The Picard mission has two scientific objectives which are the study of the origin of the solar variability and the study of the relations between the sun and the Earth's climate.
These studies will be based on measurements carried out from orbit and from ground, and the modeling of the Sun and the climate.
The various scientific objectives of the mission Picard are explained in the following paragraphs:
- Periodic variations of the climate
- Measurements of the solar diameter
- The shape of the Sun
- The modelling of the Sun's functioning
- The energy received by the Earth and its climate
- The Climate during the XVIIth century
- The long-term variability of the Sun
- The modelling of the climate
- The physics of the atmosphere
- The space weather
The Picard mission using three instruments will implement the following observations and programs:
- SOVAP measures the total solar radiance.
- PREMOS measures the solar spectral radiance in some spectral domains in infrared, visible and UV relevant of the ozone photochemistry which are essential measurements for the physics of the atmosphere and the climate of the Earth.
- SODISM measures the diameter, the shape of the sun, the activity, the differential rotation in several spectral domains, and carries out a major survey of the solar interior structure by use of the heliosismology method.
All these measurements will make possible to understand their relation by using solar and climate modelling as well as their variations. The combined use of absolute spectral measurements by PREMOS with the total solar radiance by SOVAP as well as the images by SODISM will make possible to check and refine our current theoretical understanding of the variations of solar radiance, by identifying the characteristics responsible for these variability. With regard to the Earth, they will be used as inputs to GCM simulations with aim to study the response of the Earth's atmosphere to the variations of spectral and total solar radiance.
|Solar physics||diameter, luminosity, activity||SODISM I|
|solar asphericity, shape of limb||SODISM I|
|differential rotation||SODISM I|
|solar diameter/stellar reference||SODISM I|
|heliosismology||SODISM I, PREMOS|
|solar variability||SOVAP, PREMOS, SODISM I|
|Climate||diameter/luminosity||SODISM I, SOVAP, PREMOS|
|Physics of the atmosphere||diameter and shape of limb ground/orbit|
|SODISM I, PREMOS, PREMOS ground instruments|
|Space Weather||Image at 215 nm, and 393 nm (Ca II)||SODISM I|
This table shows the scientific objectives, the measurements and the instruments which will carry them out. SODISM I and II are two identical instruments dedicated to the measurement of the solar diameter, the first being placed in orbit, and the second operated on the ground.
References for the whole Picard site.
To fullfil its scientific objectives, the Picard mission must satisfy the following constraints:
- The first constraint is linked to the orbit.
An orbit with a permanent viewing of the Sun is mandatory for the helioseismologic measurements (internal structure) and is an optimum for the instrument thermal stability (diameter measurements).
A Sun synchronous orbit (SSO) with an ascending node at 6 h and an altitude of about 725 km meets these requirements; the satellite pointing accuracy is of 0.01 arc degree around the Sun's axis. Thanks to the SODISM guided primary mirror, the solar image centring is achieved within a precision of 0.1 arc second.
- A second contrainst is linked to the launch date.
To be in the best conditions for the study of the relation between the solar luminosity and the diameter variations, it is preferable to operate during the rising phase of the solar cycle. All other Picard objectives being also linked to solar activity, observations are scheduled to start at the beginning of the next solar cycle (cycle 24).
The launch took place on June 15, 2010. The mission minimum lifetime is 2 years. The objective which consists in studying the relationship between the diameter and the solar luminosity suggests a longer mission.
Insertion of Picard mission in the future solar missions context
The schedule of the next solar missions is very favourable to the Picard mission. On board Sorce, the solar spectrum and total solar irradiance measurements should be still in operation as well as for the Soho mission. Picard will ensure the continuity of the measurements up to the turn over by NPOESS mission in 2011. Moreover, the International Space Station operates solar instruments since the beginning of 2008, gathering measurements of the total solar irradiance and of the solar spectrum (Thuillier, et al., 2005; Schmidtke et al., 2005). Other missions will enable the observation of the external layers of the solar atmosphere such as Solar B and Stereo which launches are scheduled in 2006. Their lifetime should ensure concomitant measurements with Picard. Solar Dynamics Observatory is scheduled for launch at about the same time as Picard. A strong synergy exists with Picard, because SDO does not have radiometric measurements, but will measure the distribution of the solar magnetic field and will achieve a deep sounding of the solar interior. These two missions will enable to relate the internal dynamic with the energy emerging from the photosphere.