Spitting Image

11 August 2021

Illustration of what the Sun may have been like 4 billion years ago. NASA’s Goddard Space Flight Center/Conceptual Image Lab
Illustration of what the Sun may have been like 4 billion years ago.

Our Sun is about 4.6 billion years old. We know that from models of Sun-like stars, as well as through our observations of other stars of similar mass. We know that the Sun has grown hotter over time, and we know that in about 5 billion years it will become a red giant star before ending its life as a white dwarf. But there are many things about the Sun’s history that we don’t understand. How active was it in its youth? What properties of the young Sun allowed life to form on Earth billions of years ago?

If we had a time machine, we could travel to the distant past and observe the Sun’s youth directly. But since that’s not possible, we can do the next best thing. Look for young stars that are very similar in size and composition to our Sun. The spitting image of the Sun, if you will. This has been done before with older stars. HIP 102152, for example, is a solar doppelganger that’s about 4 billion years older than our Sun. Now a team has studied a young solar doppelganger known as κ1 Ceti.1

An artist concept of a coronal mass ejection hitting young Earth's weak magnetosphere. NASA/GSFC/CIL
An artist concept of a coronal mass ejection hitting young Earth’s weak magnetosphere.

The star has been studied since the 1940s. It’s very similar to the Sun in mass and metallicity, but it’s only about 600 million years old. For this study, the team integrated observational data of κ1 Ceti with evolutionary solar models. From this, they could make predictions about how the Sun behaved at a similar age. Based on their model, the Sun likely rotated about three times faster than it does now, had a much stronger magnetic field, and emitted more solar flares and high-energy particles.

This interesting thing about the Sun at around 600 million years old is that life on Earth first appeared around this time. Understanding the Sun at this age could give us clues about how terrestrial life formed. This study holds some tantalizing possibilities. Because the Earth’s magnetic field was weaker back then, solar flares and coronal mass ejections from the young Sun would have exposed Earth to more high-energy particles than they do today. These particles could have helped complex molecules to form on Earth. If that’s the case, an active young Sun could have played a key role in forming the building blocks of life.

This is an initial study, so the connection to life is tenuous. But the team hopes to gather data from other Sun-like stars at various ages. With more observations, they will be able to fine-tune their model and create a more accurate history of the Sun.

  1. Vladimir S. Airapetian, et al. “One Year in the Life of Young Suns: Data-constrained Corona-wind Model of κ1 Ceti.” The Astrophysical Journal 916.2 (2021): 96. ↩︎