Astronomers at the Harvard-Smithsonian Center for Astrophysics estimate that the elongated shape of first interstellar asteroid known, 'Oumuamua, operates like a candle that explains its unexpected acceleration.
They speculate with a artificial origin of the object, designed for the journey of interstellar reconnaissance by an advanced civilization, but whose mission has ended and has become the "waste of a shipwreck". The study, "Could the pressure of solar radiation explain the peculiar acceleration of 'Oumuamua?", Published in arXiv, was carried out by Shmuel Bialy, postdoctoral researcher at the Institute of Theory and Computing, and Abraham Loeb, director of this center .
'Oumuamua was first seen by the Pan-STARRS-1 survey 40 days after its closest passage to the Sun (on September 9, 2017). At this point, it was about 0.25 AU from the Sun (a quarter of the distance between Earth and the Sun), and it was already coming out of the Solar System. At that time, astronomers noticed that it seemed to have a high density (indicative of a rocky and metallic composition) and that was spinning rapidly.
While it showed no signs of degassing as it passed close to our Sun (which would have indicated it was a comet), a research team was able to obtain spectra indicating that 'Oumuamua was more ice cream than previously thought. Then, when it began to leave the Solar System, the Hubble Space Telescope took some final images of 'Oumuamua that revealed some unexpected behavior.
After examining the images, another international research team discovered that 'Oumuamua had increased in speed, instead of slowing down as expected. The most likely explanation, they said, was that 'Oumuamua was discharging material from its surface due to solar heating (also known as degassing). The release of this material, which is consistent with the way a comet behaves, would give the 'Oumuamua the constant thrust it needed to achieve this speed increase.
To this, Bialy and Loeb offer a counter-explanation. If 'Oumuamua was really a comet, why did not he experience degassing when he was closer to our Sun? In addition, they cite other research that showed that if the degassing were responsible for the acceleration, it would also have caused a rapid evolution in the turn of 'Oumuamua (which was not observed).
Basically, Bialy and Loeb consider the possibility that 'Oumuamua could be, in fact, a light candle, a form of spacecraft that depends on the radiation pressure to generate propulsion, similar to what is working on Breaktrough Starshot, the project to send small ships to other systems. Similar to what is planned for Starshot, this light candle can be sent from another civilization to study our Solar System and look for signs of life. As Professor Loeb explained to Universe Today by email:
"We explain the excess acceleration of 'Oumuamua away from the Sun as a result of the force that the Sunlight exerts on its surface." For this force to explain the measured excess acceleration, the object must be extremely small, of the order of a fraction millimeter thick but tens of meters in size, this makes the object light for its surface area and allows it to act as a light sail. Its origin could be natural (in the interstellar medium or protoplanetary discs) or artificial (like a probe sent for a reconnaissance mission in the inner region of the Solar System). "
Could it survive a galactic trip?
Based on this, Bialy and Loeb calculated the probable shape, thickness, and mass-area ratio of such an artificial object. They also tried to determine if this object could survive in interstellar space, and whether or not it could withstand tensile stresses caused by rotation and tidal forces.
What they found was that a candle with 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 trip across the galaxy, although this depends largely on of the mass density of 'Oumuamua. Thick or thin, this candle could withstand collisions with dust and gas grains that impregnate the interstellar medium, as well as centrifugal and tidal forces.
As for what I would be doing extraterrestrial light sail In our Solar System, Bialy and Loeb offer some possible explanations for that. First, they suggest that the probe may actually be a defunct sail that floats under the influence of gravity and stellar radiation, similar to the debris from the wrecks of ships floating in the ocean. This would help explain why Breakthrough Listen found no evidence of radio transmissions.