The question of whether life exists somewhere in our solar system is one of the most pressing questions mankind has, and NASA just recently announced a bold plan to drill through the icy crust of Jupiter’s moon Europa with a probe to search for life in its subterranean ocean. It shows we’ll go to just about any lengths to find life outside of Earth, but what are the best candidates out there in our solar system?

Europa is a strong candidate because of its subterranean ocean, which exists in just the right conditions that some form of microbial life could exist deep below the moon’s icy surface. NASA just announced plans to send a probe 400 million miles to the moon in 2031.

Enceladus is another promising candidate. The sixth largest moon of Saturn may actually be our best bet because of its good temperature and apparent presence of water. Like Europa, it may also have a liquid ocean underneath its icy surface.

Mars is a place we’ve already looked at quite a bit, and although we haven’t found anything yet, the presence of water on the Red Planet suggests that there may be evidence that microbial life once existed there somewhere on its surface, we just have to find it.

Saturn’s biggest moon Titan is often put forward as a candidate. It has a thick atmosphere that is filled with methane. It is pretty cold, so like other candidates, any life-hosting water would probably have to be deep under its surface.

Finally, Jupiter’s moon Io actually has an atmosphere and has the chemicals necessary for life. It also stays warm because of volcanoes, but because it is inside Jupiter’s magnetic field, the radiation levels would be extreme.