When they collided with the ancient earth, comets helped fill our oceans, but it's also possible that they delivered something else.
Did comets also bring us life?
As far as we can tell, the earth was a hard dead rock planet, and yet here we are. So, what actually brought the building blocks of life to the earth? When comets impacted with the earth, those impacts may have been a key stage in the formation of life, by fusing amino acids together to form proteins.
There are trillions of comets in our solar system and any of these have the ability to seed life in a planet. Keeping this thought in mind and, if comets managed to bring life to earth, there's a good possibility that it may have happened elsewhere. We are not alone.
After a series of mission failures, July 1965 saw the first successful flybys of Mars. The US Mariner 4 became the first spacecraft to take close up pictures of another planet, beaming 22 images of the impact-cratered Martian surface back to Earth. Since then, more than 20 successful missions have explored the red plant’s atmosphere and surface.
Was there or is there life on Mars?
Researchers found out that many years (billions), Mars had the three critical ingredients for life. It had an abundance of chemical building blocks, liquid water on it's surface and an energy source to power the chemical reactions that make life possible. Today, the inhospitable surface of Mars is thought to be unsuitable for life, but the possibility of life existing deep beneath the surface hasn't been ruled out.
The moons of Jupiter
Let's take a look at a series of missions to the moons of Jupiter and Saturn. These missions have revealed these planet's potential to harbour life. Jupiter is the biggest planet in our galaxy and is located 5th from the sun. It is gas planet and is similar to a star but never got big enough to start burning. This huge planet has a lot of moons, and these moons can be split into three groups; Inner Moons, Galilean Moons and Outer Moons.
Let shift our focus to Europa, which is one of Jupiter's inner moons. Europa is icy and has the potential to host life. This is based on the pictures and data collected by the Galileo spacecraft. This information suggests that Europa has a layered structure like Earth: an iron-rich core, a rocky mantle and a crust of ice. Magnetic field measurements found an electric current inside, consistent with a salty liquid ocean beneath the thick crust of ice around the whole planet. This ocean contains more water than the pacific.
The discovery of water excited the scientists, because whenever we think of water, we think life. However, if there's life in Europa, the greatest challenge it would face is the thick ice that covers the water. Too much ice at the top for the sun to penetrate, so it's pitch black,freezing cold and no oxygen.
Europa’s surface resembles Earth’s sea ice in Antarctica, explains François Poulet from the Institute of Space Astrophysics at the Université Paris-Sud in France: ‘It indicates that the ice is geologically pretty young and it could be proof of its interaction with a reservoir of liquid water.’ In December 2012, the Hubble Space Telescope also detected water vapour above Europa’s South Pole and it was proposed this came from erupting water plumes. Spacecraft have not yet seen these plumes, however, so if they do exist they must be intermittent.
So, Europa has water, it has a source of energy coming from the friction of being pulled towards Jupiter's gravitational field by different amounts during different stages of it's elliptical orbit. The is also plenty of radiation around Jupiter to potentially start a chemical reaction or more. Are we alone ?