The ionosphere is a region between 48km and 965km above sea level. This is high enough that Earth’s magnetic field is weaker and less protection is offered from solar radiation yet low enough that atmospheric gases are still present. As a result, solar radiation breaks down these gases and creates the many ions that give the region its name. In fact, there are sufficient charged particles in the ionosphere that the region interacts with electric and magnetic fields in a way that other atmospheric regions generally do not.
The primary cause of earthquakes is geological faults and the movement of tectonic plates. This movement results in acoustic waves which travel up through the atmosphere and disturb the ionosphere. For decades now, studies have been able to correlate seismic activity with electron resonance in the ionosphere and some studies have been able to identify similar disturbances in the ionosphere up to a month ahead of large earthquakes.
It’s theorised that measurement of the ionosphere could be used to predict earthquakes. However, constant interaction with any magnetic or electric fields makes electron measurements noisy in the region. One of the main limitations this branch of research is currently facing is the lack of data required to distinguish seismically related electron disturbances from any other. The goal of APSS-1 is to take measurements and increase the amount of such data that is publicly available.
In order to measure disturbances in the ionosphere, APSS-1 makes use of two Langmuir probes. By inserting electrodes into a plasma–such as that of space–and measuring either the voltage between the electrodes or between the electrodes and the surrounding vessel, the electron properties of a plasma can be determined. This includes electron temperature, electron density, and plasma potential.
APSS-1 was launched in collaboration with Rocket Lab in 2020 and unfortunately, communications with the spacecraft could not be established. In January 2024, the spacecraft naturally de-orbited.
Since the launch of APSS-1, research into ionospheric earthquake precursors has intensified. Multiple spacecraft focused on the characterisation of electron disturbances in the ionosphere have been designed and launched with the same goals as APSS-1.
Contributors
Andrew Alder
Aryan Lobie
Elsdon Greenough
Emma Doolin
Francis Moynihan Lavey
Harith Wannigama
Harry She
Hunter Linton
Hunter Linton
Jerry Fan
Keison Tang
Kevin Zhong
Leif Healy
Louis Habberfield-Short
Max Kingham
Navidu Bulathsinhala
Noel D’Souza
Radi Baboe
Sam Duanmu
Snigdha Saha
Summer Xia
Thomas Andrews
Timothy Gray
Tony Liu
Travis Jay Sua
William Li