Artistic imagination of a meteor entering the atmosphere.
On January 8, 2014, a meteor crossed the sky and crashed into the Pacific Ocean near Manus Island in Papua New Guinea. The meteor has a burning yield of about 110 tons of TNT explosives. Meteors of similar size are not uncommon, and dozens of such meteors scurry across Earth's sky each year. But the meteor caught the attention of Abraham Loeb, a professor of astronomy at Harvard University, and his student, Amir Siraj.
They calculated that the meteor came from interstellar space beyond the solar system. Considering that its discovery predates the extraterrestrial body Oumuamua discovered in 2017 and the extratempera comet Borisov's Comet discovered in 2019, this meteor became the first exoplanet object discovered by humans so far. Although they published the results of the study as early as April 2019, the validity of the data was not officially confirmed by the U.S. government until March 2022, three years later.
Shooting stars in the Pacific Ocean
The meteor fell off the inaccessible ocean, and sensors on a military satellite used by the U.S. military to monitor missile launches from other countries became the only device to record the meteor. Because of the cooperation between the U.S. Department of Defense and NASA, data on the meteor are published in a public database at nasa's Jet Propulsion Laboratory (JPL) Center for Near Earth Object Studies (CNEOS), which contains data on more than 900 meteors recorded by U.S. government probes since 1988. In this database, the meteor is numbered CNEOS 2014-01-08 according to the date of discovery, and Slaji called it the "Manus Meteor" when he studied it.
The data recorded in the database for these meteors includes discovery date, time, longitude, latitude, altitude, velocity, three-dimensional velocity component, combustion equivalent, and so on. However, in this database, the margin of error for the vast majority of measurements is deliberately omitted, thus preventing leakage of the accuracy of the detection capabilities of U.S. military satellites.
In October 2017, astronomers first discovered the mysterious cigar-like object Oumuamua in a telescope. Since then, astronomers have calculated based on Oumuamua's orbit that it could not be a celestial body in the solar system, but came from interstellar space outside the solar system, so it became the first interstellar visitor to the solar system discovered by humans at that time. Astronomers believe that because Oumuamua originated outside the solar system, we can learn a lot about the universe near our solar system that we could not get before.
Loeb also studied Oumuamua in depth after it was discovered, and also put forward the surprising idea that Oumuamua is a spaceship of an alien civilization. Although the astronomical community does not agree with Loeb's views, and there is still controversy about the nature and classification of Ofumua, there is a consensus on the significance of studying extrasyneous objects such as Omemovia.
In April 2019, Slaji had been studying Oumuamua for 8 months under Loeb's guidance. At the time, they wondered whether it would be possible to look for other exo-celestial objects for study in addition to Oumuamua, and locked their eyes on the database of the Near-Earth Object Research Center.
After preliminary analysis, Sraj found that the meteor that fell near Manus Island in 2014 could be a candidate for an interstellar meteor. Loeb suggested that Slaji combine the speed of the impact with the dynamics of small groups of objects in the solar system to estimate the possibility that the meteor came from interstellar space. Along this path, Slaji took into account the gravitational influence of the Sun and the planets in the solar system and proposed a more precise way to calculate the trajectory of the meteor.
A twist and turn of the study
At this distance between the Earth and the Sun, objects moving faster than about 42 km/s will be too fast to be captured by the Sun's gravitational pull. Any object moving faster than the limit of this celestial body's velocity could come from interstellar space beyond the solar system and, if unhindered, would rush out of the solar system again and return to interstellar space.
According to satellite observations, the manus island meteor enters the Earth's atmosphere at a velocity of about 45 km/s, but this speed is superimposed on the meteor's motion relative to Earth and the Earth's movement around the Sun. Slaji used a computer program to isolate these superposition effects and found that the meteor had caught up with the Earth from behind before crashing into the Earth's atmosphere, with a relative velocity of nearly 60 km/s with the Sun. Even with large errors, the orbits of the meteors he calculated were clearly untethered by the Sun's gravity.
After that, Loeb and Slaji also used validated, independent data from other meteors in the database and other literature to inverse estimates of measurement errors from military satellites. After this hard work, they came to the same conclusion that the Manus Island meteor came from interstellar space. On April 15, 2019, Slaji and Loeb uploaded their paper to the preprint website arXiv, published their findings, and submitted the paper to an academic journal.
However, journal reviewers find it difficult to grasp the errors in the data in the paper and therefore do not agree to accept their paper. Since then, Loeb and Sraji have received help from two scientists with advanced security clearances, Alan Hurd and Matt Heavner, at Los Alamos National Laboratory in the United States. In a very short time, Harvin contacted an anonymous analyst. It was the analyst who got the velocity component of the meteor from observations from military satellites, and he confirmed that the error of each value did not exceed 10%.
Slaji and Loeb added this information to their error analysis and concluded that there was a 99.999% chance that the meteor would come from outside the solar system. However, the reviewers again rejected their paper, this time raising the objection that the statement about the error came only from a private correspondence with an anonymous U.S. government employee, not from an official statement from the U.S. government. Loeb and Slaji tried many more times, but were never able to meet the requirements of the journal's reviewers. They could only regret to turn to other studies, and the truth about the Manus Island meteor hung in the air.
But a year later, things took a turn for the better. Pete Worden, president of the Breakthrough Prize Foundation, contacted them and introduced them to Matt Daniels, who was then working in the Office of the Secretary of Defense. Dennis read their paper and was willing to help them get a certificate from the U.S. government. After another year of approvals within the U.S. government, dennis finally received official proof of the error from Lt. Gen. John Shaw, deputy commander of the U.S. Space Force, and Joel Mozer, chief scientist at the Space Force's Space Operations Command. The statement, signed by Lt. Gen. John Shaw, states: "Dr. Moser confirms that the speed estimates reported to NASA are precise enough to confirm an interstellar trajectory. ”
In this way, Loeb and Slaji gained strong support for the conclusion that the meteor came from outside the solar system. Three years after the initial discovery, their study was able to confirm that the meteor CNEOS 2014-01-08 is the first known interstellar meteor.
Artistic imagination of OuMuamua. (European Southern Observatory/Photo)
The history of interstellar visitors
On the evening of October 19, 2017, Robert Weryk, an astronomer at the University of Hawaii in the United States, discovered a small object that had never been recorded before. After more than a month of observations, astronomers confirmed that it came from beyond the solar system.
Astronomers usually classify newly discovered small bodies as comets or asteroids, but this small body does not have the typical characteristics of comets or asteroids, and all previously discovered comets and asteroids come from some region in the interior of the solar system. The International Astronomical Union (IAU), which is responsible for naming the newly discovered object, created a new category different from comets (C) and asteroids (A) – interstellar objects (I) – to name the object. The official scientific name for this extraterrestrial object is "1I/2017 U1", where 1 in 1I represents the first of these objects and I stands for Interstellar. As the discoverer of the object, astronomers at the Harea Akala Observatory in Hawaii named it Oumuamua in the local language, which means "the first messenger from afar", which translates to Chinese "Oumuamua".
Oumuamua was the first interstellar object discovered by astronomers, so they were virtually unprepared for The arrival of Oumuamua. When they found out, Oumuamua was already on its way away from us. Soon, the small, dark Oumuamua disappeared from the optical telescope's field of view, and astronomers' attempts to track the infrared band with the Spitzer Space Telescope failed.
On August 30, 2019, Gennady Borisov, an amateur astronomer from the MARGO Observatory on the Crimean Peninsula, discovered what looked like a comet, which he discovered with a homemade 0.65-meter aperture telescope. In the week since, astronomers from all over the world have observed it, resulting in enough data. The IAU Minor Planet Center has preliminarily calculated its orbit, proving that it is from an extrasolar celestial body.
Since it was the second object discovered by astronomers at the time from outside the solar system, it was named 2I. At the same time, the International Astronomical Union named the object 2I/Borisov, Or Borisov, Borisov, in accordance with the convention of naming the comet after the discoverer.
Comet Borisov reached perihelion on December 7, 2019, when it was 2 astronomical units from the Sun and 2 astronomical units from Earth. After that, it began to drift away from the sun and eventually flew out of the solar system. Unlike Oumuamua, because astronomers discovered it earlier, there was plenty of time to make detailed observations of Comet Borisov. Observations show that Comet Borisov, although from outside the solar system, is nothing special compared to other comets in the solar system.
Both Comet Ouumamua and Comet Borisov have left us, and as the first certified exo-celestial body, the Manus Island meteor, which is "in close contact" with The Earth, is undoubtedly of great value for our study of extrasygous objects.
Treasure of the Outer Messenger
Slaj believes that after confirming that the Manus Island meteor came from outside the solar system, we can get a lot of valuable information. First, the size of the meteor suggests that each star will produce a huge number of similar objects during its lifetime, so that we can observe such meteors, and also indicate that we have the opportunity to find more interstellar meteors in the future. According to their estimates, for every planetary system near the solar system, 0.2 to 20 times the mass of the Earth will be ejected, eventually forming such interstellar meteors.
Meanwhile, the high velocity of the Manus Island meteor suggests that it may have been ejected from the interior of another planetary system within the Milky Way's thick disk, near the central star. This is somewhat surprising because, in general, we might think that interstellar objects originate in regions around stars that are very far away from the star, that is, from comet clouds on the outer periphery of the star system, because there are relatively low escape velocities there.
At present, astronomers already have a relatively mature meteor database. At the same time, they also hope to build new observation networks to study interstellar meteors in the future. Observing the burn-out process of an interstellar meteor in real time will allow us to perform spectroscopic studies to analyze its chemical composition and gain an understanding of the chemistry of other planetary systems.
There is no more direct and effective way to study interstellar objects than to obtain physical samples of these objects. Slaji and Loeb are studying the pacific ocean floor near Manus Island to look for meteor debris and what scientifically possible gains there are. Any large enough interstellar meteor discovered in the future will also produce a lot of debris, which we can also track and analyze. In addition, there is another way to obtain samples, which is to send probes to these interstellar objects to obtain samples. This was one of the goals of the Galileo Project, initiated by Loeb, and Sraji was one of the members of the project team. Through a collaboration with Alan Stern, chief scientist of NASA's New Horizons mission, they have received funding to develop a concept for a space mission to future discovered interstellar objects.
Such a new field of interstellar meteor research will be of great help in helping us understand our position in the universe. Further study of the various properties of Manus Island meteors will provide us with a whole new perspective on the cosmic environment in our vicinity. Comparing the characteristics of the Manus Island meteor with the characteristics of Theomamua and Borisov's Comets, we can also expect to gain a more comprehensive understanding of interstellar objects.
Carrying the secrets of the origin and evolution of the universe, galaxies, and planetary systems, these extrastop messengers finally entered the field of astronomers after countless brushes or "intimate contact" with the earth, becoming a huge treasure worth discovering.
Southern Weekend contributed to Ju Qiang