“How would a foreign observer view our Solar System?” This is the curious question that a group of scientists from the Queen’s University of Belfast and the Max Planck Institute of Germany have asked in a study where the results indicate that nine of the thousands of known exoplanets are located in a position ideal for observing the Earth, although none of them is habitable.
According to the study, published in the Royal Astronomical Society’s Monthly Notices, there are sixty-eight exoplanets – planets found outside our Solar System – from which hypothetical observers would see one or more planets in our Solar System and, in concrete, only from nine could the Earth be seen. Astronomers estimate that there are approximately ten other exoplanets – not yet discovered – that can support life as we know it, from which the Earth can also be observed. However, this is not confirmed.
To arrive at these results, the researchers have imagined that the so-called observers would use the same method that we have used to detect their exoplanets . This procedure consists of detecting the new planets when they pass between us and the star of their own solar system, around which they orbit. This movement, known as a transit, allows us to see the light of that host star intermittently and regularly every time the planet passes between us and it. Thanks to this method, carried out on missions like SuperWASP, astronomers have found thousands of exoplanets that orbit stars, just as the Earth orbits the Sun.
Large planets are more difficult to observe
During the study they have assumed this procedure in reverse, looking for parts of the sky from which the planets of our Solar System could be seen passing in front of the Sun, in what are known as transit zones. The results indicate that, from outside our system, there are more possibilities to see the terrestrial planets – Mercury, Venus, Earth and Mars – than the gas giants – Jupiter, Saturn, Uranus and Neptune – despite the fact that the latter they are much larger. “Large planets would block much of the sunlight, which would be more difficult to see from the outside,” explains Robert Wells, a researcher at Queen’s University of Belfast and lead author of the study. “However, the really important factor it is how close the planet is to its parent star, and since terrestrial planets are much closer to the Sun than gas planets, they are more likely to be seen during transit, “says Wells.
Another conclusion they have obtained is that, from anywhere outside the Solar System, a maximum of three planets in our system can be seen. And not all combinations of three planets are possible to observe. Katja Poppenhaeger, co-author of the study, explains: “We estimate that a randomly positioned observer would have approximately a one in forty chance of observing at least one planet in our system. The probability of detecting at least two planets would be ten times less, and detecting three would be ten times less than this “.
This research, which is part of a larger mission, NASA’s Kepler K2, will continue to hunt for new exoplanets, hoping to find any of those ten that are estimated to be habitable.
Reference: R. Wells et al. Transit Visibility Zones of the Solar System Planets, Monthly Notices of the Royal Astronomical Society (2017). DOI: 10.1093 / mnras / stx2077
