Let there be light! Stars’ vital role in how life began

Let there be light! Stars’ vital role in how life began

Astronomers have taken an important step towards learning how life began by discovering how the substances that make it up were formed. 

We often hear how the building blocks of life, meaning carbon-based chemistry, have been found in material such as comet dust or martian soil. But how did those building blocks themselves come to exist?

Orion Nebula
This unusual view of the familiar Orion Nebula was produced in infrared light by the European Space Agency’s Hershel Space Observatory. Image credit: ESA/NASA/JPL-Caltech

New evidence from the European Space Agency’s Herschel Space Observatory shows that simple starlight plays a key role in creating molecules that make up the chemicals essential for life.

It is important to note that this is a long way from the formation of life itself. But it is a crucial part of the process of how life began and has long been a mystery to astronomers and astrobiologists. And it is the latest in a string of discoveries from the ESA telescope, including water in a nebula and alien comets.

The new discovery was made when a team of scientists turned Herschel on the Orion Nebula, a well known celestial nursery, or star-forming region, that is bright enough to be seen as a blur with the naked eye.

Their results showed that ultraviolet light from stars was a vital factor in creating the carbon-based molecules. This came as a surprise as it had been thought the cause was turbulence within such a cloud of dust and gas, due to such events as stellar explosions.

An artist’s impression of the Herschel Space Observatory observing in deep space. Image credit: ESA

The scientists studied the carbon chemistry in this nebula by mapping the amount, temperature and motions of the carbon-hydrogen molecule (known as CH, or “methylidyne” to chemists), the carbon-hydrogen positive ion (CH+) and their parent, the carbon ion (C+). An ion is an electrically charged atom or molecule, due to it having an imbalance of protons and electrons.

Patrick Morris, a researcher at the Infrared Processing and Analysis Center at Caltech, Pasadena, led the discovery team. He said in a statement: “On Earth, the Sun is the driving source of almost all the life on Earth. Now, we have learned that starlight drives the formation of chemicals that are precursors to chemicals that we need to make life.”

The astronomers had been puzzled by how much warm CH+ there was in molecular clouds such as the Orion Nebula, because it is a molecule that needs a lot of energy to form, but gets destroyed when it interacts with hydrogen within the cloud.

Because the now defunct Herschel was an infrared telescope, it could observe cold objects like never before, and was able to study the whole cloud of gas and dust rather than just hot stars. Its instrument used in this study, called HIFI, was also able to map precisely the motion of the gas within the nebula.

Orion Nebula schematic
A zoom into the Herschel image of the Orion Nebula indicated how ionised carbon formed. Image credit: ESA/NASA/JPL-Caltech

Herschel’s results showed the team that the CH+ molecules were probably produced by ultraviolet emission from very young, hot and massive stars in the Orion Nebula. This ultraviolet light heats up and excites molecules of hydrogen, producing perfect conditions for hydrocarbons to form.

As the interstellar hydrogen gets warmer, carbon ions that originally formed in stars begin to react with the molecular hydrogen, creating CH+. Eventually the CH+ captures an electron to form the neutral CH molecule.

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The study showed that, conversely, there was no correlation observed between shock waves passing through the nebula and the production of CH+.

Co-author of the study John Pearson, a researcher at NASA’s Jet Propulsion Laboratory, Pasadena, California, said: “This is the initiation of the whole carbon chemistry. If you want to form anything more complicated, it goes through that pathway.”

So it seems that, let there be light, and there was . . . life. Or the first step towards it anyway.

As an aside, the writer put together this story while staying in the German town of Friedrichshafen, on the shore of Lake Constance. The last time he was here was to see the Herschel telescope being prepared for its mission.

Herschel was launched, along with another telescope, Planck, in May 2009 and sent to a gravitationally stable location in space known as Lagrangian Point, 1.5 million km from Earth. Its mission had a limited life because it carried an essential coolant that ran out in April 2013.

By Paul Sutherland

Paul Sutherland has been a professional journalist for nearly 40 years. He writes regularly for science magazines including BBC Sky at Night magazine, BBC Focus, Astronomy Now and Popular Astronomy, plus he has authored three books on astronomy and contributed to others.

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