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Good soup! Raw ingredients for life abundant in the swirling discs around newly forming planets
Approximately 4 billion years ago, the raw ingredients for life combined in just the right way, through some yet unknown process, and life emerged here on Earth. To date, we’ve been unable to confirm the existence of life anywhere else in the universe, but new research suggests that the ingredients for life may be more common than we previously supposed.
Combining them in the right way is another question entirely, but astronomers using a telescope known as the Atacama Large Millimeter/submillimeter array (ALMA) in Chile have determined the basic building blocks could be common in planetary nurseries.
Dr. John Ilee from the School of Physics and Astronomy at the University of Leeds, along with a team of colleagues across eight different countries, used the telescope to investigate five protoplanetary discs. These discs are swirling masses of dust and gas, between 1 million and 10 million years old, in the process of accreting into planetary systems.
It was already known that planetary discs contained organic molecules, but the prevalence of complex organic molecules (COMs) of the type needed for the construction of things like amino acids has been difficult to determine. This is largely due to the complexity of those molecules. Typically, bigger structures are easier to find in space, but “big” is relative when talking about molecules floating in clouds lightyears away.
“We’ve known that discs are host to these types of molecules for a few years,” Ilee told SYFY WIRE. “The surprising result for our analysis was just how much we were able to detect in the discs, up to 100 times more than we expected from our best models.”
In the case of molecules, bigger isn’t always better. Chemical composition of distant structures is determined via spectroscopy — the process of observing the wavelengths of radiated light emitted by the object. Each chemical compound from hydrogen on up emits a specific spectral pattern, like a fingerprint, which allows observers to determine composition at a distance.
Larger molecules, with more individual atoms strung together, have more complex emission patterns. An unfortunate result of this is emissions are weaker and harder to detect. This means that while complex organic molecules may have been waiting for us out there in the distant reaches of space, they had to wait for us to develop telescopes and observation methods sensitive enough for us to find them.
Measuring spectral lines of moving objects is particularly challenging because of Doppler shift. As objects move, their light (whether visible or not) is shifted toward one end of the spectrum or the other, depending on their direction of motion. As an object moves away, relative to an observer, its light is redshifted. As it moves toward an observer, it’s blueshifted.
Orbiting objects, like protoplanets circling within an accretion disk, may move toward Earthbound observers at some times and away from them at others, depending on the angle of observation. That shift in frequency plays havoc with spectral measurements and has to be accounted for. The team used software to plug in the known geometry and rotation of the discs and to correct for rotational Doppler shift, resulting in single spectrum.
This method, and the sensitivity of the equipment, allowed the team not only to confirm the existence of complex organic molecules in protoplanetary discs, but also to identify their approximate locations. Of the molecules they were looking for, they successfully found them in four of the five studied discs, indicating COMs are very likely prevalent in planetary nurseries.
“We certainly aren’t suggesting that anything like alien life has been detected, but rather some of the raw ingredients for life as we know it here on Earth. A key component of these molecules is the carbon-nitrogen bond. This has been demonstrated to be important in the synthesis of molecules such as sugars, amino acids, and the bases of RNA. The molecules we have observed therefore represent the most complex (yet) detected in protoplanetary discs with this bond and demonstrate that these stages of molecular complexity can be built up in the vicinity of forming planets,” Ilee said.
The outlier system, IM Lup, did not exhibit strong indications of complex organic molecules. This could be explained by its relatively young age. Of the five observed discs, IM Lup is the youngest, with an estimated upper age of 1.3 million years old. If these complex molecules are formed within the disk during accretion, it’s possible that IM Lup simply hasn’t had the time to form them. Other factors, like the size and density of the disc could also obscure complex molecules if they exist. Understanding which factors contribute to the apparent lack of measured COMs will require more robust models.
The findings are good news for life elsewhere in the universe. It’s clear that planetary chemistry favors the formation of complex organic molecules of a kind which, at least once, resulted in the emergence of life. Given the scope of the universe, it seems unlikely they wouldn’t find themselves in the correct distribution and configuration for life someplace else.