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Just a quick note linking to an intriguing story on spaceweather.com about the possibility that the interstellar object 'Oumuamua that zipped through the solar system last fall--the first such interstellar interloper ever detected--may have been a light sail built by an extraterrestrial civilization.
This isn't wide-eyed speculation from a tabloid, but a serious analysis by two respected researchers at the Harvard Smithsonian Center for Astrophysics, Shmuel Biali and Abraham Loeb. What caught their attention was the fact that 'Oumuamua didn't follow a purely gravitationally-driven trajectory as it careened through the solar system. Instead, it accelerated away from the sun with a force proportional to the inverse square of its distance from the sun.
That would have been understandable if the object had been a comet, accelerated by jets of gas and dust triggered by the sun's heat. However, astronomers were unable to detect traces of any comet-like activity from 'Oumuamua, which left the anomalous acceleration unexplained. To Loeb, who chairs the advisory board of the Breakthrough Starshot solar sail project, 'Oumuamua's one-over-r-squared acceleration exactly matched the way a lightweight solar sail would have acted.
Loeb and Biali went on to analyze in detail the properties of a solar sail following 'Oumuamua's trajectory. They found that it would have to be constructed of very thin material, less than a millimeter in thickness, weighing no more than a tenth of a gram per square centimeter. They also calculated the wear and tear on a sail of this description speeding through interstellar space, colliding with gas and dust as well as being stressed by its own rotation. They conclude that it could have survived a trip of at least 16,000 light years, about one-sixth of the way across our home galaxy.
(Note that there's nothing mysterious or hypothetical about a solar sail with these specifications. We humans have made, tested and deployed a variety of solar sails.)
'Oumuamua sailed out of the solar system before astronomers could perform more definitive studies, and it's not going to return. So it's nature will remain a mystery. Critics point out that that makes the hypothesis that it was an alien craft untestable, and so not scientific. However, Loeb and Biali point out, even the possibility that it was the product of an alien technological civilization warrants an active search for more such visitors.
It's a bit technical, but you can read their article here.
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This isn't wide-eyed speculation from a tabloid, but a serious analysis by two respected researchers at the Harvard Smithsonian Center for Astrophysics, Shmuel Biali and Abraham Loeb. What caught their attention was the fact that 'Oumuamua didn't follow a purely gravitationally-driven trajectory as it careened through the solar system. Instead, it accelerated away from the sun with a force proportional to the inverse square of its distance from the sun.
'Oumuamua's trajectory through the solar system
Credit: Nagualdesign/Tomruen
That would have been understandable if the object had been a comet, accelerated by jets of gas and dust triggered by the sun's heat. However, astronomers were unable to detect traces of any comet-like activity from 'Oumuamua, which left the anomalous acceleration unexplained. To Loeb, who chairs the advisory board of the Breakthrough Starshot solar sail project, 'Oumuamua's one-over-r-squared acceleration exactly matched the way a lightweight solar sail would have acted.
Artist's representation of 'Oumuamua as an elongated asteroid
(Observers estimated that it was 10 times longer than its width)
(Observers estimated that it was 10 times longer than its width)
Credit: ESO/Kornmesser
Loeb and Biali went on to analyze in detail the properties of a solar sail following 'Oumuamua's trajectory. They found that it would have to be constructed of very thin material, less than a millimeter in thickness, weighing no more than a tenth of a gram per square centimeter. They also calculated the wear and tear on a sail of this description speeding through interstellar space, colliding with gas and dust as well as being stressed by its own rotation. They conclude that it could have survived a trip of at least 16,000 light years, about one-sixth of the way across our home galaxy.
(Note that there's nothing mysterious or hypothetical about a solar sail with these specifications. We humans have made, tested and deployed a variety of solar sails.)
'Oumuamua sailed out of the solar system before astronomers could perform more definitive studies, and it's not going to return. So it's nature will remain a mystery. Critics point out that that makes the hypothesis that it was an alien craft untestable, and so not scientific. However, Loeb and Biali point out, even the possibility that it was the product of an alien technological civilization warrants an active search for more such visitors.
It's a bit technical, but you can read their article here.
-----
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