Free Astronomy Magazine September-October 2020

SEPTEMBER-OCTOBER 2020 have some minimal chance of receiving the message. In this regard, we must remember that the instruments used in the various SETI projects have aimed their targets only for periods between less than a minute and less than an hour a day. It is true that even such short periods may be enough to record a continuously repeated signal, but only if two essential conditions are met: (1) ET wants to communicate with us; (2) we aim at the right star. Even if we want to be optimistic about the first condition, the real problem is the second. Very few people truly realize how many stars there are in our galaxy, and it doesn't help much to say that there are “a few hundred billion.” To provide some per- spective - if there were 1000 technological civilizations in the Milky Way (a number per- haps disproportionate, given that the most conservative estimates range from one to a few dozen), in order to receive a message re- peated continuously by one of them, we would have to plan to aim at, on average, from 100 to 400 million stars. So far, all SETI projects have targeted a few thousand stars overall. So, let us not be surprised if nothing has been found so far and if govern- ment agencies prefer to allocate tax- payers' money to missions to Mars and Europa. Leaving aside all the problems re- lated to SETI, let's suppose we have the lucky fortune of picking up a real alien signal. After what has been said above, it is very likely that it is intended for us and that it was sent by a relatively close and certainly more advanced civilization than ours, as we are not currently able to do the same. How do we behave? What reasoning did ET have (or do) before sending it? Do we have to an- swer? What consequences could our response have? ! T he video below intro- duces NASA's Europa Clipper mission to Eu- ropa, the Jovian moon that houses an ocean below its frozen surface. Life could exist in the waters of that ocean. [NASA/JPL- Caltech]