Researchers have even been able to identify the specific location where life might be most likely to exist outside Earth. NASA's Cassini Spacecraft, in the final months of a 20-year mission earlier in 2017, pinpointed Enceladus, an icy moon of Saturn, as a key site for further exploration. The surface of the moon is covered by an ocean encased in a thick shell of ice. The Cassini also observed that plumes of gas, including hydrogen, were spewing out of a geyser and into space. Hydrogen is a vital building block for life for micro-organisms, suggesting that some form of life could inhabit Enceladus. Despite all these advances, extra-terrestrial life remains a mystery. The director of NASA, Charles Bolden, told British schoolchildren in 2015 that he believed that "we will someday find other forms of life or a form of life, if not in our solar system, then in some of the other solar systems." Bolden decided to put a timescale on such a discovery and other experts including popular astrophysicist Neil DeGrasse Tyson- have it at least 50 years away. More optimistic scientists have said it could happen more quickly. These include NASA's chief scientist, Ellen Stofan, who said in 2015 that she thought researchers would find "strong indications of life beyond Earth within a decade, and I think we're going to have definitive evidence within 20 to 30 years." Stephen Hawking, who has recently said that humans should find alternative planets on which to live, has warned that if alien life forms reach out to Earth, human beings should be careful in how they respond. While space researchers are close to being able to identify extra-terrestrial life, current telescopes do not allow them to spot the chemical fingerprints- traces of water and gases that indicate life, known as biosignatures- on planets outside the solar system. That will soon change. In 2018, NASA will launch the James Webb Space Telescope, an ultra-sensitive device that means they will be able to observe traces of extra-terrestrial life, should they exist. If NASA had already found evidence of alien life, it's unlikely that they would be able to keep it from people. The discovery would be a momentous political win for the United States, akin to winning the so-called space race against the Soviet Union in July 1969 when Neil Armstrong stepped onto the moon.