A group of Canadian scientists is awaiting delivery of an outer space postcard from the past.
On Sept. 24, seven years after it blasted off from its Florida launch pad, NASA’s OSIRIS-REx spacecraft is expected to drop a capsule into the Earth’s atmosphere containing matter plucked from the surface of an asteroid dating from the early history of the solar system.
“I’ve never worked with extraterrestrial material,” said Dominique Weis, a geoscientist at the University of British Columbia, who’s in line to get a tiny sample.
The material comes from Bennu, previously known as near-Earth object 101955, a frozen chunk of rock about 500 metres across and roughly 450,000 kilometres from Earth. OSIRIS-REx has orbited within a couple hundred metres of its surface, scooped up a shovelful of it and is on its way home to drop off the package of whatever it found.
A Canadian-built set of lasers helped guide OSIRIS to its destination and produced a relief map of Bennu accurate to within a couple centimetres of height.
“In six weeks, we took data that provided the most detailed asteroid model ever,” said Michael Daly of York University’s Centre for Research in Earth and Space Science, who headed the team that designed the lasers. “You could see fractures and details in the rocks.
“We’re very proud of that.”
Bennu was chosen for several reasons.
It’s a doable distance. It’s large enough for a spacecraft to orbit—although OSIRIS set a record for the smallest orbit yet. And it’s considered “primitive,” relatively unmodified since its origin billions of years ago.
That makes it a window into the early history of the solar system, said Weis.
“The idea is to go as far back in time as possible,” she said.
Alan Hildebrand, a University of Calgary geoscientist, who is also to receive a Bennu bit, said that sheds light on Earth’s history as well.
“The Earth was formed by asteroids getting together,” he said. “Studying asteroids helps you understand the origins of our planet.”
Bennu can help answer questions such as how the early crust of the Earth formed, he said.
As well, Bennu is from an area of space that cooled off well before the central part of what became the solar system, “freezing” those materials before they were altered by heat. And grabbing samples directly from the asteroid’s surface means scientists don’t have to account for the effects that flying through Earth’s atmosphere has on meteorites.
“The rocks comprising Bennu are from an older part of the solar system,” Hildebrand said. “We get to see the whole suite (of constituents) without the atmospheric filter.”
Finally, Bennu is thought to be rich in carbon. That could mean it contains organic compounds—those composed of carbon, hydrogen, oxygen and nitrogen.
Some scientists think those compounds could offer clues to how life began on Earth—although Hildebrand points out planets such as Mars and Venus are also showered with such material and don’t appear to host life.
Bennu’s bits won’t be the first asteroid pieces brought to Earth. Two previous Japanese missions have brought back samples.
But the yield from OSIRIS is expected to be much larger. The Hayabusa missions brought back about five grams of asteroid—OSIRIS’s yield is estimated at anywhere between 60 grams and two kilograms.
“We'll have more material to do more things,” Hildebrand said.
Canadian scientists are getting samples of Bennu because of Canada’s $61-million investment in OSIRIS. But before any lab starts to warm up its mass spectrometer, NASA makes sure recipients know how to handle the precious grains, practising protocols on fragments of meteorites.
“We rehearse and rehearse and rehearse and rehearse some more,” said Weis. “We are working on the methods to be as sensitive and precise as possible.”
OSIRIS has already led to the publication of dozens of research papers. The arrival of its Bennu samples is expected to lead to many more.
The spacecraft also has enough fuel in its tank to take on more work after its return.
OSIRIS-REx, renamed OSIRIS-APEX, is to head off to study Apophis, an asteroid roughly 370 metres in diameter that will come within 32,000 kilometres of Earth in 2029. The spacecraft will then use its thrusters to try to dislodge dust and small rocks on and below that asteroid’s surface.
