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Home » Space/Science

"Assuming no non-gravitational forces..." November 29, 2017 7:29 am hank

The latest official info on our interstellar visitor. (Assuming, of course, NASA, the gummint and the MSM are not covering something up.)

http://exoplanet.eu/catalog/1i/2017_u1/

This website has an excellent summary and plenty of links to the flurry of literature on this object which has been published in just the last few weeks. Highly recommended.

Incoming direction:
RA = 18h 42m
Dec = 34d 18′

Outgoing direction:
RA = 23h 52m
Dec = 24d 48′

Perihelion: 0.25 au (9 Sep 2017)

It was one quarter of our distance from the sun, which implies it was being exposed to 16 times the solar radiation Earth receives. If it had been a comet-like object, the boiling off of volatiles and the release of dust should have provided an easily visible tail or coma. This is a solid object, rock–or metal.

I presume the above are heliocentic coordinates, although it is not made clear in the text. They would differ slightly, but not significantly, if they were Earth-centered. I have inspected these areas in a detailed star atlas and found nothing near those locations which suggests a likely point of origin or destination. OTOH, this by itself means little, at the slow speeds this object is traveling at, it has been drifting between the stars for so long that the proper motion of nearby systems has moved them substantially from our point of view.

from the E. Mamajek monograph cited in the link above: https://arxiv.org/abs/1710.11364

The initial Galactic velocity vector for the recently discovered hyperbolic asteroid 1I/’Oumuamua (A/2017 U1) is calculated for before its encounter with our solar system. The latest orbit (JPL-13) shows that ‘Oumuamua has eccentricity > 1 at 944\sigma\, significance (1.19936 +- 0.00021), i.e. clearly unbound. Assuming no non-gravitational forces, [emphasis my own--hank] the object’s inbound Galactic velocity was U, V, W = -11.457, -22.395, -7.746 (+-0.009, +-0.009, +-0.011) km/s (U towards Galactic center), with total heliocentric speed 26.32 +- 0.01 km/s. When the velocity is compared to the local stars, ‘Oumuamua can be ruled out as co-moving with any of the dozen nearest systems, i.e. it does not appear to be associated with any local exo-Oort clouds (most notably that of the Alpha Centauri triple system). ‘Oumuamua’s velocity is within 5 km/s of the median Galactic velocity of the stars in the solar neighborhood (<25 pc), and within 2 km/s of the mean velocity of the local M dwarfs. Its velocity appears to be statistically "too" typical for a body whose velocity was drawn from the Galactic velocity distribution of the local stars (i.e. less than 1 in 500 field stars in the solar neighborhood would have a velocity so close to the median UVW velocity). In the Local Standard of Rest frame (circular Galactic motion), 'Oumuamua is remarkable for showing both negligible radial (U) and vertical (W) motion, while having a slightly sub-Keplerian circular velocity (V; by ~11 km/s). These calculations strengthen the interpretation that A/2017 U1 has a distant extrasolar origin, but not among the very nearest stars. Any formation mechanism for this interstellar asteroid should account for the coincidence of 'Oumuamua's velocity being so close to the LSR.

  • I really wish we could explore it... by RL 2017-11-29 18:33:22
    • When worlds collide. by hank 2017-11-30 06:41:56
    • For those who wish to follow up on this: by ER 2017-11-29 09:17:50

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