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ROMFORSK-Program for romforskning

Cosmic dust in the solar-terrestrial physics: exploring the inner heliosphere

Alternative title: Kosmisk støv i solens jordisk fysikk: utforske den indre heliosfæren

Awarded: NOK 4.1 mill.

Project Manager:

Project Number:

262941

Application Type:

Project Period:

2017 - 2023

Funding received from:

Cosmic dust particles are one of the major constituents of the interplanetary medium of our heliosphere: the region around the Sun that is filled with the solar wind and shielded from the majority of particles outside in the interstellar medium. The ESA mission Solar Orbiter explores the inner heliosphere from Earth orbit to less than 0.3 AU where 1 AU is the distance between Earth and Sun. The spacecraft measures electric fields with antennas and these antennas also detect dust impacts. At the same time the NASA mission Parker Solar Probe makes similar observations from 0.3 AU and closer at just a few solar radii distance from the Sun. Both space missions started operation in 2018 and will continue over several years. They cross regions that spacecraft never encountered before. The interplanetary dust cloud near the Sun is largely unexplored, it is an open question to what extent interstellar dust particles play a role that close to the Sun and it is unclear how much dust is ejected away from the Sun and leaves the solar system. The dust that leaves the solar system crosses Earth orbit, it can hit the Earth and it contributes to the cosmic dust flux into the atmosphere of Earth. The primary objective of the project is to study the fluxes and interactions of cosmic dust in the inner heliosphere, that is the region between Sun and Earth orbit. The secondary objective is to derive from the data the dust flux onto Earth where impacting dust influences processes in the upper atmosphere above 80 km height and possibly also contributes to the highest clouds observed, the noctilucent clouds. During the project, we carried out model calculations that improved understanding the dynamics of very small dust particles. The particles with sizes smaller than a ten thousands part of a millimeter, called nanodust are very much affected by their electric surface charges and by the external electric fields. We investigate the trajectories of these nanodust particles close to the Sun and close to other sun-like stars that are also surrounded by planets (i.e. exoplanets). We refined models of the dust destruction by the impacting solar wind particles and how this reduces the size of the dust particles. Together with other groups we compared the dust impact signals observed with antennas from different spacecraft and with different parameters of surrounding plasma which allows us to retrieve more information on the impacting dust particles from the antenna signals. The description of the impact charge production that generates the antenna signals is based on laboratory measurements within a limited range of parameters. We developed a semi-empirical model to describe the dust impact process in the limit of small impact speed beyond the velocity range covered so far. By comparing the first results on impact rates observed with Parker Solar with dynamical and collision models we prepared and estimate of the nano-meter dust flux onto Earth. We also participated in anlysing the first dust flux measurements with Solar Orbiter. We investigated the trajectories of dust particles that enter the solar system from interstellar space and the impact velocities at Solar Orbiter of such interstellar dust particles. We found that Solar Orbiter can observe a large fraction of the interstellar dust that streams into the heliosphere. We developed machine learning tools to find the dust impact signals in the data. These tools are made public; using the machine learning tools enhances the number of identified dust impacts in comparison to previous methods. It also speeds up the data analysis and this is important because it is time-consuming to search for these dust impact signals. We finally developed an analysis method applying Bayesion statistics. Bayesion statistics can be used also for data with small numbers of signals and this enables us to investigate smaller data samples. This project includes international collaboration with Paris Observatory in France, the Space Research Institute of the Polish Academy of Sciences, Charles University in Prague, Czech Republic, The Space Science Laboratory at University of California, Berkeley in the USA, Swedish Institute of Space Physics, and Umeå University in Sweden and colleagues in Europe, Japan and the United States. The project results are important for understanding the evolution of dust in the exoplanet systems around other stars, for the investigation of interstellar dust and for investigation of meteoric material into Earth atmosphere and in the atmospheres of Earth-like exoplanets. The methods that we developed are made open and can be used by researchers who work on other space missions. Master students and student internships were involved in all parts of the project and many of them continue working in in space research and space industry.

The project provides an improved understanding of nanodust trajectories close to Sun and main-sequence stars which supports the investigation of planetary debris discs around stars that host exoplanets. The refined model of the dust destruction and dust erosion by solar wind sputtering that we developed supports the interpretation of the dust composition measurements that are planned for the near future and supports estimating dust lifetimes like in supernovae and in the interstellar medium. We published a first estimate of the nano-meter dust flux onto Earth based on Parker Probe data. We participated in the first dust flux measurements derived from Solar Orbiter observations. We made a description of interstellar dust trajectories and their impact velocities at Solar Orbiter to be used for further analysis of ongoing measurements. Aside from obtaining basic knowledge on the dust in the inner heliosphere, this project makes important contribution to further develop the dust detection with antenna measurements. This is important solar system exploration because antenna experiments operate on many spacecraft: We developed a model to describe the dust impact process in the limit of small impact speed beyond the velocity range covered by previous models. The comparative study of the dust impact signals observed with antennas from different spacecraft and with different parameters of surrounding plasma that we achieved together with our collaborators helps to further strengthen the use of antenna measurements for the observations of dust fluxes. We developed machine learning tools to analyse dust impact signals in antenna data facilitates easier analysis of large data sets. And development data analysis method applying Bayesion statistics helps reliable analysis of smaller samples. Based on the project results we are in a good position to analyse the dust components in the outer solar system based on observations of the NASA mission New Horizon. We continue the investigation of Solar Orbiter and Parker Solar Probe observations and can compare them to other space observations like with STEREO, WIND, BepiColombo, IMAP and Destiny+. This project is an excellent preparation for future research to investigate the interstellar dust in the heliosphere and to investigate the processes of cosmic dust injection into the atmosphere of Earth.

Cosmic dust particles are one of the major constituents of the interplanetary medium of our heliosphere: the region around the Sun that is filled with the solar wind and shielded from the majority of interstellar medium plasma. In the vicinity of the Sun dust destruction generates atoms and ions and dust particles that are ejected from the vicinity of the Sun contribute directly to the flux of cosmic dust material into Earth atmosphere. The up-coming mission Solar Orbiter will explore for more than 7 years the inner heliosphere from Earth orbit to less than 0.3 AU including onboard a radio and plasma waves experiment (RPW) that is able to detect dust impacts. We propose to carry out model calculations and supporting simulations to derive from RPW measurements the fluxes and mass distribution of dust particles. We will also use comparison to observations with similar instruments and first measurements from FIELDS on NASA's Solar Probe Plus. The outcome of the project will be studies of dust fluxes in the inner heliosphere and a set of tools for deriving dust information from the RPW observations during the duration of the mission We will also derive from first observations estimates of the dust flux onto Earth and a plan how to connect RPW observations to studies of dust flux onto Earth with meteor observations of the future EISCAT_3D radar. The project will be carried out at Tromsö University (UiT) with a long experience in cosmic dust and dusty plasma research and we collaborate with international experts in the field. The project manager is about to move to UiT, is member of the RPW and FIELDS science teams, has previously worked with the Ulysses and Galileo dust experiments, and works together with the RPW PI institution on analysing dust impacts in STEREO plasma wave observations.

Publications from Cristin

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Funding scheme:

ROMFORSK-Program for romforskning