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By NASA // November 17, 2018
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In 2017, NASA's Spitzer Space Telescope discovered the object called "Oumuamua".
In November 2017, scientists directed NASA's Spitzer Space Telescope to an object called "Oumuamua – the first known interstellar object to visit our solar system. The infrared Spitzer was one of many Oumuamua-oriented telescopes in the weeks following its discovery in October. (Image of NASA)
(NASA) – In November 2017, scientists led NASA's Spitzer Space Telescope to the object called "Oumuamua – the first known interstellar object to visit our solar system. The infrared Spitzer was one of many Oumuamua-oriented telescopes in the weeks following its discovery in October.
Oumuamua was too weak for Spitzer to detect it more than two months after the closest approach to the object on Earth in early September. However, the "non-detection" imposes a new limit on the size of the strange object.
The findings are reported in a new study published today in the Astronomical Journal and co-authored by scientists at NASA's Jet Propulsion Laboratory in Pasadena, California.
The new size limit is in line with the findings of a research paper released early in the year, according to which degassing was at the origin of slight changes in speed and direction. Oumuamua during the follow-up of it last year: the authors of this article conclude that the expelled gas acts as a small propellant gently pushing the object.
This determination depended on the fact that Oumuamua was relatively smaller than typical solar system comets. (The finding that Oumuamua experienced degassing suggests that it was composed of frozen, comet-like gases.)
"Oumuamua has been full of surprises from the first day, so we can not wait to see what Spitzer could show," said David Trilling, lead author of the new study and professor of astronomy at Northern Arizona University. "The fact that Oumuamua is too small to be detected by Spitzer is actually a very valuable result."
& # 39; Oumuamua was detected for the first time by the Pan-STARRS 1 telescope of the University of Hawaii at Haleakala, Hawaii (the object name is a Hawaiian word meaning "visitor from afar , arrived first "), in October 2017, while the telescope was looking for asteroids close to the Earth. .
The scientists concluded that the vents on the surface of 'Oumuamua had to emit gas jets, which gave the object a slight speed gain, which the researchers detected by measuring the position of the object when it was passed by the Earth in 2017. (NASA Image)
Subsequent detailed observations by several NASA ground-based telescopes and the Hubble Space Telescope have detected reflected sunlight on the surface of Oumuamua. Large variations in the brightness of the object have suggested that 'Oumuamua is very elongated and probably less than half a mile (2,600 feet) in its largest dimension.
But Spitzer follows asteroids and comets using the infrared energy, or heat they emit, which can provide more specific information about the size of an object than the optical observations of light reflected from the sun.
The fact that "Oumuamua was too weak to be detected by Spitzer imposes a limit on the total area of the object. However, since the non-detection can not be used to derive a shape, the size limits are presented as what the Oumuamua diameter would be if it were spherical.
Using three distinct models that emit slightly different assumptions about the composition of the object, the "spherical diameter" of Oumuamua, undetected, allowed to limit the "spherical diameter" to 1,440 feet (440 meters), 460 feet (140 meters) or perhaps as little as 320 feet (100 meters). . The wide range of results stems from assumptions about Oumuamua's composition, which affect the visibility (or fainting) that it would seem to Spitzer of a particular size.
Small but reflective
The new study also suggests that 'Oumuamua can be up to 10 times more reflective than the comets that reside in our solar system – a surprising result, according to the authors of the paper.
Since infrared light is largely a thermal radiation produced by "hot" objects, it can be used to determine the temperature of a comet or asteroid; in turn, this can be used to determine the reflectivity of the surface of the object – what scientists call albedo. Just as a dark t-shirt exposed to the sun heats faster than a light, low-reflectivity object retains more heat than an object with high reflectivity. So, a lower temperature means a higher albedo.
The albedo of a comet can change throughout one's life. When it passes near the sun, the ice of a comet heats up and turns itself directly into gas, sweeping away dust and dirt from the surface of the comet and revealing a more reflective ice.
"Oumuamua had been traveling in interstellar space for millions of years, far from any star able to refresh its surface. But its surface may have been refreshed by such "outgassing" when it came extremely close to our Sun, just over five weeks before its discovery. In addition to removing dust and dirt, some of the released gas may have covered the surface of Oumuamua with a reflective layer of ice and snow, a phenomenon also observed in the comets of our solar system.
"Oumuamua is coming out of our solar system – almost as far from the Sun as the orbit of Saturn – and is not within reach of any existing telescope.
"Usually, if we get a weird measure of a comet, we measure it again until we understand what we're seeing," said Davide Farnocchia, of the Center for Studies in Human Factors. near-Earth objects (CNEOS) of the JPL. and a co-author on both papers. "But this one is gone forever; we probably know as much as we will ever know. "
JPL manages the Spitzer Space Telescope mission for the NASA Science Mission Directorate in Washington. The scientific operations take place at the Caltech Spitzer Science Center in Pasadena, California.
The spacecraft operations are based at Lockheed Martin Space Systems in Littleton, Colorado. The data is archived in the infrared scientific archive housed at IPAC in Caltech. Caltech manages the JPL for NASA.
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