Recently, a paper published in the important journal in the field of astrophys. J, has triggered great attention from media in various countries. The author of the article, two scientists from the Harvard-Smithsonian Center for Astrophysics, in the United States, speculated that the " Oumuamu " that humans first observed last year may be a light sailing spacecraft of an alien civilization.
Figure | Figure 1 Aomumo's imagination map (Picture source: NASA/ESA/STScI)
Mysterious celestial body
A full year ago, humans observed a mysterious small celestial body in the solar system. At first it was considered an comet , so it was named C/2017 U1, where the letter "C" stands for "comet". Then, scientists discovered that the guy didn't have a hive - a cloud-like object surrounding the comet nucleus, so it was renamed A/2017 U1, and "A" stands for "asteroid". Comets and asteroids are common celestial bodies in the solar system, so this astronomical discovery will not attract much attention.
However, soon as the astronomers discovered that this guy didn't seem that simple. Comets and asteroids from the solar system have limited speeds when they orbit the sun. However, the newly discovered celestial body has an angular velocity far exceeding that of comets and asteroids, which means that the sun's gravity cannot bind it at all...
Combining other factors, scientists realize that this newly discovered mysterious star was not born in the solar system, but a traveler from outside the solar system!
Figure | Figure 2 The trajectory of Aomumo. The solar system is just a stop on its long journey. (Image source: EarthSky)
Therefore, it became the first celestial body numbered with "I (interstellar object)": 1I/2017 U1. And its name, "Oumuamua", comes from Hawaiian, meaning "scout" (from other galaxies).
This undoubtedly aroused great curiosity among scientists. Who is this first star body observed in the solar system from outside the system? Where did you come from? What are you doing?
- Who is it?
I don’t know... I only know that the shape of Oumuamu is likely to be similar to a cigar, and the size may be about 180~200m × 30m × 30m × 30m.
Figure | Figure 3 May be like an Oumamu. (Image source: ESO/M.Kornmesser)
- Where does it come from?
Sorry, we don’t know this either. And, most likely, never know.
- What is it doing?
At present, we only know that it is possible that it is following a hyperbolic orbit, flying while flipping like a popped up cigarette, leaving the solar system.
Figure | Figure 4 Possible trajectory of Oumuamu (Picture source: Wikipedia)
However, with in-depth research on its running track, scientists discovered another magical thing about Oumuamu - its trajectory seems a bit strange!
The orbits it observes have a deviation that cannot be ignored from the orbits calculated using gravity. The following figure is an example. If it is only affected by gravity, its orbit should be shown as the red line in the figure. However, what is actually observed is the position shown by the blue line. This 40,000-kilometer deviation casts another veil of mystery on Oumuamu.
Figure | Figure 5 In addition to gravity, Aomumo is also affected by other forces (Picture source: NASA JPL)
This means that the magical Aomumo is not only born into a mystery, but its movement method is also a mystery: in addition to gravity, Aomumo also has an additional driving force. What is the extra motivation for
? There were many different opinions in the scientific community.Is it the reaction force generated by the gas emitted by itself like a comet? But it is not a comet, it does not have the Huifa Comet Tail! Until last week, Avi Loeb, chair of the Department of Astronomy at Harvard University and professors Avi Loeb, and his postdoctoral fellow Shmuel Bialy, gave an amazing explanation:
, this Oumuamu may not be an ordinary celestial body in the shape of a cigar, but an alien light sail spacecraft propelled by light pressure!
Figure | Figure 6 Imagination of light sail spacecraft (Picture source: Wikipedia)
Alien light sail spacecraft?
The so-called light sail spacecraft refers to a spacecraft that uses the light pressure generated by solar radiation to propel.
Yes, light will also produce pressure. Just as gas molecules hit the surface of an object, it will generate air pressure. Photons irradiate the surface of an object, and will also transmit their momentum to the irradiated object. So why, when basking in the sun, can’t we feel any pressure from the sun? This is because, in most cases, the light pressure is very small. For example, the light pressure generated by the sunlight that reaches the earth is less than one billionth of the earth's atmospheric pressure. Therefore, as long as there is an atmosphere, the light pressure can be ignored.
However, in the universe, light pressure is a force that cannot be ignored. In fact, for many celestial bodies, in addition to gravity, light pressure is the only force they can feel in the universe. Where strong light is exposed, the light pressure can even reach the same order of magnitude as gravity. The "long tail" dragged by the comet always points in the direction away from the sun because it is subject to light pressure generated by the sun's light.
Therefore, using light pressure to provide propulsion power for the spacecraft has become a feasible solution. Since the light pressure is very small, we can increase the area that can receive light and retain the light mass of the spacecraft. In theory, light pressure can push the spacecraft forward: just like the sail on a sailboat, as long as the sail is large enough, no matter how small the wind is, it can sail far away. Therefore, as long as the sail is large enough, the light sailing spacecraft can power interstellar navigation.
However, the sail must be very large and very thin to allow the spacecraft to obtain enough light pressure thrust under the premise of being light enough; and the mechanical structure supporting the light sail must also be strong to withstand the long-distance test of interstellar travel . Humans have successfully launched two light sail spacecraft, although both are only in the kilogram level.
Figure | Figure 7 The IKROS light sail spacecraft of Japan Space Agency has flew over Venus in 2010 and is flying deeper into the solar system. (Picture source: Andrzej Mirecki) This paper by
Shmuel Bialy and Avi Loeb is based on this idea. Could the extra force of Aomumo be light pressure?
After rigorous calculations, they found that Aomumo's mysterious thrust can be explained by light pressure. If its "mass-area ratio" can reach a range of about 0.1 grams per square centimeter and a thickness of between 0.3-0.9 mm, it can obtain enough light pressure, and can also withstand the impact of interstellar dust, gases, and the impact of tidal and centrifugal forces on it, maintain sufficient momentum, and complete the real-life interstellar crossing.
However, 0.3-0.9 mm is too thin. They couldn't help asking, what exactly can have such a small mass-area ratio and such a thin thickness? The mass-area ratio of asteroids and comets is much larger than 0.1. If Aomumo's magical orbit is indeed a result of light pressure, then it is very likely that it is not a naturally formed "ultra-thin celestial body", but an artificially manufactured spacecraft!
So, they wrote a sentence in their paper that was repeatedly quoted by various media:
Aumuamu may be a probe designed to send to the earth by alien civilizations. How to prove
?
This paper stirs up a thousand waves in one stone. Many people began to ask questions, what about the evidence with such a bold speculation?
After all, although there is no conclusion on the magical thrust of Aumuamu for the time being, there are still other possible explanations. For example, it may be a fragment of a planet in its galaxy after a star explodes.Although this guess is not as fascinating as the Light Sailing Spaceship, it is also very reasonable!
So, what exactly is Aomumo? We may never know the answer to
from Aomumo. Shmuel Bialy and Avi Loeb wrote in the paper that it is too late to send chemical-enabled rockets to chase after them. Oumuamu was suddenly discovered without any preparation, and our effective observations were only a few weeks, and Hurricane Maria gave way to the Arecibo Observatory in Puerto Rico for a period of time.
Figure | Figure 8 Aomumo has gone far away. (Picture source: NASAJPL/Caltech)
The secret about Aomumo can only be hoped in the future. We can discover something similar to Aomumo and explore its origin and nature. Although Aumuamu is the first interstellar celestial body named by humans, it is definitely not the first foreigner to visit the solar system, nor is it the last one.
No matter whether Oumuamu is an alien spacecraft or not, this is a magical celestial body that has been recorded in the history of mankind and will be repeatedly mentioned in the future. Our fantasy about him actually comes from our expectations: we want to build more advanced interstellar spacecraft that can send hundreds of tons, not thousands of grams, into outer space. For humans, the moon and Mars are just the first and second steps for us to explore the universe.
One day, the angle of human beings looking at the vast stars will no longer be looking up from afar.
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