Earliest interstellar visitor may have collided with Earth in 2014: Harvard study

Fewer than ten observable asteroid collisions have taken place in the Earth's in the current millennia.

Fewer than ten noticeable asteroid collisions have taken place in the Earth's recent past. Many of these space rocks, like the 2019 GC6 asteroid expected to do a fly-by of Earth on 18 April, are visitors that make a brush with one or more planetary orbits in our solar system every few years or decades.

It is also only the second interstellar visitor overall to be recorded in our vast solar system. The first recorded comet visiting our solar system from another one was 'Oumuamua, which was spotted in 2017 and flew past Earth a year later in 2018, leaving scientists baffled at its many peculiarities.

'Oumuamua was a cigar-shaped, 400-meter-space rock, thought to have originated from one of four stars in the Milky Way based on its speed and trajectory.

Researchers have identified a meteor less than a meter wide that was picked up by satellites on collision-watch on 8 January 2014 at an altitude of 18.7 kilometers above Papua New Guinea in the South Pacific Ocean. It supposedly struck the atmosphere at speeds of 216,000 kmph as it hurtled towards the Earth from outside the solar system.

Earth's atmosphere can be a handy detector for meteors too small to otherwise spot, Avi Loeb, Chairman of astronomy at Harvard University told Space.com.

"One would expect smaller interstellar visitors to be far more common, with some of them perhaps colliding with Earth often enough to be noticeable."

After analyzing data from the Center for Near-Earth Object Studies' catalog, an exhaustive collection of meteor events compiled by American government sensors, the Loeb and his team picked out the fastest among them. This, because the high speed suggests that the meteor likely isn't gravitationally-bound to the Sun, and thus, likely from outside the solar system.

This artist’s impression shows the first interstellar asteroid, `Oumuamua, as it passes through the solar system. Image: ESO

This artist’s impression shows the first interstellar asteroid, `Oumuamua, as it passes through the solar system. Image: ESO

Be combing through thirty years of data, the team uncovered two meteors that struck the atmosphere with roughly the same speeds. While one of them was gravitationally-bound to the Sun, the other was evidently an interstellar visitor to our planetary neighbourhood.

The researchers estimated there are roughly a million such objects in any 150 million km-stretch of our galaxy. Essentially, each star in the galaxy has around 60 billion trillion rocks that are up to 20 times Earth's mass flying around in its solar system.

Just so one of these doesn't hit us without fair warning, astronomers are working on an alert system with telescopes trained to zero-in on meteors zipping through the solar system at high speeds. They want to analyze what gases these interstellar rocks are made up of, according to Loeb.

"From that, we could infer the compositions of interstellar meteors," he said.

The findings from the study were pre-published in arXiv on 15 April.

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