swaps.marscoin.org: a live market for Bitcoin and Marscoin
Since this week there is a place where you can watch Bitcoin and Marscoin trade without an exchange: swaps.marscoin.org.
Behind it runs an always-on market maker. It posts real MARS offers to the open order book, locks MARS for buyers, and collects the bitcoin, all through atomic swaps: two contracts on two blockchains, opened by the same secret. Nobody holds anyone’s coins in between. Either both sides of a trade happen, or neither does.
The page itself is a window onto that market. Everything on it is live, and everything on it comes from public sources you can check yourself.
What you see
The order book
Every offer from every Marscoin relay server, cheapest first. Each offer fills completely in a single swap. It shows its price in satoshis per MARS, its premium over the market price, and how long until it expires.
The dashboard also checks each offer the same way the Electrum-Mars wallet does before you pay. Is there a safe gap between the buyer’s refund and the seller’s? An offer that fails gets marked UNSAFE. A wallet would refuse it.
A quote for every offer
Pick an offer, or type how much bitcoin you want to spend. The panel shows exactly:
- what you pay and what you receive
- the price against the market
- the network fees on both chains
- how long settlement takes
Below that are the three guarantees that make the trade safe for you:
- The seller locks the MARS first. Your wallet checks that lock on the Marscoin blockchain before it shows you where to send bitcoin.
- Your refund comes first. The seller can’t take the MARS back until well after you could recover your bitcoin, even if Bitcoin blocks run slow.
- Nothing can get stuck. If the other side disappears, your bitcoin is refundable from a specific Bitcoin block, about four hours later.
The swap itself happens in Electrum-Mars, where your keys stay. The page shows you step by step how to take the offer.
How a swap settles, with real block heights
A normal swap finishes in about half an hour. The timeline shows what happens if someone stops halfway. It uses the current block heights on both chains to show when the buyer could refund and when the seller could, with the safety margin between them.
The thin blue bar at the start is today’s light travel time from Earth to Mars, for scale.
Earth and Mars, right now
Your browser computes where Earth and Mars are in their orbits, and how long light takes between them: about 12½ minutes this week. That delay is why this matters. A Mars settlement can’t ask a bank on Earth and wait for an answer. Atomic swaps don’t need to: each side checks its own chain, and the refund windows are hours long. This is the idea behind InterPlanetary Atomic Swaps, presented at the Mars Society Convention this week.
How the maker keeps itself safe
The maker is a program called atomicswapd. It runs the same swap engine as the Electrum-Mars wallet, with the limits an always-on maker needs:
- It locks MARS only for buyers whose terms are safe, and it never claims bitcoin so late that a buyer could take both sides.
- At most 30% of its inventory is ever on offer or locked in swaps. Even if every offer were taken at once, the exposure is bounded.
- One swap in progress per buyer.
- No guessed prices. Without a fresh market price, it posts nothing.
The page is read-only. No keys, secrets or controls are reachable from it.
Run your own
The exchange here is the protocol: the order book relayed by Marscoin’s servers, plus contracts on both blockchains. This maker is just the first participant. Anyone can run another one and compete on price.
atomicswapd is open source under the MIT license. The README walks through a complete setup on fly.io, a few commands for about $6 a month, or on any server with Docker. There is also an AGENTS.md so an AI assistant can deploy and run a maker for you, with checks at every step. It never sees your seed, and it leaves every money decision to you.
Update your wallet
To take an offer you need Electrum-Mars 4.4.3 or later:
- 4.4.2 made the buyer’s side safe: your wallet now pays only after the seller’s MARS is locked and verified.
- 4.4.3 fixes the macOS app, which didn’t start on macOS 14 and 15.
Download Electrum-Mars · Buying MARS with Bitcoin, step by step · The live market
