system
Given the following post, respond as if you're commenting on Reddit:
human
Using current technology, would it be possible to have a shared internet network between Mars and Earth?

Wondered this the other day if each planet had its own internet network would it be possible to link them both together? Would the latency be too drastically high for it to be functional? Or would it just not be possible without having a large number of satellites to link the two planets?

Slight credit goes to Roosterteth/DrunkTank podcast for sparking this conversation.
gpt
Latency would definitely be a problem, depending on where the planets happen to be relative to each other it'll take between 4 and 20 minutes for light to go one way. Current networking protocols are not designed to work with such latencies so they wouldn't work. In other words a normal WIFI will not work even if you can get the signal to go through by boosting the power and using a directional antenna or whatever. You will need some kind of a new protocol to do the extreme latency hop between the two planets. And even if you get things working up to the network layer, that is get internet packets moving between the planets, TCP certainly wouldn't work as just the handshake would take tens of minutes. If TCP doesn't work then you can't really connect to any ordinary web servers.

A simple solution would be for you at Mars to contact some proxy on Earth using some interplanetary protocol. Then the proxy would communicate on your behalf with whatever webserver you want using our current protocols. Once it has all of the page then it can send it back to you again using the interplanetary protocol. And you'd get the page you asked some 8-40 minutes after you asked for it. So that'd get it to work technically but there'd be a huge usability issue with latency.

A better way would be to have a big proxy at Mars. Whatever webpage you want, you ask the proxy server, which would have a copy of it. The communication would never go to Earth at all. Essentially you'd have a copy of the Earth Internet on the Mars proxy. The proxy would be updated through some means and obviously there'd be some latency with the updating. And none of the highly interactive web services would work at all with a system like that.

To get the interactive web services to work you'd really need to have a separate Mars server for Mars stuff. Then it's up to the service to synchronise things between Mars and Earth. Of course this wouldn't work for things like Skyping with your friends on Earth, there's no way around the latency with communicating with Earth. But say like internet banking. You do you banking stuff with the Mars banking server which would happen (practically) instantly. That would then update your account balance with the Earth through some means, this would necessarily take at least that 4-20 minutes. Of course the bank would need some system to guard against you arranging a withdrawal at both ends at the same time and overdrawing your account.

So yes, we do have the technology to communicate between the two planets. Normal protocols we use today wouldn't work but we could build systems that would. However, a practical solutions would probably avoid sending anything to Earth at all directly.