If astronomy research has taught us anything in the last couple of decades, it’s that all rocky planets are /definitely/ not alike.
For example, Earth has big puzzle pieces of crust that can run into each other to form mountain ranges, or slide under each other to melt and recycle old rock. Meanwhile, parts of Venus’s crust just seem to jostle around without sliding under each other at all. Scientists are always trying to understand these places, but they’re also interested in understanding other worlds far from home, even hypothetical planets we haven’t found yet.
Like, in a paper first published online last month, in the Journal of Geophysical Research: Planets, a team announced the possibility of “eggshell planets,” worlds with relatively featureless surfaces and thin, brittle crusts. And they may have even /identified/ a few in the real world. In this paper, the researchers were trying to learn what affects a planet’s lithosphere, or outermost layer. On Earth, the lithosphere has two main parts.
The inner layer is hot and a bit squishy, and the outer layer is cool, hard, and brittle. It’s the part that can build up features like mountains — and how thick this brittle layer has a big effect on what a planet is like. ~ If a planet has a thicker brittle layer, it might be able to support plate tectonics, like Earth.
That’s the process where big pieces of the lithosphere move around the planet, forming mountains and getting recycled. But tectonic plates are also important for releasing a planet’s internal heat into space, as well as how gases leak out and help sustain an atmosphere. So, they play a role in how /habitable/ a planet is.
So, it’s no surprise that scientists want to know more about lithospheres on other worlds. Unfortunately, our telescopes aren’t good enough to see surface features on planets beyond our solar system, or exoplanets. Instead, astronomers have to find ways of inferring what an exoplanet looks like based on things they can measure, like the planet’s mass, size, age, and distance from its star. So, to learn more about exoplanet lithospheres, this team built a computer model, based on equations scientists had previously figured out for how different rocks behave on Earth.
Then, they ran simulations with thousands of exoplanets, all of which had a composition similar to our planet’s. In the end, the models showed that the exoplanets’ masses, surface temperatures, and the ages of their lithospheres all had an influence on the thickness of that brittle layer. So, planets that are small, old, or chilly, like because they’re far from their stars, were more likely to have /thick/ lithospheres.
They also found that planets with a thin brittle layer, which they called “eggshell planets,” were likely to have a few things in common. They found that they’re likely to be more massive than Earth, and have enough surface heat to keep that brittle layer thin, heat could come from multiple places. Like, the planets could be geologically young, have a lot more radioactive materials for extra long-term heating, or both. They might also be closer to their stars, and/or have thick atmospheres that trap a lot of heat. In /our/ solar system, Venus has some of those things relative to Earth.
And in fact, Venus’s flat lowlands might be what an eggshell planet’s crust looks like, meaning we might have at least a partial example of an eggshell planet nearby. But this team may have also found some proper eggshell worlds.
They identified three exoplanets scientists have already observed that might have brittle layers less than five kilometers thick. And with how many exoplanets there are, more may be out there.
Either way, having a way to understand what an exoplanet’s lithosphere is like is a major way to understand what things might be like on that world, if it could potentially be a habitable place with plate tectonics, like Earth… or if it’s more like Venus. Figuring out if a world light-years away could support life is a big challenge, so the more tools we have, the more we’ll understand. Closer to home, our next story comes from a paper published last week in Communications Earth & Environment, and it focuses on Earth’s long-term relationship. Not with the Moon, but with the quasi-moon Kamo’oalewa. This tiny space potato was discovered in 2016 by the PanSTARRS survey in Hawai’i.
It’s called a quasi-moon because it doesn’t really orbit the Earth like the actual Moon does, but it’s almost always pretty close to us while we go around the Sun. Also, it’s orbit is a bit askew, so its position changes from being ahead of the Earth in its orbit, to being behind it, and back again.
Now, Earth has had other quasi-satellites before, but they tend to come and go. Meanwhile, this quasi-moon seems to have been in our vicinity for the past century, and calculations suggest it’ll stick around even longer.
And that makes it a prime target to learn about quasi-satellites in general. In this new study, one team observed the quasi-moon with two ground-based telescopes, looking at the different wavelengths of light reflected off its surface. By doing this, they confirmed that this space potato is spinning pretty fast, making one full rotation every 28 minutes. They also confirmed that it’s mostly made of silicate minerals.
Except… the exact composition of those minerals wasn’t in line with the other asteroids in this part of the solar system. So, where did Kamo’oalwea come from? One hypothesis is that it came from some larger rock that got ripped apart by the gravity from the Earth-Moon system.
Although, that kind of pushes the question back, because like, where did that /rock/ come from? But another idea is that this quasi-satellite was chipped off the Moon itself, which is also made of silicate materials. To test this lunar origin idea, the team compared Kamo’oalewa’s apparent composition to those of different Moon rocks. And although it wasn’t a perfect match, there were a lot of similarities.
To the point where some of the researchers think this is the most likely explanation, based on what we know now! That said, if this space potato did break of the Moon, figuring out where and how is going to be a challenge. To learn more, scientists will need to get samples from the Moon as part of some upcoming mission, and will need to learn more about Kamo’oalwea itself. But luckily, in the meantime, this quasi-moon will continue to be our quasi-close companion for a few more centuries.
And that’s plenty of time to unlock its secrets. And something that unlocked other space secrets for years was the legendary Arecibo observatory which we have immortalized as this month’s pin to commemorate all its discoveries. So if you would like to take a tiny version of this observatory home you should visit DFTBA.com/SciShow. But you need to act fast because it’s available only in November, because in December, we’ll have a whole new pin for you.