Asteroid Itokawa sample study provides fresh insights on how Earth got so much water

Asteroid Itokawa samples were collected by the Japanese Hayabusa mission in 2005 and delivered to Earth in 2010. 
Mrigakshi Dixit
Asteroid Itokawa as seen by the Hayabusa spacecraft
Asteroid Itokawa as seen by the Hayabusa spacecraft

The University of Arizona 

In the entire solar system, our blue world turned out to be one lucky planet. Water on any planet distant from the Sun will turn to ice, while the ones closer to the star will barely hold on to water.  

The Earth is perfectly positioned in relation to the Sun, allowing liquid water to exist. 

But how did so much water come to exist on Earth in the first place? Scientists have been actively searching for sources and associated evidence. One of the most reigning sources has been asteroids that delivered water to Earth's surface. 

A team of astronomers from the University of Arizona has now narrowed down a type of asteroid that — in addition to other sources — may have brought a large amount of water to Earth

Presence of tiny salt crystals  

Asteroid Itokawa samples were collected by Japan's Hayabusa mission in 2005 and delivered to Earth in 2010. 

The team studied these samples using various techniques, including an electron microscope. 

The existence of tiny salt crystals of sodium chloride (table salt) was discovered in the samples of this peanut-shaped S-type asteroid. When the sample was examined under a microscope, the small particles were noted to be about 150 micrometers in diameter — roughly twice the diameter of a human hair. 

The researchers believe that these crystals could have developed only in the presence of liquid water.

Another noteworthy element of this research is that S-type asteroids are often devoid of water-bearing materials. However, these types of near-Earth asteroids are common in space. 

However, the discovery of sodium chloride suggests that S-type asteroids may contain far more water than previously thought. And may not be as dry as previously imagined.

It has been widely assumed that organic-rich C-type asteroids were one of the primary sources of water on Earth. 

"The most likely scenario is that comets or another type of asteroid known as C-type asteroids, which resided farther out in the solar nebula, migrated inward and delivered their watery cargo by impacting the young Earth,” said Tom Zega, the study's senior author, in an official release

The findings suggest that this population of asteroids might have delivered some amount of water during the planet's early years. 

How this asteroid got Sodium chloride

Itokawa is approximately 2,000 feet long and 750 feet in diameter and is thought to be a fragment of a larger parent asteroid. 

“It is conceivable that frozen water and frozen hydrogen chloride could have accumulated there [parent body], and that naturally occurring decay of radioactive elements and frequent bombardment by meteorites during the solar system's early days could have provided enough heat to sustain hydrothermal processes involving liquid water,” explained the official release. 

The parent body eventually split up into smaller bits, resulting in the formation of Itokawa.

"If it now turns out that the most common asteroids may be much 'wetter' than we thought, that will make the water delivery hypothesis by asteroids even more plausible," said Zega. 

Water covers over 70 percent of our planet's surface. Finding how water arrived on Earth is important to understand how and when life started to flourish on Earth. 

The results have been published in Nature Astronomy.

Study abstract:

Carbonaceous chondrites contain widespread mineralogical evidence for water–rock interactions, indicating that the C-type asteroids from which they are derived had active hydrothermal systems. In comparison, ordinary chondrites contain secondary minerals that are predominantly anhydrous, suggesting that their parent S-type asteroids were relatively dry. The returned particles from the Hayabusa Mission allow us to probe directly the alteration history of S-type asteroid Itokawa. Here we report nanometre-sized NaCl crystals identified in the interior of an Itokawa particle. These crystals are intimately associated with secondary albitic plagioclase, indicating coupled formation. The NaCl most likely formed through precipitation from an aqueous fluid prior to complete metamorphic dehydration on asteroid Itokawa. Our results therefore imply that asteroid Itokawa supported an active hydrothermal system and suggest that the once-hydrated S-type asteroids could have potentially delivered water to terrestrial planets.

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