Space dust that regularly hits Earth could contain proof of alien life

JWST? Whatever, I found ET in my dustpan

If we want to find evidence for alien life we don't need to keep looking for chemicals in exoplanet atmospheres or distant radio signals, says a Japanese astronomer. Instead, we should be studying the thousands of micrometer-sized bits of interstellar dust that hit Earth every year.

University of Tokyo Professor Tomonori Totani proposed the new approach in a paper in which he suggests bits of space dust could contain the remains of single-celled organisms or other chemical evidence of life.

This dust would, of course, have to make it through the inhospitable gauntlet of its own solar system and millions of years of travel through the void of space without being intercepted first. Despite the incredibly low chance that pieces of dust ejected from an exoplanet millions of years ago actually make it to Earth, Totani believes around 100,000 pieces of dust worth a look land on our planet every year.

"Given there are many unknowns involved, this estimate could be too high or too low, but the means to explore it already exist so it seems like a worthwhile pursuit," Totani said. 

Dust may already be here – but how can we tell it apart from ours?

Plenty of space rocks hit Earth each year, leaving behind meteorites filled with potential scientific discoveries. Unfortunately, in the process of entering the atmosphere, heat burns off a lot of material – like traces of biological life.

But the same rule doesn't apply to dust particles smaller than 10-100 micrometers, which Totani said are able to survive atmospheric entry without generating much heat, meaning biosignatures on or in the dust could survive the trip.

Micrometeorites have been found both in snow and ice samples from Antarctica, and deep-sea sediment, Totani said in the paper. He also noted, however, that identifying interstellar dust wouldn't be easy.

"Extrasolar particles scattered by giant planets and then bound to the Solar System may be difficult to distinguish from particles ejected from Earth, even if they contain biosignatures," Totani said in the paper. "Searching for particles with origins outside the solar system is like looking for grains of sand that have fallen into the desert," he added. 

To catch these particles, Totani suggests trying to do so in space, instead of waiting for them to fall to Earth, by using material like aerogel, a super-lightweight foam made from silica that's 95 percent air. NASA has already applied aerogel to such a purpose, in fact: During the Stardust mission in the early 2000s, aerogel was used to catch bits of dust coming off a comet in a manner similar to what Totani proposes. 

Why look at dust when we've got these cool telescopes?

With all the unknowns, and Totani's admission that "more quantitative considerations" and experiments are needed to prove his idea is feasible, the obvious question is why we should even bother going this route to find evidence of extraterrestrial life.

We're already scanning for distant radio signatures, and finding an identifiable one would be an unambiguous sign that life does exist somewhere outside Earth. Totani said these observations only look for intelligent life, which is probably far rarer than plants and unintelligent animals, potentially leaving tons of life undiscovered. 

As for gathering profiles on the chemical makeup of exoplanet atmospheres, Totani said any candidate biosignature found in that way would be controversial because oxygen and other indicators of life can occur in its absence. 

If – and this is a pretty big if – we could find a way to sort the interstellar dust from the stellar, or if we could build a dust catcher with an effective area Totani described as "hopefully comparable to Earth … to expect one particle detection per year," then we might be able to find a dust particle that might contain traces of alien life. 

Totani said: "If there are signs of life in dust grains, not only could we be certain, but we could also find out soon." ®