Aditya MadanapalleApr 14, 2017 12:09:03 IST
Two long running Nasa missions, the Hubble Space Telescope and the Cassini mission to Saturn, are providing the evidence necessary for further scientific investigations into extraterrestrial life.
Global subsurface oceans on other planetary bodies in the Solar System are prime locations where life could exist outside the Earth. The Cassini team published a research paper showing that there is a chemical source of energy on Saturn's moon, Enceladus. The Hubble team has published additional evidence of plumes of water erupting from the surface of Europa, a moon of Jupiter.
Life as we know it on Earth requires liquid water, a source of chemical energy to support metabolism, and the right mix of ingredients including oxygen, nitrogen, carbon, phosphorous and sulfur. Cassini has detected the presence of nearly all the requirements on Enceladus, except for phosphorus and sulfur.
Scientists suspect that the rocky core of Enceladus may have phosphorous and sulfur as well, considering the elements were found in meteorites that are thought to be chemically similar to the kind of rocky core Enceladus has.
If only Cassini had the right instruments needed to study the plumes erupting from Enceladus, the Nasa researchers would have more direct evidence on the subsurface ocean on the icy moon. Unfortunately, Cassini does not have the required instruments as the plumes were discovered by Cassini only after making the long trip to Saturn.
Cassini only had instruments designed to investigate the outer atmosphere of another of Saturn's moons, Titan. The same instruments were used to study the plumes of water erupting from Enceladus, and found that 98 percent of the plume is water, with trace amounts of hydrogen, ammonia and methane.
The finding indicates that if microbes are on Enceladus, they can thrive in the environment. Hunter Waite, lead author of the Cassini study says, "Although we can't detect life, we've found that there's a food source there for it. It would be like a candy store for microbes".
The plumes of water from icy moons with global subsurface oceans such as Enceladus and Europa, allow scientists to study the subsurface oceans without having to drill through the ice sheets covering most of the planets, and sending robotic probes into the oceans.
— NASA (@NASA) April 13, 2017
Thomas Zurbuchen, associate administrator for Nasa's Science Mission Directorate says "This is the closest we've come, so far, to identifying a place with some of the ingredients needed for a habitable environment. These results demonstrate the interconnected nature of NASA's science missions that are getting us closer to answering whether we are indeed alone or not." Linda Spilker, Cassini project scientist says "Confirmation that the chemical energy for life exists within the ocean of a small moon of Saturn is an important milestone in our search for habitable worlds beyond Earth."
The Juno spacecraft is in orbit around Jupiter, but the mission has been designed in such a way that Juno does not go anywhere near Europa, to avoid contaminating the icy moon in case it had life. The Hubble space telescope is observing Europa from a distance for evidence of plumes of water, similar to the ones seen on Enceladus. New evidence points to a region on Europa where activity suspected to be water plumes have been consistently observed years apart. Observations from the Galileo spacecraft was used to corroborate the Hubble findings, to show that the region was unusually warm. William Sparks of the Space Telescope Science Institute in Baltimore, Maryland said "The plumes on Enceladus are associated with hotter regions, so after Hubble imaged this new plume-like feature on Europa, we looked at that location on the Galileo thermal map. We discovered that Europa’s plume candidate is sitting right on the thermal anomaly". Although Europa was long suspected to have a global subsurface ocean, scientists only confirmed it last year after directly imaging what were suspected to be plumes erupting from the surface using the Hubble Space Telescope.
The plumes on Europa are an attractive site for future robotic explorations of the subsurface ocean. The Nasa Europa Clipper mission planned to be launched in the 2020s is an autonomous drone meant to explore the ocean and hunt for evidence of life. A fleet of underwater drones is being tested in the oceans of the Earth, in preparation for the Europa clipper mission.
Jim Green, Director of Planetary Science, at Nasa says, "If there are plumes on Europa, as we now strongly suspect, with the Europa Clipper we will be ready for them."
Nasa accompanied the announcement with the launch of a sub site, dedicated to the known sources of water in outer space. The Orion Nebula produces enough water every day to replace all the water in the oceans of the Earth sixty times over. Water molecules have been found in accretion disks around stars, during the phase in stellar evolution when planets are being formed. There is evidence for liquid water in the interiors of asteroids and comets. Mars once had an ocean on its surface, similar to the one found on Earth.
There are believed to be oceans on three of the moons of Jupiter, including Ganymede, Callisto and Europa. Ganymede could even have a saltwater ocean. Water is believed to exist on three Saturn moons as well, Enceladus, Titan, and Mimas.
Triton, a moon of Neptune, might have a subsurface ocean, but this is a theory that requires confirmation. Mysterious fault lines on Pluto could also be evidence of a subsurface ocean. Water vapour has been discovered in the atmosphere of HAT-P-11b, an exoplanet 120 light years away.
Nasa's Spitzer, Hubble and Kepler missions are investigating exoplanets across the universe. Nasa will soon add the most powerful space telescope ever built, the James Webb Space Telescope to its arsenal.
Among other objectives, one of the aims of the James Webb Space telescope is to investigate the possibility of life on the Trappist-1 exoplanets. Seven earth sized planets in orbit around an ultracool dwarf star 40 light years away, is a promising candidate for the presence of extraterrestrial life.
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