Introduction
Millions of rocky travellers are zooming into the space like tiny explorers, these are asteroids. While a tiny crumb of these giant rocks are asteroid grains like sand grains. They fall on Earth when asteroids break or collide.
Fascinatingly, these tiny particles carry invaluable information about the early solar system’s history. These grains are often composed of minerals and organic materials formed in the protoplanetary, the primordial cloud of gas and dust surrounding the young Sun. First studied in meteorites—fragments of asteroids and other bodies that fall to Earth—these grains preserve records of processes such as stellar nucleosynthesis, nebular condensation, and planetary accretion.
At Space India, through Space Explorers Workshop, “Cosmic Fireworks”, Students unravel the mystery of shooting stars and why they are called so. The fascinating concepts including the difference between meteors, meteoroids, and meteorites, why meteors are attracted towards Earth and much more about the beautiful streaks of lights visible in the sky for very short durations will inspire students to do and plan meteor shower observation on their own!
Notable discoveries
- Pre-solar grains and microscopic particles predating the Sun, which are found in meteorites like Murchison and offer a glimpse into ancient stars’ contributions to our solar system.
- Modern sample-return missions, such as JAXA’s Hayabusa2 to asteroid Ryugu and NASA’s OSIRIS-REx to asteroid Bennu, have advanced our understanding by delivering pristine, uncontaminated grains directly from their parent bodies.
These grains provide clues about the chemical composition, magnetic environment, and physical conditions of the early solar nebula, offering a window into the processes that shaped the planets and other celestial bodies billions of years ago.
Tiny grains collected from the distant asteroid Ryugu are offering fresh insights into the magnetic forces that shaped the outer solar system 4.6 billion years ago. Scientists from MIT and other institutions analyzed samples retrieved by JAXA’s Hayabusa2 mission, which returned these particles to Earth in 2020. Ryugu is believed to have originated in the outermost regions of the early solar system before migrating inward to the asteroid belt, eventually settling in its current orbit between Earth and Mars.
Through meticulous examination, researchers searched for traces of ancient magnetic fields that may have influenced Ryugu’s formation. Their findings suggest that any magnetic field present during the asteroid’s early development was likely very weak, with an intensity of no more than 15 microtesla, a stark contrast to Earth’s current magnetic field strength of 50 microtesla. Despite its faintness, this weak magnetic field could have been sufficient to drive the aggregation of gas and dust in the outer solar system, possibly playing a significant role in the formation of giant planets like Jupiter and Neptune.
Rewinding the tape
The asteroid Ryugu, thought to have originated in the outer reaches of the early solar system beyond 7 astronomical units (AU), offers a rare glimpse into the solar system’s distant past. JAXA’s Hayabusa2 mission returned samples from Ryugu to Earth in December 2020, enabling scientists to study what might be a relic of the early, remote solar nebula. Researchers analyzed several millimetre-sized grains from the asteroid using a magnetometer, a device designed to measure the strength and direction of magnetic fields in a sample. By applying alternating magnetic fields to demagnetize the particles, the team essentially “Rewound” the magnetic history of the samples to determine if they retained traces of an ancient magnetic field.
“Magnetic Fields in the Outer Solar System: Insights from Ryugu
The analysis revealed no clear evidence of preserved magnetism in the Ryugu samples. This finding implies that the outer solar system either lacked a significant nebular magnetic field at the time of Ryugu’s formation or that any existing field was too weak to be recorded. To deepen their understanding, researchers revisited data from ungrouped carbonaceous chondrites, a class of meteorites believed to have formed in the distant solar system. A reanalysis of these meteorites revealed they were closer in age to the solar system’s origin than previously thought, suggesting they might have formed in the outer regions. Intriguingly, one of these samples displayed a weak magnetic field of about 5 microtesla, consistent with an estimated upper limit of 15 microtesla for the outer solar system.
These findings, combining Ryugu grains and meteorite data, suggest that a weak magnetic field existed beyond 7 AU in the early solar system. While faint, this field was strong enough to draw material inward, playing a role in forming the outer planets, including Jupiter and Neptune. As MIT’s Weiss explains, even a weak field in the distant solar system could significantly influence the aggregation of gas and dust due to the lower intensity required at greater distances from the Sun. Further confirmation of these results could come from samples of asteroid Bennu, delivered by NASA’s OSIRIS-REx mission in September 2023, which may provide additional evidence of the early solar system’s magnetic environment.
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