Great question! The use of "es" in this sentence, even though it's referring to the future, is because "es" expresses a scheduled or planned event, which is common in Spanish when talking about events in the near future.
In Spanish, the verb "ser" (in its present form "es") is often used to talk about events that are considered certain or scheduled, especially when talking about things like plans or appointments. It’s similar to how we might say "Our trip is next week" in English to describe something scheduled for the future.
So, even though the trip is in the future, it is being treated as a scheduled event, and "es" is used to express this.
Here’s a comparison:
Nuestro viaje a Argentina es la semana que viene ("Our trip to Argentina is next week" – planned/scheduled event)
Nuestro viaje será la semana que viene ("Our trip will be next week" – future event, but more general)
Both are correct, but using "es" makes it feel more like a confirmed plan.