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On October 19, 2017, the Panoramic Survey Telescope and Rapid Response System-1 (Pan-STARRS-1) in Hawaii announced the first-ever detection of an interstellar asteroid, dubbed 1I / 2017 U1 (AKA & # 39; Oumuamua).
In the following months, several follow-up observations were made, allowing astronomers to gain a more accurate idea of its size and shape, while revealing the characteristics of both the comet and the insect. ;asteroid.
Interestingly enough, there has been speculation that, due to its shape, "Oumuamua could actually be an interstellar spacecraft (Breakthrough Listen even monitored it for signs of radio signals!).
A new study by two astronomers from the Harvard Smithsonian Astrophysical Center (CfA) has gone a step further, suggesting that "Oumuamua could well be a light wing of extra-terrestrial origin.
(Starshot breakthrough)
The study, titled "Could the Solar Radiation Pressure Explain the Particular Acceleration of Oumuamua?", Recently published online, was led by Shmuel Bialy and Professor Abraham Loeb. While Bialy is a postdoctoral researcher at the Institute of Theory and Computation (ITC) of the CfA, Professor Loeb is the director of ITC, science professor Frank B. Baird Jr. at l & # 's 39, Harvard University and the chief president of Breakthrough Starshot. Consultative Committee.
To recap, "Oumuamua was spotted for the first time by the Pan-STARRS-1 poll 40 days after its closest passing in the sun (September 9, 2017).
At this point, it was about 0.25 AU from the Sun (a quarter of the distance between the Earth and the Sun) and was already coming out of the solar system. At that time, astronomers noticed that it appeared to have a high density (indicating a rocky and metallic composition) and that it was spinning rapidly.
Although he showed no signs of gas-freezing when he passed near our Sun (which would have indicated that it was a comet), a research team was able to obtain spectra indicating that "Oumuamua was colder than previously thought.
Then, as he began to leave the solar system, the Hubble Space Telescope captured final images of Oumuamua that revealed unexpected behavior.
After reviewing the images, another international research team discovered that Oumuamua had increased its speed rather than slowing down as expected. According to them, the most likely explanation was that "Oumuamua evacuated materials from its surface due to solar heating (AKA degassing).
The publication of this material, consistent with the behavior of a comet, would give Oumuamua the momentum needed to achieve this speed gain.
Bialy and Loeb propose a counter-explanation. If 'Oumuamua was actually a comet, why then did not have the experience of degassing when it was closer to our Sun?
In addition, they cite further research that showed that if degassing was responsible for the acceleration, this would also have caused a rapid evolution of the spin of 'Oumuamua (which did not been observed).
Bialy and Loeb believe in principle that "Oumuamua could actually be a light sail, a form of spaceship that relies on radiation pressure to generate propulsion – similar to the one that Breakthrough Starshot works on. Similar to what is planned for Starshot, this light sail could have been sent by another civilization to study our solar system and look for signs of life. As Professor Loeb explained to Universe Today by email:
"We explain Oumuamua's excess acceleration away from the Sun, resulting in the force that sunlight exerts on its surface.That this force explains the measured excess of acceleration, the object should be extremely thin, from a fraction of millimeters thick but tens of meters in size, making the object lighter for its surface and allows it to It can be natural (in the interstellar or proto-planetary disk) or artificial (like a probe sent for a reconnaissance mission in the inner region of the solar system) ".
On this basis, Bialy and Loeb set out to calculate the shape, thickness and probable mass / area ratio that such an artificial object would have. They also tried to determine if this object would be able to survive in interstellar space and whether or not it would be able to withstand the tensile stresses caused by rotation and tidal forces.
They discovered that a sail of only a fraction of a millimeter in thickness (0.3-0.9 mm) would be enough for a sheet of solid material to survive the crossing of the entire galaxy – although this Much depends on the density of Oumuamuam (which is not well constrained).
Thick or thin, this sail would be able to withstand collisions with grains of dust and gases that enter the interstellar medium, as well as centrifugal and tidal forces.
(Wikimedia Commons / Andrzej Mirecki)
Bialy and Loeb offer some possible explanations on what an extra-terrestrial light sail would do in our solar system. First, they suggest that the probe could actually be a defunct floating sail under the effect of gravity and stellar radiation, similar to the debris of shipwrecks floating in the ocean. This would help explain why Breakthrough Listen has found no evidence of radio transmission.
Loeb then illustrated this idea in a recent article that he wrote for Scientific American, in which he suggested that "Oumuamua could be the first known case of artificial relic that has floated in our solar system since the first time." interstellar space.
In addition, he notes that light sails of similar dimensions have been designed and constructed by humans, including the Japanese-designed IKAROS project and the Starshot initiative in which he participates.
"This opportunity is a potential basis for a new frontier of space archeology, namely the study of remnants of past civilizations in space," wrote Loeb.
"The search for debris elements of artificial origin in space would provide an affirmative answer to the secular question" Are we alone? This would have a dramatic impact on our culture and add a new cosmic perspective to the meaning of human activity. "
On the other hand, as Loeb tells Universe Today, "Oumuamua could be an active element of extraterrestrial technology coming to explore our solar system, in the same way that we hope to explore Alpha Centauri with the help of Starshot and similar technologies:
"The alternative is to imagine that" Oumuamua was on a reconnaissance mission. The reason I'm considering the possibility of recognition is that the assumption that "Oumumua followed a random orbit requires the production of ~ 10 ^ {{}} objects per star in our galaxy." This abundance is a hundred times higher than that expected from the solar system, according to a calculation that we carried out in 2009. A surprisingly high glut, unless'Oumuamua is a probe probe during a reconnaissance mission and is not a member of a population d & rsquo; Random objects. "
According to Loeb, there is also the fact that the orbit of Oumuamua has brought it to 0.25 AU from the Sun, which is a good orbit to intercept the Earth without too much emit solar radiation. In addition, it was 0.15 AU from the Earth, which could have been the result of orbital corrections designed to facilitate overflight.
Alternatively, it states that it is possible that hundreds of such probes could be sent out so that one of them gets close enough to the Earth to study it. The fact that the PAN STARRS-1 investigation barely detected Oumuamua at its closest approach could indicate that many other objects of this type have not been detected, which supports the thesis according to which & # 39; Oumuamua is one of the many probes of this type.
(European Southern Observatory / M. Kornmesser)
Given that astronomers recently concluded that our solar system had probably captured thousands of interstellar objects such as' Oumuamua, this opens up the possibility of future detections that could help prove (or disprove) the case from a veil of interstellar light.
Of course, Bialy and Loeb acknowledge that there is still too much to know for sure what Oumuamua really is. And even though it was a piece of natural rock, all the other asteroids and comets previously detected had higher surface mass ratios than current estimates of 'Oumuamua'.
This, and the fact that the radiation pressure seems to be able to accelerate it, would mean that "Oumuamua represents a new class of thin interstellar materials that has never been seen before. If this is true, it opens up a whole new set of mysteries, such as how this material was produced and by what (or who).
Although our telescopes have been out of reach for almost a year now, Oumuamua will certainly remain the subject of extensive study for many years. And you can bet that astronomers will be looking for more of them! After all, "Ramans do everything in three", right?
This article was originally published by Universe Today. Read the original article.
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