Extraterrestrial aliens may possibly exist on other planets, or moons like Europa. Their biochemistry may be based on carbon as on Earth. More exotic space aliens may also be possible. Some scientists believe silicon based life is possible. In that case silicon would take the place that carbon takes in the biochemistry of Earth. Study or speculation about extra-terrestrial life is called Exobiology. Serious scientists with the SETI project are looking for alien signals but have so far found nothing conclusive. Not all scientists are convinced that aliens are likely.