The Heliospheric Imager
Unique view of the Milky Way, as seen by HI
The Heliospheric Imager (HI) is a wide-angle visible-light imaging system for the detection of coronal mass ejection (CME) events in interplanetary space and, in particular, of events directed towards the Earth.
The protective covers, or doors, of the HI instruments were opened at the end of 2006 and early in 2007 on the two spacecraft revealing an unprecedented view of the space between the Sun and the Earth. Within the first months of operation, HI had observed the dark-side of the Moon, several CMEs, asteroids and, in the very first images received from HI-B, a spectacular view of comet McNaught.
Since then, in addition to observing and cataloging many more CME, the HI instruments have made a number of spectacular observations and discoveries, including:
- The impact of a CME on Venus and the interpretation of its effects by comparing HI images with data received from spacecraft in orbit around the planet
- The collision of a CME with a comet, resulting in the stripping off (or "disconnection") of the comet's tail
- The discovery of the element iron, in atomic form, in the tail of a comet
- The imaging for the first time of the very faint optical emission associated with so-called Corotating Interaction Regions (CIRs) in interplanetary space, where fast-flowing Solar wind catches up with slower wind regions
The HI instrument has been developed by a UK-led consortium which includes the Centre Spatial de Liege, Belgium, and the Naval Research Laboratory, USA.
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