In October 2017, a team of researchers using the Pan-STARRS telescope discovered the interstellar object Oumuamua. Our first interstellar visitor turned out to be very strange and unlike anything we've seen before. This stellar body resembles neither an asteroid nor a comet. Oumuamua has six features that could kickstart a new era in space science.
On October 19, 2017, a team of researchers using the Pan-STARRS telescope, during observations, discovered the interstellar object Oumuamua. The impression was that a guest from another country unexpectedly arrived for dinner. Having studied this guest, we can learn a lot about the culture of this country, and we will not even have to go there. In this case, this is very useful, because on a conventional rocket, even the nearest star can only fly in a hundred thousand years.
Surprisingly, our first interstellar visitor turned out to be very strange and unlike anything we've seen before. When we realized this, the guest had already left our house and disappeared into the darkness of the night, because of which we did not have the opportunity to look closely at its mysterious properties. Below is a list of six features that set Oumuamua apart from other properties.
1. Assuming that other planetary systems are similar to our solar system, the Pan-STARRS team should not have detected either this or any other interstellar object at all. In a paper published 10 years ago, we predicted that there are a lot of interstellar asteroids in space, which are many orders of magnitude (2-8) smaller than the size that can explain the discovery of Oumuamua, assuming that it is a member of a random population of objects. Simply put, Oumuamua indicates that there are many more interstellar objects than expected. Each star from the Milky Way must release 1,015 such objects in its lifetime to explain the existence of such a huge set, which is indicated by Oumuamua. Thus, the incubators of Oumuamua objects should be different fromwhat we know about our own solar system.
2. "Oumuamua" originates from a special coordinate system called the local standard of rest and is associated with the Sun. This standard is derived from the average of the random movements of all stars near the Sun. In this frame of reference, only one in 500 stars moves as slowly as Oumuamua. The local rest standard is ideal for camouflage, namely to hide the origin of the object and not associate it with any particular star. The movement of "Oumuamua" relative to the Sun reflects the movement of the Sun relative to the point of the local standard of rest. Oumuamua looks like a dormant buoy on the surface of the ocean, and the solar system is approaching it like a fast ship. Or maybe there are many such buoys,which serve as relay stations in the network or as signposts making up the galactic reference system in interstellar space?
3. It is believed that most interstellar asteroids detach from the parent star if they are on the outskirts of their home planetary system (like the Oort cloud in our solar system, which extends up to 100 thousand astronomical units (the average distance from the Earth to the Sun), so how they are very weakly attracted by the star. Being on the outskirts, they can fly away under the influence of a weak high-speed shock less than a kilometer per second. In this case, the asteroid will maintain the speed of its parent star relative to the local standard of rest. If Oumuamua flew from an ordinary star, then it was given an unusually strong initial acceleration.that the impulse in value should be equal and opposite to the velocity of the parent star relative to the local standard of rest, which for a typical star like the Sun is about 20 kilometers per second. Oumuamua's dynamic origins are exceptional, no matter how you look at it. This is surprising, since according to statistics, the first foreign guest who arrives for lunch should be the most ordinary (especially considering that there are more of them than usual, as mentioned in paragraph 1).than usual, as discussed in item 1).than usual, as discussed in item 1).
4. We do not have a snapshot of Oumuamua, but in the course of rotation with a frequency of eight hours, its brightness from the reflected sunlight changed 10 times. This indicates that the object is elongated, and its estimated length is 5-10 times its width. Moreover, analysis of the Oumuamua rolls indicates that this object is in the highest state of excitement that can be expected from its restless flight, if its shape resembles a pancake. Its supposed shape is more unusual than all those asteroids that have already visited our solar system, since they have a maximum length-to-width ratio of three to one.
5. The Spitzer Space Telescope did not detect any heat in the infrared radiation of Oumuamua. Taking into account the surface temperature that an object should have on its flight path near the Sun, the upper limit of its size is several hundred meters. Based on this, Oumuamua should be unusually shiny, having a reflectivity at least 10 times higher than that of the asteroids of the solar system.
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6. The trajectory of the movement "Oumuamua" deviated from the expected due to the Sun's gravity alone. This is a minor deviation (tenth of a percent), but it is extremely important for statistics. Comets behave this way when ice on their surface heats up and evaporates from sunlight, creating jet thrust. An additional push "Oumuamua" could give the release of gases, like comets, if at least a tenth of its mass evaporated. But such a large evaporation would naturally lead to the formation of a cometary tail, and scientists did not see it. Observations with the Spitzer telescope also indicate that there are few carbon molecules and dust around the object, and scientists say that there is no usual gas emission, like comets, in this case (this would be possible only if the object consisted of one water). Furthermore,the evolution of gases would create a torque, but this would not be observed. All this indicates that the object "Oumuamua" does not look like a typical comet and a typical asteroid, although it represents a population more numerous than expected.
The additional impulse of force that the Oumuamua's orbit demonstrates cannot be caused by the disintegration of the object into parts, since such an event would provide a single dynamic impulse, and scientists observed a constant impulse of force. If gassing is ruled out and the supposed excess force is real, only one possible explanation remains: the additional force impulse due to the sun's radial pressure. For such an impulse of force to be effective, Oumuamua must be less than a millimeter thick and at least 20 meters in size (to be an ideal reflector). In this case, it should look like a man-made light sail. If so, Oumuamua would be like a solar sail from the Japanese ICAROS spacecraft or a light sail for the Starshot project. If the object is of artificial origin,the astonishing possibility arises that we have found a "letter in a bottle" after years and unsuccessful searches for radio signals from extraterrestrial civilizations. Such a sail of light should survive despite collisions with interstellar atoms and dust while traveling through the galaxy.
Thinking about the possibility of artificial origin, we must keep in mind what Sherlock Holmes said: "If we exclude the impossible, what remains will be true, no matter how incredible it may seem." The Kepler Observatory has shown that about a quarter of all stars in the Milky Way have a habitable planet the size of Earth, where the surface can have liquid water and the chemical composition of life as we know it. Therefore, it is likely that interstellar space is full of artificial debris. These are either the remnants of reconnaissance vehicles or non-working equipment. But to be convinced of the exotic artificial origin of Oumuamua, we need more data. As Carl Sagan said, "Extraordinary claims require extraordinary evidence."
In fact, if Oumuamua is a space mission, that explains a lot. It is unlikely that 1,015 solar sails are launched per star to form a random population of Oumuamua-like objects. To do this, you will need to launch them at an incredible speed once every five minutes, based on the planetary system, even if all civilizations live as long as the Milky Way. The required number can be significantly reduced if objects similar to Oumuamua do not fly at random in all kinds of orbits, but move in special orbits, diving into the closest to the center and habitable parts of planetary systems, such as our solar system.
Oumuamua is flying too fast, and our rockets will no longer be able to catch up with it without the gravitational assistance of the planets. But since this object will take thousands of years to completely leave our solar system, we can take a closer look at it from a spacecraft on a flyby. But for this, in the next 10-20 years we need to develop new technologies to increase the speed of space flights. Curiously, some interstellar objects flying close to Jupiter can lose energy and are captured by the solar system. These are the guests who after dinner hit the wall with their foreheads at the exit and decided to stay. The Sun-Jupiter system acts as a fishing net. If we can identify gravitationally trapped interstellar objects by their unusually curved orbits and unusually large tilt relative to the plane of the solar system, we can fly to visit them and learn more about their nature.
We can also wait until the next interstellar guest arrives. In a few years, a wide-angle observation telescope (LSST) will be commissioned, which will be much more sensitive and will be able to detect objects similar to Oumuamua. It is hoped that he will find many such objects in the first year of his work. And if he does not find it, it will become clear to us that Oumuamua is a special object, and that we must set off in pursuit in order to find out its origin.
Exploring interstellar objects reminds me of my favorite pastime while walking with my daughters on the beach. We love collecting seashells washed ashore and finding out where they came from. From time to time we come across a plastic bottle, which is, of course, artificial. Similarly, astronomers must investigate any object that enters the solar system, studying its properties. There is no doubt that the six features of Oumuamua are capable of opening a new and revolutionary era in space science.
Abraham Loeb
