Season 17, Episode 22: Asteroid Bennu and the Origin of Life in the Solar System

Hey StarTalkians! Neil and Chuck sat down with Professor Harold Connolly Jr. for season 17, episode 22, talking about his work on the OSIRIS-Rex mission and the asteroid Bennu. After covering the basics of the mission, they briefly discussed what it could mean for the origin of life in the solar system: 

Secrets of Asteroid Bennu with Harold Connolly Jr. - StarTalk Radio

(From 53:55)

The discussion touches on the “panspermia” hypothesis. The overall idea is unlikely, to say the least, but a limited form of it could be more promising.

What They Found on Bennu

As Professor Connolly explains in the podcast, the asteroid Bennu contained a lot of organic materials.

One paper he co-authored describes what they found on the carbon-rich asteroid. Most importantly, this included 14 out of 20 terrestrial amino acids, the building blocks of life. Interestingly, these may have been formed in low-temperature reactions involving ammonia ice, unlike previous cases that depended on mild temperatures and liquid water.

Another paper added a 15th terrestrial amino acid, noting that such prebiotic molecules could have been deposited onto the young Earth by asteroid impacts.

The Panspermia Hypothesis

This leads into Chuck’s question about “lithopanspermia,” a variant of the panspermia hypothesis. This is the idea that the earliest forms of life may have developed away from the Earth, eventually being delivered to our planet by asteroid impact events (hence “litho”) and evolving terrestrially.

This hypothesis isn’t super likely, though. After all, could life really survive the journey through space and the impact itself? And the whole thing requires extra-terrestrial life to exist in the first place.

Pseudo-lithopanspermia – A Viable Alternative?                              

Instead of living microbes making the unlikely journey through space, the more likely “pseudo-panspermia” hypothesis posits that prebiotic organic molecules arrived on Earth that way. If this came from an asteroid like Bennu, we might call this “pseudo-lithopanspermia.”

Professor Connolly’s research shows that such molecules certainly exist. Additionally, modelling suggests that plenty of material from other bodies ends up on Earth – including 21 million landing from Mars alone over 3.5 billion years.

This removes a lot of problems with panspermia, and it’s definitely an interesting possibility. However, Neil’s point in the podcast pours cold water ammonia over this: why would we need extra-terrestrial amino acids if they seem to form everywhere anyway?