IN popular culture, asteroids play the role of apocalyptic threat, get blamed for wiping out the dinosaurs- and offer an extraterrestrial source for mineral mining.
But for researcher Nicholas Hud, asteroids play an entirely different role: that of time capsules showing what molecules originally existed in our solar system. Having that information gives scientists the starting point they need to reconstruct the complex pathway that got life started on Earth.
Director of the NSF-NASA Center for Chemical Evolution at the Georgia Institute of Technology, Hud says finding molecules in asteroids provides the strongest evidence that
such compounds were present on the Earth before life formed. Knowing what molecules were present helps establish the initial conditions that led to the formation of amino acids and related compounds that, in turn, came together to form peptides, small protein-like molecules that may have kicked off life on this planet.
“We can look to the asteroids to help us understand what chemistry is possible in the universe,” said Hud. “It’s important for us to study materials from asteroids and meteorites, the smaller versions of asteroids that fall to Earth, to test the validity of our models for how molecules in them could have helped give rise to life.
We also need to catalog the molecules fromasteroids and meteorites because there might be compounds there that we had not even considered important for starting life.” NASA scientists have been analysing compounds found in asteroids and meteorites for decades, and their work provides a solid understanding for what might have been present when the Earth itself was formed, Hud says.
“If you model a prebiotic chemical reaction in the laboratory, scientists can argue about whether or not you had the right starting materials,” said Hud. “Detection of a molecule in an asteroid or meteorite is about the only evidence everyone will accept for that molecule being prebiotic. It’s something we can really lean on.”
“We now have a really good way to synthesise peptides with amino acids and hydroxy acids
working together that could have been common on the early Earth,” he said. “Even today, hydroxy acids are found with amino acids in living organisms – and in some meteorite
samples that have been examined.”
Hud believes there are many possible ways that the molecules of life could have formed. Life could have gotten started with molecules that are less sophisticated and less efficient than what we see today. Like life itself, these molecules could have evolved over time.
“What we find is that these compounds can form molecules that look a lot like modern peptides, except in the backbone that is holding the units together,” said Hud.
“The overall structure can be very similar and would be easier to make, though it doesn’t have the ability to fold into as complex structures as modern proteins. There is a tradeoff between the simplicity of forming these molecules and how close these molecules are to those found in contemporary life.”
“There are probably a lot more clues in the asteroids about what molecules were really there,” said Hud. “We may not even know what we should be looking for in these asteroids, but by looking at what molecules we find, we can ask different and more questions about
how they could have helped get life started.”