The Solar Mass Ejection Imager and Its Heliospheric Imaging Legacy

Abstract

The Solar Mass Ejection Imager (SMEI) was the first of a new class of heliospheric and astronomical white-light imager. A heliospheric imager operates in a fashion similar to coronagraphs, in that it observes solar photospheric white light that has been Thomson scattered by free electrons in the solar wind plasma. coronagraphs, this imager differs in that it observes at much larger angles from the Sun. This in turn requires a much higher sensitivity and wider dynamic range for the measured intensity. SMEI was launched on the Coriolis spacecraft in January 2003 and was deactivated in September 2011, thus operating almost continuously for nearly nine years. Its primary objective was the observation of interplanetary transients, typically coronal mass ejections (CMEs), and tracking them continuously throughout the inner heliosphere. Towards this goal it was immediately effective, observing and tracking several CMEs in the first month of mission operations, with some 400 detections to follow. Along with this primary science objective, SMEI also contributed to many and varied scientific fields, including studies of corotating interaction regions (CIRs), the high-altitude aurora, zodiacal light, Gegenschein, comet tail disconnections and motions, and variable stars. It was also able to detect and track Earth-orbiting satellites and space debris. Along with its scientific advancements, SMEI also demonstrated a significantly improved accuracy of space weather prediction, thereby establishing the feasibility and usefulness of operational heliospheric imagers. In this paper we review the scientific and operational achievements of SMEI, discuss lessons learned, and present our view of potential next steps in future heliospheric imaging.

Measurements and an empirical model of the Zodiacal brightness as observed by the Solar Mass Ejection Imager (SMEI)

“…Conceived as an all-sky imager ( Jackson et al, 1989 ), SMEI viewed the outward flow of CMEs and other heliospheric structures by recording Thomson-scattered sunlight ( Jackson et al, 2004;Tappin et al, 2004;Webb et al, 2006 ). SMEI began providing data on 5 February 2003, and was deactivated on 28 September 2011 after 8.5 years of operation ( Howard et al, 2013 ).…”

The application of heliospheric imaging to space weather operations: Lessons learned from published studies

“…The Helios zodiacal light photometer concept was extended into the realms of what we would now consider as true visible‐light heliospheric imaging by the Solar Mass Ejection Imager (SMEI) instrument [ Eyles et al ., ; T. A. Howard et al ., ], launched aboard the low‐Earth orbiting Coriolis spacecraft in 2003. SMEI consisted of three narrow‐format cameras, each with a 60° × 3° instantaneous field of view, mounted on the spacecraft such that—over the whole 102 min high‐inclination orbit—the instrument provided full‐sky imaging in visible light (barring an exclusion zone extending to some 18° elongation from Sun center).…”

“…As well as CMEs, the SMEI images revealed other solar wind phenomena, such as SIRs/CIRs, as well as a host of other features, not all of which were expected or conducive to the instrument's objective of tracking CMEs. The latter included high‐altitude aurora which, prior to SMEI, were rarely thought to be present above the 842 km orbit of Coriolis but which, it transpired, were a ubiquitous source of stray‐light contamination of the SMEI images particularly during geomagnetically active conditions [e.g., T. A. Howard et al ., ]; note that the severity of this contamination was, to no small degree, due to the peculiarities of the SMEI instrument design and orbital configuration. Potential contamination of the images by high‐altitude aurora is not the only reason why Earth orbit is less well suited for visible‐light imaging of the heliosphere—or indeed the corona—particularly, it is stressed, in an operational rather than scientific context (for more detail on the intricacies of this issue the reader is urged to refer to DeForest and Howard []).…”

“…The Helios zodiacal light photometer concept was extended into the realms of what we would now consider as true visible-light heliospheric imaging by the Solar Mass Ejection Imager (SMEI) instrument [Eyles et al, 2003;T. A. Howard et al, 2013], launched aboard the low-Earth orbiting Coriolis spacecraft in 2003.…”

Regarding the detectability and measurement of coronal mass ejections

“…The nature of this background is very well explored in the literature and I will not revisit it here. The reader can refer to Thompson et al (2010) and Frazin et al (2012) for recent papers involving background subtraction for white light coronagraphs, and DeForest et al (2011), Tappin et al (2012), and Howard et al (2013b) for those involving heliospheric imagers.…”