Solar Terrestrial Probes: choose missions to test missing physics

NASA’s Solar Terrestrial Probes program investigates fundamental physical processes linking the Sun with Earth and the wider heliosphere. Its questions concern moving plasma, changing magnetic and electric fields, and the transfer of energy between regions. Successive missions address gaps in understanding rather than simply repeat one standardized satellite design.

Examples show the breadth of the program: TIMED investigated the upper atmosphere, Hinode studied solar processes through an international partnership, STEREO observed solar eruptions from separated viewpoints, and the Magnetospheric Multiscale mission studied magnetic reconnection. These are different experiments with complementary purposes. NASA’s STP contribution does not erase another country’s leadership or responsibility in a shared mission.

STEREO launched two spacecraft in 2006 to provide different perspectives on the Sun and outward-moving material. A bright feature in one image is projected along a line of sight; it does not directly reveal the feature’s full three-dimensional shape. Another viewpoint can help constrain its geometry, provided the observations refer to compatible times and structures.

In a fictional reconstruction, an eruption appears wide from one spacecraft and narrow from another. That may be a projection effect rather than a physical contradiction. Compare the spacecraft locations, observing bands and exposure times before choosing a model. Multiple viewpoints add evidence, but they do not automatically remove ambiguities in identifying the same feature.

STP and Living With a Star both contribute to heliophysics, but their program definitions and selected missions should be traced through documented relationships. Neither name is a universal label for every spacecraft observing the Sun. The value of a mission comes from the measurement it enables and how that measurement tests a specific scientific question.

The STEREO-B preparation photograph shows one of the two original spacecraft during ground handling. It does not imply that both members operated continuously throughout every later year. When using archived observations, identify the actual spacecraft and available data for that period. A strong program history combines the original experiment design with the real observing coverage that followed.