Where, in your opinion, is the best planet/moon to look for life in the solar system? – Mike Hadfield

It seems almost impossible that we are the only life in the Universe, but how about the only life in our Solar System?

In order to pick the most likely candidate we must first ask ourselves, what are we looking for in a planet or moon that could support life?

Well, for a start we can only speak from experience, we study life on our own planet and draw conclusions based on our evidence on conditions that life requires. Plants for example need sunlight for photosynthesis as well as oxygen; some of the earliest life on our planet was photosynthesising algae that formed a layer on top of the swamp of particles and molecules that were brewing around 3.4 billion years ago.

Micro-organisms on the other hand, such as bacteria, viruses and Fungi, can survive in the most unimaginable environments. Hundreds of thousands have been found on Earth at the bottom of the ocean in hydrothermal vents, deep within glaciers and icebergs and even in a thin layer on top of extremely radioactive waste.

Another well know factor is water. Liquid H2O is a necessity for life here on Earth along with a combination of other elements, mainly Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus and Sulphur. Water is one of the main things we will be looking for in our search for extra-terrestrial life. It is worth noting though that liquid Ammonia, Methane and Nitrogen, though less optimal, are also possible liquid elements capable of supporting life.

As it happens we do have some candidates for life lined up already. The top 3 being Titan, Enceladus, and Europa.

Image Titan

Titan, Saturn’s largest moon has very similar geological processes to Earth. Rivers, lakes, rain and seas are all present but in the form of liquid Methane. It is possible that methane based life could evolve just like our carbon based molecules did here on Earth. However, Titans temperatures and atmosphere are extremely hostile and it is incredibly unlikely that life could survive these conditions, but hey, isn’t it incredibly unlikely that we survived too?


Enceladus and Europa… both are moons (of Saturn and Jupiter respectively), both have icy surfaces and both are believed to have liquid water oceans beneath those icy exteriors. The oceans are present because  the gravitational pull from their planets and their elliptical orbits causes a rise in temperature.

Europa is bigger than Enceladus but there is a down side to that. The icy surface of Europa is predicted to be at least 100 miles deep, this means that it is almost as dark as a cave under the surface reducing the likelihood of photosynthetic organisms, but not ruling it out. This is also has its practical disadvantages perhaps making Europa the least likely candidate of the two for the next mission. In order to take samples of the salty waters within we would need to drill through this thick layer of ice, this will be extremely costly and will take a long time to build such technology, but perhaps there is another way …


One of most exciting images taken by the Cassini spacecraft sent out to orbit Saturn, besides that of our home planet, was that of the plumes of water and ice particles discovered spurting out of Enceladus. Not only do such geological processes confirm our suspicions that the moon hotter in the centre as tremendous pressure is needed to produce these plumes, but also it provides us with a wonderful opportunity to gather samples of the planets interior without drilling into the ice or perhaps without even landing at all. It is hoped we may build a spacecraft to orbit Enceladus and do precisely that.


Artist depiction of plumes on Europa. (Above)


Hubble images of Europas plumes (Above and below)


Recent exciting Astronomy news tells us that once again, The Hubble Space telescope has pushed us forward in our knowledge of the Universe around us, these same plumes were photographed at ultraviolet wavelength, spurting out from Europa too. The US were under a lot of pressure to increase the budget of planetary science to support a mission to Europa, now that the mission costs are dramatically reduced, there really is no excuse. It costs NASA around $3.2 billion to run the Cassini Space craft mission start to finish. This is around one-quarter of the amount of money spent annually on perfumes in Europe and the United States. 245 times more money is spent every year worldwide on the military. (If this is something you feel strongly about and would like to help please take a look at the Billy Nye’s planetary society campaign “Save our Science”

As usual the advancement of humanity is held back by money and politics, for this reason I would like to give Enceladus and Europa joint first place for the most likely place for life in our Solar System as the question is not on which are we more likely to find  life, but which are we more likely to find life on first?