Uploaded March 2022 | Updated September 2026, 8 hours ago
The origin of the exoplanet radius gap
Dr. James Owen (Imperial College London )
Fowler (A) Award
Exoplanet discovery missions have been enormously successful, detecting thousands of planets over the last decade. The most common type of planet discovered to date has a radius in-between that of the Earth and Neptune, yet orbits its host start closer than Mercury to the Sun. With no previously known analogue, the nature of these planets was uncertain. Density measurements indicated that some were so dense they must be terrestrial, while others were so low density they must contain voluminous envelopes of hydrogen gas. In 2017, spectroscopy of 1000s of exoplanet host stars provided more precise stellar radii measurements, allowing the precision on the planetary radii to be increased by a factor of about 4.
This work revealed that the population of planets contained two sub populations, planets either have radii of around 1.3 Earth radii or 2.6 Earth radii, planets with radii in the range 1.8-2 Earth radii being rare. In this talk, I will discuss how these planetary populations are created by mass-loss from a population of planets born with large hydrogen dominated envelopes. Those planets close to their stars or with low masses are vulnerable to complete loss of these atmospheres creating the populations of planets with radii of 1.3 Earth radii, while those planets further away or with higher masses retain their envelopes, creating the peak at 2.6 Earth radii.
Turbulence-Driven Magnetic Reconnection in Collisionless Plasmas: New Insights from NASA’s Magnetospheric Multiscale Mission
Dr. Julia Stawarz, (Imperial College London)
Winton (G) Award
Many plasmas throughout the Universe – from the plasmas within our solar system to those within accretion discs and galaxy clusters – undergo complex, highly nonlinear dynamics, known as turbulence. Turbulence leads to the formation of a multitude of different structures and fluctuations within the plasma and the dissipation of these fluctuations can facilitate the acceleration of particles and heating of the plasma. Thin current sheets are one type of structure that can be formed by the turbulent dynamics and can be sites where a process known as magnetic reconnection can occur, in which energy that has been stored in the magnetic field is suddenly released and converted into particle flows and heating. While magnetic reconnection has long been suggested to play a role in turbulent dynamics, these turbulence-driven magnetic reconnection events have traditionally been challenging to examine observationally.
Launched in 2015, NASA’s Magnetospheric Multiscale (MMS) mission is a four-spacecraft formation of Earth-orbiting satellites, capable of measuring high-resolution 3D particle distribution functions, electromagnetic fields, and spatial gradients at scales approaching the characteristic scales of the electrons – allowing for an unprecedented examination of small-scale reconnection events within turbulent plasmas. In this talk, I will present a recent survey of turbulence-driven magnetic reconnection events observed by MMS in the region of space downstream of Earth’s bow shock, known as the magnetosheath. I will discuss how the properties of the turbulent fluctuations can influence the nature of the magnetic reconnection events in the nearly collisionless plasmas that are often found in space, leading to so-called “electron-only” reconnection, in which the positively charged ions do not fully couple to the newly reconnected magnetic field lines to form reconnection jets, and I will discuss the potential impact these reconnection events have on the small-scale dynamics and energy dissipation of the turbulence.
For speaker bios, please go to ras.ac.uk: ras.ac.uk/events-and-meetings/ras-meetings/ordinary-meeting-march-2022
The origin of the exoplanet radius gap
Dr. James Owen (Imperial College London )
Fowler (A) Award
Exoplanet discovery missions have been enormously successful, detecting thousands of planets over the last decade. The most common type of planet discovered to date has a radius in-between that of the Earth and Neptune, yet orbits its host start closer than Mercury to the Sun. With no previously known analogue, the nature of these planets was uncertain. Density measurements indicated that some were so dense they must be terrestrial, while others were so low density they must contain voluminous envelopes of hydrogen gas. In 2017, spectroscopy of 1000s of exoplanet host stars provided more precise stellar radii measurements, allowing the precision on the planetary radii to be increased by a factor of about 4.
This work revealed that the population of planets contained two sub populations, planets either have radii of around 1.3 Earth radii or 2.6 Earth radii, planets with radii in the range 1.8-2 Earth radii being rare. In this talk, I will discuss how these planetary populations are created by mass-loss from a population of planets born with large hydrogen dominated envelopes. Those planets close to their stars or with low masses are vulnerable to complete loss of these atmospheres creating the populations of planets with radii of 1.3 Earth radii, while those planets further away or with higher masses retain their envelopes, creating the peak at 2.6 Earth radii.
Turbulence-Driven Magnetic Reconnection in Collisionless Plasmas: New Insights from NASA’s Magnetospheric Multiscale Mission
Dr. Julia Stawarz, (Imperial College London)
Winton (G) Award
Many plasmas throughout the Universe – from the plasmas within our solar system to those within accretion discs and galaxy clusters – undergo complex, highly nonlinear dynamics, known as turbulence. Turbulence leads to the formation of a multitude of different structures and fluctuations within the plasma and the dissipation of these fluctuations can facilitate the acceleration of particles and heating of the plasma. Thin current sheets are one type of structure that can be formed by the turbulent dynamics and can be sites where a process known as magnetic reconnection can occur, in which energy that has been stored in the magnetic field is suddenly released and converted into particle flows and heating. While magnetic reconnection has long been suggested to play a role in turbulent dynamics, these turbulence-driven magnetic reconnection events have traditionally been challenging to examine observationally.
Launched in 2015, NASA’s Magnetospheric Multiscale (MMS) mission is a four-spacecraft formation of Earth-orbiting satellites, capable of measuring high-resolution 3D particle distribution functions, electromagnetic fields, and spatial gradients at scales approaching the characteristic scales of the electrons – allowing for an unprecedented examination of small-scale reconnection events within turbulent plasmas. In this talk, I will present a recent survey of turbulence-driven magnetic reconnection events observed by MMS in the region of space downstream of Earth’s bow shock, known as the magnetosheath. I will discuss how the properties of the turbulent fluctuations can influence the nature of the magnetic reconnection events in the nearly collisionless plasmas that are often found in space, leading to so-called “electron-only” reconnection, in which the positively charged ions do not fully couple to the newly reconnected magnetic field lines to form reconnection jets, and I will discuss the potential impact these reconnection events have on the small-scale dynamics and energy dissipation of the turbulence.
For speaker bios, please go to ras.ac.uk: ras.ac.uk/events-and-meetings/ras-meetings/ordinary-meeting-march-2022
