Its atomic number is 2 and its atomic weight is 4.002602. It melts at -272.2C and boils at -268.93C.

It is the only liquid that cannot be solidified by lowering its temperature. You also have to increase the pressure. It also makes balloons at kids' birthday parties float.

We call it helium.

It is the second-most abundant element in the universe after hydrogen. Unfortunately, most of it is found in stars, making it pretty tough to get at.

On this planet, it is a byproduct of radioactive decay and is trapped with natural gas. It's extracted from the gas by a process called fractional distillation.

The world's biggest producer of helium is the United States. In 2006, it sold more than 70 per cent of the helium used around the world. Much of that is stored at a gas field northwest of Amarillo, Texas.

Most of the rest of the world's supply is supplied by Russia and Algeria.

The gas stored near Amarillo makes up the U.S. Federal Helium Reserve, a stockpile that had grown to 170,000 tonnes by 1996. That year, the U.S. government decided to start getting out of the helium management business. It passed a law mandating the sale of all but 2,900 tonnes of the stockpile by 2015.

The Bureau of Land Management, the agency that oversees the reserve, estimates that total U.S. helium resources will disappear by 2035 because of rising demand. In a report on its website, the bureau says there could be worldwide helium shortages.

“The bottom line in terms of helium supply is that there is very little excess helium-refining capacity, and domestic supplies of crude helium are growing tighter,” the report states. “Until overseas plants are fully online and/or additional plants are built, we’re potentially facing additional supply disruptions, if not shortages.”

French astronomer Pierre Janssen is credited with first detecting helium as he observed a solar eclipse in 1868. He noticed a yellow line in the sun's light spectrum. Later, an English astronomer — Sir Norman Lockyer — determined that the line could not be produced by any element known at the time. His theory was that the line was produced by an element that existed on the sun. He called it helium.

In 1895, Scottish chemist Sir William Ramsay, was able to isolate helium from a mineral containing uranium.

Helium was first discovered in natural gas during the drilling of an exploratory well in Kansas in 1903. The well produced a gas that would not burn off. Natural gas can contain concentrations of helium of up to seven per cent in areas where there is a lot of uranium ore.

The U.S. government created a federal helium program in 1925 to ensure that there would be enough of the gas to handle defense needs. The program eventually switched focus to provide the U.S. government with refined helium for research and aerospace needs.

If helium is not extracted from the natural gas during the refining process, it will escape into — and eventually out of — the atmosphere because it weighs so little.

That light weight has also made helium a popular choice for party balloons. A litre of air weighs about a gram while a litre of helium comes in at 0.1785 grams. That makes the balloon lighter than air and its tendency to float away if not tied to the wrist of a young child.

Balloons make up a small chunk of the worldwide demand for helium. It is used for arc welding because it creates an inert atmosphere around the flame — it does not react with the metal being welded. NASA uses the gas to pressurize space shuttle fuel tanks. The U.S. space agency goes through more than 2 million cubic metres a year.

But the biggest demand for helium is as a cooling agent for nuclear reactors, infrared detectors, wind tunnels and the superconductive magnets in Magnetic Resonance Imaging equipment.

It's the use of MRI machines that has been largely responsible for the growing demand for helium — a demand that has jumped by 25 per cent since 2003. Meantime, production has increased by only about half that.

Reports of helium shortages have been surfacing for much of the current decade. They intensified in late 2006 when three major helium producing plants — two in Algeria and one in Qatar — experienced delays in becoming fully operational. It happened at the same time that two major American plants were down for maintenance. And on New Year's Day 2007, a storm damaged power lines to refiners in Kansas and Oklahoma.

As supply dwindled, prices rose. In some cases, retailers couldn't get supplies.

"We were told there's no helium, so that's going to change the face of our business, temporarily if not long term," Leah Garven, who runs a party decorating business in Saskatoon, told CBC News in Sept. 2007.

"We've been trying to figure out what we can do with air and still satisfy the customer because let's face it, everyone loves a helium balloon."

Shortage or not, inhaling helium is not recommended. While the resulting high-pitched voice might win laughs, helium can cause lungs to collapse. Too much of it can cause death by asphyxiation, without any of the signs of oxygen starvation.