Jupiter is the largest planet in our solar system—but it may also be the oldest. As Lisa Grossman reports for Science News, new research suggests that the planet was the first in our celestial family to take shape. Earth may even owe its presence to the gaseous giant.
Scientists previously pelieved that Jupiter formed within the first 10 million years of our solar system's birth, which began with the first minerals taking shape some 4.57 billion years ago, Phil Plait writes for Syfy Wire. Along with other gaseous giants—Saturn, Neptune and Uranus—Jupiter's swirling clouds likely originated from the massive spinning disk of gas and dust around our young star, a formation that only lasted around 10 million years, Grossman reports. But how long that took and when Jupiter actually began forming has still been up for debate. Now a new study, published this week in the Proceedings of the National Academies of Science, uses evidence from meteorites to suggest that Jupiter was the first of these giants to form.
Most Earth-bound meteorites are fractions of space rock that break off from asteroids residing in a large asteroid belt between Mars and Jupiter, Plait writes. Primarily composed of cosmic leftovers from the formation of our solar system, asteroids bear fingerprints from this momentous event. These chemical signatures take the form of isotopes, elements with the same number of protons but different number of neutrons, which can help scientists figure out both the age and origin of the space rocks.
So researchers studied the isotopic ratios of the heavy metals tungsten and molybdenum in 19 samples from iron meteorites at the Natural History Museum in London and Chicago’s Field Museum. They dissolved a bit of each sample in acid, reports Grossman, and then separated out the tungsten and molybdenum for analysis.
The results suggest that the meteorites could be separated into two general categories: a group that formed closer to the sun than Jupiter's current orbit and one that formed further out. But according to the data, both groups of meteorites formed at the same time, roughly one to four million years after the solar system began.
So why where they clustered into two different groups? A young Jupiter, whose gravity could keep the meteorite populations apart.
“The only mechanism or way to do this is to have a gas giant in between them,” study author Thomas S. Kruijer of the Lawrence Livermore National Laboratory tells Amina Khan at The Los Angeles Times. “Because only such a body is large enough to separate such large reservoirs.”
Researchers believe Jupiter's solid core grew to 20 times the size of the Earth in those first million years, Khan reports. Besides keeping asteroids apart, the planet's gravity could have also gobbled up much of the debris swirling around during the early solar system. This could be one reason our celestial family has smaller rocky planets like Earth, Mars, Venus and Mercury near the sun while other systems discovered so far commonly have so-called super-Earths and gas giants zipping around their inner layers.
If not for Jupiter’s early birth, we may not exist at all. “Without Jupiter, we could have had Neptune where Earth is,” Kruijer tells Grossman. “And if that’s the case, there would probably be no Earth.”
Plait points out that the study is no smoking gun, and that some models suggest Jupiter does not even have a core, but condensed into a gas giant from all the dust and debris surrounding the sun. Data from the Juno probe, which is currently poking around Jupiter, shows something in between: a squishy core that could be much larger than scientists currently think.
The gaseous giant likely has many more secrets to reveal. Just this week, researchers found two new moons orbiting the planet, bringing its total count up to 69. Who knows what else the stormy giant may be hiding.