An article published in the journal “Nature” describes a research on the interstellar asteroid 1I/2017 U1 ‘Oumuamua whose authors believe that after all it’s a comet as its discoverers initially thought. A team of researchers led by Marco Micheli from the ESA SSA-NEO Coordination Center in Frascati, Italy, used observations made with the Hubble Space Telescope and various ground-based telescopes to follow ‘Oumuamua’s trajectory finding that it was different from the one calculated taking into account the various gravitational influences. The conclusion is that there’s a cometary activity that generates an additional boost.
The discovery of the object subsequently formally classified as 1I/2017 U1 and named ‘Oumuamua raised the interest of many astronomers after the orbital calculations indicated that it arrived from interstellar space. The big problem is that it’s moving away from the Earth into a hyperbolic trajectory that’s taking him out of the solar system and now can’t be observed anymore.
The last images of ‘Oumuamua were captured by the Hubble Space Telescope in January 2018, other observations of the previous period were carried out with the Canada-France-Hawaii Telescope in Hawaii, the Gemini South Telescope and ESO’s VLT (Very Large Telescope) in Chile. At that time it was already moving away from the Sun at high speed so it became impossible to keep on following it even with such powerful instruments because it’s a small object that reflects little light.
Analyzing ‘Oumuamua’s trajectory, the researchers realized that it was not that expected but there was a slight acceleration that caused its deviation, the opposite of what they expected calculating the gravitational forces that influenced it. Various possibilities were considered such as solar wind effects such as radiation pressure or thermal effects, other interactions with the solar wind, a collision with a smaller asteroid or that it’s not a single celestial body but two asteroids bound by gravity.
Those alternatives were examined and ruled out, leaving the most likely one, which is that ‘Oumuamua is really a comet as its discoverers initially thought. In that case, it’s possible that a cometary activity with emission of dust and gas generated a new acceleration and the deviation from its trajectory discovered in this research.
The classification of ‘Oumuamua as an asteroid derives from the fact that no cometary activity was detected. However, an article published in December 2017 in the journal “Nature Astronomy” claims that, due to exposure to cosmic rays, a superficial layering of organic and insulating materials occurred on it and it may contain ice.
The release of a small amount of dust or of only gas generated by the sublimation of the ice may have been too limited to be detected. ‘Oumuamua is a small object, no more than a few hundred meters long, so limited emissions maybe coming from a small area of its surface could be impossible to detect.
The researchers made various hypotheses based on dust distribution and the relationship between dust and ice. They admit that it’s impossible to draw firm conclusions based on the observations because they provided insufficient information. ‘Oumuamua once again confirms that it’s an interesting object but unfortunately too far away to keep on studying it.