NARRATOR：

Listen to part of a lecture in an environmental science class.

MALE PROFESSOR：

Now last week, when we discussed the serious energy challenges we're going to face as the world's population continues to grow and we place more stress on our finite supply of fossil fuels- especially natural gas and oil- well, maybe it's not all doom and gloom.

In a number of areas, scientists are "thinking outside the box" and trying to come up with unusual, uh, novel solutions to the energy question.

Not that a positive outcome is inevitable by any means, but...

Well, let's take a look at one of these creative ideas, involving the gas helium-3.

Helium-3 is an isotope of helium that has tremendous potential for use in practical energy applications.

Remember, ah, an isotope is a form of a chemical element that has the same number of protons in its atomic nucleus but a different number of neutrons.

The most common isotope of helium on Earth is helium-4, which does not have any known or potential uses as an energy source.

Helium-3, in comparison, is extremely rare; there isn't very much of it on Earth, plus the, uh- well the main source of helium-3 in our solar system is solar wind- a stream of lethal radiation and particles pouring off of the Sun- and Earth's magnetic field fortunately prevents that wind from reaching us.

So why is helium-3 so exciting?

Well, it seems a sure bet that helium-3 is available in abundant quantities on the Moon.

Since the Moon doesn't have a magnetic field, the solar wind must have been depositing helium-3 there for billions of years; in fact, Apollo astronauts have already discovered it in the Moon's dust.

Some estimates hold that there may be over a million tons of helium-3 buried on the lunar surface.

And one ton is more than enough energy for a city of ten million people for a whole year.

So you can see, this would certainly solve most of our energy problems.

But how could this be possible?

Well, we think helium-3 would have to be used in nuclear fusion reactors.

Keep in mind that a nuclear fusion reactor is completely different from our existing nuclear fission reactors.

Basically, a nuclear plant powered by nuclear fission derives its energy from the splitting of atoms, while a plant based on nuclear fusion utilizes the energy produced when atoms are fused together.

Fusion is the same nuclear reaction that fuels stars, which as you know, produce almost unfathomable amounts of energy.

Researchers have identified two isotopes of hydrogen as the most promising fuel sources for fusion power plants.

However, there is a real drawback- they both produce a large amount of radioactive material in a fusion reaction.

But helium-3 fusion produces no radioactive material.

In fact, one proponent stated you could safely build a helium-3 power plant in the middle of a city!

A clean, safe source of power.

Almost sounds too good to be true, doesn't it?

Well, of course this is all very theoretical, and there are issues that have to be addressed.

For one thing, we still haven't created a single nuclear fusion plant, despite decades of research and development.

An often-heard joke about fusion is that a nuclear fusion plant has been "just decades away" from being created for several decades now.

Nuclear fusion research is still ongoing, strong as ever in fact.

But we still don't have a full scale fusion plant to point to.

And there's a rather big logistical problem as well: how to get the helium-3 off the Moon.

Digging the stuff up is challenging because the distribution of helium-3 is so diffuse across the lunar surface.

One estimate is that you'd need to heat a million tons of lunar soil to about 800 degrees Celsius to yield about 70 tons of helium-3 gas.

It's kind of like digging out a crater with a spoon to find a single nugget of gold.

Kind of ridiculous, right?

There's a camp that believes it'll take more energy to extract helium-3 gas than the gas itself would provide.

So there are concerns.

But given the lure of the possibilities and the pressing nature of our energy difficulties, it's possible that helium-3 could be a significant driver of future exploration of the Moon.

And it certainly could ease the pressure on the demand for fossil fuels- if and when the numerous challenges-and not just the ones we've talked about- are solved.