You might almost be forgiven for thinking that a Spinoza Prize is nothing special; after all, Leiden receives them quite regularly. Just take Leiden Observatory, a small institute with some hundred employees that has acquired three. Nevertheless, this award is the highest scientific distinction in the Netherlands.

Two and a half million Euros is a lot of money, even for astronomers whose research equipment can cost as much as half a million Euros. Judged by the crude standards of citation scores and publications, the scientists who receive this award are the best in their field. And though the Leiden astronomers have already earned three, it has taken Wageningen and the Vrije Universiteit with a whole university each to achieve that same number since the prize was first presented in 1995.

So, it is quite understandable that Leiden astronomer Xander Tielens was slightly nonplussed when he heard he was to be presented with one. "I only realised what a major prize it was when my children googled it and sent me a very excited email."

Tielens studies molecules in the space between the stars, and helps design equipment necessary for that research. He is the Netherlands' most cited, still-active astronomer and is particularly known for his work on polycyclic aromatic hydrocarbons (PAKs), known on earth for being the molecules that cause cancer if you leave your steak on the barbie for too long. They are even more of them in outer space. "When stars reach the end of their existence, they either explode or go out like a candle. In the latter event, they start to smoke, emitting a lot of soot into the universe", Tielens explained in his acknowledgement.

The "soot" is incredibly important and, although there might be approximately only one PAK molecule in every ten cubic metres in the rarity of the interstellar gas clouds, the homeopathic-like dosage makes all the difference. Tielens explains: "The PAKs couple very easily to the light from the stars, releasing energy which heats the gas." The particles in the gas clouds then coagulate slowly but surely to form new stars and planets. The speed at which that occurs depends partly on the temperature of the cloud – our universe would be a very different place without those molecules.

Their influence might be even greater: once the planets have formed from the space cloud, PAKs are still present in, and on, the planets, disintegrating into smaller pieces, molecules containing carbon that are essential building blocks in fact, as life cannot exist on earth without carbon. All carbon atoms in the human body were once produced in stars, and it is likely that the majority of them were once space PAKs.

The main question is now whether those PAKs are only a source of carbon, or something more. When the earth was formed, it contained no life as we know it, but life was there a billion years later. What happened in the meantime is one of the great mysteries of biochemistry: did life form spontaneously or was the earth contaminated by microbes from space? And if so, where did that life come from? What happened to the non-living stuff to turn into living stuff?

Perhaps the substances produced by the disintegration of the space PAKs had a major part in that process. It is probable that life can only evolve when the right molecules do the right thing at the right time. Biochemists have been trying to mix the right ingredients together in labs for decades to find out what happens, but the results have been disappointing so far.

"I want to follow the trail from the other end", says Tielens. "Where do the substances that are the building blocks of life come from? Are they produced when PAKs disintegrate? Into which molecules did they disintegrate in the circumstances on our newly-formed earth?" The astronomer wants to use at least part of his Spinoza cash to find the answers to these questions.

In addition, he will keep on looking into outer space, but not just to look for polycyclic aromatic hydrocarbons. Earlier this year, Tielens published a paper on buckyballs, large symmetrical carbon molecules that also occur in space. They are presumably produced by PAKs when the hydrogen atoms are stripped from them one by one under the influence of radiation. "We suspect that this happens via an intermediary step, i.e. graphene, a carbon form with a structure that looks like chicken wire. But we haven't seen this substance yet, because we don't have its spectral signature – the exact type of light that is produced by space graphene." Lab testing will be required for that, to supplement the data from telescopes. "Otherwise it would be like looking for a needle in a haystack."