Great Britain’s Royal Mail honored the historic moment of the European Space Agency landing a spacecraft on a comet just two days after it occurred.

On Nov. 12, the Philae lander touched down on comet 67P/Churyumov–Gerasimenko, and on Nov. 14 Royal Mail began using a special postmark with the message” “Celebrating the first ever landing on a comet. Congratulations to the European Space Agency.”

The postmark also will be in use Saturday, Nov. 15.

The Philae probe is part of the European Space Agency’s Rosetta mission. Named for the famed Rosetta stone, the mission’s objective is to “help understand the origin and evolution of the Solar System,” according to the space agency.

The agency also reported that the mission was launched March 2, 2004, and traveled 6.4 billion kilometers through the solar system before reaching the comet in August.

The European Space Agency’s director general Jean-Jacques Dordain said, “Our ambitious Rosetta mission has secured a place in the history books: not only is it the first to rendezvous with and orbit a comet, but it is now also the first to deliver a lander to a comet’s surface.”

Andrew Hammond from Royal Mail said: “We’re thrilled to be marking the European Space Agency’s fantastic achievement with one of our special postmarks.

“The Rosetta mission has captured the public’s imagination and excitement about space exploration, and we’re pleased to be recognising this historic moment in this unique way.

“Our postmark is set to take off and will appear on mail delivered by our postmen and women across the UK.”