Question

Astronomers looking for some of the earliest stars in the universe were surprised to find a planetary system called HIP 11952, which existed \(12.8\) billion years ago. This was very early in the universe's history, when stars still consisted largely of hydrogen and helium. Do you think there were terrestrial planets in this system? Why or why not?

Short answer

No, HIP 11952 likely did not have terrestrial planets due to the lack of heavier elements.

Step-by-step solution

- Understand the Components of Early Stars

Early stars in the universe mainly consisted of hydrogen and helium because these were the primary elements formed after the Big Bang. Heavier elements (like those needed to form terrestrial planets) were not yet significantly present.

- Consider the Formation of Terrestrial Planets

Terrestrial planets are primarily composed of heavier elements such as iron, silicon, and oxygen. These heavier elements were formed in later generations of stars through processes like supernovae which fused lighter elements into heavier ones.

- Analyze the Timeframe

Considering the HIP 11952 system existed 12.8 billion years ago, this was very early in the universe’s history, and it is unlikely that enough heavier elements were available to form terrestrial planets at that time.

- Draw a Conclusion

Given the lack of heavier elements needed to form terrestrial planets in the early universe, it is unlikely that HIP 11952 had terrestrial planets.

Key concepts

Formation of Elements

Right after the Big Bang, the universe was extremely hot and dense. It quickly expanded and cooled, leading to the formation of the first basic elements. Initially, the universe was mostly composed of hydrogen and helium. These are the lightest and simplest elements in the periodic table.
There was a process called Big Bang nucleosynthesis, which happened within the first few minutes of the universe’s existence. During this time, protons and neutrons combined to form nuclei of these simple elements.
However, the universe didn’t have more complex elements like carbon, oxygen, or iron at this point. These heavier elements are essential for the formation of terrestrial planets. They were created much later in the interiors of stars through nuclear fusion.

Terrestrial Planet Formation

Terrestrial planets are rocky and have solid surfaces. Examples in our solar system include Earth, Mars, Venus, and Mercury.
For a terrestrial planet to form, there needs to be a sufficient amount of heavy elements. These heavy elements, such as silicon, oxygen, iron, and magnesium, are crucial parts of the planet’s structure.
These materials come together, accrete, and form planetesimals. Over millions of years, these planetesimals collide and merge to eventually form terrestrial planets.
Because the early universe had very few heavy elements, it would have been exceedingly difficult for terrestrial planets to form at that time. Only later did stars create and spread the necessary heavy elements into space.

Supernova Nucleosynthesis

Supernova nucleosynthesis is the process where exploding stars create heavy elements. When a star runs out of fuel, it can end its life in a supernova explosion.
During this explosion, the intense heat and pressure allow nuclear reactions to create elements heavier than iron. This includes elements like gold, uranium, and lead.
These newly formed elements are blasted into space by the force of the explosion. Once in space, they can eventually become part of new stars and planets.
Since supernovae create essential heavy elements for terrestrial planets, the first generation of stars couldn’t create these planets. They had to wait for subsequent generations of stars to pour these materials into the universe.

Early Stars Composition

Early stars, also known as Population III stars, were predominantly made of hydrogen and helium. These stars were different from stars we see today.
They lacked heavier elements because those elements hadn’t been formed yet. Being composed of only the lightest elements, these stars were massive and hot but had short lifespans.
Because they were composed of only the basic elements, they didn’t have the raw materials needed to create planets like Earth.
The formation of heavy elements in the cores of these stars via fusion eventually led to supernova explosions. These explosions spread heavy elements throughout the galaxy, enabling the formation of second-generation stars and planetary systems rich in heavy elements.