Scientists question claims of interstellar debris falling to Earth: here’s why

Comet 2I/Borisov is the second interstellar object scientists have observed on Earth.Source: NASA, European Space Agency, and Dr. Jewett (University of California)

A research team made headlines last week when it claimed to have extracted fragments of a meteorite from outside our solar system from the seafloor.1. Finding such an interstellar sample on Earth would be exciting because it could shed light on how planets and stars transcend our shape. But a number of scientists say that the evidence that the material came from another planetary system is not yet convincing.

here, nature It explores how scientists determine when something is truly interstellar — and how they prepare to study many of these objects after a new telescope debuts next year.

Have we seen interstellar objects before?

As long ago as 1705, astronomer Edmund Halley, of Halley’s Comet fame, speculated that some comets might come from outside the solar system. Since then, scientists have thought that icy bodies from other planetary systems might make their way into our solar system. This prediction was realized in 2017, when astronomers detected an object making its way across the sun in an orbit that, when traced back, would mean that the object originated outside the solar system. Scientists have many ideas about what the object, named 1I/’Oumuamua, could be. For example, it could be part of a comet, a hydrogen iceberg, or even a piece of nitrogen ice from a distant dwarf planet similar to Pluto.

Another interstellar object, 2I/Borisov, was spotted two years later. These are the only two confirmed interstellar objects so far. They both flew close to the sun and left the solar system.

How common are they, and where do they come from?

Researchers estimate that there are a quadrillion interstellar objects in the cubic parsec of space around the sun, a region that does not extend as far as its nearest neighbor, Alpha Centauri. If one of these objects gravitationally interacted with another object in the right way, it could be propelled on a trajectory that would send it into our solar system. As happened with Oumuamua and Borisov, it will initially look like a comet or an asteroid from our solar system. But its hyperbolic orbit, which indicates that it is not gravitationally bound to the sun, would reveal it as an interstellar intruder.

Interstellar dust particles fly through the solar system all the time in hyperbolic orbits. Researchers have captured and studied bits of this dust using high-flying aircraft and space missions. NASA’s Stardust spacecraft collected interstellar dust in 2004 and returned it to Earth for study2.

But larger interstellar objects – “Oumuamua was the size of a skyscraper” – can provide much more information about the chemistry of distant planetary systems. For this reason, scientists are keen to monitor and study as many interstellar objects as possible.

What would be the chemical composition of an interstellar object?

The chemical composition of an interstellar object reflects the gas and dust in the system in which it formed.

In the latter claim, it was published on the arXiv preprint server before peer review1Avi Loeb, an astrophysicist at Harvard University in Cambridge, Massachusetts, announced that his team has found hundreds of tiny metal spheres on the sea floor off the coast of Papua New Guinea. Scientists say these balls came from a meteorite that hit Earth in 2014, which they say arrived from interstellar space. Other specialists disagree, arguing that the flash of light observed when an object hit Earth’s atmosphere in 2014 cannot be proven to have come from an interstellar object.3, which is very little of any meteor that would have survived the Force Return anyway. Confirming the interstellar origin of any meteor requires careful measurement of all sides of the incoming fireball4This has not been done accurately enough for the 2014 flash, says Maria Haidukova, an astronomer at the Slovak Academy of Sciences in Bratislava.

Loeb’s team says many of the globules are unusually rich in the elements beryllium, lanthanum and uranium, which they claim could have come from the magma ocean on the iron-rich orb. But the abundance of these trace elements is not the place to look for “hard evidence” of an interstellar origin, says Larry Netler, a cosmologist at Arizona State University in Tempe. A better approach, Netler says, is to analyze the oxygen isotopes in the spheres. These isotopes are very similar in objects in the solar system but different in those in other planetary systems. Oxygen analysis was not reported in the initial version, but Loeb says nature His team plans further analyses, including an oxygen isotope assessment.

What’s next for interstellar studies?

The Vera C. Rubin Observatory, a program of the National Science Foundation's NOIRLab Laboratory, is pictured below the Milky Way.

The Vera C. Rubin Observatory in Chile will likely discover more interstellar objects passing through our solar system after it comes online.Credit: RubinObs/NOIRLab/NSF/AURA/B. Quint

Astronomers are keen to monitor more interstellar objects and learn what they are made of. “Observers are now very excited to get a glimpse of the chemistry of any future interstellar objects,” says Stephen Desch, an astrophysicist at Arizona State University.

Discoveries are expected to increase exponentially after the new Vera C. Rubin Observatory in Chile becomes operational early next year. The Rubin telescope will scan the entire southern sky every three nights, and will be able to detect much fainter objects than those detected in previous sky surveys. The telescope may discover dozens of interstellar objects during the ten-year survey5.

It may soon become possible to study the entire history of the Milky Way from interstellar objects, says Michelle Bannister, a planetary astronomer at the University of Canterbury in Christchurch, New Zealand. These parts of other planetary systems make up a cosmic sea of ​​evidence of galactic evolution6.

“This is the real promise of interstellar objects,” Bannister says. “They don’t just tell us about the history of our local area — they likely tell us about the history of our own galaxy.”

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