Space is not as empty as you might think. While most of us imagine space as an empty waste, it turns out that the room between the stars is full of chemicals. Some chemicals are necessary ingredients for life, which lends support to the theory that life began in outer space and was seeded on Earth through comets. Other molecules are not even found on Earth at all. Scientists are finding more kinds of chemicals every year in outer space, and this is having a huge impact on our understanding of how planets like the Earth are formed.
As more complex molecules are found in interstellar clouds, astronomers have to do far more chemistry than ever before: some are now designated as “molecular astrophysicists,” such as Dr. Ewine F. Van Dishoeck of the Leiden Observatory in the Netherlands. She presented a lecture, “From Molecules to Planets,” on Thursday, January 20th at the Medical Sciences Building.
She explained that there are vast regions between the stars in our Milky Way galaxy that are teeming with particles-or at least, teeming by intergalactic standards. It is estimated that the concentration of particles in these interstellar clouds is roughly ten-thousand parts per cubic centimetre, and, while that might sound like a lot, anything below 100 billion parts per cubic centimetre is considered a vacuum.
It is not just isolated elements, such as hydrogen or helium, that float around in the clouds, but there are also many complex molecules and icy dust. The use of heat-sensing technology has led to the discovery of over 120 molecules floating in the space between the stars. Astronomers may even find in outer space molecules that don’t exist on Earth.
Many common molecules found on Earth, such as sugar and ethanol, have been found; but others, such as caffeine, have not. Van Dishoeck maintained that caffeine, while it may not be “necessary for the origin of life, is necessary for the maintenance of life,” to laughter from the audience.
Why study these clouds of molecules and dust? Because they may eventually form into solar systems, possibly even ones like our own. These clouds (such as the famous Eagle nebula) are often called “stellar nurseries” for their ability to spawn new stars. This happens when a cloud of particles and molecules begins to collapse under the force of gravity and form a proto-star. The star becomes surrounded by a disk of dust and molecules that may eventually form planets.
The material not formed into planets is then blown away, leaving the system in a state much like our present solar system, with a star, planets, and some smaller rocky asteroids floating in between. But how and why any planet forms is not yet fully understood. However, more than 50 per cent of young stars are surrounded by disks of matter, and they generally have enough mass within them to form up to ten Jupiter-sized planets.
“The ingredients are widely available,” noted Van Dishoeck, and indeed of the 135 known planets orbiting stars other than our Sun, many are larger than Jupiter.
One way to learn more about the make-up of interstellar clouds is to study comets that pass by Earth, many of which spend most of their time on the edge of the Earth’s solar system. This means that the chemical composition of comets (which are essentially huge snowballs) is similar to the make-up of interstellar ices. So if molecules exist in interstellar space and end up on comets, could they theoretically contribute to developing planets? “That’s still the part that is most difficult to quantify,” said Van Dishoeck.
Determining the composition of a comet is the mission of NASA’s Stardust spacecraft, which collected samples from the tail of the comet Wild-2 in January 2004 and will return the samples to Earth in mid-2006.
