We like to think of our Sun as an ordinary yellow dwarf star, one of billions of solar-type stars in our Milky Way galaxy. But only in the last few decades have astronomers been able to do comparative galactic science of stars like ours. Asteroseismology, the study of seismic interstellar oscillations, is an essential key to understanding our Sun and the billions of other solar systems in the galaxy.
Later this decade, the European Space Agency's PLATO mission will observe hundreds of thousands of stars like ours. Plato is responsible for discovering Earth's analog, planetary transits and stellar oscillations, but measurements of its stellar brightnesses over time will help theorists better understand stars that host planets like ours.
During a recent visit to Italy's Catania Astrophysical Observatory on the island of Sicily, I spoke with two researchers who are eagerly awaiting data from PLATO. I asked them why understanding the stellar physics of solar-type stars is important.
Stars are the basic building blocks of our galaxy, Enrico Corsaro, staff scientist at the Catania Astrophysical Observatory and member of the PLATO science team, told me at the lab. He says that if we want to better understand our galaxy, we must first understand the stars that look like the Sun. And if we want to better understand whether or not our solar system is unique, we first need to understand the entire planetary system, says Corsaro.
PLATO will provide a new understanding of the galaxy
Among other things, PLATO will significantly improve our understanding of the internal dynamical processes in solar-type stars, Sylvain Breton, a postdoctoral researcher at the Catania Astrophysical Observatory and member of the PLATO science team, told me at the lab. And it will characterize the masses, radii and ages of solar-type stars, especially those hosting planets, with great precision, he says.
ESA says Plato will carry the largest integrated digital camera ever flown in space. And it will receive light from 26 smaller telescopes, all mounted on the same satellite platform, ESA notes.
During its nominal four-year mission, which could be extended to eight years, PLATO will have a very wide field of view covering a total area of the sky of about 2,250 degrees. It is 2000 times larger than the full moon.
How important are observations of the Sun in explaining astronomy?
They are important; „The Sun has been our primary laboratory for testing and understanding the variability of stellar luminosity,” Breton says. By refining the models, he says, it could be applied to stars like the Sun. And if the ages of stars can be measured with great precision, Breton says, the ages of planets can be measured in a similar way.
Our main goals are to improve our understanding of how stars work, how stars form in the interior and how they evolve over time, says Corsaro.
„I strongly believe that to classify exoplanets, we really need to know the stars,” Corsaro says.
Stars before planets
To understand a planet's story, we first need to understand the star better, says Breton. He says you need to monitor the star's brightness variation over a long period of time.
Oscillations and fluctuations in the level of light from the star are subject to variations over time, says Corsaro. This tells us about the composition of the star's interior, he says.
The main characteristic of the star we're about to see is the convective envelope, which makes up roughly 10 to 40 percent of the star's total radius, Breton says. At the star's core, nuclear reactions that fuse hydrogen into helium create energy, and on long time scales, what is produced in the core is transported to its surface, Breton says.
By analyzing how a star's sound waves travel across its surface, researchers can learn more about its interior.
Is there anything special about our Sun?
There are many stars with similar properties to our Sun.
But because of our star's proximity, Corsaro says, we know the Sun in a way that we can't know any other star. In another hundred years, he says, that could change.
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