[ad_1]
An object outside our solar system may have already visited Earth: a meteor that burned in the atmosphere of the planet in 2014, say astronomers. If it was confirmed, it would be the first interstellar object known to have entered the atmosphere.
The first interstellar visitor known to have approached Earth was the 400-meter-wide asteroid named "Oumuamua". It plunged about 24 million kilometers from the planet in October 2017 (SN: 25/11/17, p. 14). His very pointed approach to the solar system and his equally strange departure have led astronomers to suggest that "Oumuamua could have been anything from a fluffy skeleton of a comet to an alien spacecraft (SN online: 02/27/19).
Astronomers felt that if there had been an interstellar intruder, there would probably have been more, including some that would have collided with the Earth.
For example, astronomer Avi Loeb and undergraduate student Amir Siraj, both of Harvard University, went through a catalog of NASA meteors that burned in the Earth's atmosphere to see if they had took a strange trajectory, similar to that of Oumuamua.
The pair identified a 0.9 meter wide object that disintegrated in January 2014 in the skies above the South Pacific, off the northern coast of Papua New Guinea. The meteor had approached the sun at a rapid speed of 60 kilometers per second, suggesting that it was not bound by the gravity of the sun. Reassembling the orbit of this meteor in time shows that the object probably comes from the solar system, perhaps from the inner part of another planetary system, in the thick disk of the Milky Way, report astronomers in line the April 15th on arXiv.org.
This origin could mean that the object came from the habitable zone of another star – the region around a star where temperatures are conducive to the survival of liquid water and perhaps life. "If an interstellar object comes from another planetary system, it can bring life to the solar system from the outside," says Loeb.
The object in question was so small that it caught fire in the Earth's atmosphere and could not have sent microbes to the Earth's surface, the team said. But as the duo found only one interstellar meteor in a database spanning several decades, Loeb and Siraj believe the Earth could be affected every ten years. That would mean that about 450 million interstellar meteors could have hit the Earth during its history of about 4.5 billion years ago. "We do not need to live once a decade, we just need it once every few billion years," Loeb says.
If scientists could identify one of these visitors before it entered the Earth's atmosphere, they could understand its composition by studying the meteor's light as it burned. "In hindsight, it's obvious that this should be a very good way to find an interstellar object and get to know its composition," Loeb said.
This is not the first time that astronomers are looking for interstellar meteors, says astronomer Eric Mamajek, who is not convinced that the 2014 discovery is the real deal.
"The result is interesting, but relies on measurements for a single event," says Mamajek, of NASA's Jet Propulsion Laboratory and Caltech in Pasadena, California. The answer seems to reside either in inaccessible government sensors or in a fine shower of powdered dust falling on the Pacific. "
[ad_2]
Source link