Is the Sun Really That Special? A Closer Look at Its Chemical Makeup

Astronomers have long known that the Sun appears to be a little different compared to other stars that are almost exactly like it—so-called “solar twins.” In particular, the Sun has fewer refractory elements (elements that condense into solid grains at high temperatures, like iron and aluminum) and is relatively rich in volatile elements (those that stay gaseous longer, like carbon and oxygen). This unusual composition raised an intriguing question: could the presence of planets, especially gas giants like Jupiter, be responsible for this chemical oddity? The new study by Carlos et al. sets out to test this idea using detailed measurements of 50 Sun-like stars, about half of which are known to have giant planets.

Methods: High-Precision Spectroscopy and Stellar Forensics

To investigate, the researchers examined high-quality spectra—essentially light fingerprints—from the HARPS spectrograph, a powerful instrument used to study stars in great detail. They focused on F- and G-type stars (like the Sun) and analyzed the abundances of 19 elements in each one. By comparing each star’s light to that of the Sun, and by applying corrections to account for technical effects such as 1D models or assuming perfect thermodynamic balance (called LTE), they ensured their results were as accurate as possible. Some of these corrections used cutting-edge 3D models that reflect the true physics of stellar atmospheres more realistically. They also studied how element abundances vary with “condensation temperature”—a measure of how easily elements form solid dust grains in space.

Results I: Lithium – The Curious Case of a Fragile Element

Lithium (Li), a fragile element easily destroyed inside stars, serves as a useful probe of a star’s history. Interestingly, previous studies suggested stars with planets may show less lithium. But in this study, Carlos et al. found no clear difference in lithium content between stars with and without giant planets, once differences in age and temperature were taken into account. Still, the Sun stood out—it was the most lithium-poor among its closest solar twins. One possible explanation for this is that the Sun may have burned through more of its lithium, or perhaps some stars gained lithium through rare events like engulfing planets.

Results II: Chemical Patterns Among the Stars

Beyond lithium, the team looked at a wide array of elements. They compared their findings to earlier research, particularly a study by Bedell et al. (2018), which had used similar methods but simpler models. While most elemental trends agreed between the two studies, this new work—thanks to its more precise modeling—showed smaller scatter in the results for some elements. The data confirmed that the Sun is indeed a bit unusual, but not drastically so, when compared to other Sun-like stars in its chemical neighborhood.

Results III: The Role of Condensation Temperature

A key part of this research was studying how element abundances changed with condensation temperature. This is important because the materials that form rocky planets like Earth are the same refractory elements that the Sun is missing. Carlos et al. found that the slopes of these abundance trends correlate strongly with metallicity (the total amount of elements heavier than hydrogen and helium, measured by [Fe/H]). This means that the Sun’s peculiar composition might be less about its planets and more about when and where it formed in the Milky Way—a result of galactic chemical evolution. Differences between stars with and without giant planets were marginal at best.

Discussion: Galactic History Over Planetary Influence

While earlier studies proposed that the formation of planets—especially giant ones—could change a star’s surface chemistry, this work suggests otherwise. The authors found no convincing evidence that having gas giants leads to a star being poor in refractory elements. Instead, the main factor seems to be a star’s metallicity and its place in the Galaxy’s history. Some small differences did emerge when comparing stars with and without planets, but they were within the margin of error and only slightly more pronounced after using more sophisticated models.

Conclusion: The Sun Isn’t So Special After All

Ultimately, this study suggests that the Sun’s unusual elemental makeup is likely not caused by the presence of giant planets. Instead, it reflects larger-scale processes in the Milky Way that affect the chemical environment in which stars form. While the Sun may still be a bit odd—particularly in its low lithium content—it's probably not as exceptional as once thought. This finding helps astronomers refine their understanding of star and planet formation and brings us one step closer to understanding our place in the cosmos.

Source: Carlos