Solar Terrestrial Relations Observatory (STEREO)

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NASA’s Solar Terrestrial Relations Observatory (STEREO) launched on October 25, 2006.  Its mission is to act as our eyes on the Sun through the use of two nearly-identical solar observatories.  Specifically, STEREO monitors what are known as Coronal Mass Ejections (CME) – energetic eruptions from the Sun that can cause massive magnetic disruptions on Earth, have detrimental effects on satellite operations and communications, as well as affect the global climate.

Designed and built at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, the twin STEREO observatories operate through the use of two instruments and two instrument suites aboard each satellite.  This combination provides a total of 16 instruments per observatory, most of which are housed in the SECCHI (Sun-Earth Connection Coronal and Heliospheric Investigation) and IMPACT (In situ Measurements of Particles and CME Transients) instrument suites. 

The SECCHI, carrying the name of the 19th century Italian astronomer Angelo Secchi, is a suite of 5 telescopes (SCIP, and HI) that observe the solar corona and inner heliosphere from the surface of the Sun to the Earth.  SCIP (the Sun-Centered Imaging Package) consists of two white light coronagraphs and an Extreme Ultraviolet Imager with a Guide Telescope.  A Heliospheric Imager performs wide-angle imaging for the detection of CME events, particularly the ones directed towards the Earth.

Consisting of 7 instruments, the IMPACT suite samples the 3-D distribution of electrons in the solar wind plasma, the characteristics of the solar energetic particle ions and electrons, and the local magnetic field

Among other instruments is the STEREO/WAVES, an interplanetary radio burst tracker that traces the creation and propagation of radio waves from the Sun to the Earth.  It acts as both a remote-sensing and an in-situ instrument.

The satellites’ unique vision of the Sun works by having one satellite lead Earth’s solar orbit and having one trail it.  To achieve this, the twin observatories first launched from Earth on a single Delta II with one observatory (the lead) sitting atop the other (the trail).  Once in space, the observatories used a series of lunar swingbys, taking advantage of the Moon’s gravity in order to slingshot them into their new orbital paths. 

Just as the slight offset between our eyes provides us with depth perception of our environment, the distance between the two observatories (many millions of miles) provides images of the Sun in stereo.  When combined with data from observatories on the ground or in low-Earth orbit, STEREO's data allows scientists to track the buildup and lift-off of magnetic energy from the sun and the trajectory of Earth-bound CMEs in 3-D.

For more information please visit the STEREO site, the SECCHI site, the HI site, and the IMPACT site.

Nicholas Hunt-Walker (Summer intern 2007)