Oumuamua was less than scientists expected

In the course of the new study, new data were obtained about the first known interstellar object that flew through the solar system.

Oumumua was first recorded in October 2017 using the Pan-STARRS 1 telescope in Hawaii during a survey of near-earth asteroids. Further observations made by a multitude of ground-based telescopes and the Hubble Space Telescope showed that sunlight was reflected from the object’s surface. Large variations in the brightness of the object led to the conclusion that Oumuamua is oblong and most likely not more than 800 meters in length.

Recently, a new study appeared in the Astronomical Journal, according to which some assumptions about Oumuamua do not quite correspond to reality.

The Spitzer Space Telescope monitors asteroids and comets through infrared energy — or heat — emitted by them. It can provide more accurate information about the size of the object than optical observations or reflected sunlight. The fact that Oumuamua was too dim for the Spitzer sets certain boundaries on the total surface area.
 

Oumuamua in the artist’s view / © M. Kornmesser / ESO
 
Using three different models that provide different assumptions about the composition of the object, Spitzer limited the spherical diameter of Oumuamua to 400, 140 and 100 meters. The big difference in the results is due to hypotheses about the composition of Oumuamua, affecting how much he sees the “Spitzer” at a certain size.

“Oumuamua was full of surprises from day one, so we couldn’t wait to see what Spitzer showed,” says study lead professor David Trilling of the University of Northern Arizona. “The fact that Oumuamua is too small for Spitzero to register it is actually a valuable result.”

New size limits are in line with a recent study by astronomer Marco Micheli from ESA. According to them, small changes in the speed and direction of Oumuamua occurred as a result of degassing. In other words, the gas extracted from the surface acted as a small accelerator.