We don’t know anything about dark matter or dark energy

The study of the universe is called cosmology. The whole universe is a single object. Scientists try to understand the origins, history, evolution, contents, and ultimate fate of this place that we call our home. About a hundred years ago, astronomer Edwin Hubble discovered that there are two remarkable things: that the universe is very far away from us and that some of the universe are moving away from us. He discovered that the universe is expanding and that it is very large.

Our universe was smaller, hotter, and denser a long time ago, according to the big bang theory. We have a lot of evidence to back up this simple statement, but that doesn’t mean we know everything about the universe. There are two glaring holes in our understanding. Dark matter was discovered in the 1970s. As far as we can tell, dark matter is made of a new particle with a mysterious identity. Dark matter takes up most of the mass in the universe, even though it doesn’t interact with light or normal matter.

Dark energy is the other giant hole. The expansion of the universe was discovered in the late 1990s by two teams of astronomer. Our universe is getting bigger and bigger every day, and it is also getting bigger and faster every day. We named the effect dark energy because we had no idea what was happening. Dark energy takes up 70% of all the mass energy in the entire universe, completely dominating everything else. There is a weird place where modern cosmology is located.

We understand the general picture of the big bang, and we are able to make some really cool statements, like the age of the universe is 13.77 billion years old, or that all the hydrogen atoms were formed when the universe was only a dozen minutes old. We know that we are on solid ground because we can back up all those statements. We don’t have an understanding of the vast majority of the contents of our universe. We know how they act, but they are not what they are. The name of the game in modern cosmology is to keep measuring the properties of dark matter and dark energy as precisely as possible and hope that something interesting pops up. The latest result is from the PANTHEON+ survey, which measured the precise positions of about 1,500 supernovae. The team behind the study used the data to find that the universe is made up of dark energy and dark matter. We’re going to have to keep digging because PANTHEON+ didn’t find any surprises when it came to the twin mysteries.

Mercury is the smallest of the four inner rocky planets of the solar system. It’s a big ball of rock. Why did NASA send a probe to the planet in 1974? The MESSENGER was a decade ago. Why did the Japanese and European space agencies join forces to develop BepiColumbo? There is a secret to Mercury. Mercury is a dead world. By its craters, you can tell. Worlds that are capable of active resurfacing, like from plate tectonics, will eventually erase their scars. A lot of craters on the surface of the Earth are not visible. Mercury hasn’t been molten in a long, long time.

The temperatures on Mercury are very cold. Because it is the closest planet to the Sun, it gets blasted in the daytime, with temperatures reaching up to 800 degrees. On the night side, away from the Sun, the temperatures can plunge to -270 degrees. There is water ice on the surface. craters are deep enough that they stay in the shadows all day long, even in the daytime, without much atmosphere to speak of. Mercury’s magnetic field is a big mystery. It is barely 1% of the Earth’s strength. Mercury is not supposed to have a magnetic field.

Planets have magnetic fields in their cores. Iron and nickel are the heaviest elements of a planet, found in those cores. The metals will melt if the cores are too hot. As the planet spins, the metal, molten core, which is exactly the conditions you need to power up a magnetic field, swooshes around. Mercury doesn’t have much of a molten core. It is so small that its inner core has cooled off and is now rock solid. It still has a liquid outer core, but it is not quite large.

Mercury is barely rotating. A day on Mercury lasts 58 Earth days. Astronomers and planetary geologists assumed that Mercury couldn’t form a magnetic field because it wasn’t able to get its act together. It was staring them in the face. The purpose of BepiColumbo and MESSENGER is to understand the origins of the magnetic field.

Inspired by Paul M. Sutter: https://www.discovery.com/space/mercury