Scientists believe they have estimated the lifetime of the solar nebula, which is a key stage during which much of the solar system evolution took shape.
New research led by scientists from the Massachusetts Institute of Technology (MIT) suggests that the gas giants Jupiter and Saturn formed within the 4 million years of the solar system’s formation and must have completed gas-driven migration of their orbital positions by this time.
“So much happens right at the beginning of the solar system’s history,” Benjamin Weiss, professor of earth, atmospheric and planetary sciences at MIT, said in a statement. “Of course the planets evolve after that, but the large-scale structure of the solar system was essentially established in the first 4 million years.”
The research team studied magnetic orientations in pristine samples of ancient meteorites that formed 4.6 billion years ago to determine that the solar nebula lasted around 3 to 4 million years, which is a more precise figure than previous estimated, which placed the solar nebula’s lifetime at between 1 and 10 million years.
They reached this conclusion by analyzing four angrites, which are some of the oldest and most pristine of planetary rocks.
Angrites are igneous rocks, many of which are thought to have erupted onto the surface of asteroids very early in the solar system’s history and then quickly cooled, freezing their original properties—including their composition and paleomagnetic signals—in place.
Angrites are often viewed as excellent recorders of the early solar system, particularly as the rocks contain high amounts of uranium, which scientists can use to precisely determine their age.
The researchers measured the ratio of uranium to lead in samples of each of the four meteorites, which fell to Earth at different places and times. They also measured the rocks’ remnant magnetization using a precision magnetometer.
“Electrons are little compass needles, and if you align a bunch of them in a rock, the rock becomes magnetized,” Weiss said. “Once they’re aligned, which can happen when a rock cools in the presence of a magnetic field, then they stay that way.
“That’s what we use as records of ancient magnetic fields.”
The researchers observed very little remnant magnetization in the angrites, indicating there was very little magnetic field present when the angrites formed.
The team then tried to reconstruct the magnetic field that would have produced the rocks’ alignments or lack thereof by heating the samples up and then cooling them down again in a laboratory-controlled magnetic field.
“We can keep lowering the lab field and can reproduce what’s in the sample,” Weiss said. “We find only very weak lab fields are allowed, given how little remnant magnetization is in these three angrites.”
The team found that the angrites’ remnant magnetization could have been produced by an extremely weak magnetic field of no more than 0.6 microteslas, 4.563 billion years ago or about 4 million years after the start of the solar system.
The solar nebula was formed 4.6 billion years ago from an enormous cloud of hydrogen gas and dust, that collapsed under its own weight and eventually flattened into a disk.
According to the researchers, most of the interstellar material contracted at the disk’s center to form the sun and part of the solar nebula’s remaining gas and dust condensed to form the planets and the rest of our solar system.
MIT postdoc Huapei Wang, the first author of this study, explained that the discovery gives the researchers a better idea on how the solar system was formed.
“What’s more, the angrites’ paleomagnetism constrains the lifetime of our own solar nebula, while astronomical observations obviously measure other faraway solar systems,” Wang said in a statement. “Since the solar nebula lifetime critically affects the final positions of Jupiter and Saturn, it also affects the later formation of the Earth, our home, as well as the formation of other terrestrial planets.”