Category: collision

Rocky Planets May Only Get Moons From One Sour…

Rocky Planets May Only Get Moons From One Source: Giant Impacts

“If your gravity rises up to a point where you can pull yourself into hydrostatic equilibrium — a sphere if you’re static, an ellipsoid if you’re rotating — you cannot be pulled apart by tidal forces so easily. But you could, in principle, develop moons through three methods: initial formation from a protoplanetary disk, capturing another passing body through gravitational forces, or from the debris of a large collision.

While the gas giants display moons that appear to have arisen from all three, the rocky planets, including both major and minor planets, appear to obtain moons from collisions alone. It may be the case that the other options are viable but rare, and we simply have yet to discover them. But following the evidence we have today, perhaps Earth’s moon isn’t atypical after all. Until further notice, giant impacts are the only known way for rocky planets to gain moons.”

When we first visited the Moon and returned samples back to Earth for analysis, scientists were surprised to learn that the lunar surface was practically identical to Earth’s surface. The elements were the same; the isotope ratios were the same; the ages were the same. Unlike the other moons around other planets, the Earth’s moon appeared to be made out of the exact same material as our own world. This helped lead to the giant impact hypothesis as the origin of the Moon. Surprisingly, Mars’ moons and Pluto’s moons appear to have a similar origin: from a giant impact. Of all the planets and dwarf planets with moons, in fact, it looks like giant impacts explain them all.

Here’s the science of what we know so far. It’s possible that, for rocky worlds, either a giant impact generates your moons, or you have no moons at all.

Ask Ethan: Why Haven’t We Bumped Into Another …

Ask Ethan: Why Haven’t We Bumped Into Another Universe Yet?

“If the Multiverse Theory is true, shouldn’t our expanding universe have bumped into another universe by now? After all, our universe is now so large that some describe it as “infinite” in size.”

The Multiverse is one of the most fascinating ideas to arise out of the past few decades. In short, it says that our Universe, as we know it, is just one of countlessly many in a vast sea of inflating spacetime. But with all of those other Universes out there, and with all of them expanding just as our own is, shouldn’t we have collided with another one by now? And if so, where’s the evidence for it? It’s a question that needs to be taken seriously, because if we make a scientific prediction that isn’t borne out, we need to understand why. But before we ever get there, we need to understand exactly what predictions come out of our theories, including the fact that even if our Universe is infinite, that doesn’t mean there isn’t another, bigger infinity preventing us from ever colliding with another one.

Come find out why our Universe shouldn’t have bumped into another one by now, and come to better understand the Multiverse while you’re at it!