'Oumuamua

On Sun, 3 Dec 2017 23:27:57 -0500, Mike_Duffy
wrote:

My point re-phrased should thus have had something to do with an estimate
of the fraction of the known objects in the Solar System that have
perihelion less than 'Oomuamua.

Objects in the distant parts of the Solar System are continually being
perturbed in a way that increases the eccentricity of their orbits,
resulting in Sun-diving comets (and in some cases, asteroids) which
have perihelia well inside that of Mercury, sometimes even
intersecting the surface of the Sun.

I do understand that, for a given 'hyperbolic excess velocity', a smaller
course-change angle will be seen in objects with greater perihelion, and
thus are less likely to be observed. (Because they are further away from
our 'scopes).

Not sure what you mean by this. There is no course change with any
object orbiting the Sun, whether in a closed (elliptical) orbit or an
open (hyperbolic orbit). Whether we see these things are not is simply
a matter of chance. We can run the numbers based on different models
and conclude how many such objects exist, but we only see the ones we
see. It is virtually certain that we will soon start getting
observations that allow us to test our models, however, since there
are an increasing number of rapid survey telescopes coming on line,
meaning that essentially nothing over a certain size will escape our
observation.

I suppose it's 'suspicious' closeness to the sun really needs to be
compared to perihelia of other extra-System objects (i.e. the 'several'
estimated per year even though we have never seen any of them.) Otherwise,
I am generalizing on one unique event.

A comparison we won't be able to make until we start regularly
detecting extrasolar objects.

And as others have pointed out, what is REALLY suspicious is its shape. I
suppose we need to compare the shapes of all those 'several' other such
objects.

There's nothing "suspicious" about it. If accurate, it's simply
interesting. We know little about the shape of most small bodies in
the Solar System, and we know nothing about the history of this body.
Furthermore, the suggested shape isn't certain, it's just a conclusion
based on the varying brightness as the body rotates. That does not
produce a single solution. The proposed shape is statistically sound,
but far from certain.

On Mon, 04 Dec 2017 07:38:01 -0700, Chris L Peterson wrote:

Not sure what you mean by this. There is no course change

It was poor phrasing. What I called 'course change' is the angle between
the incoming & outgoing straight-line approximations of the hyperbola.

On Mon, 4 Dec 2017 10:41:45 -0500, Mike_Duffy
wrote:
On Mon, 04 Dec 2017 07:38:01 -0700, Chris L Peterson wrote:

Not sure what you mean by this. There is no course change

It was poor phrasing. What I called 'course change' is the angle
between
the incoming & outgoing straight-line approximations of the
hyperbola.

And that follows directly from elementary celestial mechanics,
nothing suspicious here.

On Mon, 04 Dec 2017 18:50:12 +0100, Paul Schlyter wrote:

And that follows directly from elementary celestial mechanics,
nothing suspicious here.

What is suspicious was that the course change was acute vs obtuse. In other
words, a random distribution of incoming velocities would give greater
chance of objects passing so far from the Sun that their trajectory in and
out are almost co-linear. (i.e their velocity is barely affected.)

The consenus here seems to be that such objects are, in fact, more
prevalent. We just cannot observe them unless they do pass close to the
sun.

On Mon, 4 Dec 2017 16:39:39 -0500, Mike_Duffy
wrote:

The consenus here seems to be that such objects are, in fact, more
prevalent. We just cannot observe them unless they do pass close to the
sun.

We're more likely to observe them if they're brighter, and being
closer to the Sun helps in that regard. But generally, no, it
shouldn't make any difference if they're particularly close to the
Sun. Just being in the inner part of the Solar System (roughly, inside
the orbit of Jupiter) should be all that really makes much difference.

On Mon, 4 Dec 2017 16:39:39 -0500, Mike_Duffy
wrote:
On Mon, 04 Dec 2017 18:50:12 +0100, Paul Schlyter wrote:

And that follows directly from elementary celestial mechanics,
nothing suspicious here.

What is suspicious was that the course change was acute vs obtuse.
In other
words, a random distribution of incoming velocities would give
greater
chance of objects passing so far from the Sun that their trajectory
in and
out are almost co-linear. (i.e their velocity is barely affected.)

The consenus here seems to be that such objects are, in fact, more
prevalent. We just cannot observe them unless they do pass close to
the
sun.

Sure - but there's still nothing to be suspicious about.