On 10/27/2017 11:24 PM, Sam Deen wrote:

......

At any rate, I'm confident that within the month we'll be able to find

the progenitor star: ...

On 10/28/2017 4:19 PM, Al Harris wrote:

Well, no, I'd say the odds are less than the proverbial snowball's

chance in hell. U1's velocity approaching the sun was 26 km/sec, and

will be essentially unchanged leaving. 26 km/sec is about .0001 the

speed of light, so the object goes about one light year in 10,000 years,

a hundred light years in a million years, and a hundred thousand light

years in a billion years,

The limited sample of the motion will also work against back-tracking

origination at some level. There is currently only tracking data after

the September 9th 0.254 au perihelion.

In 3000 BC, the formal (i.e., optimistic) heliocentric uncertainties

of the current orbit solution (JPL #4) are +/- 1.7439 degrees in RA and

+/- 0.9676 degrees in DEC (3-sigma), around Galactic System II longitude

and latitude (63.3059, 16.7968) degrees.

In terms of absolute location uncertainty, ICRF cartesian 1-sigma

position vector uncertainties for A/2017 U1 in 3000 BC are:

X +/- 227.793 au,

Y +/- 317.755 au,

Z +/- 3.728 au

Growth in ICRF position 1-sigma uncertainties will have a RATE of:

delta_x = +0.0462 au/yr,

delta_y = +0.0644 au/yr,

delta_z = +0.0007 au/yr

So A/2017 U1's position uncertainty is growing at a rate of about

1 light year per 800,000 years.

The velocity 1-sigma ICRF uncertainties in 3000 BC:

V_x +/- 215 m/s,

V_y +/- 300 m/s,

V_z +/- 0.003 m/s

Uncertainties can narrow a little if additional astrometry is obtained

over the remaining days of detectability, but the most useful for improved

back-tracking would have been data prior to perihelion.

Then there is the issue of matching the growing volume of space where

A/2017 U1 could have been against the historical 3-D motion of stars through

the galaxy over great spans of time.

But if a possible solution is only a couple hundred light years or less

out, and not much else is around, maybe a case could be made.

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Jon Giorgini | Navigation & Mission Design Section

Senior Analyst | Solar System Dynamics Group

Jon.Giorgini@jpl.nasa.gov | Jet Propulsion Laboratory

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