Grains of dust from an asteroid, a relic of the early solar system, have revealed a fascinating secret about the reach of magnetic systems in the cosmos. This discovery, gleaned from samples returned by the Japanese Hayabusa-2 mission, sheds light on where magnetic fields existed during the formative years of our solar system and their potential influence on planet formation.
Evidence from Asteroid Ryugu: A Magnetic Fossil
The asteroid Ryugu, a subject of intense study by the Hayabusa-2 mission, is no ordinary space rock. Believed to be a fragment of a larger celestial body shattered by ancient collisions and possibly an extinct comet, Ryugu offers a unique window into the past. Hayabusa-2 not only observed this intriguing asteroid but also collected precious samples from its surface and subsurface, delivering them back to Earth for detailed analysis.
Within these samples, scientists discovered grains of material that had preserved a snapshot of the magnetic environment at the time of Ryugu’s formation. The analysis of these grains revealed the presence of a magnetic field estimated to be around 15 microteslas. While this might sound weak compared to Earth’s magnetic field, which is over three times stronger, or the potentially more intense magnetic field of the early inner solar system, this faint magnetism carries significant implications.
Implications for the Outer Solar System’s Formation
Despite its relative weakness, the magnetic field detected in Ryugu samples is considered strong enough to have played a crucial role in the formation of celestial bodies much farther from the Sun than Earth. Imagine a region stretching more than seven times the distance between the Earth and the Sun – this is where this magnetic field could have exerted its influence.
This includes the zones where the gas giants – Jupiter, Saturn, Uranus, and Neptune – were born, along with countless comets, asteroids, and smaller worlds inhabiting the outer reaches of our solar system. The finding suggests that magnetic systems were not confined to the inner solar system where rocky planets formed, but extended far beyond, influencing the accretion of matter in the outer regions as well.
The Protoplanetary Disk: Birthplace of Magnetic Systems
The Sun’s birth was marked by the collapse of a vast cloud of interstellar gas. Following the Sun’s ignition, a portion of this cloud flattened into a swirling disk known as the protoplanetary disk. This disk, composed of gas and dust, was the cradle of our solar system. Crucially, this disk was filled with ionized gas, making it a dynamic arena for magnetic interactions with the young Sun.
The interplay of gravity, magnetism, and the angular momentum within this rotating disk orchestrated the birth of planets. Magnetic fields are now recognized as a fundamental force in this process, helping to transport mass and shape the architecture of planetary systems. Interestingly, this nebular magnetic field is believed to have dissipated relatively quickly, disappearing roughly 3 to 4 million years after the solar system’s formation. Scientists are keen to understand the precise role it played during this critical period of planetary genesis.
Confirmation from Distant Meteorites and Future Research with Bennu
To further validate their findings, the research team examined meteorites believed to have originated from the distant solar system. These meteorites also exhibited signs of magnetic fields, albeit weaker, generally consistent with the upper limit of 15 microteslas found in Ryugu samples. This corroboration strengthens the idea that a weak but pervasive magnetic system existed in the outer solar system during its early stages.
Looking ahead, the scientific community eagerly anticipates the analysis of samples from another asteroid, Bennu, collected by NASA’s OSIRIS-REx mission. Bennu, like Ryugu, is a primordial asteroid, and studying its magnetic properties promises to offer even more insights into the nature and extent of the early solar system’s magnetic field, and ultimately, where such magnetic systems can be found in the cosmos.
