The project main steps
PICARD is an investigation dedicated to the simultaneous measurement of the absolute total and spectral solar irradiance, the diameter and solar shape, and to the Sun's interior probing by the helioseismology method. These measurements obtained all along the mission will allow to study their variations as a function of the solar activity.
Its objectives are to improve our knowledge of:
- the functioning of our star through new observations,
- the influence of the solar activity on the climate of the Earth.
The PICARD mission was named after the French astronomer of the XVIIth century Jean Picard (1620-1682) who achieved the first accurate measurements of the solar diameter. These measurements are especially important as they were made during a period when the solar activity was minimum characterized by a sun nearly without sunspots between 1645 and 1710. This period was found by G. Spörer using sunspots observations gathered in Europe and this period is now named Maunder minimum. By comparison between the diameter during the Maunder minimum and the diameter when the sun was active, a variation has been found leading to the question still without answer "are diameter and activity linked". During this period in Europe, there was an unusually cold climate.
The PICARD payload is composed of the following instruments:
- SOVAP SOlar VAriability PICARD: composed of a differential absolute radiometer and a bolometric sensor to measure the total solar irradiance (previously called solar constant),
- PREMOS PREcision MOnitor Sensor: a set of 3 photometers to study the ozone formation and destruction, and to perform helioseismologic observations, and an absolute differential radiometer to measure the total solar irradiance.
- SODISM SOlar Diameter Imager and Surface Mapper: an imaging telescope accurately pointed and a CCD which allows to measure the solar diameter and shape with an accuracy of a few milliarc second, and to perfom helioseismologic observations to probe the solar interior.
Jean Picard (1620-1682), member of the French Sciences Academy, following "Le ciel" from A. Berget (1923).