I grew up in coastal British Columbia where the weather was easy to predict. If you could see the mountains, you knew it was going to rain. If you could not see the mountains, it was raining already.
We had a student in our high school who was from an African desert nation. Other students would playfully tease him about his ancestors worshiping the Sun. His usual retort was, “You would, too, if you ever saw it.”
Of course, nobody worships the Sun these days. However, the Sun should certainly cause us to worship and praise its Creator. As I have written in numerous articles over the past three decades,1 we astronomers have not been able to find another star sufficiently like the Sun that could sustain advanced life on a conceivable planet orbiting it. Only the Sun appears to possess all the fine-tuned features that advanced life requires in its host star.
It is not for lack of searching that astronomers have been unsuccessful in finding an adequate twin to the Sun. Several teams of astronomers have spent over six decades in their quest to find the Sun’s twin. That search has led them to discover several stars that are twins of one another, but so far no “twin” for the Sun.
The astronomical literature mentions the recent discovery of over a dozen solar “twins.” Astronomers define a solar twin as a main sequence G-type star with an effective temperature within 50° centigrade of the Sun’s value, an abundance of elements heavier than helium within 89–112% of the Sun’s value, an age within 1 billion years of the Sun’s age, and no stellar companion.
To date, however, none of the solar twins that have been discovered are sufficiently Sun-like to be a candidate to support advanced life on a planet orbiting it. Such a star would need to be a G2-type star with an effective temperature within 5° centigrade of the Sun’s value, with a luminosity variation of less than 0.1%, with the same abundance of elements heavier than helium and with the same relative abundances of these elements as the Sun, and match the Sun’s age (4.566 billion years) to within 1 million years (some physicists would say within 0.1 million years).
The mission to find a real twin of the Sun continues, and the latest findings reveal even more of the Sun’s special features that make it a unique star for sustaining advanced life on one of its planets. A high-resolution spectroscopic survey of rich open star cluster M67 revealed an unusually Sun-like star, M67-1194.2 M67-1194 is the first known solar “twin” that belongs to a star cluster. Chemically, M67-1194 is much more similar to the Sun than all the other known solar “twins.” This result provides more evidence that the Sun was born in a rich cluster of stars and soon after its formation was strongly ejected from its birth cluster.3 M67-1194 is not a true solar twin, however. It is about 5% richer in elements heavier than helium and about a half billion years younger. Also, its current residence in a rich cluster of stars would be a problem for advanced life.
Another star that is chemically quite similar to the Sun is HIP 56948. Its chemistry would be nearly identical to the Sun if the equivalent of three Earth masses of a mix of Earth and meteoritic material were deposited into HIP 56948’s convection zone.4
Unlike the known solar “twins,” the Sun possesses comet and asteroid belts. (An infrared wavelength survey of 216 solar siblings, twins, and analogs showed that the 60 most Sun-like stars in the survey revealed no detectable dust, a signature for the presence of asteroids and comets, in the stars’ vicinities.5) The absorption of comets and asteroids over the Sun’s long history may explain its chemical difference compared to HIP 56948.
In the last three years, new discoveries have nearly doubled the list of solar “twins.” These new additions to the list, however, either manifest considerably more chromospheric activity and variability than the Sun,6 are at least a half billion years older than the Sun,7 or are at least a billion years younger than the Sun.8
Yes, the latest and most diligent searches for solar twins have nearly doubled the list of known solar “twins.” It still remains, however, that the Sun stands alone among all the stars that astronomers have identified as the most Sun-like in possessing all the stellar features that advanced life requires.
As several astronomers have noted in the conclusions of their papers concerning the search for solar twins, only the most Sun-like stars should be SETI (Search for Extraterrestrial Intelligence) candidates.9 So far, there are no sufficiently Sun-like candidates, which implies that the funding for SETI, at least for now, should be diverted to causes that have the possibility of being more productive. The complete lack of such candidates after many decades of scouring the Milky Way Galaxy’s inventory of stars should cause us to consider just how remarkably fine-tuned and designed the Sun is to make our existence and our advanced civilization possible. Next time you gaze upon a sunrise or a sunset, may it move you to burst out in praise toward our God for his bountiful provision in the way he designed the Sun for your benefit and purpose.
Featured image credit: HalloweenNight