The asteroid that recently dominated the headlines, 3I/ATLAS, may be between 10 and 12 billion years old, a new analysis of the isotopic composition of the comet has shown. This so-called “invader” in our planetary system is only the third object reported to enter our cosmic environment from beyond.
If these predictions of new comet ages are true, they may suggest something 3I/ATLAS appeared within a few billion years after the birth of the neck.
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So, based on the speed of the comet, astronomers Aster Taylor and Darryl Seligman of the University of Michigan and Michigan State University, respectively, determined that 3I/ATLAS has a “kinematic” age somewhere between 3 and 11 billion years. It is a range with great doubts – but now, a new study led by Martin Cordiner of NASA Goddard has appeared in favor of the old end of the range, based on and the isotopic composition of the comet.
From studies and James Webb Space Telescope‘s Near-Infrared Spectrometer (NIRSpec), Cordiner and his team measured both the ratio of carbon-12 to carbon-13 in 3I/ATLAS and how the water in 3I/ATLAS is enriched with molecular deuterium, one of the two stable isotopes of hydrogen. Both of these elements are important tools for inferring the age and origin of a comet.
Isotopes exist atoms of the same thing with the same amount of protons but different numbers of neutrons. Carbon-12 is the common form of carbon, with 6 protons and 6 neutrons. Carbon-13 is an isotope, with 6 protons and 7 neutrons. Deuterium has one proton and one neutron (unlike the primitive hydrogen, which has one proton and no neutrons).
Carbon isotopes are found in 3I/ATLAS in compounds such as carbon monoxide and carbon dioxide, and even organic molecules such as methanol, formaldehyde and methane.
NIRSpec found that 3I/ATLAS has more carbon-12 relative to carbon-13 than anything we see. solar systemor indeed even in nearby disks that form planets around each other starsor molecular clouds in the region. This tells us that 3I/ATLAS is not from here at least.
Carbon-13 builds up over time in interstellar atmospheres and star-forming molecular clouds. Therefore, the low amount of carbon-13 relative to carbon-12 indicates that 3I / ATLAS must have been formed long ago – before carbon-13 was able to build up to modern times.
We can turn to models of stellar evolution to hazard a guess as to how long ago it was.
After the Milky Way was formed about 13 billion years ago, it experienced a starburst: the explosion of stars. Most of these stars changed quickly red giants before they leave, they pull off their outer layers and form a planet nebula while they leave behind their hot, inert core, which we call a a white person.
In a nearby binary system with another star, a white dwarf could steal enough material to ignite a thermonuclear explosion on it. We call this a nova, and such events are spectacular producers of carbon-13. As a result, a burst of nova explosions is expected in the first four billion years of the Milky Way’s history. For 3I/ATLAS to have a low ratio of carbon-13 relative to carbon-12, yet still contain heavy elements, it must have formed in the middle of all this, before most of the carbon-13 had a chance to accumulate in the galaxy.
This would put the age of 3I/ATLAS as 10-12 billion years.
The development of deuterium in 3I/ATLAS also tells us about the origin of interstellar comets. Deuterium can replace one or two of the normal hydrogen atoms in water, which scientists refer to as deuterium enrichment. The enrichment of deuterium in water 3I / ATLAS has a D/H ratio that is an order of magnitude higher than that of the typical comets that formed in our planetary system.
This level of enrichment occurs in certain areas. Water ice can be formed in deuterium at temperatures below 30 degrees above absolute zero (30 kelvin/–243 degrees Celsius/–405 degrees Fahrenheit), which is the core of interstellar clouds, and in environments poor in heavy matter, dating back to the early formation of our galaxy.
Comets form together with planets, so if these findings are correct, then 3I/ATLAS may be part of the first planetary systems in the galaxy. Can 3I/ATLAS tell us anything about these first planets they created together?
Comets, which are icy bodies, are thought to form in the far reaches of planetary systems, far from the heat of their host star that would cause the ice to vaporize. The boundary in the disk that forms the planet between where water exists as water vapor or liquid, and where it exists as ice, is called snow.
“We believe that the comets generally represent planets outside of the water snow in the protoplanetary disk,” Cordiner told Space.com. “So perhaps the same is true of interstellar comets, and they provide unique insights into where extrasolar planets may form.”
Scientists are still building a complete picture of the 3I/ATLAS chemical inventory, but there are a few things they can say at this stage.
“Both 2I/Borisov and 3I/ATLAS show a relatively carbon-rich composition compared to solar system comets,” Cordiner said. “At the very least, this means there was a lot of carbon in the early planetary system. 3I/ATLAS also has a lot of water.”
The presence of deuterium, and various compounds of carbon and oxygen, is an indication of the complex chemistry that occurred on the dust and ice on which the 3I/ATLAS planetary system may have formed, telling us that organic molecules and water were important components of the planets even at the beginning of the history of the universe.
However, the true purpose of 3I/ATLAS remains a mystery, and probably always will be. Tracing its path back more than 10 million years is difficult or impossible, due to the gravitational interactions between 3I/ATLAS and the stars it passes by, which distort its path.
However, the knowledge of its age slows things down a bit.
The Milky Way is divided into two parts – a narrow, 1,000-light-year-old “disk” where most of the star formation in our galaxy now takes place (and where our sun was born), and the other in a very dense disk (about 3,000 light-years across). The view of the stars in the dense disk is the European Space Agency’s Gaia mission suggests that the thick disk first formed about 13 billion years ago, while the thin disk is thought to be much younger, about 9 billion years ago. If these ages are correct, then 3I/ATLAS may have originated from a dense disk star.
“That seems to happen to adults [3I/ATLAS] yes,” Cordiner said.
In fact, 3I/ATLAS is so old that the star system it produced may no longer exist. Is 3I/ATLAS really a relic from a lost era of planetary formation?
The findings are currently awaiting peer review, but are available via first edition.
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