Dec 14th 2017
’OUMUAMUA, an object tumbling through space that was discovered on October 19th, has already made history. The speed at which it is moving relative to the sun means that it cannot be native to the solar system. Its official designation is thus 1I/2017 U1, with the “I” standing for “interstellar”—the first time this designation has ever been used.
That is exciting. Some scientists, though, entertain an even more exciting possibility: what if ’Oumuamua is not an asteroid, as most think, but an alien spacecraft? Asteroids come in all sorts of shapes and sizes, but ’Oumuamua seems particularly odd. As best as astronomers can tell, it is cigarlike, being roughly 180 metres long but only about 30 metres wide. That makes it more elongated than anything known of in the solar system. Such a shape would be a sensible choice for a spaceship, since it would minimise the scouring effect of interstellar dust.
The Economist
Spectroscopy and thermal modelling of the first interstellar object 1I/2017 U1 ‘Oumuamua
During the formation and evolution of the Solar System, significant numbers of cometary and asteroidal bodies were ejected into interstellar space. It is reasonable to expect that the same happened for planetary systems other than our own. Detection of such interstellar objects would allow us to probe the planetesimal formation processes around other stars, possibly together with the effects of long-term exposure to the interstellar medium. 1I/2017 U1 ‘Oumuamua is the first known interstellar object, discovered by the Pan-STARRS1 telescope in October 2017. The discovery epoch photometry implies a highly elongated body with radii of ~ 200 × 20 m when a comet-like geometric albedo of 0.04 is assumed. The observable interstellar object population is expected to be dominated by comet-like bodies in agreement with our spectra, yet the reported inactivity of ‘Oumuamua implies a lack of surface ice. Here, we report spectroscopic characterization of ‘Oumuamua, finding it to be variable with time but similar to organically rich surfaces found in the outer Solar System. We show that this is consistent with predictions of an insulating mantle produced by long-term cosmic ray exposure. An internal icy composition cannot therefore be ruled out by the lack of activity, even though ‘Oumuamua passed within 0.25 au of the Sun.
Nature
