Scientists have long wondered how the complex molecules needed for life could have formed around the turbulent and violent environment of the sun in its youth.
A family of meteorites called “chondrites” are thought to have delivered the right ingredients for life to Earth. But the question is, how did the complex organic molecules containing elements like carbon, nitrogen and oxygen get sealed in these meteorites in the first place?
New research suggests that the “hot spot” for the creation of these macromolecules, the basic building blocks of life, may be so-called “dust traps” in the swirling disks of matter around newborn stars. Here, intense starlight from the central young star could irradiate the accreting ice and dust to form carbon-containing macromolecules in just decades, which is relatively fast.
This would mean that macromolecules could already be present when larger planetesimals form planets, or they could be locked up in asteroids in the form of small pebbles. These asteroids could then be broken up by repeated collisions in space to form smaller bodies. Some of them may have arrived on Earth in the form of meteorites.
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“It’s incredible to discover a key new role for dust traps in creating the macromolecular matter that planets may need to host life,” team member Paola Pinilla of University College London’s Mullard Space Science Laboratory told Space.com. “Dust traps are beneficial areas for dust particles to grow into pebbles and planetesimals, which are the building blocks of planets.”
Pinilla explained that in these regions, very small particles can be continuously renewed and replenished by ongoing destructive collisions. These tiny micron-sized grains can easily be lifted into the upper layers of the flattened cloud of star-forming material that surrounds the newborn star, called the protoplanetary disk.
Once here, Pinilla said, these particles can receive just the right amount of radiation from their newborn star to effectively transform these tiny ice particles into complex macromolecular matter.
Replication of the early days of the solar system in the laboratory
Stars like the sun are born when dense patches form in massive clouds of interstellar gas and dust. An infant stellar body first becomes a protostar and collects matter from what is left of the nascent cloud, accumulating the mass needed to trigger the nuclear fusion of hydrogen into helium in its cores. This is the process that defines the lifetime of a “main sequence” star, which for a star the mass of the Sun will last approximately 10 billion years.
This young star is surrounded by a protoplanetary disk, material that was not consumed during its formation and ascent to the main sequence. As the name suggests, it is from this material and within the disk that plants form, but it is also behind the origin of comets and asteroids.
Our solar system went through this process of creation about 4.5 billion years ago.
Previous research conducted in laboratories here on Earth has shown that when these protoplanetary disks are irradiated with starlight, complex molecules of hundreds of atoms can form within them. These molecules are made up mostly of carbon and are similar to black carbon black or graphene.
Dust traps are high-pressure places in protoplanetary disks where molecular motion is slowed and dust and ice grains can accumulate. Lower velocities in these regions may allow grain growth and largely prevent collisions that cause fragmentation. This means that they could be necessary for the formation of planets.
Wanting to know whether the radiation that starlight brings to these regions can cause complex macromolecules to form, the team tested the idea using computer modeling. The model was based on observational data collected by the Atacama Large Millimeter/submillimeter Array (ALMA), an array of 66 radio telescopes in northern Chile.
“Our research is a unique combination of astrochemistry, ALMA observations, laboratory work, dust evolution and the study of meteorites from our solar system,” said team member Nienke van der Marel of Leiden University. “It’s really cool that we can now use a model based on observations to explain how large molecules can form.”
The model revealed to the team that creating macromolecules in dust traps is a feasible idea.
“Of course we were hoping for this result, but it was a nice surprise that it was so obvious,” said team leader Niels Ligterink of the University of Bern. “I hope that colleagues will pay more attention to the effect of heavy radiation on complex chemical processes. Most researchers focus on relatively small organic molecules with the size of a few tens of atoms, while chondrites contain mostly large macromolecules.”
“In the near future, we look forward to testing these models with additional laboratory experiments and observations with powerful telescopes such as the Atacama Large Millimeter Array (ALMA),” concluded Pinilla.
The team’s research was published Tuesday (July 30) in the journal Nature Astronomy.