& # 39; Oumuamua a year later

A year ago this week, astronomers discovered an unusual object moving in space not far from Earth's orbit. A few days later, they realized that he could not act either an asteroid or a comet – his ride showed that he was not gravitationally bound to the solar system. It is therefore the first interstellar body discovered in our solar system and coming from outside. He was given the Hawaiian name "Oumuamua," scout ".

Astronomers have long thought that comets and asteroids existed in other planetary systems – perhaps that Oumuamua had come from one of them. Most current models of our own solar system suggest that these small bodies are remnants of the era of planet formation, and that other planetary systems should also have produced comets and asteroids. Their study would better understand the similarities and differences in the formation of the planetary system. Until now, however, it was impossible: the large presumed populations of comets and asteroids found in exoplanetary circumstellar disks are remote and their individual members are weak and spatially unresolved.

"Oumuamua could therefore be a rare scientific resource, and it became the subject of an intense, though brief, observation campaign because it was so fast that it became too distant and too weak to be detected. Nevertheless, the completed observations revealed that it was reddish in color with no apparent spectral characteristics and no sign of gas or dust. All this suggests that it could be a primitive asteroid ("type D"), although in fact, no analog analogues are known in our solar system. The most remarkable of all, by rotating its variable light curve, revealed a very elongated shape: six times longer than wide.

The Spitzer Space Telescope's IRAC camera is currently about 155 million kilometers from the Earth and has a very different viewing angle than Oumuamua compared to terrestrial telescopes. CfA astronomers Joe Hora, Howard Smith and Giovanni Fazio, along with their long team of scientists from Near Earth Object and other colleagues, told the IRAC where predictions place Oumuamua. (because it is not related to the solar system). and moves so fast, the trajectory of Oumuamua in the sky was relatively difficult to calculate).

After 30 hours of observation, which is relatively long, the object was not detected and subsequent orbital analyzes confirmed that the camera was correctly directed towards him. The limit of its emission was however so low that it allowed the team to limit some of its physical properties. The absence of infrared signal, for example, suggests that there is no gas or dust, a species that could be expected if it is safe. acted of a cometary type body. Scientists have also calculated that, based on its exact composition and reflectivity, Oumuamua measures at least 240 meters (and perhaps even a kilometer) in its largest dimension (for Star Trek aficionados, some fans believe that the length of the Enterprise is 725 meters). The object has now gone too far for one of our telescopes to see it. Thus, even if it will remain an interstellar mystery, it reminds us once again that our cosmic neighborhood is full of surprises.

Explore further:
& # 39; Oumuamua probably came from a binary star system

More information:
Spitzer Observations of Interstellar Object 1I / Oumuamua, Astrophysical Journal (in press) 2018