Did Asteroids Invent Gum Billions of Years Ago?

What is “gum”? Most people have probably never considered this question, and might answer something like a chewy material you can put in your mouth. But, to a scientist they might answer something like “nitrogen-rich polymeric sheets”, because precisely defining the chemistry of a material is important to them. Or at least, that’s what they called a type of organic material found in the sample collected of the asteroid Bennu by the OSIRIS-REx spacecraft. But more informally, scientists have taken to calling it “space gum”, and the process it formed under is making some of them question current models of asteroid formation.

Scientists have been poking and prodding the samples from Bennu for almost two years now, but still publishing fascinating results regularly. Part of the reason it is taking so long is the complex tests the samples have to undergo. This particular sample had an even more extreme pre-test processing than most.

To isolate the sample, researchers had to reinforce it with strips of platinum. Then they welded a microneedle made of tungsten to it and separated it from the rest of the sample while under an transmission electron microscope. After separating it, the sample was subjected to a barrage of tests, including electron microscopy, x-ray spectroscopy, a focused ion beam, and a synchrotron. After all of that testing, the researchers could say one thing definitively - the sample was a polymer.

Fraser discusses the OSIRIS-REx mission with Dr. Jamie Molaro

Polymers are a common occurrence on Earth and make up everything from plastic to your own DNA. Essentially, they are just repeating chains of molecules that form the basis of organic chemistry. On Bennu, the polymer the researchers found contained plenty more oxygen and nitrogen than typical samples from asteroids, which are just carbon and hydrogen (like coal). As part of its structure, it contained amides, which are what amino acids, and therefore proteins, are made of, as well as amines, which are the fundamental building blocks of common plastics.

One question remained though - how exactly did the “space gum” survive on Bennu for so long? We know that Bennu was part of a larger asteroid that had hydrothermal vents, meaning the asteroid itself was subjected to water. Complex organic molecules, like the “space gum” usually either dissolve or break up when subjected to hot water. So how had this particular sample avoided that fate?

The authors proposed a timeline of how the sample might have formed that can be thought of as the “Cold-First” theory. Back when it was originally forming, Bennu was made up of ammonia and carbon dioxide ices and dust. During this “cold” phase, where the temperatures were below -70℃, the ices still reacted to create a chemical known as ammonium carbamate. Over time, this reactive chemical linked up different chunks to form the large polymer chains seen in the sample. By the time the radioactive elements inside the asteroid had heated up enough to create the water, the “plastic” sheets of polymer were already formed, and in fact were water resistant, thereby getting trapped by the rocks on the asteroid's surface, where they were eventually picked up by an intrepid space probe.

John Michael Godier discusses the weird gum found on Bennu. Credit - John Michael Godier YouTube Channel

This sample from Bennu is different from the other asteroid sample from Ryugu, which doesn’t have as much nitrogen in its polymer chains. The differences hint that the sample from Bennu might have underground unique processes that created the particular polymers. Bennu’s sample also differs from meteorites, who are likely contaminated by both reentry as well as surviving in the environment on Earth, making the survival of these types of pristine polymer much less likely.

Ultimately, this paper adds more evidence to the idea that the precursor chemicals for life could have been formed on an asteroid, and just needed a kick-start to get going on Earth. We might never know the exact process by which life got started on Earth, but our increasing understanding of the abundance of organic molecules spread throughout the solar system showcases how likely they might be in other solar systems as well - whether in the form of “gum” or not.

Learn More:

NASA - Sugars, 'gum,' stardust found in NASA's asteroid Bennu samples

S. A. Sandford et al. - Nitrogen- and oxygen-rich organic material indicative of polymerization in pre-aqueous cryochemistry on Bennu’s parent body

UT - Asteroid Bennu Is Like A Time Capsule From The Early Solar System

UT - Scientists Solve the Mystery of Why Similar Asteroids Look Different Colours