This episode is sponsored by Wren, a website where you can calculate your carbon footprint.

Click the link in the description to learn more about how you can make a monthly contribution to offset your carbon footprint or support rainforest protection projects. [♪ INTRO]. If you look at the solar system, one thing that stands out is that it’s pretty well-organized: The small, rocky planets are all relatively close to the Sun, and all the gas giants and ice giants are farther away.

Well, last week in the journal Science Advances, one team might have found out at least part of the reason why: A huge gap in the dust and gas surrounding an infant Sun. If you want to make planets, you gotta start with a protoplanetary disk. That’s a massive disk filled with dust and gas that forms around a baby star, and it provides material to make everything from rocky planets to gas giants.

Thanks to ever-improving technology, astronomers are getting more and more detailed images of these disks around other stars. But to study our neighborhood, they often turn to meteorites. These rocks are like time capsules: The stuff they are made of hasn’t been altered since the rocks formed about four and a half billion years ago, which means they can clue us into how the solar system might have formed.

In particular, over the past decade, scientists have found that meteorites from the inner part of the solar system have less of certain elements than those from farther out. Elements like chromium, nickel, and titanium. So, they’ve speculated that our Sun’s protoplanetary disk could have had a major gap in it, physically separating the two regions.

Except, there have also been other explanations for why those groups of meteorites are different. So with this new paper, one team was hunting for evidence of a gap. But instead of looking at what the meteorites are made of, they looked for remnants of magnetic fields in the rock.

See, baby solar systems are known for having strong magnetic fields in their protoplanetary disks. So, in a newly-formed space rock, molten, iron-filled globs of material will collectively align themselves along the local magnetic field, just like a bunch of compass needles. Then, after cooling down, these crystals retain a record of how strong that magnetic field was.

In a previous study, this team had measured the magnetic field strength from meteorite samples originating less than three astronomical units from the Sun, that is, three times the distance of Earth’s orbit. For reference, the main asteroid belt ranges from about 2.1 to 3.3 astronomical units, and it’s another two to reach Jupiter. This time, they looked at two meteorites that formed between three and seven astronomical units from the Sun.

And there was a huge difference. The grains inside these more distant rocks formed inside a much stronger magnetic field. And after running computer models, this team concluded that you’d most likely need a huge, hard-to-cross gap in the protoplanetary disk to explain the differences!

Now, this team only looked at a small sample of rocks, but this is still the first solid evidence that this gap in our Sun’s protoplanetary disk really existed. What we don’t know is what might have caused it. One idea that might partly explain things is that as Jupiter grew, its gravitational influence could have thrown small bodies in the area into the solar system’s suburbs.

Another hypothesis is that the interaction between the magnetic field and the local dust and gas could have created a type of wind that pushed out material, instead. Still, whatever the source, this research offers another idea about why the two regions of our solar system look so different, why the terrestrial planets are on one side, and the gas and ice giants are the other. Our next story takes us to a much larger space rock: Jupiter’s moon Europa.

In an article from Geophysical Research Letters first published online in September, an astronomer revealed that this moon has a bunch of water vapor in its atmosphere… but only on one side. You may have heard of Europa because it’s one of a few water worlds in our solar system. It’s so cold that its surface is covered in ice, but temperatures are warm enough farther down that some of the moon’s water can stay liquid.

In fact, data suggest Europa has more liquid water than the Earth, despite being smaller than our Moon! Now, since the ocean is under the surface, we can’t directly see it, but astronomers have inferred it’s there by detecting water vapor from geysers up to 160 kilometers tall! But according to this new paper, there also might be another source of water vapor.

So, a few months ago, a team used a new method to find evidence of water vapor in the atmosphere of another one of Jupiter’s moons: Ganymede. They’d used the Hubble Space Telescope to hunt for signatures of oxygen in a way that could infer the existence of water vapor. And they found evidence of that vapor coming directly from ice on the surface:.

Sunlight was warming it up enough to change it directly into a gas. In this new paper, one astronomer from that team applied this same method to Europa, and made the same discovery there! He saw evidence of water vapor across 15 years of Hubble data, water generated not by Europa’s geysers, but by sunlight and surface ice.

What was extra surprising, though, was that the water vapor signature wasn’t spread over the entire atmosphere. It only appears to exist on the back on the moon, that is, the side opposite the direction Europa is moving. And while there are some hypotheses, it is still a mystery why.

So just like with the gap in our solar system’s disk, this is another case of a discovery leading to even more questions. Another long-standing discovery that has just led to a lot more questions is the climate crisis and today’s sponsor Wren might just have some solutions. They’re a website where you can calculate your carbon footprint then offset it by projects that plant trees and protect the rainforest.

You can start by signing up, answering a couple of questions about your lifestyle from what you eat to your favorite way of commuting, and that will calculate our carbon footprint and how to offset it. Like by signing up to make monthly contributions for Wren projects to plant trees and protect rainforests. And the best thing is that you get to see the trees you planted, and what your money is spent on.

And as a bonus, we’ve partnered with Wren to plant 10 extra trees for the first 100 people who sign up using our link in the description! And as always, thank you for supporting SciShow Space. [♪ OUTRO] .