Anders Sandberg decided to make an effort to answer a Physics StackExchange question. Sandberg, a researcher, science debater, and futurist took the seemingly silly question very seriously. The question sounded like this:
“Supposing that the entire Earth was instantaneously replaced with an equal volume of closely packed, but uncompressed blueberries, what would happen from the perspective of a person on the surface?”
First of all — okay, that is… a question. But on a closer look, there’s actually a lot of physics hidden in that question, which Sandberg addressed in a small study published on arXiv.
First, we need to get an idea of how planets are formed. Our Solar System was once a bunch of gas and dust — a nebula. The center coalesced to form the Sun, and the dust of the inner solar system is responsible for the formation of Earth. Then, gravity takes part and everything depends on it.
The precise gravitational field of our planet is ideal for keeping us here on the surface, along with liquid oceans, a Moon that makes tides possible, not too many earthquakes, and maybe the most important of all, for humans — our atmosphere. Blueberries would wreak hell on all that.
Welcome to Blueberry Earth
Secondly, you need to clarify what blueberries you’re talking about. The species of blueberries Sandberg considered is the Vaccinium corymbosum blueberry, which is succulent and bigger than the other types of the fruit. To make a planet out of berries (and instantaneously) we need to consider the ingredients’ density — in this case, the blueberries’ density is 700 kg/m³, around 7 times lower than the Earth’s.
Changing the density and maintaining the volume of the Earth means the planet will lose some mass. If made entirely of the fruit, our planet’s mass will drop to 13% of what it is now, which means the gravitational attraction of the Blueberry Earth also drops substantially. We can no longer keep the Moon gravitationally locked, and presumably, the Moon would just fly away.
Because of the change in the planet’s radius, its rotation changes. It’s like a ballerina speeding down her rotation by extending her leg and then speeding up by retracting it. This is the conservation of angular momentum. A smaller planet has a faster rotation velocity, which results in a shorter day. A day in the Blueberry Earth would last approximately 19 hours.
So what happens to the berries?
So, we now have no moon. It’s time to focus on how the planet merged its ingredient and formed a spherical structure. Blueberries are not a particularly sturdy material, so coalescing them together will have some effects. Sandberg estimates that while the surface of Blueberry Earth will be free blueberries, they will start pulping a few meters below (around 11.5 meters below). The pulping effect will further cause the planet’s radius to shrink.
The Blueberry Earth’s gravitational pull will now be comparable to that of the Moon — which spells trouble for our atmosphere. With a different gravitational pull, the atmosphere is just not the same — and neither is the temperature. Everything is different, and you would not like the El Niño season in Blueberry Earth. Our sky is now blueish (go figure), but the clouds are still white).
Lava or jam?
Some geology may still happen on Blueberry Earth, but it’s not the geology we’re used to. Considering the pulp mechanism as possible, and also considering the air between the blueberries and a lower gravitational field — we end up with mechanisms that can produce colossal geysers. However, they’d be made of blueberry hot juice or jam. So… yum?
We could imagine geysers similar to Enceladus, one of Saturn’s moons which ejects water vapor and ice particles. Enceladus is small, six Enceladus fit in Amazonas – the biggest Brazilian state. Its surface is covered in ice and scientists discovered that below the icy crust there are oceans made of water.
Due to the pressure between the fruits, the core would be dense enough to become ice. Yes, even with high temperatures, Blueberry Earth’s core could basically become icecream. Considering the amount of water in blueberries we can see the formation of ice at very high pressures for the water molecule, using the phase diagram. In our case, the result would be ice VII, which forms above nearly 30,000 times the sea-level pressure.
A day on Blueberry Earth
Without our planet’s metallic core, there would also be no magnetic field to protect us from radiation — this would make us and all other species exposed to solar radiation and cosmic rays, not a nice place to live in (to put it mildly). Let’s not forget this planet would be made of organic material, so the planet itself couldn’t survive the fury of electromagnetic waves travelling the universe.
Blueberry Earth wouldn’t be stable enough for a regular rocky planet lifetime. Our good old iron-silicate-basaltic planet is much better, we can live on it, hold the atmosphere we need, and plant berries in it. Unless you are an adapted extremophile Mummy Berry citizen, you’re gonna have a bad time on Blueberry Earth. Sandberg sums it up thusly:
“So, to sum up, to a person standing on the surface of the Earth when it turns into blueberries, the first effect would be a drastic reduction of gravity. Standing on the blueberries might be possible in theory, except that almost immediately they begin to compress rapidly and air starts erupting everywhere. The effect is basically the worst earthquake ever, and it keeps on going until everything has fallen 715 km.”
“While this is going on everything heats up drastically until the entire environment is boiling jam and steam. The end result is a world that has a steam atmosphere covering an ocean of jam on top of warm blueberry granita. The final state of Blueberry Earth is somewhat similar to oceanic exoplanets.”
So as cool as it sounds, Blueberry Earth is not exactly where you’d want to spend your time. But you can spend your time having some blueberries on Earth, and that’s probably a better idea.