The Sun belongs to the category of relatively massive stars and resembles billions of others in our Milky Way galaxy. With a life expectancy of about 10 billion years, our star is already halfway through its lifetime. In 5 billion years’ time it will become a red giant and expand and engulf the inner planets.
The Sun makes up 99.8% of the solar system’s mass and spans 1.4 million km (roughly 110 times the diameter of Earth). It rotates on itself in 25 Earth days and revolves around the Milky Way in 200 million years.
The Sun’s core makes up one-fifth of its volume. This is where nuclear fusion of hydrogen atoms occurs, releasing energy in the form of photons. This energy takes 100,000 years to reach the Sun’s surface as light.
The radiative zone extends outwards from the core to a distance that is 70% of the Sun’s radius. Temperatures in this zone are from 1.5 to 15 million °C as the energy from the core radiates towards the surface.
This energy then reaches the convective zone, where it is transported by rising and descending hot gases in huge bubbles called convection cells. Temperatures here are between 5,500 and 1.5 million °C.
The energy finally arrives at the visible surface of the Sun, called the photosphere, where it escapes and reaches us as light and heat.
The Sun’s atmosphere consists of two main layers: the chromosphere, where jets (spicules) eject matter up to 10,000 km above the surface, and the corona, composed of ionized gas (plasma), which is a very active and dynamic region.
Sun key data
- Diameter: 1,393,684 km
- Mass (Earth = 1): 333,000, i.e. 1,989.1027 t
- Radiated energy: 385 million billion gigawatts
- Surface temperature: 5,500 °C
- Core temperature: 15 million °C
- Distance from Earth: 150 million km
- Age: about 4.6 billion years
- Life expectancy: about 10 billion years
CNES’s main contribution to solar research comes from technical support and funding for French science teams working on European and international missions.
CNES notably funded instruments for the Ulysses mission to study turbulence in the solar wind, especially outside the ecliptic plane (the plane of Earth’s orbit around the Sun); the Cluster mission to study interactions between the solar wind and Earth’s magnetosphere (the region around the planet where the magnetic field is strong enough to block the solar wind); the Double Star mission (follow-on to Cluster); the STEREO mission to study solar flares and how they impact Earth’s environment; and the SOHO mission to monitor coronal mass ejections (CMEs), the clouds of plasma generated in the Sun’s corona.
CNES also initiated the Picard mission and conducted the satellite’s orbital operations from 2010 to 2014. Picard acquired more than 1 million pictures of the Sun and many other measurements besides that scientists are now sifting through to better understand our star’s processes, variations and activity.
CNES will be contributing to the Solar Orbiter mission scheduled to launch in 2018. This satellite will take pictures of the Sun at unprecedented resolution and acquire measurements very close to our star. CNES is also involved in NASA’s Solar Probe Plus project to study the solar corona close up, also scheduled for launch in 2018.