School: Delhi Public School - East
In my opinion Europa will be the best destination to return with another spacecraft to explore for extra-terrestrial life. Europa is thought to be one of the few celestial bodies in our solar system which can potentially have life. It’s believed that three main ingredients of life potentially exists in Europa , water, energy and chemical reactions which are essential elixir for a life as we know it from our own Earth’s experience.
Europa is thought to have an iron core, a rocky mantle and an ocean of salty water. Europa is icy from outside with lots of cracks and ridges hence scientist believes there are huge oceans of salty water beneath it almost double than that of Earth’s. The various fractures on the moon are thought to have been caused by the tidal flexing exerted by Jupiter. Tidal forces are thought to generate the heat that keeps Europa's ocean liquid and likely powering volcanic activity. Similar ecosystem exists on our own planet's seafloor, where volcanic rifts create hydrothermal vents.
At the bottom of Europa’s ocean lays a rocky seafloor which is in direct contact with the water, possibly supplying chemical nutrients into the ocean by hydrothermal activity. Life on Europa could exist clustered around these hydrothermal vents on the ocean floor, or even below the ocean floor just like how many odd types of deep sea creatures reside at the bottom of Earth’s oceans. The way endoliths are known to inhabit on Earth or the way bacteria and algae exists in Earth’s polar regions.
Evidence suggests that hydrogen peroxide is abundant across much of the surface of Europa. We know hydrogen peroxide decays into oxygen and water when combined with liquid water, if such conditions exist in Europa that could be an important energy supply for simple life forms. In 2016, a study suggested that Europa produces 10 times more oxygen than hydrogen, which is similar to Earth. This could make its probable ocean friendlier for life. Europa’s ocean is believed to have been in liquid state since the moon's formation hence on Europa, life might have had time to evolve.
In May 2018, astronomers provided supporting evidence of water plume activity on Europa -something like an ice geyser that spews the deep contents of the ocean out into the space before it falls back to the surface. A spacecraft powered by RPS (radio isotope power systems) could collect samples to study the chemistry of this potentially life-bearing ocean by flying through them. Though it’s quite a possibility that microbial life might not survive because of off-world excursion but by products of life might. Ideal would be to plant a lander on the moon’s surface for few days to collect sample and screen material for traces of life, such as biomolecules and metabolites.
No matter how future studies and missions turned out to be, but I strongly believe all these evidences are compelling reasons for NASA to explore this enigmatic moon of Jupiter.