Vital ingredients for the presence of life have been independently identified on both an asteroid and a comet. The findings don’t necessarily build the case for panspermia – the idea life on Earth was seeded from space – but they do suggest there may have been major contributions of key ingredients from beyond our atmosphere.
The first claim rests on a single grain of the near-Earth asteroid Itokawa, brought back to Earth by the Japan Aerospace Exploration Agency (JAXA) Hayabusa mission in 2010. The mission returned 1,500 grains, most less than 10 microns across – but with teams worldwide keen to study them, getting access to even one isn’t easy.
Dr Queenie Chan of the Royal Holloway University of London was among the lucky ones. In Scientific Reports, she announces what may be the most important outcome of the whole mission. Chan reports the grain contains both water and organic material, including evidence that both come from the asteroid rather than being contamination resulting from the return to Earth, a possibility left open in previous specimens.
“After being studied in great detail by an international team of researchers, our analysis of a single grain, nicknamed ‘Amazon’, has preserved both primitive (unheated) and processed (heated) organic matter within ten microns (a thousandth of a centimetre) of distance,” Chan said in a statement. The nickname came from the 50 μm (0.002 inch) long grain’s South America-like shape.
The combination of primitive and unprocessed material is important, indicating that “The asteroid had been heated to over 600°C in the past. The presence of unheated organic matter very close to it, means that the in fall of primitive organics arrived on the surface of Itokawa after the asteroid had cooled down,” Chan added. “Our findings suggest that mixing of materials is a common process in our solar system.”
The high temperatures, almost certainly from a collision that blew apart a predecessor asteroid, would have vaporized any water. That means the water Chan found must also have arrived afterward.
Perhaps the most significant aspect is that Itokawa is an S-type asteroid, the source of most meteorites. Previously, the search for organic materials from space has focused on carbonaceous chondrite meteorites, which were considered far more likely to carry the prized materials, but are also much rarer. For example, both Hayabusa2 and OSIRIS-Rex visited carbonaceous asteroids.
If Itokawa collected water and organic materials after the heating event, perhaps the Earth was collecting large quantities of both at the same time.
With one of those coincidences in timing that science sometimes produces, the Itokawa announcement coincides with the publication of a paper in The Planetary Science Journal revealing the abundant presence of carbon in Comet Catalina’s tail.
Catalina is an Oort Cloud comet, a visitor from the outermost Solar System. Carbon’s capacity to form the basis of complex and diverse molecules is considered essential for life. Although common in the universe – since, unlike most elements, it does not require supernova explosions or neutron star collisions to make it – carbon is thought to have been driven from the inner Solar System early on. This creates what is called the “carbon deficit problem”.
"We're still not sure if Earth could have trapped enough carbon on its own during its formation, so carbon-rich comets could have been an important source delivering this essential element that led to life as we know it,” lead author Professor Charles Woodward of the University of Minnesota Twin Cities said.
Carbon has been found in comets before, but the observations of Catalina suggest those originating from the Oort cloud may have more than we realized, making it easier to understand how Earth ended up with so much.
