Heliospheric Imagers
Research in modern heliophysics has increasingly focused on “multi-messenger” studies, where scientists bring together multiple types of measurements and multiple vantage points to better understand the complex three-dimensional (3D) nature of what we observe. This is particularly true for understanding the nature of coronal mass ejections (CMEs) and the dynamic solar wind, where we must connect remote-sensing observations of their birth in the solar corona to their in situ plasma measurements at spacecraft. One extremely useful tool for providing this connection is a wide-angle imager, or “heliospheric imager”, that measures visible light from the corona and inner heliosphere across a broad range of distances, often even to 1 astronomical unit or beyond.
Because we now include a coupled time-evolving heliosphere model in this latest prediction (see the Connectivity page), we can synthesize data for several of the heliospheric imagers currently operating in space. In the above collage of movies, we show predicted observations for the following instruments: Purple; the WISPR imager onboard Parker Solar Probe (currently at the aphelion of its highly elliptical orbit near Earth); Red: the SECCHI/HI-1 imager aboard the STEREO-A spacecraft (currently ahead of Earth by 60); Blue: the SolOHI imager aboard Solar Orbiter (just past the far side of the Sun, looking left); and Green: The composite imaging field of view of the PUNCH mission (currently orbiting Earth, see our dedicated PUNCH page).
Due to practical limitations, most heliospheric imagers on other spacecraft are designed to point slightly away from the Sun and off to one side (with the exception of PUNCH). This fact, combined with their wide fields of view and long integration paths at large elongation angles, can sometimes make it challenging to understand both the source of a structure and its position in 3D space along a given line of sight. This is another situation where the combination of 3D models and synthetic observations can be used to help scientists interpret what we see in imaging observations.
The central movie shows a top-down rendering of the heliosphere with the orbital positions of each imager marked in their respective colors. Next we plot shaded colored surfaces to represent how the field of view of a given heliospheric imager projects onto the equatorial plane. We use semi-transparency to emphasize the expected location of maximum emission in each field of view, which is weighted by the density falloff with distance from the Sun () and the Thomson scattering kernel. Where the emission would be expected to be the strongest, a.k.a. the Thomson Sphere, the color is deepest, and increased transparency indicates smaller and smaller expected contributions.
Although it is a complex visualization, this helps highlight the often overlapping views of our suite of wide-field heliospheric imagers, which constantly changes in time as the spacecraft move around. This visualzation also helps connect what we see to a spatial location. Try to look back and forth between the central movie and a given imager observation. See if you can tell which features are being tracked!
