Finding the stuff of life

Photo: cdn.sci-news.com/

NASA's OSIRIS-REx Spacecraft arrives at Asteroid Bennu

Earth was born about 4.5 billion years ago, along with the Sun and all the other bodies making up the Solar System.

Since living things appeared on Earth pretty well as soon as the planet was cool enough for water to puddle on its surface, the raw materials of life must have arrived by then.

All life on Earth is based upon the element carbon, so some primordial mix of carbon compounds must have been available for things to get started. What were these chemicals? How did we get them? If we can answer these questions, we can get an idea of how life got started.

We stand little chance of finding these primordial carbon compounds by looking at the Earth. Over time, the material from which the Earth formed has been part of living things, built into rocks, recycled by sub-duction and re-emergence at the surface, probably multiple times.

It is unlikely there are anything more than faint traces of these primordial carbon compounds left, and if so, how could we conclusively identify them?

Out in space there is still a huge amount of Solar System construction material left over. It ranges from fine-grained dust to lumps hundreds of kilometres in diameter. On any clear night we will see the odd meteor, or shooting star: a short-lived bright streak across the sky.

This marks the arrival of a grain or chip of this construction material. It is moving at tens of kilometres a second and the heat of friction when it crashes into our atmosphere vaporizes it. The result is a continuous tenuous rain of fine dust, adding up to tens of tonnes each day, distributed over the whole world.

Planet construction has not yet finished. However, this dust has been vaporized and has reacted with the gases of our air. It does not tell us what the material was like before it hit our atmosphere.

On occasion larger pieces arrive, and survive to reach the ground more or less in one piece, or at least as large fragments — meteorites. Sometimes those pieces are bits that have been knocked off the Moon, or other planets, such as Mars.

Most meteorites are made of the cosmic material. However, the heating and chemical changes that happened during their fiery passage through the atmosphere destroys important evidence, and then, sitting on the ground, in the weather, waiting for us to find them adds further contamination.

We do know however that some of them contain evidence of carbon compounds. Clearly, to get unadulterated material we need to go out into space to collect it. We have visited comets and asteroids. However, none of those gave us the primordial carbon compounds we seek.

Then came asteroid Bennu.

This asteroid first became of interest when we realized it might actually hit the Earth. It is a roughly octahedral-shaped object about 500 metres across, weighing almost 80 million tonnes.

However, what makes it really interesting is that it is really dark coloured. Could this be due to large concentrations of carbon compounds?

This is why on  Oct. 20, after orbiting the asteroid for about two years, studying the surface and selecting a landing site, the NASA spacecraft OSIRIS-Rex landed gently on Bennu, grabbed a sample of surface material and boosted off again.

The surface gravity of Bennu is so low it takes over seven minutes to fall 10 metres, so thrusters were used on the way down and on the way up.

The samples will be delivered back to Earth in 2023. There is a Canadian instrument on board. It is a high-precision laser altimeter, which will be used to create a 3D map of Bennu.

Images sent back so far show a starkly lit, rocky surface, not the sort of place you would, without prior knowledge, expect to find the raw materials of life.

• After dark, Saturn and Jupiter lie low in the south
• Mars is rising in the east.
• Venus rises in the early hours.
• Mercury lies low in the dawn glow.
• The moon will be new on the 14th. 

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.