This article was first published by The Conversation. Space.com's Expert voices: Op-Ed and Insights was contributed by the publication.
Lorenzo Spina is a Postdoctoral Research Fellow at the Italian National Institute for Astrophysics and was previously Research Fellow at Monash University.
Our solar system is rare! Since the discovery of planets orbiting stars other then our sun 30 years ago, we have discovered that planetary systems are quite common throughout the galaxy. Many of these systems are very different to the solar system that we know.
Our solar system's planets revolve around the sun in stable, almost circular orbits. This suggests that the orbits have not changed much from when the planets were formed. However, many of the planetary systems orbiting other stars have had a chaotic past.
Related: Will the sun's death affect our solar system?
Our solar system's relatively peaceful history has helped to support the growth of life on Earth. If we have a way of identifying systems with similar peaceful pasts, we can narrow our targets when searching for alien worlds that might contain life.
This issue was tackled by an international team of astronomers in research published in Nature Astronomy. Our research revealed that sunlike stars consume between 20% and 35% their own planets. The most likely number is 27%.
This means that at least 25% of the planetary systems orbiting stars like the sun have experienced a chaotic and dynamic past.
Binary stars and chaotic histories
Exoplanetary systems have been observed in which large and medium-sized planets moved significantly, according to astronomers. These planets could have acted as a gravity, causing them to move in unpredictable orbits.
It is possible that some planets have also fallen into the star hosting these dynamic systems. We didn't know how common these chaotic systems were relative to systems like ours, which have a more orderly architecture that has allowed for the flourishing life on Earth.
Binary stars are formed simultaneously from one cloud of gas. They usually have exactly the same mixture of elements. (Image credit: ALMA (ESO/NAOJ/NRAO), Alves et al.)
It would be difficult to determine this even with the most accurate astronomical instruments. Instead, we looked at the chemical compositions of stars in binary systems.
Binary systems are composed of two stars orbiting around each other. These stars were formed from the same gas at the same time, so it is expected that they will contain the same mixture of elements.
If a planet is placed in one of the two stars it will be dissolved in its outer layer. This can alter the chemical composition of the star. We see more elements that make rocky planets, such as iron, than we would otherwise.
Traces of rocky worlds
By analysing the spectrum light they emit, we were able to determine the chemical composition of the 107 binary systems made up of sunlike stars. We were able to determine how many stars had more planetary material than the companion star.
Three other things were also discovered that provide unambiguous evidence to support the theory that binary pairs' chemical differences are caused by planets that eat.
First, stars with a thinner outer coating have a greater chance of being richer than their companions in iron. This is consistent in planet-eating as the planetary material that is diluted in a thinner outer layer makes a larger change to the layers' chemical composition.
[2108.12040] Lorenzo Spina, Parth Sharma, Jorge Melndez et al. : Chemical evidence for planetary ingestion in a quarter of Sun-like stars https://t.co/SQzTYph2ON https://t.co/6OpNci45gc #astro_ph_SRAugust 30, 2021 See more
Second, stars with higher levels of iron and other rocky planet elements have more lithium than their counterparts. Stars quickly destroy lithium, but planets retain it. A star with an unusually high level of lithium must have formed after it formed. This fits well with the theory that the planet carried the lithium until it was consumed by the star.
Third, stars with more iron than their companions also have more stars than other similar stars in the galaxy. The same stars also have standard amounts of carbon, which is volatile and is not carried by rocks. These stars were chemically enhanced by rocks from planets and planetary material.
The hunt for Earth 2.0
These findings are a major breakthrough in stellar astrophysics, and exoplanet research. We have discovered that eating planets can alter the chemical compositions of sunlike stars. Additionally, a large fraction of their planetary system underwent a dynamic past unlike our solar system.
Our study also opens up the possibility of chemical analysis being used to identify stars more likely to be host to true analogs of our calm, solar system.
There are many stars that are very similar to the sun, and there are many millions. The search for Earth 2.0 won't be easy without a way to find the most promising targets.
This article was republished by The Conversation under Creative Commons. You can read the original article.
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