The research was inspired by the arrival of the interstellar asteroid Oumuamua, which came flying into our solar system in October and sparked a wave of interest in the astronomical community.
One team suggested the asteroid could contain signs of alien life. While their efforts to scan its surface proved unsuccessful, the new study suggests rocks just like it could be a form of alien spacecraft after all.
The theory of “panspermia”, which suggests life originated somewhere other than Earth, has existed in one form or another for decades, with scientists proposing different mechanisms for the interstellar dispersal of life over the years.
Upon the arrival of Oumuamua, astronomers Manasvi Lingam and Abraham Loeb saw an opportunity to examine this theory in more detail.
“In principle life can be transferred between planets through rocks; we know that rocks from Mars for example reach the Earth and vice versa,” Professor Loeb told The Independent.
He noted that some creatures on Earth, such as microscopic tardigrades, are capable of surviving the kind of extreme environments found in space. Alternatively, chemical “seeds” for life could be delivered inside rocks from distant solar systems.
“The solar system acts as a fishing net – it capture objects from interstellar space that belong to other planetary systems, and Oumuamua is the first object discovered to originate from outside the solar system.”
While astronomers know there are objects in our solar system that originated elsewhere, calculating their abundance has historically been tricky because – prior to our recent visitor – they had never been observed before.
“Now with Oumuamua we have a data point, a calibration of that abundance,” said Professor Loeb.
Asteroids and other space debris can enter our solar system, as Oumuamua did, and become trapped there due to the gravity of the Sun and Jupiter.
“At any given time you should have thousands of objects trapped from interstellar space, and the objects – if they came from another planet that had life – could in principle transfer the life into the solar system, for example by colliding with a planet like the Earth,” said Professor Loeb.
Using computer models, the scientists calculated the number of objects that would have been pulled into our vicinity prior to the emergence of life on Earth.
They found that around 400 interstellar objects 100 metres in size, and 10 objects about a kilometre in size, could have struck the planet prior to the emergence of life 3.8 billion years ago.
The study is currently awaiting publication in The Astrophysical Journal, and is available as a pre-print.
Besides understanding our own origins, the Harvard researchers suggested their work could also have a role in the search for alien life.
If astronomers can determine which of the objects in our solar system originated elsewhere, by analysing their chemical composition for example, it might be possible to find aliens in our own backyard.
“It’s not just primitive life; we could also look for artefacts associated with intelligence life,” said Professor Loeb. “There is a possibility that advanced civilisations could produce robotic spacecraft that roam through interstellar space and every now and again one of these could be trapped in the solar system.”
This work could make the search for alien life considerably easier.
“Instead of travelling in interstellar space, going to another planetary system we can actually just wait and see what our ‘fishing net’ captures in our own neighbourhood, and examine the fish that are in that net,” said Professor Loeb.