It has been more than twenty-five years since the National Aeronautic and Space Administration (NASA) last sent a craft to land on the moon. The Lunar Prospector took off in January of 1998, in the first moon shot since astronauts last walked on the moon in
1972. This time, the moon-traveller is only a low-cost robot, who will spend a year on the surface of the moon, collecting minerals and ice. Unlike the moon shots of the 1960s and 1970s, Lunar Prospector does not carry a camera, so the American public will not get to see new pictures of the moons surface.
______________________________. Scientists are anxious for the results of one exploration in particularthat done by the neutron spectrometer. Using this instrument, Prospector will examine the moons poles, searching for signs of water ice. There has long been speculation that frozen water from comets may have accumulated in craters at one of the moons poles and may still be there, as this pole is permanently shielded from the sun. The neutron spectrometer seeks out the hydrogen atoms in water and can detect the presence of as little as one cup of water in a cubic yard of soil.
On the basis of above passage please answer the following question.
Which of the following is the best meaning of the word "speculation" as it is used in the second paragraph of the passage?