Aditya MadanapalleSep 27, 2016 13:17:24 IST
Yesterday Nasa held a conference call on a major new discovery by the Hubble telescope, related to the global saline sub surface ocean on Europa, a moon of Jupiter. This announcement was that the Hubble Space telescope had used ultraviolet imaging to obtain direct pictures of plumes of water emanating from the surface of Europa. The images were captured against the bright background of Jupiter, as Europa went across it. This is not absolute proof that there are plumes on Europa, but more evidence.
The images were obtained at the very limit of the abilities of the Hubble telescope. The plumes apparently rush out to more than 160 kilometers into space. If confirmed, this would mean that it is the second time that a global subsurface ocean has been discovered on the moons of Gas Giants. The Cassini spacecraft had observed such plumes on Enceladus in 2005. The major advantage to scientists of these plumes, is that there is no need to ship drilling machines to Europa to break through the ice to get to the subsurface ocean.
The subsurface ocean is a strong candidate for the existence of life, and studying the ocean for signs of life is a point of interest to scientists. If there were no plumes on Europa, this would mean drilling through the ice shell believed to be between 15 to 25 kilometers thick, to gain scientific access to the subsurface ocean. The plumes make it easier for researchers to study the contents of the ocean. A flaw in this plan is if the plumes originate from a shallower body of water, an underground lake embedded in the icy shell between the subsurface ocean and the surface. Tidal forces could contribute to stress in the icy shell, leading to warm regions where these underground lakes may exist. There is a lot of tectonic activity on Europa, which leads to ridges. The tectonic activity could lead to the existence of the water plumes, or they might also lead to muddying the interpretation of the data.
The scientific knowledge is increasingly growing with each mission. The Hubble telescope, along with Cassini, Galileo, Voyager and Juno have all contributed to the increased understanding of the region. The James Webb Space Telescope to be launched in 2018 will image Europa in the infrared and confirm the presence of Plumes. Nasa is also planning a flyby mission to Europa, which could study the plumes from up close. The Hubble space telescope was the only telescope in a position to image Europa in ultraviolet.
The component on the Hubble telescope used to image Europa is called the Space Telescope Imaging Spectrograph (STIS). The STIS stopped working in 2004, and was fixed in a spacewalk by Astronauts in 2009. This was the final servicing mission approved for Hubble, the telescope would not have been functional if it were not for a public outcry against shutting down the telescope. Continuing the theme of one mission benefitting another, it was due to this mission that the Hubble was able to find evidence of water plumes on Europa.
Nasa scientists are very considerate about the possibility of life on Europa, which is why they are taking active measures to minimise contamination. The Juno spacecraft around Jupiter for example, was specifically scheduled to go nowhere near Europa. Since there are no spacecraft in the vicinity of Europa, the Hubble telescope was the next best thing. Hubble plans to remain in operation indefinitely. Yesterday, Isro celebrated the second anniversary of the Mars Orbiter Mission. The MoM mission has also been extended indefinitely, well beyond the initially planned period of six months.
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