NASA’s Asteroid Samples Upend Our Understanding Of Early Solar System

It’s humbling to realize that we are the first sentient beings to successfully sample Bennu, a 500-meter-sized asteroid that’s been around even longer than planet earth. Samples from the carbon rich Bennu are already providing new clues about the ubiquity and diversity of chemical compounds in our early solar system.

But a page-turning new book offers an inside nuts and bolts look at how such missions get done.

In The Asteroid Hunter: A Scientist’s Journey to the Dawn of Our Solar System, Dante Lauretta deftly chronicles his journey from college-aged short order cook to one of the primary architects of a space mission that represents one of the signal scientific achievements of the 21^st century.

The history of the mission dates from a casual meeting over drinks with a Lockheed Martin executive, the director of the University of Arizona’s Lunar and Planetary lab, and Lauretta in an upscale Tucson hotel bar. In only a matter of minutes, Lauretta had roughed out the basic concepts of what would go on to become OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer).

Within two short decades of that first cocktail bar meeting, OSIRIS-REx had successfully returned a 4.5-billion-year-old sample from Bennu and safely delivered it a Utah desert. There, Lauretta and colleagues were eagerly awaiting the pristine sample’s return.

What has the mission taught us about Bennu?

That Bennu is a fragment of a much larger object that was shattered in the main asteroid belt on the order of a billion years ago, Lauretta, principal investigator for OSIRIS-REx and an astrobiologist at the University of Arizona in Tucson, told me by phone. That object was about 200-km in diameter and originated much farther out in the solar system, probably around where Saturn resides right now, he says. All of the basic building blocks of life are found in this object, says Lauretta, and its parent was probably either an ocean world or a muddy world very early in solar system history.

Ancient Clay Mud

Bennu’s parent asteroid had to have been a giant convecting ball of mud, circulating fluid for millions of years and completely altering the original mineralogy, Lauretta writes in The Asteroid Hunter.

Bennu likely broke off from a much larger carbon-rich asteroid about 700 million to 2 billion years ago, says NASA.

Low Density Object

Most of the asteroids in the inner solar system are stony, high-density, near-earth objects, says Lauretta. But Bennu is much more porous, and much less dense than we ever expected, he says.

Why are asteroids so important in understanding life in the solar system?

If you start to try to piece together the history of our planet, you get to a point about 4 billion years ago, where there’s no rock record left, says Lauretta. You have to go to the asteroids to understand all the way back to the very beginnings of minerals and organics and ice formation in our solar system, he says. They hold the earliest stages of solar system evolution, he notes.

A Rugged Surface

Bennu’s surface was much more rugged and rocky than predicted from our analysis of the telescope data, says Lauretta. We had thought it was going to be sandy, or maybe gravel like, and it was just dominated by these giant boulders, he says.

Sample Surprise

Upon analysis, the phosphates found on Bennu look like evaporates from an ancient ocean world, something like an icy satellite we see around Saturn, says Lauretta. And we’re really excited about the diversity of organic material, he says.

Why is phosphorus so crucial to life?

The two rails that form DNA’S double helix structure are phosphates bonded to sugars, Lauretta explains. So, phosphate is essential in making DNA and RNA, he notes. It’s also really an important element for the energy carrying molecule called Adenosine triphosphate (ATP), says Lauretta, since the P stands for phosphate. And then once you get to animals like us, phosphate minerals also make up our bones and teeth, he says.

In terms of mass, phosphorus is the fifth most important biologic element, after hydrogen, carbon, oxygen, and nitrogen, Lauretta writes in his book. But where terrestrial life got its phosphorus is a mystery, he writes.

An Abundance Of Amino Acids

We found 13 of the 20 amino acids that are used in biology in our samples, says Lauretta.

As for the other seven?

We can’t rule them out just yet, they may have been below our current detection limit, says Lauretta. We also found all four of the nucleobases or the letters of the genetic code used in DNA; that means earth received those compounds from these carbon rich asteroids, he says.

The samples could even reveal some sort of microfossils or evidence for past life if it’s there.

That is something we’re paying a lot of attention to, says Lauretta, but there’s something fundamental that we’re missing in understanding the origin of life. He particularly wonders what happens to go from mere geologic material to something that’s alive. Lauretta is also baffled as to why molecules self-organize into living organisms with preservation instincts and the ability to react to their environment.

As for OSIRIS-REx?

Some 20 minutes after the OSIRIS-REx spacecraft released its sample return capsule into earth’s atmosphere, the spacecraft fired its engines to set off on a new mission, says NASA. Redubbed the OSIRIS-Apophis Explorer, the spacecraft is due to reach the asteroid Apophis in 2029.