The calculating capabilities are certainly not the
> limiting factor, but rather the limited amount of observations
> (35) on a limited number of nights (5), each with small (but
> a-priori unknown) error limits the accuarcy.
>
> A number of possible orbits for such an asteroid can be found
> that agrees with the available observations. On some of these
> orbits, the asteroid will have a close encounter with Earth in
> 2029, on others (on 1 in 300 or so) the object will collide with
> our home planet. There is no way to tell which of these orbits
> is the "true" path along which the asteroid moves, unless more
> data is collected.
>
> When additional observations are added (the object is observable
> until May 2005), the number of orbits compatible with the available
> observations will be narrowed, the uncertainty in the predicted
> position for 2029 will decrease, and in all likelyhood, the impact
> solutions will be removed.
>
> Happy holiday to all!
>
> Herbert Raab
>
> ______________________________________________
> Meteorite-list mailing list
> Meteorite-list_at_meteoritecentral.com
> http://six.pairlist.net/mailman/listinfo/meteorite-list
Received on Fri 24 Dec 2004 03:39:25 AM PST