Learn Turkish: Bir uzaylı gelirse şaşırırdım. - I would be surprised if an alien came.

The verb is şaşırmak (to be surprised). To express 'would' for a hypothetical or imaginary result, Turkish combines the aorist tense suffix (-ır) with the past tense suffix (-dı). So, şaşır + ır + dı + m gives you the 'would be' meaning.

Why does the sentence use gelirse instead of gelse?

In strict textbook grammar for hypothetical situations, you usually match -se (unreal condition) with -erdi (would result): Bir uzaylı gelse şaşırırdım. However, in everyday speech, native speakers sometimes mix an open condition like gelirse (if it comes) with a hypothetical result like şaşırırdım (I would be surprised).

How is the word uzaylı formed?

It comes from the noun uzay, which means 'space'. By adding the suffix -lı, which means 'from' or 'belonging to a place' (just like in Amerikalı or İstanbullu), it literally translates to 'from space'—which is the Turkish word for 'alien'.

Could I say şaşırırım instead of şaşırırdım at the end?

Yes! If you say Bir uzaylı gelirse şaşırırım, you are using just the aorist tense without the past tense suffix. This changes the meaning from a hypothetical 'I would be surprised' to a realistic prediction: 'If an alien comes, I will be surprised'.