Cooking Up Life in the Cosmic Kitchen

Ever burnt meat or grilled chicken till the skin was crisp? If you have, you’ve made some PAHs. Overcooked meats, burning wood and automobile exhaust release PAHs, complex molecules composed of carbon (shown here at “C”) and hydrogen (“H”). This ball-and-stick figure represents benzo[a]pyrene, a PAH commonly produced when cooking food or burning wood has 20 carbon atoms and a dozen hydrogens. Credit: Dennis Bogdan with additions by the author
Kitchens are where we create. From crumb cake to corn on the cob, it happens here. If you’re like me, you’ve occasionally left a turkey too long in the oven or charred the grilled chicken. When meat gets burned, among the smells informing your nose of the bad news are flat molecules consisting of carbon atoms arranged in a honeycomb pattern called PAHs or polycyclic aromatic hydrocarbons.

PAHs make up about 10% of the carbon in the universe and are not only found in your kitchen but also in outer space, where they were discovered in 1998. Even comets and meteorites contain PAHs. From the illustration, you can see they’re made up of several to many interconnected rings of carbon atoms arranged in different ways to make different compounds. The more rings, the more complex the molecule, but the underlying pattern is the same for all.

Both simple and complex organic (carbon-containing) molecules have been found in space. Carbon is formed in the cores of red giant stars, where it gets cycled to the surface and dispensed into space. Credit: IAC; original image of the Helix Nebula (NASA, NOAO, ESA, the Hubble Helix Nebula Team, M. Meixner, STScI, & T.A. Rector, NRAO

All life on Earth is based on carbon. A quick look at the human body reveals that 18.5% of it is made of that element alone. Why is carbon so crucial? Because it’s able to bond to itself and a host of other atoms in a variety of ways to create a lots of complex molecules that allow living organisms to perform many functions. Carbon-rich PAHs may even have been involved in the evolution of life since they come in many forms with potentially many functions. One of those may have been to encourage the formation of RNA (partner to the “life molecule” DNA).

In the continuing quest to learn how simple carbon molecules evolve into more complex ones and what role those compounds might play in the origin of life, an international team of researchers have focused NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA) and other observatories on PAHs found within the colorful Iris Nebula in the northern constellation Cepheus the King.

This photo is a combination of three infrared color images of the Iris Nebula (NGC 7023) from SOFIA (red & green) and Spitzer (blue) that shows different types of PAH molecules in different parts of the nebula. Credits: NASA/DLR/SOFIA/B. Croiset, Leiden Observatory, and O. Berné, CNRS; NASA/JPL-Caltech/Spitzer

Bavo Croiset of Leiden University in the Netherlands and team determined that when PAHs in the nebula are hit by ultraviolet radiation from its central star, they evolve into larger, more complex molecules. Scientists hypothesize that the growth of complex organic molecules like PAHs is one of the steps leading to the emergence of life.

Strong UV light from a newborn massive star like the one that sets the Iris Nebula aglow would tend to break down large organic molecules into smaller ones, rather than build them up, according to the current view. To test this idea, researchers wanted to estimate the size of the molecules at various locations relative to the central star.

The research team used a telescope on board NASA’s SOFIA Observatory, a modified Boeing 747, to fly high above most of the water vapor in the atmosphere to get a better view of PAHs in the Iris Nebula in infrared light. Credit: NASA

Croiset’s team used SOFIA to get above most of the water vapor in the atmosphere so he could observe the nebula in infrared light, a form of light invisible to our eyes that we detect as heat. SOFIA’s instruments are sensitive to two infrared wavelengths that are produced by these particular molecules, which can be used to estimate their size. The team analyzed the SOFIA images in combination with data previously obtained by the Spitzer infrared space observatory, the Hubble Space Telescope and the Canada-France-Hawaii Telescope on the Big Island of Hawaii.

The analysis indicates that the size of the PAH molecules in this nebula vary by location in a clear pattern. The average size of the molecules in the nebula’s central cavity surrounding the young star is larger than on the surface of the cloud at the outer edge of the cavity. They also got a surprise: radiation from the star resulted in net growth in the number of complex PAHs rather than their destruction into smaller pieces.

A view of the Iris Nebula in normal or visible light showing the bright, young central star. Light from the star illuminates clouds of gas and dust that show the nebula’s flower-like shape. Credit: Hunter Wilson

In a paper published in Astronomy and Astrophysics, the team concluded that this molecular size variation is due both to some of the smallest molecules being destroyed by the harsh ultraviolet radiation field of the star, and to medium-sized molecules being irradiated so they combine into larger molecules.

So much starts with stars. Not only do they create the carbon atoms at the foundation of biology, but it would appear they shepherd them into more complex forms, too. Truly, we can thank our lucky stars!

Bob King

I'm a long-time amateur astronomer and member of the American Association of Variable Star Observers (AAVSO). My observing passions include everything from auroras to Z Cam stars. I also write a daily astronomy blog called Astro Bob. My new book, "Wonders of the Night Sky You Must See Before You Die", a bucket list of essential sky sights, will publish in April. It's currently available for pre-order at Amazon and BN.

View Comments

  • Reminds.. I am grateful that the SOPHIA telescope is still flying as she quite nearly met her demise in 2006 AND in 2013. The DLR or Deutsches Zentrum für Luft- und Raumfahrt e.V. had to press it's case for saving SOPHIA as they had invested heavily in this observatory. Here's hoping she flies long and high as no other IR facility has this 'on demand' capability and is able to fly anywhere in the world in practically a moments notice to do the deeds!

  • Thank you Bob :)
    It is truly wonderful that the line of evidence shows that the process of stellar fusion that in most cases destroys life also contributes to forming it in the quieter recesses of galaxies :)

  • "PAHs make up about 10% of the carbon in the universe"
    I thought that most of the carbon in the universe was in the form of CO, carbon monoxide, or stuck in white dwarfs. So 10% of all carbon atoms are in PAH. Fantastic! Where can I learn more about this? Is it on the same sites which claim that the non-increasing temperature is our doomsday if we don't give away all of our money to the politicians? Universe today is really very trustworthy...
    Do you sell craters on the Moon too?

      • So, by how many degrees has the global temperature increased since 1998? By ZERO! How does that compare with the fear mongering climate doomsday prophecies of Al Gore et al back then? The hockey stick is scientifically discarded because it has been more than two standard deviations WRONG!

        Since it is a fact that the temperature HAS NOT increased, there cannot be any kind of climate change caused by the increasing CO2 emissions. CO2 in itself does not melt glaciers or cause other doomsday scenario, if it does not increase the temperature. Do you understand that much about climate?

        CO2 emissions have only had very positive effects for life on Earth. The world is greening thanks to it. Agriculture productivity per hectare is increasing so fast thanks to our anthropocentric CO2-emissions that we need lesser and lesser agricultural land to feed the growing population. The wild nature is taking back our abandoned farm lands thanks to our CO2-emissions. And the jungle and the taiga are getting more lively, thanks to our increased use of fossil fuel.Taking back dead minerals from the underground and turning it into the gas of life.

        Climate panic is an irrational religious doomsday belief. Irrational believers like Phil Plait search desperately for spurious statistics which confirms their prejudice belief. July month-on-month. So, how do his charts look for the other eleven months? Why doesn't he mention them? However could temperature increase only in July?

      • So what about 10% of all carbon in the universe being in PAH molecules? Do you believe that too, because some idiot wrote it here? Are you that gullible? Do you believe anything anyone tells you. Do you use authoritarians as a substitute for your own mind? It is comfortable to just obey orders and follow the blind sheeple all the way to the gas chambers without having to think, isn't it.

        But if you think that you will be absolved from doomsday by giving away all of your money to some god like politician, I can give you my account number to let you save your poor soul...

        • i care whether my beliefs are true and science is the most reliable path to find that.
          feelings are not facts
          i feel sorry for you

          • So if you make prognosis that a catastrophy will happen in two decades, and two decades later it turns out that your prognosis was wrong by way more than two standard deviation, then you ignore reality and hang on to your old religious belief anyway? The climate panic was wrong. We know that now in hindsight. The CO2 emissions have instead had very good effects on wild life and the economy.

            Blind religious believers like you deny the facts and just refer to your authoritarian priests. You were once told that doomsday is coming because of our sins. Even though doomsday doesn't happen, you lack the brains to think a new thought. No ability to adapt to reality. Just keep on failing.

            10% of all carbon being PAH, is that "science" to you too, since an "authority" has told you so? You have no clue about what science even is.

          • WOW... you. are. a C.U.N. double chopstix, son.

            BTW, anyone who's A) that angry and demeaning and B) uses the word "Sheeple" is 9x out of 8, a fringe whack job.

            Also too, mentioning gas chambers is a full-on Godwin, so grats for that, psycho.

            "Do you use authoritarians as a substitute for your own mind? It is comfortable to just obey orders and follow the blind sheeple all the way to the gas chambers without having to think, isn’t it?"


            ~FarAwayLongAgo (WHEN OFF HIS MEDS)


    • If you don't like this blog, then why do you come here to ridicule.... oh.... NM. That susses it there: You're a bully with a desperate need to prove himself superior to not even other people, but to thousands of scientists and entire established and agreed upon fields of study, because he needs to boost his self esteem by trolling pages he disagrees with. You're a petty, self important child.



      • I like this blog, I'm just disappointed at blatant errors and the stressful attitude that life is everywhere in the universe and that astronomy is only about finding aliens. Talk about prejudice beliefs and ignoring reality for wishful thinking!

        It is a fact that the climate models from the 1990s were totally wrong. It is true that CO2 emissions are good for wild life and farming. Can you tell me anything which could disprove the climate panic in your belief system? The complete lack of warming doesn't seem to be a reason to rethink global warming. Now it's just global warming without warming! Enjoy the good news instead, doomsday has been canceled.

  • "One of those may have been to encourage the formation of RNA (partner to the “life molecule” DNA).

    This is philosophical naturalistic ideology not science. There is no scientific basis to make such conjecture, only wishfulness, which is not a scientific process.

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