An artist's depiction of SOLO on station a mere 26 million miles from the sun. Image courtesy ESA

The European Space Agency is developing an observatory that would settle questions about the sun from a unique location: inside the orbit of Mercury. The Solar Observatory, or SOLO, would perform heretofore unprecedented measurements of the heliosphere and solar wind as well as magnetic storms and coronal mass ejections, not easily available from our neck of the solar system due to the sun’s 25 day sidereal rotation and small obliquity with respect to the plane of earth’s orbit:

The spacecraft will provide remarkable views of the Sun’s polar regions and farside. Its elliptical orbit will be tuned such that it can follow the star’s rotation, enabling it to observe one specific area for much longer than is currently possible.

That kind of proximity doesn’t come without consequences to design and cost. SOLO will dwell well inside the Goldilocks’ Zone where water is a liquid, making one orbit about every 60 days. In this vicinity exposed surfaces could be roasted to a toasty 800° depending on the material . SOLO survives and thrives only by staying oriented behind a robust heat shield with slots through which cameras and other detectors peer out at a sun many times larger than seen from earth. That’s why the fully equipped spacecraft could run a whopping one-billion euros and may not be ready for launch until 2019.