How did the Earth, believed to have been covered in bubbling oceans of magma billions of years ago, transform into the ‘blue planet’ and become covered in water? In an article published in the journal Nature Astronomy on Monday (August 15), scientists from Japan suggest that water and organic materials might have been brought to our planet from the outer edges of the solar system.
The scientists made the hypothesis after analysing samples from the asteroid Ryugu, collected by the Japan Aerospace Exploration Agency’s (JAXA) Hayabusa-2 probe, which had brought 5.4 grams of rocks and dust from the asteroid to Earth in December 2020.
The Hayabusa-2 mission was launched in December 2014 when the spacecraft was sent on a six-year voyage to study the asteroid Ryugu. According to a report by Deutsche Welle from 2020, the spacecraft, which was approximately the size of a refrigerator, traveled more than 5 billion kilometers during its journey.
The spacecraft arrived at the asteroid in mid-2018 after which it deployed two rovers and a small lander onto the surface. In 2019, the spacecraft fired an impactor into the asteroid’s surface to create an artificial crater with a diametre of a little more than 10 metres, which allowed it to collect the samples.
In December 2020, Hayabusa-2 delivered a small capsule that contained the rock and dust samples when it was 220,000 km from the Earth’s atmosphere, which safely landed in the South Australian outback.
Hayabasu2’s predecessor, the Hayabusa mission, brought back samples from the asteroid Itokawa in 2010.
What were the findings of the study?
Since the capsule landed on Earth, scientists have been studying the invaluable material — weighing merely a few grams, but approximately 4.6 billion years old — in order to explore the foundations of the solar system. Their analyses of the samples have helped us explore the origins of life on our planet.
In June, a group of scientists found that the materials contained amino acids, and suggested that these building blocks of life might have formed in space.
The current study, published on Monday, states that “Volatile and organic-rich C-type asteroids may have been one of the main sources of Earth’s water,” which is essential for the emergence of life. While the delivery of volatiles (water and organics) to Earth has been a subject of debate amongst scientists, the materials found in the “Ryugu particles, identified in this study, probably represent one important source of volatiles.”
The study claimed that the organic material collected probably originated from the fringes of the Solar System, but was “unlikely to be the only source of volatiles delivered to the early Earth”.
While the composition of particles collected from Ryugu closely matches water on Earth, the study notes there were slight differences, leading scientists to hypothesise that our planet’s water might have also originated from places other than asteroids, as reported by Kyodo News.
“In a broad sense, it is possible that small celestial bodies brought things that led to water and life on Earth,” Motoo Ito, a senior researcher of geomaterials science at the Japan Agency for Marine-Earth Science and Technology was quoted as saying by the agency.
Asteroids are rocky objects that orbit the Sun, much smaller than planets. They are also called minor planets. According to NASA, there are 994,383 known asteroids, the remnants from the formation of the solar system over 4.6 billion years ago.
Asteroids are divided into three classes. First are those found in the main asteroid belt between Mars and Jupiter, which is estimated to contain somewhere between 1.1-1.9 million asteroids.
The second group is that of trojans, which are asteroids that share an orbit with a larger planet. NASA reports the presence of Jupiter, Neptune and Mars trojans. In 2011, they reported an Earth trojan as well.
The third classification is Near-Earth Asteroids (NEA), which have orbits that pass close to the Earth. Those that cross the Earth’s orbit are called Earth-crossers. More than 10,000 such asteroids are known, out of which over 1,400 are classified as potentially hazardous asteroids (PHAs).
Ryugu is also classified as a PHA and was discovered in 1999 and was given the name by the Minor Planet Center in 2015. It is 300 million kilometres from Earth and it took Hayabusa-2 over 42 months to reach it.
Why do scientists study asteroids?
Since asteroids are one of the oldest celestial bodies in the Solar System, scientists study them to look for information about the formation and history of planets and the sun.
Another reason for tracking them is to look for asteroids that could possibly crash into Earth, leading to potentially hazardous consequences.
NASA’s OSIRIS-REX mission had collected samples from the asteroid Bennu in October 2020, which will be brought to Earth in 2023. Scientists are interested in studying asteroids such as Bennu, because it hasn’t undergone drastic changes since its formation over billions of years ago and therefore it contains chemicals and rocks dating back to the birth of the solar system. It is also relatively close to the Earth.