Based on Job 14:5 and Psalm 139:16, I believe God determines the time and location of every human’s birth to ensure that we are optimally positioned to fulfill the specific purposes for which he created us. As I reflect on my own life, I’m persuaded that my birth date and my birth location were optimal for the ministry roles God wanted me to fulfill in my life.

Recent astronomical discoveries persuade me that what is true for every human being is also true for the Sun and its system of planets. Astronomers have now accumulated a wealth of evidence that the birth of our solar system was optimally orchestrated, in multiple independent ways, to make the existence and flourishing of advanced life on Earth possible.

Solar System’s Birth Location 
The majority of stars within the disk of the Milky Way Galaxy (MWG) formed within star clusters.1 About 90% of these stars formed in clusters of 100 or more stars. 

Three observations convince most astronomers that the solar system formed in a cluster of at least 500 stars:

1. The high orbital eccentricities of solar system bodies beyond Neptune indicate past close encounters with stars in the Sun’s birth cluster.2
2. Isotopic composition of presolar grains differs from the Sun’s current composition in a manner indicating that these grains originated from a core-collapse supernova (CCSN).3 (Core collapse supernovae are extremely massive stars that, at the end of their nuclear burning, collapse rapidly—within 2–3 minutes—from a few tens of millions of miles in diameter to about 12 miles.)
3. An injection of dust grains from a CCSN into the emerging solar system uniquely explains the evidence for short-lived radionuclides, especially aluminum-26 and iron-60, found in meteorites.4 While the aluminum-26 and iron-60 has long since decayed away, the decay products, or daughter isotopes, that remain in recovered meteorites enable astronomers to determine the original abundances of aluminum-26 and iron-60 in these meteorites.

Size of the Solar System’s Birth Cluster 
Astronomers Sota Arakawa and Eiichiro Kokubo recently conducted an in-depth analysis of the daughter isotopes of short-lived radionuclides to produce the most accurate determination, to date, of the size of the star cluster in which our solar system was born.5 They found two distinct types of calcium-aluminum inclusions coexisting in the solar system’s primitive meteorites. One type was rich in aluminum-26, the other, poor in aluminum-26.

Arakawa and Kokubo’s finding that both types of inclusions coexisted in primitive solar system meteorites implies that the injection of aluminum-26 into the solar system must have occurred within a short time period at the very beginning of the solar system’s formation. Their calculations established that the injection of aluminum-26 materials into the solar system from a nearby CCSN must have occurred within the first hundred thousand years of the solar system’s existence. Furthermore, their calculations showed that to explain the amount of aluminum-26 injected into the solar system, the star that became a CCSN must have had a mass between 20 and 60 times the Sun’s mass.

Only a small fraction of a percent of the MWG’s stars are as massive as 20 times the solar mass. Such stars are short-lived. The burnout time for the Sun’s nuclear furnace is about 9 billion years. Stars greater than 20 times the Sun’s mass burn out in less than 4 million years.  

Based on the relative population of stars more massive than 20 times the Sun’s mass and the short time window for the injection of aluminum-26 into the solar system, Arakawa and Kokubo estimated the number of stars that must have existed in the solar system’s birth cluster. If the duration of star formation in the solar system’s birth cluster were 12 million years, the minimum number of stars in the cluster would be 2,000. For the much more likely case that the duration of star formation was 5 million years, the minimum number of stars would be 20,000. For an idea of what such a star cluster looks like, see the figure below.

Figure: NGC 6139, a Star Cluster with 10,000–20,000 stars
Credit: NASA/ESA/STScI

The Significance of Such a Size
The number 20,000 is 25 times larger than any previously published estimate of the number of stars in the Sun’s birth cluster.6 The new number implies that the solar system was born in a rare star cluster, rather than a relatively common one. Even though the MWG’s mass is 1.2 trillion times that of the Sun, it includes only 152 clusters of more than 10,000 stars.

If the Sun and its system of planets had remained in its birth cluster, advanced life in the solar system would not have been possible. The ongoing gravitational encounters and radiation from nearby stars and the radiation from the cluster’s growing intermediate-mass black hole would have proved deadly. However, the more massive and dense the solar system’s birth cluster, the less likely the solar system’s gravitationally induced ejection in a short enough time frame for advanced life to become possible. The solar system’s birth cluster must be the just-right mass and the stars nearest to the solar system must be structured and arranged in the just-right way to allow the solar system’s ejection from the cluster at the just-right time.  

For advanced life to be possible, a solar system must be born in a star cluster that allows for early delivery of certain elements from a CCSN. However, a CCSN not only expels short-lived radioisotopes such as aluminum-26 and iron-60, it also ejects (and delivers into the solar system) enormous quantities of elements heavier than iron, which explains why Earth’s crust has an abundance of copper, zinc, molybdenum, tin, and iodine that is 21, 6, 5, 3, and 4 times greater, respectively, than the average abundance throughout the MWG. These five heavy elements are recognized as vital poisons. Too low an abundance of any of them rules out the possibility of advanced life. Too high an abundance of any of them also rules out advanced life. The emerging solar system must have been exposed to a CCSN at just the right time and place to acquire the quantities of copper, zinc, molybdenum, tin, and iodine that advanced life requires. This exposure also provided Earth with huge quantities of uranium and thorium, elements that contributed to Earth’s internal heat flow and, thus, made enduring plate tectonics and a protective magnetosphere possible.  

Due to the solar system’s early exposure to a CCSN, Earth’s crust has 40 times more aluminum-27 than the MWG average. This huge abundance formed lubricating compounds that enable Earth’s tectonic plates to slip past, under, or over one another efficiently. Thanks to Earth’s enduring, strong plate tectonic activity, life-critical nutrient cycles remain in operation and correctly compensate for the Sun’s increasing luminosity.7 Earth’s hyperabundance of aluminum has also significantly contributed to global civilization and technology.

Not only must the size of the solar system’s birth cluster be fine-tuned to make advanced life possible, so must the structure and dynamics of the solar system’s birth cluster. Evidence for this additional fine-tuning was determined by astronomers Arakawa, Kokubo, and eight others working in Japan, Portugal, and the United States. Their discoveries and the implications drawn from them will be addressed in my next Today’s New Reason to Believe article. For now, it seems reasonable to say that the fine-tuned size of the solar system’s birth cluster alone illustrates the biblical principle that the more we learn about the realm of nature, the more evidence we uncover for the supernatural handiwork of God, work that makes possible the existence of human beings, human civilization, and human redemption.

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Endnotes

1. Charles J. Lada and Elizabeth A. Lada, “Embedded Clusters in Molecular Clouds,” Annual Review of Astronomy and Astrophysics 41 (September 2003): 57–115, doi:10.1146/annurev.astro.41.011802.094844.
2. Alessandro Morbidelli and Harold F. Levison, “Scenarios for the Origin of the Orbits of the Trans-Neptunian Objects 2000 CR105 and 2003 VB12 (Sedna),” Astronomical Journal 128, no. 5 (November 2004): 2564–2576, doi:10.1086/424617.
3. Larry R. Nittler and Fred Ciesla, “Astrophysics with Extraterrestrial Materials,” Annual Review of Astronomy and Astrophysics 54 (September 2016): 53–93, doi:10.1146/annurev-astro-082214-122505.
4. Gary R. Huss et al., “Stellar Sources of the Short-Lived Radionuclides in the Early Solar System,” Geochimica et Cosmochimica Acta 73, no. 17 (September 2009): 4922–4945, doi:10.1016/j.gca.2009.01.039. 
5. Sota Arakawa and Eiichiro Kokubo, “Number of Stars in the Sun’s Birth Cluster Revisited,” Astronomy & Astrophysics 670 (February 2023): id. A105, doi:10.1051/0004-6361/202244743.
6. Fred C. Adams, “The Birth Environment of the Solar System,” Annual Review of Astronomy and Astrophysics 48 (September 2010): 47–85, doi:10.1146/annurev-astro-081309-130830.
7. Hugh Ross, Designed to the Core (Covina, CA: RTB Press, 2022), 199–220.