In November 2017, a few weeks after the discovery, the NASA’s Spitzer space infrared telescope focused on Oumuamua, the first known interstellar wanderer to visit our solar system.
Two months after the closest approach to the Sun, Oumuamua was already too weak for Spitzer, and the telescope could not see it. However, this non-detection is an important result and sets new limits on the size and nature of the object.
-David Trilling, lead author of the study at the University of Northern Arizona (USA)
On October 19, 2017, the Pan-STARRS 1 telescope in Hawaii registered a faint glowing point moving across the sky. She looked like a typical asteroid. But when his orbit was calculated, it turned out that this body, without any doubt, did not form inside the Solar System, like all other asteroids or comets that were ever observed, but came from interstellar space.
Subsequent detailed observations made by several ground-based telescopes and the Hubble space telescope showed large variations in the sunlight reflected from the Oumuamua surface. Such variability in the brightness of the object suggests that it has a very elongated shape, and its large side can reach 800 meters.
Oumuamua was full of secrets from the first day he was discovered, so we really wanted to know what“ Spitzer ”could tell about him. And the fact that the interstellar wanderer was too small for a telescope is in fact a very valuable discovery.
-David Trilling
Spitzer tracks asteroids and comets, capturing the heat they emit, which provides more accurate information about the size and area of an object than optical observations of reflected sunlight. However, a telescope cannot be used to determine the exact shape of a body, and dimensions are displayed for a spherical object. Calculations showed that if Oumuamua was spherical, its diameter, depending on the composition, could reach 440, 140 or 100 meters, which is significantly less than previous estimates.
This size is consistent with the findings of a study presented in early 2018, which stated that degassing, that is, gas escaping from the surface of the “guest” under the sun’s radiation, acts as a small engine, gently nudging object.
The results of the Spitzer observations also suggest that Oumuamua reflects 10 times less light than comets living in the solar system. Since infrared radiation is largely related to thermal radiation, it can be used to determine the temperature of a comet or an asteroid. In turn, this can be used to determine the reflectivity of the surface of the object, that is, albedo.
Just as a dark T-shirt in the sunlight heats up faster than a light one, an object with low reflectivity retains more heat than an object with a high albedo.
A comet’s albedo may change throughout its life. When it passes near the Sun, “dirty” ice on the surface heats up and turns into gas, which volatilizes along with dust into space and exposes layers that are hidden but well reflect light.
Oumuamua traveled through interstellar space for millions of years, being far from any star that could“ refresh ”its surface. But when he approached the Sun, degassing took dust and dirt off him, exposing reflective layers of ice and snow. Such a phenomenon is characteristic of our native comets.
-David Trilling
Oumuamua is now far from the Sun and is not available for any existing telescopes.
Usually, if we see that a comet looks weird, we continue research until we understand its nature. But Oumuamua is gone forever, and we will not learn anything new about him.
-David Farnokkia, co-author of the study at NASA’s Jet Propulsion Laboratory
NASA unveiled new details about the mysterious asteroid Oumuamua
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