Dark matter is a form of matter thought to account for approximately 85% of the matter in the universe and about a quarter of its total energy density. Most dark matter is thought to be non-baryonic in nature, possibly being composed of some as-yet undiscovered subatomic particles. [a] Its presence is implied in a variety of astrophysical observations, including gravitational effects which cannot be explained by accepted theories of gravity unless more matter is present than can be seen. For this reason, most experts[who?] think dark matter to be abundant in the universe and to have had a strong influence on its structure and evolution. Dark matter is called dark because it does not appear to interact with observable electromagnetic radiation, such as light, and is thus invisible to the entire electromagnetic spectrum, making it undetectable using existing astronomical instruments.
The existence of ample amounts of hydrogen in the subsurface ocean of Enceladus indicates that microbes--if any exist there--could use it to obtain energy by mixing with carbon dioxide dissolved in water. This particular chemical reaction, termed methanogenesis, because it manufactures methane as a byproduct, may have been of critical importance in the emergence of life on our planet.
There is a bizarre rocky landscape, well hidden from our prying eyes, in the secretive shadows under the oceans of our Earth. Here, in this strange and alien domain, it is always as dark as midnight. Thin, tall towers of craggy rock emit billows of black smoke from their peaks, while all around the towers stand a weird, wavy multitude of red-and-white, tube-like organisms--that have no eyes, no intestines, and no mouth. These 3-foot-long tubeworms derive their energy from Earth itself, and not from the light of our nearby Sun--a feat that most biologists did not believe possible until these wormish creatures were discovered back in 2001. The extremely hot, superheated black water, billowing out from the hydrothermal vents erupting on Earth's seafloor, provides high-energy chemicals that sustain the tubeworms, as well as other weird organisms that apparently thrive in this very improbable habitat.
The team's findings can also be applied to exoplanets, which are planets that circle stars beyond our own Sun. Some super-Earth exoplanets, which are rocky planets more massive than our own, have been proposed as "water worlds" covered with churning oceans. Could they have life? Perhaps. The potential would certainly be there. Dr. Vance and his team believe laboratory experiments and more sophisticated modeling of exotic oceans might help to find answers to these very profound questions.