Speaker
Description
Since the 1960s, cosmic dust particles in the solar system have been investigated in situ using dust impact instruments on spacecraft near Earth and in planetary space. These particles, largely stemming from comets and from asteroid collisions, can occur in cometary streams or are more dispersed into the zodiacal dust cloud. Also interstellar dust moves through the solar system as the solar system moves through the local interstellar medium.
Cosmic dust particles are charged via photo ionisation and charge exchanges with the plasma environment. Sub-micrometer dust has charge-to-mass ratios large enough that their trajectories are influenced by electromagnetic forces related to the dynamic solar wind (in particular for the smallest particles down to nanometer sizes). Interstellar dust, beta-meteoroids (particles escaping the solar system due to solar radiation pressure) and nanodust trajectories therefore depend on the 22-year solar magnetic cycle. On the short term, observations with plasma wave antennas on the Wind and STEREO spacecraft showed a solar rotation frequency in the dust impact data. Corotating Interaction Regions (CIRs) in the solar wind were proposed as a source mechanism and a reduction in average count rate was observed during CIRs and Coronal Mass Ejections (CMEs), although its physical mechanism is not yet understood. Closer to the Sun, Parker Solar Probe WISPR images also showed a temporal reduction in local dust during CMEs.
Since the time-variability on the long-term (solar cycle) and on the short term (solar transient events) and the dust-plasma interactions are both time and location dependent, observing the dust distributions synchronously from different vantage pointes in space are needed. The Sun-Earth Lagrange points offer an ideal "view".
Some future missions with a dust instrument in the Sun-Earth Lagrange points are already planned: (1) the Korean L4 mission concept (launch date in 2035) will be observing the West-limb of the Sun from the Lagrange point L4 and at an inclination of 14 degrees. It accommodates a dust instrument package on the ram side of the spacecraft that will include a compositional analyser, velocity grid, and a nanodust detector. At Earth distance, the Lunar Gateway is planned to be equipped with a dust package (Active Sensors for Telemetry of ExtrateRrestrial Impactors at Gateway, ASTERIA) for which a Phase AB study will be conducted, starting in 2025. Also at L1, the NASA mission IMAP (launch in 2025) will carry a dust compositional analyser, although it lacks a velocity grid.
In this talk we review the synergies between dust and heliospheric science and elaborate on the science case for dust and plasma measurements at the Sun-Earth Lagrange points. We focus in particular on the L4 mission and the Lunar Gateway dust instrument science, how these are complementary to the plasma wave antenna dust impact data, and argue for simultaneous dust measurements from the Lagrange point L3.
