Tails

Hey, Vsauce. Michael here. This is Earth as seen from Saturn. That is us right there. And if you look closely, ok, see this little protuberance? That's the Moon. This image was taken by the Cassini spacecraft on July 19th, 2013 at 21:27 Coordinated Universal Time. The thing is, NASA gave the public advanced warning of when it would be taken, which means that this image of Earth was the first ever taken from space that some people on Earth were actually posing for.

Our planet looks so small, insignificant, fragile. I recently attended the premiere of Sky 1's upcoming "You, Me and the Apocalypse" with some cool YouTubers and it got me thinking. In the show, the characters find out that they're only 34 days left before a comet smashes into Earth that's likely to end humanity. They all react in different interesting ways, but what would I do if I found out that there were only 34 days of human history left? Ok, my first priority would be to get back to America to be with my family. But after that? I don't really have a bucket list. Except that is exactly what I would want to spend my last few weeks doing. Making a list to put in a bucket that I would then send far out into space away from Earth's impending vaporization.

The list would contain information about us, all Earthlings. So that if libraries and monuments and YouTube videos were all destroyed, a record would still exist somewhere of what and who we were. Like a stone thrown into a lake, the ripples your life causes last long after you vanish, the tree you planted is climbed by future generations, the books you donated inform future readers. But what if it's not just your stone that vanishes, but the entire pond? Perhaps it's arrogance or vanity, but getting cosmic messages in a bottle out there, before the end, diversifies our archive and gives a better chance for future alien visitors, or whatever is left of humanity, to find out that we were once here, to show what we learned. Maybe even to warn future life forms of what we did or what we didn't prepare for. We have already sent some messages about humanity out there, beyond Earth, and if Earth is completely destroyed, those messages will be all that's left of us. What are they?

Ok, first things first. How do you write something for the future? I mean, the distant future. The message might not be found for millions of years or billions. It might be discovered by an audience that's completely different, not only in language, but in senses? What if they can't see or hear or feel or taste or smell like we do, or at all. What if their bodies destroy the very material we write the message on? What language do you even write it in? Well, in general, math and physics, which are believed to be the same everywhere in the universe, have been what we write outer space bound messages in.

Like the Arecibo message, written by Frank Drake, Carl Sagan and others, which was blasted towards the M13 star cluster in 1974. It's composed of a semi prime number of binary digits conveying some info about us and it should reach the center-ish of the M13 cluster in about 25,000 years, at which point, if something intelligent lives there and detects it, they can respond and their response will return to us another 25,000 years later. We won't be around for that.

But Earth has also been broadcasting its radio and TV signals into space. Currently it's about 200 light-years in diameter. Compared to the Milky Way, it's about this big. Aliens within that bubble could tune in and listen to programs we sent out through our airwaves, but these signals thin out as the bubble expands. Across very large distances they may be essentially impossible to tune into.

Maybe a physical time capsule would be more permanent, but it can't be buried on Earth if Earth is about to be ravaged. A time capsule in orbit might be smart, like LAGEOS-1, a satellite put into orbit in 1976 that allows for very precise laser measurements of positions on Earth, but also contains a plaque designed by Carl Sagan, upon which is written the numbers 1 to 10 in the binary, and the arrangement of the Earth's continents 250 million years ago, today and their estimated arrangement in 8.4 million years, which is how long we believe the satellite's orbit will be stable. Drag caused by the thin atmosphere up where it orbits and influences like solar activity will eventually cause it to fall back down to Earth, but its plaque will serve as a time capsule - a message from us today to whatever happens to be alive or intelligent here on Earth 8 million years in the future. To put that in perspective, the pyramids were only built about 5,000 years ago. 8 million years ago, there weren't even humans on the Earth. The latest common ancestor of humans and chimpanzees was around though. 8 million years from today, when LAGEOS returns, what will intelligent life on Earth look like? If Earth's surface is barren of life at that point, LAGEOS-1 will be alone.

But what about satellites in geostationary orbits? These orbits are far enough out that they're much safer from atmospheric drag and could remain above Earth much much longer than satellites like LAGEOS. These satellites are our pyramids. They're smaller than monuments built by past civilizations, but impervious to anything that might go wrong on the less stable surface of our planet. If alien archaeologists come by in a billion years or so, these satellites may be what their alien encyclopedias use as the picture for the humans article. So far we have erected about 450 of these geostationary monuments. When such a satellite wears down and ceases to be operational, it takes a lot of energy to slow it down so it can move out of the way and fall to Earth to burn up in the atmosphere. So instead, they're usually pushed into what's known as a graveyard orbit. A shell around the planet where they can be part without interfering with important operational satellites. It's fitting that we call these graveyard orbits because tombs are often the most stunning things we have from previous civilizations. These graveyard orbits are tombs in a way. Not for kings, but for machines. Junkyards that will out-exist the very societies and people they so largely define. Luckily, a few contain more than just our craftsmanship.

They also contain a record, like EchoStar XVI, a communications satellite launched into geostationary orbit in 2012. Aboard it is a silicon disc created by artist Trevor Paglen, containing 100 images of Earth and Earthlings. Now, unlike LAGEOS, EchoStar XVI will likely remain in orbit for billions of years, safe from discord and change down here. But here's the thing. What if our entire solar system is lost? Or what if life out there doesn't decide to ever visit our system?

Well, in that case, we have sent interstellar messages. At this moment, so far, there are 11 distinct human made things on trajectories out of the solar system into interstellar space. They're all related to five probes. Pioneer 10, Pioneer 11, Voyager 1 and Voyager 2 and New Horizons, the thing that recently made a Pluto flyby. These objects are our most distant hellos. Over the next ten thousand, million, billion years, they'll pass close enough to other star systems, maybe even planets, to possibly be discovered by other intelligent life forms. We had the foresight to include special messages on these probes.

Pioneer PlaqueThe Pioneer plaques are attached to Pioneer 10 and 11, which launched in the early 1970's, were the first human-made objects to ever be sent on a trajectory

to not just leave Earth, but to leave the solar system entirely. If discovered by other life out there, these plaques, designed by Frank Drake and Carl Sagan, could be our first chance to say "hello, we exist," or, depending on how long humanity lasts, our only chance to say "Hello, we existed. This is what we were." But will the plaques makes sense to aliens? Many human scientists have had trouble deciphering their meaning, but here's what they say. At the bottom is a map of our solar system with a path showing the Pioneer probe itself and where it came from. This element has been particularly criticized for being human centric. I mean, an arrow? Who's to say aliens will know that this depicts a path and not some structure in our solar system? Also, it's an arrow. Arrows might convey this way only two civilizations that hunted or developed pointy projectiles. Anyway. Up here, we define units. You can't tell aliens about humans or Earth by using seconds, kilometres or light years, because we made those measurements up. Instead, the plaque uses hyperfine transitions to communicate distances and time.

The hope is that curious intelligent life forms who find this will understand that this is a hydrogen atom - one proton, one electron. Hydrogen is the most abundant element in the universe, so hopefully its properties will be a common point of understanding. Now sometimes, if you've got enough hydr