Several scientific papers this year touch on the search for faint signs of life in our solar system — with a paper about Enceladus last month offering one of the most intriguing prospects.
The paper, published in the journal Nature Astronomy , is based on samples of the water plumes ejected from Enceladus taken by the Cassini space probe from to The probe found high concentrations of methane and unexpectedly high levels of hydrogen, which fit the idea that microbes have evolved to live around hydrothermal vents on the seafloor, said a co-author of the study, Regis Ferriere, an associate professor of ecology and evolutionary biology at the University of Arizona in Tucson.
The ocean on Enceladus is thought to consist of salty water 12 to 15 miles deep, topped by up to 20 miles of icy crust. The methane in the ocean might be explained by purely chemical processes, he said. Hydrothermal vents on the ocean floor on Earth — so-called black smokers — thrive with microbes that feed on the chemicals emitted by the vents. In addition to creating organic fuels, radiation from Jupiter also may drive chemical reactions that produce oxidants -- molecules such as oxygen and hydrogen peroxide that can be used to burn formaldehyde and other carbon-based fuels.
But Chyba notes that the oxidant and organic molecules formed on Europa's frigid surface "are biologically relevant only if they reach the ocean. The problem is that, if there is a liquid ocean on Europa, it's hidden beneath an ice sheet about 50 to miles 80 to km thick. So if extraterrestrial creatures are going to feast on formaldehyde, there has to be a way to get that compound through the dense layer of ice and into the liquid sea below.
Recent photographs taken by NASA's Galileo spacecraft reveal evidence of sudden melt-throughs in the ice that could allow oceanic microbes to come into quick contact with oxidants and organic food sources. The result could be a dramatic increase in population similar to "microbial blooms" that periodically occur in the Earth's oceans. Chyba points out that Europa's surface ice appears to get naturally recycled into the ocean every 10 million years -- a process that would allow a very gradual delivery of life-giving molecules to any submerged organisms.
And just how many microbes might exist in Europa's sea? Chyba's conservative estimate: one per cubic centimeter -- a far cry from the hundreds of thousands of organisms that occupy each cubic centimeter of water on Earth.
The atmosphere on Jupiter, however, has a measurement of more than 0. Join thought-provoking conversations, follow other Independent readers and see their replies.
Want to bookmark your favourite articles and stories to read or reference later? Start your Independent Premium subscription today. More about Venus Aliens Jupiter. Explore Interact with the hotspots below to learn more. Because it gets hotter the farther you go into Jupiter, these regions, which are gray-blue in color, appear hotter than the cloudy areas that cover the rest of the planet.
Called hotspots, these areas glow brightly in infrared light. In , the Galileo spacecraft dropped a probe into Jupiter and it happened to fall into one of these hotspots. It was akin to an alien craft visiting Earth for the first time and landing in a desert. We have a general idea of what happens in a hotspot.
When Jovian air enters such a region, it sinks into the hotter depths of Jupiter, where it warms up and dries out. As it flows out of the hotspot a few days later, it rises back to its original altitude.
A process called convection drives the formation of the clouds — the same basic way that clouds on Earth form. As the hot gases rise, they cool and condense into liquid droplets or ice crystals to form clouds.
Jet streams on Earth are generated in a similar fashion. Jupiter seems to have at least three major cloud layers made out of different chemicals. Each layer sits at an altitude where the temperature is cold enough for the respective chemicals to condense.
The next layer consists of ammonia hydrosulfide, which smells like rotten eggs. Farther down are water-ice clouds, which likely sit on top of a blanket of water-ammonia fog that covers the planet. Juno will determine how much water is in each of these layers.
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