Understanding why we are not observing aliens and why aliens are not communicating with us takes a diverse range of skill sets in astronomy to figure out. There is still much of space, even in relatively near parts of space that even we can’t see, recently scientists revealed techniques that helped people become aware of just how many asteroids we don’t see because they are, for most of the time, obscured by the Sun’s glare.
It has long been debated that if there are aliens, why don’t they make contact with us? One of the scariest things that people have been warned about alien races is that if they do exist, they, like us, will also search for habitable worlds to plunder. According to the latest research by astronomer Eamonn Kerins of the University of Manchester and his colleagues, we may put the fear of our planet being discovered by hostile aliens to rest.
Kerin’s team provides the reasons why the existence of our habitable Earth would be so well hidden from aliens searching for other habitable planets. We can breathe a sigh of relief that if there were hostile alien species using SETI methods similar to our own, our Earth would probably avoid their attention.
It turns out that just in the same way our Sun presents challenges for us to know about and see everything, such as potentially undetectable asteroids, our Sun and the lack of other stars behind our planet also plays a role in perhaps sheltering us from the attention of aliens searching for habitable planets.
According to what Kerins said in an interview with Physics World, “Earth would be a tough target,” in part because it is somewhat too close to the Sun to generate a significant lensing signal for the majority of possible observers. In addition to this, he stated that “our location 27,000 light-years from the galactic center of the [Milky Way’s] is somewhat of a blind area for any viewer employing microlensing.” To understand Kerins’ explanation, we must delve further into astronomers’ methods for searching for life on other planets.
Understanding the methods people use to search for life
Astronomers have a wide range of instruments at their disposal to search for planets outside our solar system that may or may not support life. As things stand, the transit technique has been by far the most effective of these, and it is responsible for approximately 75% of all the exoplanet discoveries that have been made to date.
Using the transit method requires keeping an eye out for the gradual dimming of a star’s brightness whenever a planet comes in between the star and an observer on Earth.
Astronomers are currently pioneering other methods to find exoplanets, such as the radial-velocity method, which relies on analyzing the gravitational complexity of a planetary system to observe slight wobbles of a star in a system, but using radial-velocity requires significantly more expertise. Radial velocity has not been the go-to method for discovering objects in the universe, but it was recently used in research by Birmingham University.
While Jupiter’s orbit in our solar system may be large enough to have an observable gravitational effect on our Sun, the movement of Earth wouldn’t be creating any significant wobbles to our Sun for any aliens trying to detect us using radial velocity.
The drawbacks of the transit method
The commonly used transit method has certain drawbacks, the most significant of which is that transits only take place for a tiny percentage of planets whose orbital planes are nearly perfectly perpendicular to the plane of Earth’s orbit. Photometric microlensing is an alternate method that uses the gravitational lens effect that takes place when one star passes in front of another, temporarily intensifying the light from the more distant “source” star.
This effect can be used to determine the distance between two stars. The presence of a planet in orbit around the closer star can have an additional effect on the light and cause characteristic spikes to appear in the light that is detected.
The fact that the microlensing technology is effective even at relatively great distances is one of its many appealing features. Other methods for detecting exoplanets have typically found planets up to one kiloparsec (about 3200 light-years) away from Earth. Still, most of the 130 exoplanets detected using microlensing are up to seven times that distance from Earth.
This is because microlensing can magnify the light from distant stars. Therefore, given that the Milky Way spans approximately 30 kiloparsecs, it is not out of the question for other technological civilizations to make use of the microlensing approach to identify the planet Earth from great distances across the galaxy.
Exploring the theory of “Schelling Point,” assuming that aliens with similar technology capabilities will be searching for habitable planets like ours, astronomer Eamonn Kerins of the University of Manchester and his colleagues analyzed the photometric microlensing signal of the Earth and how it would appear to other hypothetical civilizations that are more technologically sophisticated.
Understanding the Earth’s microlensing zone (EMZ)
The researchers explain that they have named the regions of our galaxy from which Earth’s photometric microlensing signal is most readily observable the “Earth microlensing zone” (EMZ). They claim that the EMZ is the microlensing equivalent of the Earth Transit Zone (ETZ), from which observers see Earth transit the Sun.
The researchers used information obtained from the Gaia telescope, operated by the European Space Agency. More specifically, the group utilized the instrument’s second data release (DR2), which has data on more than 1.1 billion stars. The researchers plotted out the locations in the sky where Earth’s microlensing signal would be detectable by first segmenting the sky into smaller and smaller sections.
Even if advanced alien civilizations were found around every star studied, the researchers discovered that the total rate of Earth discovery is only 14.7 observers per year. Assuming that technological life is relatively rare, it is “very doubtful” that anyone has spotted us using microlensing.
Why does the lack of background stars make it hard for aliens to discover Earth?
Kerins said that for an alien civilization to have a decent chance of spotting us, they would need to be located in such a way that positions a lot of background stars behind us. This would allow the Earth a fair chance of diverting the light from one of the stars in the background. “The optimum place for an observer to be is just at the edge of our galaxy,” he said, adding: “But there are very few stars at the edge of our galaxy, and therefore it is likely few observers.”
The researchers note that the galactic plane’s Orion-Cygnus arm is the direction away from Earth in which potential alien civilizations would have the best chance of detecting Earth. This is the direction in which Earth is most likely to be discovered by these possible alien civilizations. The figures for Earth’s microlensing likelihood and finding rate are 3.28 times 10 to the power of 10 and 2.35 times 10 to the power of 10 observers per year per square degree, respectively.
Aliens won’t find us unless their technology is more advanced than our own or happen to be in just the right location
The researchers concluded: “Overall, it seems the Earth is very dark to photometric microlensing discovery by other observers unless they have sensitivity way beyond our present capabilities.”
Astronomer Martin Dominik from the University of St. Andrews, who was not involved in the study, suggested extraterrestrials might use gravitational microlensing to locate potential planets. Still, they won’t be able to detect Earth passing in front of the Sun unless they are in a small strip near the ecliptic plane.
This research doesn’t explore the other possibilities that aliens that could potentially observe us may not be on static planets but could, in fact, be on floating planets. However, this research is a good indicator of why we haven’t been discovered yet.