Tiny crystals of table salt found in a sample from an asteroid may help explain the enduring mystery of how water arrived on Earth.


The crystals, found by researchers at the University of Arizona’s Lunar and Planetary Laboratory (LPL), can only have formed in the presence of liquid water, scientists said.

The find hints that many S-type asteroids – previously thought to lack water-bearing minerals – might actually be wetter than previously thought.

Detailed analysis of samples

This lends weight to the idea that most of the water on Earth probably arrived on asteroids in the early days of our planet.

Researchers performed a detailed analysis of samples collected from asteroid Itokawa in 2005 by the Japanese Hayabusa mission and brought to Earth in 2010.

Discovery of sodium chloride

Tom Zega, the study’s senior author and a professor of planetary sciences at LPL, said: “The grains look exactly like what you would see if you took table salt at home and placed it under an electron microscope.

“They’re these nice, square crystals. It was funny, too, because we had many spirited group meeting conversations about them, because it was just so unreal.

“It has long been thought that ordinary chondrites are an unlikely source of water on Earth.

“Our discovery of sodium chloride tells us this asteroid population could harbour much more water than we thought.”

Type of extraterrestrial rock

Zega said the samples represent a type of extraterrestrial rock known as an ordinary chondrite – derived from so-called S-type asteroids, such as Itokawa, which make up about 87% of meteorites collected on Earth.

Very few have been found to contain water-bearing minerals though.

Scientists largely agree that Earth, along with other rocky planets such as Venus and Mars, formed in the inner-region of the roiling, swirling cloud of gas and dust around the young sun, known as the solar nebula.

Temperatures there were too high for water vapour to condense from the gas, according to Shaofan Che, lead study author and a postdoctoral fellow at LPL.

Impacting the young Earth

He said: “In other words, the water here on Earth had to be delivered from the outer reaches of the solar nebula, where temperatures were much colder and allowed water to exist, most likely in the form of ice.

“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.”

Extraterrestrial matter

The discovery that water could have been present in ordinary chondrites, and therefore been sourced from much closer to the sun than their ‘wetter’ kin, has implications for any scenario attempting to explain the delivery of water to the early Earth.

Zega said tons of extraterrestrial matter is raining down on Earth every day, but most of it burns up in the atmosphere and never makes it to the surface.

“You need a large enough rock to survive entry and deliver that water,” he said.

Source- Yahoo