Ice blue meteorite crystals show evidence of an active young Sun

Putting together the timeline of the solar system is like putting together the bones of a dinosaur. You’ve got all these pieces lying around and you have to figure out which way they fit, how they work with all the other pieces. And sometimes you have fragments you need to piece together as well, ones that have to be put together as a subset before attaching to the bigger frame. But, when they do slide into place, you can learn surprising things.

For example, tiny fragments of ancient meteorites contain tinier fragments of even older stuff, and they tell us that when the Sun was very young it went through a phase of throwing pretty epic temper tantrums.

You’ve probably heard of solar storms: Flares and coronal mass ejections that are huge eruptions of gas exploding outward at high speeds from the Sun. These are, at their heart, magnetic phenomena. Ionized gas (called plasma) inside the Sun moves around, generating magnetic fields (moving charged particles making magnetism is a really basic rule of physics). These in turn are sustained by circulation inside the Sun, which is in part due to the Sun’s rotation.

We know the Sun rotated faster when it was young. How? As it spins, its magnetic field sweeps up charged particles flowing away from it, speeding them up — it’s like if you stand with a trash bag in your hand and spin around; the open bag will gather air and swirl it around you. But in turn that produces a drag on you, slowing you down. The same for the Sun. The drag is pretty weak, but it’s had billions of years to work, so the Sun has been slowing by a tiny amount for a long, long time. Back when it was young it spun faster.

But a rapidly spinning star will generate more powerful magnetic fields, which in turn drives more storm activity. So we think the Sun was pretty tempestuous as a youth. However, finding direct evidence of that has been difficult.

Now, though, that may have changed. We know that some meteorites that fall to Earth from space are what are called “primitive”: That is, they have minerals and structures in them that indicate that they are very old, and have remained pretty much unchanged since they formed. One such meteorite is Murchison, a 100-kilogram rock that fell in Australia in the 1960s. It was part of a larger asteroid that got broken apart, but inside it are crystals and other structures that are something like 4.56 billion years old — older than the Earth!

Hibonite crystals (inset, actual photo) formed very early in the solar system's history when it was still a swirling disk of gas and dust (artwork). Credit: Field Museum, University of Chicago, NASA, ESA, and E. Feild (STScl).

Photo: Credit: Field Museum, University of Chicago, NASA, ESA, and E. Feild (STScl).

Inside the meteorite are very tiny grains containing crystals of a mineral called hibonite^*, a hard hexagonal crystal that comes in a variety of colors. In this case, the crystals are a beautiful ice blue. Hibonite is a very simple crystal that probably was among the very first minerals to form out of the disk of gas and dust that formed our solar system, when the Sun itself was still getting its act together and the planets hadn’t even formed yet.

Hibonite has calcium and aluminum in it, and that’s important. If these elements are slammed by high-speed protons (like, say from solar storms), the nuclei can break apart to form isotopes (think of them as different flavors) of helium and neon that are otherwise pretty rare. Scientists looked at the amount of helium and neon in the crystal, and the ratios of the two as well, and found that there was a lot more of them in there than you’d expect if the crystal formed in a quiet solar environment.

Other structures (called inclusions) in Murchison don’t show these sorts of effects. The best explanation, given the circumstances, is that when the crystals of hibonite formed very early on, the Sun went through a short very active phase, blasting out powerful storms that sent high-speed protons sleeting out to space and into the surrounding disk of material. It was these protons that zapped the crystal, breaking down the calcium and aluminum, and creating the noble gases of helium and neon the scientists found.

The Sun then quieted down, and by the time the other inclusions found in the meteorite formed things had settled down. The crystals of hibonite were agglutinated into the bigger body, forming a larger asteroid, which orbited the Sun for billions of years. A few million years ago it got whacked by another asteroid, sheared off the 100+ kilogram piece, and that eventually fell to Earth.

This fits with the previous knowledge we have of the young Sun, part of which we’ve learned by studying other very young stars. We see them being magnetically active, with rapid rotation, and even sometimes with huge beams of magnetically focused material shooting out of them (these are called Herbig-Haro objects, and are gorgeous).

And so it looks like another piece of the puzzle is now in place. And like a dinosaur skeleton, the pieces seem to fit together well… and in fact are very similar: Fossilized remnants of an ancient time when things were very different than they are today, giving us a peek into the past.

And in both cases I’m glad. I’d rather not co-exist with Deinonychus any more than I’d want to be this close to a star prone to high-energy magnetic paroxysms. It’d be cool to get a closer look at both these things, honestly, but it’s better to live now, and be able to examine the past in an environment where it’s easier to stay alive.

^*This mineral was discovered by a French prospector named Paul Hibon, so I suspect it shouldn’t be pronounced HIGH-bo-nite, as I first thought, but EE-bo-nite.