Some planetary systems just aren't into heavy metal

October 24, 2018, Yale University
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."

Explore further: A better way to learn if alien planets have the right stuff

Related Stories

What kinds of stars form rocky planets?

December 3, 2015

As astronomers continue to find more and more planets around stars beyond our own Sun, they are trying to discover patterns and features that indicate what types of planets are likely to form around different kinds of stars. ...

Recommended for you

Blue Origin to make 10th flight test of space tourist rocket

January 23, 2019

Blue Origin, the rocket company headed by Amazon founder Jeff Bezos, is poised to launch the 10th test flight of its unmanned New Shepard rocket on Wednesday as it competes with Virgin Galactic to become the first to carry ...

Milky Way's neighbors pick up the pace

January 22, 2019

After slowly forming stars for the first few billion years of their lives, the Magellanic Clouds, near neighbors of our own Milky Way galaxy, have upped their game and are now forming new stars at a fast clip. This new insight ...

A fleeting moment in time

January 22, 2019

The faint, ephemeral glow emanating from the planetary nebula ESO 577-24 persists for only a short time—around 10,000 years, a blink of an eye in astronomical terms. ESO's Very Large Telescope captured this shell of glowing ...

How hot are atoms in the shock wave of an exploding star?

January 21, 2019

A new method to measure the temperature of atoms during the explosive death of a star will help scientists understand the shock wave that occurs as a result of this supernova explosion. An international team of researchers, ...

New eclipsing cataclysmic variable discovered

January 21, 2019

Using the Mobile Astronomical System of Telescope-Robots (MASTER), an international team of astronomers has detected a new eclipsing cataclysmic variable. The newfound object, designated MASTER OT J061451.70–272535.5, is ...

5 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

Nik_2213
3 / 5 (1) 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...
torbjorn_b_g_larsson
3.7 / 5 (3) Oct 25, 2018
rrwillsj
not rated yet 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.
Scroofinator
not rated yet 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.
rrwillsj
not rated yet 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?

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.