Detecting low-energy neutrinos from astronomical objects and the Earth is an essential means of accessing information about the interiors of stars and planets.
Detecting neutrinos in the Si-burning phase of a galactic supernova will allow us to predict the explosion. Disseminating the direction of the arrival of neutrinos from galactic supernova explosions to observatories will be crucial for multi-messenger astronomy. Detection of neutrinos from past supernova explosions (Diffuse Supernova Neutrino Background) will provide a picture of the average supernova explosion and the history of black holes and neutron star formations.
Observations of solar neutrinos remain essential for understanding the Sun itself, including determining the metallicity of the Standard Solar Model. It is also crucial to determine the parameters of θ12 and Δm12 through solar neutrino oscillations, and the "up-turn" of the solar neutrino survival probability can be used to verify the MSW effect and the Non-standard Neutrino Interaction.
Decays of radioactive elements in the Earth's interior generate geo-neutrinos and heat. By measuring the geo-neutrinos on the Earth's surface, the amount of heat radiated from the Earth's interior can be directly determined, and it is expected that the mantle convection structure and chemical composition of the Earth's interior can be elucidated.
The status and prospects of the experiments observing those neutrinos are reviewed.