David Kipping

And of course, we've got excited about this recently because of Oumuamua, this interstellar asteroid, which seemed to be at the time the first evidence of an interstellar object.

But when you think about the Oort cloud intermixing, it may be that a large fraction of comets, comets that are seeded from the Oort cloud that eventually come in, some of those comets may indeed have been interstellar in the first place that we just didn't know about through this process.

There even is an example, I can't remember the name, there's an example of a comet that has a very peculiar spectral signature that has been hypothesized to have actually been an interstellar visitor, but one that was essentially sourced through this Oort cloud mixing.

And so this is kind of intriguing.

The outer Solar System is like the bottom of the ocean.

We know so little about what's on the bottom of our own planet's ocean.

And we know next to nothing about what's on the outskirts of our own solar system.

It's all darkness.

Basically, all of us, 400 years of astronomy, our only window into the universe has been light.

And that has only changed quite recently with the discovery of gravitational waves.

That's now a new window.

And hopefully, well, to some degree, I guess, solar neutrinos we've been detecting, but they come from the Sun, not interstellar space.

But we may be able to soon detect neutrino messages, as has even been hypothesized as a way of communicating between civilizations as well, or just do neutrino telescopes to study the universe.

And so there's a growing interest in what we'd call multi-messenger astronomy now.

So not just messages from light, but messages from these other physical packets of information that are coming our way.

But when it comes to the outer solar system,

light really is our only window.

There's two ways of doing that.

One is you detect the light from the Oort Cloud object itself, which as I just said, is very, very difficult.

There's another trick which we do in the Kuiper Belt especially, and that's called an occultation.