A meteor during the peak of the 2009 Leonid Meteor Shower. The photograph shows the meteor, afterglow, and wake as distinct components.

Credit: Wikipedia

Using a NASA catalog of documented meteor strikes on Earth’s atmosphere, two Harvard University researchers report the detection of the first interstellar meteor ever observed in our solar system.

The one-meter diameter meteor — spotted on January 8, 2014, off the coast of Papua New Guinea — clocked in with an estimated mass of 500 kg. So, it burned up completely while traveling through the atmosphere just north of Manus Island, Abraham Loeb, the paper’s co-author and Chair of Harvard University’s Department of Astronomy, told me.

No meteor fragments were recovered, but Loeb says he’s 95% to 99% percent confident that the object that created this 2014 meteor show originated from outside the solar system.

One of Loeb’s astrophysics students, Harvard University undergraduate Amir Siraj, made the discovery after scouring NASA’s CNEOS (Center for Near-Earth Object (NEO) Studies) catalog to look for small high-velocity impactors. Siraj and Loeb’s analysis is reported in a paper just submitted to The Astrophysical Journal Letters.

“We found that one of these meteors, specifically the one that burned up in the atmosphere [in 2014], had to have been traveling extremely fast in order to hit the Earth at the direction and speed that it did,” Siraj, the paper’s lead author, told me.

Siraj says that with respect to the average velocity of stars in the solar neighborhood, this object was moving extremely fast, at around 60-km per second. Such an object’s high speed, enough to eject it from its own solar system and send it on an interstellar trajectory as a gravitationally-unbound object, can only be produced in the innermost cores of a planetary system, says Loeb, the paper’s co-author.

“One way of explaining this would be to posit that it came from a star in the thick disk of the Milky Way galaxy since thick disk stars have higher velocity dispersions,” said Siraj. However, he says, if so, this would be an unusual origin given that thick disk stars are also quite rare in the solar neighborhood.

Siraj and Loeb say that claims for Earth-striking interstellar meteors date back to at least 1940. But the speeds of such previously-claimed objects tend to hover just above the velocity threshold needed to be of interstellar origin. The difference with their new paper, says Siraj, is that this 2014 meteor can withstand a 45% reduction in its reported speed and still retain a high-enough velocity to dictate an origin from outside our solar system.

Unfortunately, the researchers have little idea from what specific group of stars this particular space rock might have originated. That’s because small errors in calculated impact speed can greatly affect the object’s pre-collision trajectory.

But they estimate 450 million such collisions over Earth’s lifetime , meaning such interstellar meteors strike Earth’s atmosphere about once every decade.

What should ground observers be doing to make better use of future such interlopers?

The authors note that future meteor surveys could flag high-velocity incoming objects for pre-impact observations .

The ability to perform spectroscopy on such objects as they burn up in Earth’s atmosphere would tell astronomers a lot about their composition. As they write in their paper, it’s expected that at least some isotope ratios in objects formed in other solar systems are expected to be markedly different than those found in our own.

Siraj and Loeb even note that precision tracking with the upcoming Large Synoptic Survey Telescope (LSST) might help track meteors of interstellar origin back to their parent systems.

Understanding the composition of such objects would teach us an enormous amount about the chemistry of other planetary systems, say Siraj.


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