What makes Earth difficult to detect for alien civilizations seeking habitable planets?

Scientists from different countries have concluded that the Earth is actually hidden from aliens and through photometric microlensing, they have looked for planets that can sustain life. They also help in finding out the areas within the galaxy, which can be targeted for better SETI in order to find other forms of life in this universe. Scientists use several methods to look for other planets that might be able to support life outside our solar system.

The most successful of them has been the transit method that accounts for about 75% of all the exoplanets discovered so far. Astronomical transits: This method entails observing fluctuations in the brightness of a star over time as a planet obstructs it from the view of an observer on Earth.

Nevertheless, the transit method has some drawbacks, with the biggest one being that transits are visible only for a small part of planets whose orbit planes are close to the plane of the Earth’s orbit. Photometric microlensing presents another method for carrying out such an experiment: it uses gravitational lensing that occurs when one star shines in the foreground of another and briefly increases the brightness of the comparatively distant ‘source’ star.

If the closer star has a planet around it, the light gets bent even more and creates spikes that can be recognized.

Long-distance technique

An important feature of the microlensing technology is that it has the potential of functioning over a large distance. While earlier methods for detecting exoplanets can identify planets only within a distance up to one kiloparsec (approximately 3200 light years) from the Earth, the majority of the 130 exoplanets discovered by such method is up to seven times that distance away. Given that the Milky Way has a diameter of roughly 30 kiloparsecs, it is quite plausible that other technological civilizations will employ the microlensing technique in order to detect Earth over vast galactic distances. Everyone always assumed that the points of space where Earth is potentially visible to settlers based on the transit method are also excellent places to search for signals in SETI research once more based on Schelling’s Point cooperation theory for two players who are looking for each other but cannot coordinate in any way.

Utilizing the same logic for the microlensing technology entails the ability to discover new and remote sights in the quest for aliens.

A new study was performed by Manchester University astronomer Eamonn Kerins and his colleagues, where they looked at how the Earth’s photometric microlensing signal could be detected from the outside, assuming other technologically developed civilizations existed.

Defining the EMZ

The researchers have called the areas of our galaxy where the photometric microlensing signal of the Earth is easiest to identify as the Earth microlensing zone (EMZ). This zone can be compared to the Earth Transit Zone (ETZ) where observers are able to see the transit of the Earth across the Sun. The team explained that they used data from the European Space Agency’s Gaia telescope and restricted themselves to the second data release (DR2), which contains information about more than 1.

To do this, they split the sky into smaller regions in which the signal from the microlensing of Earth could be detected. Still, if there are technologically superior civilizations around each of the stars investigated, the total rate of finding Earths for the entire sky is 14.

This would mean that in case technological life is rare, then the possibility of being seen through microlensing is out of the question. Kerins said that Earth is difficult to observe because it is positioned close to the Sun, which weakens the lensing signal for most potential observers.

Also, the Milky Way is situated 27,000 light years away from the galactic center and this means that there is a blind spot when using microlensing.

Background stars needed

For an alien civilization to have a good shot at identifying us, Kerins said, it would need to be oriented in such a way that there are many background stars behind it, and Earth has a good shot at obscure light from one. “The optimum position for an observer to be is right at the edge of our galaxy with us on the line of sight to the galactic nucleus. ”He further added: “However there are very few stars at the edge of our galaxy and therefore presumably few observers. ”If the ‘priority regions for detection’ is defined as those regions having discovery rates in the highest 1% then the ideal regions for detection are in the Large and Small Magellanic Clouds as well as at low Galactic latitude near the Galactic plane — there is some overlap with the ETZs.

From the perspective of the Earth, it has been estimated by the researchers that the possible extraterrestrial civilizations can easily discover the presence of the Earth if they are situated in the area of the Milky Way Orion-Cygnus arm located in the galactic plane. The microlensing probability and discovery rate for objects in the Milky Way Galaxy is 3. 35×10−2, 35×10−2, observers per year per square degree, respectively.

The findings are as follows: In conclusion, it may appear that to other observers, the Earth is very dark for photometric microlensing and thus must be located beyond their current and possibly even our present sensitivities . Martin Dominik, an astronomer at the University of St Andrews who was not involved in the current work, speculates, “Clever aliens might want to use gravitational microlensing for finding candidate planets to search for other civilizations.

” He continues: “It seems rather strange that they will not be able to observe Earth eclipsing the Sun unless they are in a very slim lane in close proximity to the plane of the ecliptic – not the finest pick to get acquainted with each other!”

The study is described in Monthly Notices of the Royal Astronomical Society.

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