It's something the etiquette books don't tell you, and Google Translate's not much better either: how do you talk to aliens?
French and American astrophysicists Dimitra Atri, Julia DeMarines and Jacob Haqq-Misra have a suggestion.
They are concerned that, since the first such attempt to communicate - the Arecibo message of 1974 - messaging to extraterrestrial intelligence, or METI, has been a disorganized affair.
"The handful of METI broadcasts have increased in content and complexity, but the lack of an established protocol has produced unorganized or cryptic messages that could be difficult to interpret," they say.
What's needed, in fact, is "a self-consistent protocol for messaging to extraterrestrial intelligence that provides constraints and guidelines for the construction of a message in order to maximize the probability that the message effectively communicates."
The three have created a new METI protocol with standard guidelines for signal encoding, message length and information content. They suggest using two frequencies commonly used in nature - 1.42 GHz or 4.46 GHz - and a simple mathematical language with regular repetition.
One big problem in devising such communications is the difficulty of avoiding anthrocentrism - the assumption that aliens will share our characteristics and attitudes of mind.
One way to help avoid this, says the team, is to create an interactive website where people across the world could start exchanging messages based on the protocol. Trough trial and error, they say, it should start to become clear which type of messages are most suited for cross-cultural communication.
"It is often said that SETI is a search for ourselves, and as we develop a message that we would send to unknown listeners, we will come to an even deeper appreciation of our diversity as humans," they say.