英语听力：自然百科 探索世界奥秘之Life On Mars(火星生命)Unit10（在线收听）

But they never got there. The first disappeared into deep space. Another missed its target when its coordinates were confused. One NASA control center was working in metric, the other in feet and inches, they never lined up and the probe exploded in the Martian atmosphere. William Boynton had lost precious equipment on both missions. But he decided to try one more time.

This is really my third attempt to get to Mars, and some of my colleagues were saying:" Bill, are you crazy? You are doing a third time? You know, why are you putting so much time into this?" And I just, I just couldn't say no, I, I think there was just a calling that I had to go back.

So once again, he set about designing an instrument to detect underground water on Mars. After the previous failures, the pressure was on.

The role my instrument has taken in the search for water on Mars is we have a device called a gamma ray spectrometer and it's designed to determine what elements are present on Mars that make up the surface, and probably the most important one of those is hydrogen 'coz that's the main constituent element in water.

We have ignition and lift off of a Delta 2 Rocket carrying NASA on an Odyssey back to Mars.

On the 7th April 2001, NASA launched Odyssey carrying Boynton's device, and this time everything went according to plan.

It's really hard to describe exactly what it's like to have an instrument that you've built be perched on top of a rocket and actually get launched off into space, and you think "I'm on my way to Mars."

Once in Mar's orbit, the instrument was deployed and the gamma ray detector could get to work. All elements when they are struck by cosmic rays from the sun and other stars release gamma rays. The wavelength of the gamma rays differs from element to element, so each has its signature wavelength.

coordinate: Mathematics Any of a set of two or more numbers used to determine the position of a point, line, curve, or plane in a space of a given dimension with respect to a system of lines or other fixed references

gamma ray: Electromagnetic radiation emitted by radioactive decay and having energies in a range from ten thousand to ten million electron volts

spectrometer: A spectroscope equipped with scales for measuring wavelengths or indexes of refraction

cosmic ray: A stream of ionizing radiation of extraterrestrial origin, consisting chiefly of protons, alpha particles, and other atomic nuclei but including some high-energy electrons, that enters the atmosphere, collides with atomic nuclei, and produces secondary radiation, principally pions, muons, electrons, and gamma rays