Some planetary systems just aren't into heavy metal

Some planetary systems just aren't into heavy metal
An Illustration of a compact, multi-planet system. Researchers have found that such systems are more likely to form around stars with lower amounts of heavy elements than our own Sun. Credit: Michael S. Helfenbein/Yale University

Small planetary systems with multiple planets are not fans of heavy metal—think iron, not Iron Maiden—according to a new Yale University study.

Researchers at Yale and the Flatiron Institute have discovered that compact, multiple-planet systems are more likely to form around that have lower amounts of heavy elements than our own Sun. This runs counter to a good deal of current research, which has focused on stars with higher metallicity.

The research team looked at 700 stars and their surrounding for the study, which appears in The Astrophysical Journal Letters. The researchers considered any element heavier than helium—including , silicon, magnesium, and carbon—as a heavy metal.

"We used iron as a proxy," said lead author John Michael Brewer, a postdoctoral researcher at Yale who works with astronomy professor Debra Fischer. "These are all elements that make up the rocks in small, ."

Brewer said an abundance of compact, multi-planet systems around low-metallicity stars suggests several things.

First, he said, it may indicate that there are many more of these systems than previously assumed. Until recently, research instruments have not had the necessary precision to detect smaller planets and instead focused on detecting larger planets. Now, with the advent of technology such as the Extreme Precision Spectrometer (EXPRES) developed by Fischer's team at Yale, researchers will be able to find smaller planets.

In addition, Brewer said, the new study suggests that small planetary systems may be the earliest type of planetary system, making them an ideal place to search for life on other planets. "Low-metallicity stars have been around a lot longer," Brewer said. "That's where we'll find the first planets that formed."

Fischer, who is a co-author of the study, demonstrated in 2005 that higher metallicity in stars increased the probability of forming large, Jupiter-like planets. This provided strong support to the core-accretion model for gas giant planet formation and established this as the leading mechanism for planet formation.

Understanding the formation of smaller planets has been more elusive.

"Our surprising result, that compact systems of multiple, small planets are more likely around lower metallicity stars suggests a new, important clue in understanding the most common type of planetary system in our galaxy," said co-author Songhu Wang, a 51 Pegasi b Fellow at Yale.

Another tantalizing possibility to explore, according to the researchers, is the connection between iron and silicon in the birth of planets. The new study shows a high silicon-to-iron ratio in stars with lower metallicity.

"Silicon could be the secret ingredient," Fischer said. "The ratio of silicon to iron is acting as a thermostat for . As the ratio increases, nature is dialing up the formation of small, rocky planets."

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Journal information: Astrophysical Journal Letters

Provided by Yale University
Citation: Some planetary systems just aren't into heavy metal (2018, October 24) retrieved 19 October 2019 from
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Oct 24, 2018
Perhaps this is back-to-front ?
If higher metallicity forms bigger planets, are they not more likely to scatter, eject and/or swallow smaller ? As yet, we only see the survivors...

Oct 25, 2018
I just realized. Considering the erratic highly energized X-Ray flares from young, small stars?

And the odds are, that the orbiting planets will be lacking iron cores? Thus no protective magnetic field? Can a Silicon core produce a magnetic field?

Planets close enough to be in their System's goldilocks zone are going to take quite a beating before their first billion years.

What a waste. More of those Stupid Design failures.

Oct 26, 2018
is the connection between iron and silicon in the birth of planets

Depends on the size of the initial gas cloud that collapsed. The bigger the cloud, the more energy released and thus heavier elements.

Oct 26, 2018
I thought nucleosynthesis, transmutation of elements, only occurs as part of a Star's fusion cycle?

I thought the produced elements could collect into clouds of different chemical mixtures and mineral combinations? From elements expelled by novae?

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