Researchers discovered the first known interstellar meteor to ever hit Earth, according to a recently released United States Space Command document. An interstellar meteor is a space rock that originates from outside our solar system — a rare occurrence.
The finding came as a surprise to Amir Siraj, who identified the object as an interstellar meteor in a 2019 study he coauthored while an undergraduate at Harvard University.
Siraj was investigating ʻOumuamua, the first known interstellar object in our solar system that was found in 2017, with Abraham Loeb, professor of science at Harvard University.
Siraj decided to go through NASA’s Center for Near Earth Object Studies database to find other interstellar objects and found what he believed to be an interstellar meteor within days.
A need for speed
The meteor’s high velocity is what initially caught Siraj’s eye.
The meteor was moving at a high speed of about 28 miles per second (45 kilometers per second) relative to Earth, which is moving at around 18.6 miles per second (30 kilometers per second) around the sun. Because researchers measured how fast the meteor was moving while on a moving planet, the 45 kilometers per second was not actually how fast it was going.
The heliocentric speed is defined as the meteor’s speed relative to the sun, which is a more accurate way to determine an object’s orbit. It’s calculated based on the angle at which a meteor hits the Earth. The planet moves in one direction around the sun, so the meteor could have hit Earth head-on, meaning opposite the direction the planet is moving, or from behind, in the same direction the Earth is moving.
Since the meteor hit the Earth from behind, Siraj’s calculations said the meteor was actually traveling at about 37.3 miles per second (60 kilometers per second) relative to the sun.
He then mapped out the trajectory of the meteor and found it was in an unbound orbit, unlike the closed orbit of other meteors. This means that rather than circling around the sun like other meteors, it came from outside the solar system.
“Presumably, it was produced by another star, got kicked out of that star’s planetary system and just so happened to make its way to our solar system and collide with Earth,” Siraj said.
Difficulty getting published
Loeb and Siraj have been unable to get their findings published in a journal because their data came from NASA’s CNEOS database, which doesn’t divulge information such as how accurate the readings are.
After years of trying to obtain the additional information needed, they received official confirmation that it was, in fact, an interstellar meteor, from John Shaw, deputy commander of the US Space Command. The command is a part of the US Department of Defense and is responsible for military operations in outer space.
“Dr. Joel Mozer, the Chief Scientist of Space Operations Command, the United States Space Force service component of US Space Command, reviewed analysis of additional data available to the Department of Defense related to this finding. Dr. Mozer confirmed that the velocity estimate reported to NASA is sufficiently accurate to indicate an interstellar trajectory,” wrote Shaw in the letter.
Siraj had moved onto other research and almost forgotten about his discovery, so the document came as a shock.
“I thought that we would never learn the true nature of this meteor, that it was just blocked somewhere in the government after our many tries, and so actually seeing that letter from the Department of Defense with my eyes was a really incredible moment,” Siraj said.
A second chance
Since receiving the confirmation, Siraj said his team is working to resubmit their findings for publication in a scientific journal.
Siraj would also like to put a team together to try and retrieve part of the meteor that landed in the Pacific Ocean but admitted it would be an unlikely possibility due to the sheer size of the project.
If researchers were able to get their hands on the “holy grail of interstellar objects,” Siraj said it would be scientifically groundbreaking in helping scientists discover more about the world beyond our solar system.
NASA and US Space Command did not initially respond for comment.