If you’re worried about extraterrestrial life coming to find us and enslave us all because we keep broadcasting our location to them, and have even handed them a star map, don’t. It turns out that we’re probably not even sending that signal anywhere near alien life.
According to a group of scientists from Queen’s University Belfast and the Max Planck Institute for Solar System Research in Germany, only tens of potentially habitable planets are within earshot of our broadcasts. In fact, the researchers believe that only nine exoplanets are actually ideally placed to observe Earth’s transmissions.
The paper, published in the Monthly Notices of the Royal Astronomical Society, reverses the concept of exoplanet discovery tools like SuperWASP and Kelper to answer the question of “how would an alien observer see the Solar System?”
Turns out the answer is not particularly well.
By looking at how often various planets in our Solar System pass in front of the Sun, researchers concluded that terrestrial planets Mercury, Venus, Earth and Mars are far more likely to be spotted than the likes of Jupiter, Saturn, Uranus and Neptune – despite their larger size.
“Larger planets would naturally block out more light as they pass in front of their star”, commented lead author Robert Wells, a PhD student at Queen’s University Belfast. “However the more important factor is actually how close the planet is to its parent star – since the terrestrial planets are much closer to the Sun than the gas giants, they’ll be more likely to be seen in transit.”
A map of where the transit of planets across our solar system can be observed from space
The astronomers then looked to how this would be seen to interstellar travellers looking to discover our own Solar System. They found that no more than three planets at any given time could be seen from outside our solar system and that not all combinations of three planets are possible.
“We estimate that a randomly positioned observer would have roughly a one in 40 chance of observing at least one planet,” explained the paper’s co-author Katja Poppenhaeger. “The probability of detecting at least two planets would be about ten times lower, and to detect three would be a further ten times smaller than this.”
Off the back of their research, the team identified only 68 worlds where observers could see one or more of our Solar System’s planets as they crossed the Sun. Of these, only nine planets could see Earth cross the sun and, of those nine, none are deemed habitable.
There is hope out there for the alien-hunters among us. Despite there being a slim chance of us being spotted, the team believes that there should be around another ten currently undiscovered planets that are capable of sustaining life within a path that allows them to view the Earth.
Perhaps all the signals we’re sending out into space could help an alien race locate us but it’s more likely that we’re just not as important to the galaxy as we first thought. You are not the centre of the universe – neither literally nor metaphorically.
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