Mystery of the missing Europa geysers

     It has been suggested that geysers spurting out of Jupiter’s moon Europa may be an opportunity to spot alien life originating beneath the surface.
     This was based on observations by the Hubble Space Telescope in December 2013 that saw water vapour being ejected from the moon, lending evidence to the existence of jets.
     But now scientists are somewhat baffled as they have been unable to explain why follow-up observations have failed to spot the same geysers.
     This could be due to a lack of suitable conditions needed by Hubble to see the plumes, namely auroral emissions.
     It could also be that the explanation for where the water vapour came from, namely plumes on the surface, was incorrect.
     However Dr Kurt Retherford of the Southwest Research Institute in San Antonio told Space.com that he thought this was unlikely.
    ‘The best explanation still is plumes for that [December 2013] dataset, no doubt about it,’ he said.
    Another suggestion is that the plumes may be too small to see; indeed, even Cassini has struggled to spot vapour associated with the plumes being expelled into space.
    The previous evidence for the jets had come in the form of water vapour spotted by Hubble above Europa.
    Although several explanations were offered, Nasa was pretty sure this vapour was due to erupting plumes on the surface.
    Confirming the existence of the plumes and studying them further will be key to any future mission going to Europa.
    However these latest findings will need to be studied further to ensure they definitely are there.
    Dr Retherford and his team will be carrying out subsequent observations with Hubble from November this year to April 2015 to confirm that the jets exist.