The conclusion of a 4 billion-mile journey could soon offer a glimpse at the Earth as it was more than 4 billion years ago.
On Sept. 24, the NASA-launched Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer — OSIRIS-REx, for short — will wrap its seven-year round trip to the near-Earth asteroid known as Bennu. That day, a capsule holding 8-plus ounces of Bennu’s rock and dust will parachute into the Utah desert, where NASA scientists will be waiting to collect it for study.
Roughly five football fields in diameter, the asteroid ranks as just one among 780,000 known hunks of rock and ice hurtling around the solar system. So why bother with Bennu? For starters, it’s (relatively) close: Whereas most known asteroids reside in the belt between Mars and Jupiter, Bennu’s orbit crosses that of Earth, taking it past the big blue marble once every six years.
There’s also the fact that Bennu and its kind are untouched by the forging but history-erasing heat that seared the face of the infant Earth. Though asteroids do contend with cosmic rays and solar winds, among other agitators, they tend to encounter fewer and far less disruptive conditions than do planets, including Earth.
“Almost all material that dates from the origin of the Earth has been destroyed by geological processes and recycled,” said Richard Kettler, associate professor of Earth and atmospheric sciences at the University of Nebraska–Lincoln.
While geologists look to meteorites and other sky-piercing material for information on early-edition Earth, Kettler said, some of that material has been subjected to geochemical processes and weathering that obscure its record-keeping. Bennu, by contrast, has sailed through the near-vacuum of space ever since a cataclysmic collision likely chipped it off its parent asteroid 1 to 2 billion years ago. Because that parent formed from the same colossus of dust that constitutes the Earth, Bennu represents a sort of time capsule that NASA scientists are keen to examine for clues about what their home planet looked like in the beginning.
For astrobiologists like Nicole Fiore, a Husker doctoral student who’s investigating whether methane-producing microorganisms could survive beneath the surface of Mars, Bennu should provide insights into how life found a way to emerge on Earth.
“To understand how life originated, we need to know the conditions that were present when it arose,” Fiore said. “Typically, the geologic record is used to infer the Earth’s history, but the surface of the early Earth was often molten, effectively melting any preexisting rock record.
“Although the Earth is estimated to be 4.6 billion years old, its oldest rock is only 4 billion years old, leaving the earliest conditions unaccounted for.”
Even prior to launching OSIRIS-REx, NASA knew that Bennu was rich in carbon, the element central to organic molecules and essential to all known life-forms. Subsequent analyses of readings taken while the spacecraft was still en route to the asteroid have indicated that Bennu may boast molecules containing both oxygen and hydrogen, too. That, in turn, hints that its parent asteroid once hosted liquid water.
Combined, those preliminary findings suggest that in-depth studies of the Bennu samples could go a long way — hopefully 4 billion miles’ worth — toward addressing some longstanding questions about Earth and the potential for life beyond it.
“There are many processes on Earth that can produce organic molecules abiotically, without life,” Kettler said. “Nevertheless, there has been consistent interest in the idea that life on Earth was ‘seeded’ by organic molecules, or even life, that formed elsewhere and eventually landed on the surface of this planet.”
“Studying the organics on Bennu might help clarify the origin of Earth’s first organics or help us understand their distribution and abundance,” Fiore said, “and, therefore, the distribution and abundance of potential alien life.”