The Martians arrived already? Spoiler alert: no

The Martians arrived already? Spoiler alert: no

The Martians arrived already? Spoiler alert: no







				

The Martians arrived already? World turmoil caused the study available this week in arXiv.org about how the object Oumuamua could - hypothetically - be a ship sent by a civilization scientifically more advanced than humanity. The press in various countries began to elucubrate with the news and panic broke out. This astrobitos will try to clarify the doubts and help to understand the reasoning of the authors.

Let's start with the observations: as our knowledge advances, so do our needs. We started 400 years ago looking with small telescopes and today they are building telescopes with 24.5m diameter. Within this spectrum, there are projects that are constantly monitoring the sky. In particular, using images from the PAN-STARRS1 project, the group of K. J. Meech discovered in October 2017 an asteroid that they called Oumuamua.

Figure 1: Discovery of Oumuamua, figure 1 of the article. Panel (a) shows the trace left by the asteroid in the image in which it was discovered and panel (b) shows an observation focused on the asteroid, which is also following its trajectory.

This body is particular for different reasons that we will attack one by one.

Analyzing the way in which the body reflects light as a function of time (the light curve from figure 2), it was discovered that Oumuamua rotates extremely fast. This implies that the asteroid has a very exotic shape and is described as pancake-like - yes, a pancake.

A key factor that helped determine the extrasolar origin of Oumuamua was its speed and acceleration. This is because the bodies gravitationally linked to the Sun move in orbits caused by our sun king (the Sun). Since the times of Kepler (About 1610) humanity has been able to explain, reproduce and even predict the position of objects that orbit the Sun. This is where the problem lies: Oumuamua does not move at the speeds that the theory predicts and therefore is an asteroid that is being affected by some other force, in addition to gravity. This phenomenon is relatively common and well studied: it is called effect Yarkovsky and it affects comets, for example. The problem is that Oumuamua does not present visible characteristics of comet.

Figure 2: Lu curve of the asteroid, used to determine the geometry of Oumuamua. Figure 3 of Article.

This is how scientists have theorized about the extrasolar origin of Oumuamua. The article under discussion succeeds in explaining the strange velocities using the geometry described above and it was determined that the anomalies observed in Oumuamua velocities can be effectively the result of interaction with Solar radiation.

It is important to mention that there is a problem with this hypothesis. For radiation to be important when competing with gravity, Oumuamua must be a 'pancake'Of approximately 16m radius, 740kg of mass and must have a thickness less than 1 mm, between 0.3mm and 0.9mm to be more precise. In this theory it is fundamental that the mass-area ratio is very small: it needs a lot of area and very little mass so that the effect of the radiation is maximum.

Following this line and assuming the way of ultra thin pancake which is necessary so that only Solar radiation causes anomalies in the speed of Oumuamua, it is possible that this body comes from outside our solar system and we can calculate the maximum distance it has traveled if it also fulfills other conditions.

Figure 3: Graph of distance traveled by Oumuamua based on the mass-area ratio. The red and blue lines are the limits derived by mass lost (vaporization) and mass gained (deceleration) respectively. Figure 1 of Article.

For example, as Oumuamua travels through the interstellar medium, it accumulates dust and molecules, which translates into an increase in its mass. As its mass increases, its speed must decrease to preserve its momentum. This is why there is a limit to the distance that Oumuamua may have traveled. The greater the distance, the greater the mass that accumulates and the lower the velocity, which could contradict the observations. It is also important to consider the mass losses due to the evaporation of material (due to collisions with gas particles), which places limits on the distance that Oumuamua has traveled.

After all this analysis - and assuming that solar radiation is the only source of anomalies in speed - the researchers consider it plausible that Oumuamua comes from outside our solar system. But, from where? It is in this context that it is proposed as an 'explanation of an exotic nature', that Oumuamua is a ship sent to explore our neighborhood. But this is only considered as one of the possibilities. It is even mentioned that Oumuamua does not emit radio waves, which are normally used for communication between the earth and the satellites sent to explore our neighboring planets.

The problem is not solved and otherwise, it will be difficult to solve because Oumuamua has already left our solar system and is not observable.

Figure 4: Orbita de Oumuamua. Central panel shows the location of Oumuamua in its discovery. Figure 2 of Article.

 



				



				

							

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