Background
Solar flares are the most powerful explosions in the solar system, each one being equivalent to more than the entire world’s nuclear arsenal going off at once. They occur when some of the Sun’s magnetic fields connect with each other, releasing magnetic energy as radiation and kinetic energy. As this happens, a large proportion of the energy goes into accelerating electrons and ions. These begin to stream along the path of the magnetic field towards the chromosphere, and then deflect and decelerate. This deceleration emits hard X-rays (HXRs), the highest energy X-rays, around the “footprints” of a flare loop – where the loop meets the chromosphere. Whether the electrons travel as a collimated beam, (with parallel rays, spreading minimally) or in a quasi-isotropic cloud (spreading close to uniformly in all orientations) is currently unknown. PADRE aims to figure this out, to better understand the underlying mechanisms of the energy conversion and particle acceleration processes that occur in the solar corona.
What is PADRE?
The Solar Polarization and Directivity X-Ray Experiment (PADRE) is a NASA CubeSat mission built to measure the degree of anisotropy of flare electron distributions – how spread out the flare electrons travel – via two independent and complementary instruments on board.
MeDDEA measures HXR directivity via stereoscopic spectroscopy. In other words, it measures how different the X-ray intensity is across different viewing angles. By observing a single flare simultaneously from two widely separated angles and comparing received spectrums of photons/second/area, scientists can pinpoint the HXR directivity of a flare. MeDDEA compares measurements with The Spectrometer/Telescope for Imaging X-rays (STIX), orbiting the Sun, with flare-by-flare calibration based on the thermal component of the flare.
SHARP, the other instrument, measures the linear polarization – the plane of oscillation- of flare HXR emission by Compton scattering. (For reference, a sine wave’s plane of oscillation is the Y-axis). PADRE spins at a rate of one rotation per minute, on a spacecraft-to-Sun axis, and incoming flare HXRs collide with a scattering component, which sends the photons generally perpendicular into 8 detectors. By watching where the scattered photons go as the ship rotates, and because scattering peaks perpendicular to the incoming polarization plane, the incoming linear polarization of the HXRs can be determined. Seeing an equal distribution of photon counts would support the claim for quasi-isotropic cloud, vs seeing a clear spike on some detectors, which would support the claim for collimated beam. (For more info/images, see the Instruments page)
Global Impact
Gaining a better understanding of how the solar flares convert energy and accelerate particles allows our space weather prediction models to become more accurate. This, in turn, gives us a better chance at saving the Earth’s satellite fleet and on-ground electronics in the case of a major solar event.
Our Teams
PADRE was built, and is supported by 7 teams, across the world. NASA provides our funding, UCB-SSL (UC Berkeley Space Sciences Lab) heads project management, built SHARP, does mission operations for the instruments, and integrated/space qualified the whole system. GSFC (Goddard Space Flight Center) designed and built, and actively manage MeDDEA, and will analyze its data to do science. SwRI (Southwest Research Institute) provided the high voltage power supplies for both instruments, and will analyze the data coming down from PADRE for science. EnduroSat provided the spacecraft with everything save MeDDEA and SHARP, and does mission operations of the spacecraft. CEA-Saclay provided GSFC the four detectors for MeDDEA, using flight-spares from STIX, and Precision Optomechanics did the mechanical engineering for MeDDEA.