Meteors
We endeavor to create the first comprehensive characterization of meteoroids and meteoroid plasmas (i.e. meteors) to understand their effects on the lower ionosphere and their threat to orbiting spacecraft. Meteoroids are naturally occurring objects in space that travel between 11 and 72.8 km/s and originate primarily from comets and asteroids. On average, over 100 billion meteoroids enter Earth’s atmosphere daily with masses larger than 1 microgram. These include shower meteoroids, which are associated with a parent body, as well as sporadic meteoroids, which form the background population. Although meteoroids have a profound effect on our space environment and produce plasma densities that are orders of magnitude greater than the background ionosphere, we understand very little about their fundamental properties. These include meteoroid mass and density that depends on orbit and velocity, the formation and distribution of irregularities in the lower ionosphere, the mass deposition rate into our atmosphere, the effects of meteoroid fragmentation on plasma formation, and the effect of the background electric and magnetic fields on plasma expansion and distribution. We seek to answer these questions by probing into the plasma that surrounds the meteoroid, known as the head echo, and behind the meteoroid, called the trail, in order to assess the threat to spacecraft. Our approach includes both experiment and modeling.
Radar studies
When a meteoroid enters the Earth's atmosphere, heats up, and ablates, a plasma forms. The plasma traveling with the meteoroid is called a meteor head, while the plasma that is left behind is called a meteor trail. By transmitting pulsed electromagnetic waves with a high-power large-aperture (HPLA) radar and measuring the waves that are scattered back, one hopes to characterize the plasma and its evolution and infer many properties of the parent meteoroid such as velocity, mass, density, and composition. The image below shows typical radar data for a meteor taken with the Jicamarca Incoherent Scatter Radar outside Lima, Peru. It plots signal to noise ratio (SNR) as a function of range and time the pulse was transmitted. The diagonal line on the left is the signal from a meteor head, while the high-SNR portion to the right is signal due to the accompanying trail.

Smaller "meteor radars" have an even longer history of observing trails. They receive what are called specular trail reflections, resulting when the radar beam is perpendicular to the meteor trail. Although the techniques are different, both radar methods provide unique insight into the meteoroid population.
Estimating Mass, Density, and Size
Since meteoroids themselves normally burn up before reaching the Earth's surface, it is impossible to directly measure their mass, density, and size. Instead we infer these values from radar measurements.
Modeling of Surrounding Plasmas
Particle-in-cell simulations provide insight into the dynamics of the plasmas that we see as meteors.
Orbit Determination

Once we know the position and velocity of a meteor with respect to the radar, we can determine its orbital elements and where it came from. While many meteors come from comet trails or asteroids, others may come from interstellar sources. High Power Large Aperture (HPLA) radars can measure a meteor's position and velocity with enough accuracy to determine whether an meteoroid's origin is interstellar or not. To further increase certainty, we model effects such as solar radiation pressure, Poynting-Robertson drag, and Lorentz forces, which disproportionately affect small particles.

People
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Aerospace Corporation (PhD 2023)
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NASA Ames (PhD 2023)
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PhD Candidate
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Graduate Student
Publications
- Limonta, L., Close, S., & Marshall, R. (2020). A technique for inferring lower thermospheric neutral density from meteoroid ablation. Planetary and Space Science, 180(104735). https://doi.org/10.1016/j.pss.2019.104735
- Tarano, A. (2020). Automated inference of impacting asteroids’ physical properties and motion [Doctoral Dissertation, Stanford University]. https://purl.stanford.edu/xy098dx4030
- Tarano, A. (2020). Automated inference of impacting asteroids’ physical properties and motion [Doctoral Dissertation, Stanford University]. https://purl.stanford.edu/xy098dx4030
- Gil, S., Estacio, B., Young, S., Matthews, I., Lee, N., & Close, S. (2020). Ejecta charging and dynamics in meteoroid impacts on asteroids and comets. AGU Fall Meeting.
- Lee, N., Hedges, T., & Close, S. (2020). Estimating neutral density of the thermosphere from meteor trajectories. AGU Fall Meeting. https://agu.confex.com/agu/fm20/meetingapp.cgi/Paper/683458
- Juarez Madera, D. (2020). Space-and ground-based measurements of radiation belt precipitation : extending the capabilities of cubesats and radars [Doctoral Dissertation, Stanford University]. https://purl.stanford.edu/vg160cx7800
- Young, S., Lee, N., Estacio, B., Matthews, I., Shohet, G., Bassette, R., Banerjee, S., & Close, S. (2019, December). Electric field polarization of electromagnetic radiation from micrometeoroid and dust impacts on spacecraft. AGU Fall Meeting. https://ui.adsabs.harvard.edu/abs/2019AGUFM.P23C3520Y/abstract
- Lee, N., & Close, S. (2019, December). Neutral density measurement from simultaneous radar observation of meteors. AGU Fall Meeting. https://iafastro.directory/iac/paper/id/54563/summary/
- Tarano, A., Wheeler, L., Close, S., & Mathias, D. (2019). Inference of meteoroid characteristics using a genetic algorithm. Icarus, 329, 270-281. https://doi.org/10.1016/j.icarus.2019.04.002
- Sugar, G., Oppenheim, M., Dimant, Y., & Close, S. (2019). Formation of plasma around a small meteoroid: Electrostatic simulations. JGR Space Physics, 124(5), 3810-3826. https://doi.org/10.1029/2018JA026434
- Sugar, G. (2019). Meteoroid mass from head echoes using particle-in-cell and finite-difference time-domain simulations [Doctoral Dissertation, Stanford University]. https://purl.stanford.edu/nz604gp3764
- Sugar, G., Oppenheim, M., Dimant, Y., & Close, S. (2018). Formation of plasma around a small meteoroid: Simulation and theory. Journal of Geophysical Research. https://doi.org/10.1002/2018JA025265
- Limonta, L. (2018). Experimentation and simulation of meteoroid ablation [Doctoral Dissertation, Stanford University]. https://purl.stanford.edu/wh601yb5230
- Sugar, G., Moorhead, A., Brown, P., & Cooke, W. (2017). Meteor shower detection with density‐based clustering. Meteoritics & Planetary Science, 52(6), 1048-1059. https://doi.org/10.1111/maps.12856
- Li, A., & Close, S. (2016). Neutral density estimation derived from meteoroid measurements using high-power, large-aperture radar. JGR Atmospheres, 121(13), 8023-8037. https://doi.org/10.1002/2015JD024547
- Goel, A. (2016). Detection and characterization of meteoroid and orbital debris impacts in space [Doctoral Dissertation, Stanford University]. https://purl.stanford.edu/xv115bk2106
- Li, A. (2016). Neutral density estimation from multiple equivalent platforms, [Doctoral Dissertation, Stanford University]. https://purl.stanford.edu/rb805sm7205
- Fletcher, A. (2015). Plasma production and radiation from meteoroid impacts on spacecraft [Doctoral Dissertation, Stanford University]. https://purl.stanford.edu/zx794nw1023
- Yee, J., & Close, S. (2013). Plasma turbulence of nonspecular trail plasmas as measured by a high‐power large‐aperture radar. JGR Atmospheres, 118(24), 13449-13462. https://doi.org/10.1002/2013JD020247
- Linscott, I., Close, S., Goel, A., Lee, N., Green, S., & Bryant, N. (2013). ISOLDE: ISS-based study of LEO debris and meteoroid electrical effects. Sixth European Conference on Space Debris. https://conference.sdo.esoc.esa.int/proceedings/sdc6/paper/93