Long before there was an Earth, asteroids large and small were orbiting our young sun. Among them was one far enough out from the sun to contain water ice, as well as organic compounds with lots of carbon. In its five billion years or so as an object, the asteroid was hit and broken apart by other larger asteroids, probably grew some more as smaller asteroids hit it, and then was smashed to bits again many millions of years ago. Some of it might have even landed on Earth.
The product of this tumultuous early history is the asteroid now called Bennu, and the destination for NASA’s OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer) mission. On October 20, the spacecraft will make its dramatic final descent, will touch the ground long enough to collect some samples of the surface, and then will in the months ahead return home with its prized catch.
The sample will consist of grains of a surface that have experienced none of the ever-active geology on Earth, no modifications caused by life, and little of the erosion and weathering. In other words, it will be a sample of the very early solar system from which our planet arose.
“This will be our first chance to look at an ancient, carbon-rich environment – the most pristine example of the chemistry of the very early solar system,” said Daniel Glavin, an astrobiologist at NASA’s Space Flight Center and a co-investigator of the OSIRIS-REx team. “Anything as ancient on early Earth would have been modified many times over.”
“But at Bennu we’ll see the solar system, and the Earth, as it was chemically before all those changes took place. This will be the kind of pristine pre-biotic chemistry that life emerged from.”
Bennu is an unusual asteroid. It orbits relatively close to Earth — rather than in the main asteroid belt between Mars and Jupiter — and that’s one of several main reasons why it was selected for a visit. It is also an asteroid with significant amounts of primeval carbon and organics, which is gold for scientists eager to understand the early solar system, planet formation and the origin of life on Earth.… Read more