Picard: Sun and climate

A satellite, belonging to the CNES and launched on 15 June 2010, is to study our star in great detail to get a better understanding of the influence its activity has on the Earth’s climate.

 

The Picard satellite (illustration). Weighing in at 150 kg, it is orbiting at 725 km above our planet. Credit: CNES - D. Ducros

This small satellite has some huge objectives! Picard is part of the Myriade series developed by the CNES, the French Space Agency, with the manufacturers in order to have a compact platform suited to several types of missions, all within a controlled budget. In this instance, the satellite successfully placed in orbit on 15 June is carrying 3 instruments, designed with Swiss and Belgian institutions, with which to “examine” the celestial body of the day.

Sun and climate: how are they linked?
The Earth’s climate machine which, all things considered, is relatively stable on a human life scale, does however experience hot and cold spells! Thus we know, to cite but recent changes, that Europe and North America were covered in ice 20,000 years ago whereas from the 10th to the 14th century, documents from the era show a generalised warming before the Small Ice Age from the 16th to the 19th century, marked by particularly harsh winters and a progression of European glaciers. The Small Ice Age disconcertingly corresponds to the “Maunder Minimum”, a period where astronomers noticed that the Sun was lacking in the spots which are the sign of peaks of activity on our star.

Sun spots (photograph taken by the SOHO satellite): colder areas on the surface of our star (photosphere) and seats of intense magnetic activity, their number is directly linked to the Sun’s activity. The bigger ones can be more than 80,000 km across (6 times the diameter of the Earth!). Credit: NASA/ESA

Although the Sun goes through a minimum every 11 years, (we should now be at the end of such a drop), this was the first time that continuous and meticulously noted observations bore witness to a number of sun spots 1,000 times less than usual! Does this then mean that there is a link between the drop in the Sun’s activity and the climate upheaval of the Small Ice Age? Picard will perhaps provide us with the answer.

Essential for the future
French astronomer Jean Picard (1620-1682) was to accurately measure the diameter of the Sun numerous times at the beginning of this “cold spell” in Europe. Obviously, the satellite pays tribute to him, as, in addition to other measurements, the CNES’s spacecraft is tasked with determining this dimension of our star with the greatest possible accuracy. This parameter is very important since certain scientists believe that the size of the Sun and its activity are linked. Therefore, by comparing the results obtained from space in future months with those of the 17th century astronomer, it is hoped that we will get a better understanding of any connection between the Sun and the Earth’s climate. A subject that is moreover far from winning unanimous support: some think that the total energy emitted by the Sun during its “ups” and “downs” varies too little to have been one of the actual causes of climates changes in the past.

The Russian-Ukrainian Dnepr launch vehicle blasts off on 15 June. At its summit: Picard and two other satellites from the Swedish mission Prisma in which the CNES is taking part. Credit: Kosmotras

However, it is also known that solar radiation in the ultraviolet light wave range plays a major role in the chemistry of the upper layers of our atmosphere, notably with regard to the ozone, on which the temperature and actual dynamics of the stratosphere are dependent. Clearly, Picard’s results will not only concern a mystery from the past, the Maunder Minimum, but will also give us solid tools for the future by improving our current climate models.

Published on 18 June 2010