Planetary nurseries have been mapped in the most detail yet, and they contain far more organic molecules than expected – the basic chemical building blocks for life to arise. Studying such maps could help us understand whether we are alone in the universe.
Planets are expected to form in discs of dust and gas called protoplanetary discs, which encircle young stars. We have observed these discs in the past, and even seen signs of planets forming in them, but the Molecules with ALMA at Planet-forming Scales (MAPS) project has mapped the chemical composition of these discs in far more detail than before, using the Atacama Large Millimeter/submillimeter Array (ALMA).
The researchers looked at the discs around five nearby stars and found that each has a unique chemical composition that varies between different areas within each disc. “We see this incredible amount of chemical variety, both between and within discs,” says Jane Huang at the University of Michigan, part of the MAPS project. “We’re seeing these intricate gap and ring structures… and without this high resolution you wouldn’t know that was there.”
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The project examined organic chemicals, which are molecules that contain carbon and are therefore important for the possibility of life as we know it. “There was a lot more of this organic material than we expected – between 10 and 100 times more than our best models had predicted,” says MAPS collaborator John Ilee at the University of Leeds in the UK.
But not every location in the discs had so much organic material. “We had expected an uneven distribution, but we hadn’t expected it to look like this,” says MAPS team member Karin Öberg at the Harvard-Smithsonian Center for Astrophysics in Massachusetts. “It might really matter where in the disc and when in the disc’s lifetime a planet forms for its inventory of organic chemicals.”
Understanding this is important to figuring out which worlds beyond our solar system might have the potential for alien life. “There are many many more steps to go before anything like a little green man is invoked, but we know that these chemicals are important to life on Earth,” says Ilee.
One of the most prominent of these organic molecules was cyanide, which the researchers found in all five discs. “Despite being terrible for well-developed, complex life forms such as ourselves, cyanides seem to be very good for kick-starting the chemistry of life,” says Öberg.
The ubiquity of cyanide-based molecules may be a hint that many worlds scattered around the universe have the right ingredients for life, a promising sign that our solar system may not be particularly special. The chemical compositions of the discs matched up well with the chemicals that we see in comets in our solar system, which are the last remaining relics of our own protoplanetary disc.
But before we can make sweeping statements about all protoplanetary discs, we’ll have to observe more of them in detail to find out if these five are typical. These are some of the biggest, brightest discs we’ve seen, which made them easier to observe, but it also means that we can’t necessarily use them to generalise about planet nurseries.
These measurements have given us a window into the early formation of planets – some of the discs even seemed to contain the beginnings of new worlds – but there is a long way to go to understand how these chemicals might come together to build a habitable planet. “These are the building blocks for planets, and figuring out the recipes of how those building blocks are combined is decades of future work, but it’s very exciting,” says MAPS team member Ian Czekala at Pennsylvania State University. “This is just the tip of the iceberg.”
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