The 1I/2017 U1 is sub-kilometre in size, with a slightly reddish colour (which has been reported previously, and is less red than is typical for outer solar system objects) and rotates in about 8.26 hr. So far, so unspectacular. But what is remarkable is that the brightness varies by 2.0 ± 0.2 magnitudes, which translates to a shape 6 times as long as it is wide (~35m x 230) if it's brightness does not change across it's surface. This is most remarkable but not quite unprecedented. Asteroid 4116 Elachi has a 1.6 magnitude brightness variation over a 38 hr period for an implied shape 4.3 times as long as it is wide.
To hold together under it's own gravity, a body this size and shape but with no strength would need a density of 5 times that of water (ice in interstellar space). This implies that the body has significant cohesion strength and is not a "rubble pile".
If the surface reflectance (albedo) does vary across the surface, the shape may not be as extreme as the 6:1 brightness ratio suggests, but there is not enough colour data available to adequately assess this question.
With only one example known at this time it is not known if this is typical of interstellar bodies, or unusual. However this single detection implies around 10000 such bodies in the "inner" solar system (within the orbit of Neptune), staying here for around 10 years each, and with future telescope plans, around one such discovery a year in the foreseeable future.
Some aspects of this body are unremarkable (it much resembles Jupiter's "Trojan" asteroids, which probably got to their current orbits by violent scattering in the early development of the Solar System. This is certainly not inconsistent with the object having been scattered out of it's origin system. But that shape is unusual among the Solar System's minor planets and detritus.
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