Ravens is a spacecraft mission concept proposed to the European Space Agency's Cosmic Vision M-class mission call of 2015. If selected, it would be launched in 2025. Ravens has been proposed by an international team of scientists from Europe, Scandinavia, Canada, and the US, with the aim of improving our understanding of the interaction between the solar wind and the Earth's magnetosphere, the influence on our atmosphere, and the societal impacts of this interaction.
The Ravens mission will comprise two spacecraft to image the auroras from space and the plasma regions surrounding the Earth, including the ionosphere, plasmasphere, and ring current region.
The full text of the Ravens science case can be found here.
- Ravens will study the Earth's auroras and the region of space surrounding the Earth, often known as geospace.
- Ravens will comprise two identical spacecraft in highly elliptical polar orbits.
Ravens is named after Muninn and Huginn, the ravens who flew forth each day to gather the news of the world to bring back to the Norse god Odin.
The Ravens mission will monitor the global response of the magnetosphere to incoming solar wind disturbances using a suite of remote-sensing instrumentation including Far Ultraviolet (FUV) and X-ray auroral imagers, Extreme Ultraviolet (EUV) plasmasphere imagers, and energetic neutral atom (ENA) ring current imagers. Ravens will provide for the first time (a) continuous measurements of the northern hemisphere auroras, (b) frequent and systematic measurements of the southern hemisphere auroras (true “global auroral imaging”), and (c) continuous and stereoscopic remote-sensing of the plasmasphere and ring current.
To the right is an example snapshot of the Far Ultraviolet auroras taken by the NASA Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) spacecraft in 2001. Ravens will make similar measurements simultaneously from two spacecraft, continuously at high temporal resolution. [Click here for a movie - or right-click on the link to download the file to open in Quicktime.]
Superimposed on the raw images are the outlines of the continents (green) and lines of latitude and longitude (grey). The cyan axes mark the Geocentric Solar Ecliptic (GSE) coordinate system, in which X points towards the Sun. The blue lines mark the geographic rotation axis of the Earth, whereas the red lines mark the geomagnetic poles. The red ovals mark the regions within which the auroras are most commonly seen.
Ravens will comprise two identically-instrumented spacecraft in highly-elliptical polar orbits, with apogee close to 8 RE above the northern and southern poles and perigee near 2 RE. The orbits of the two spacecraft will be phased such that one spacecraft is at perigee while the other is at apogee. Hence, at least one of the spacecraft will always be in a position to monitor auroral activity, and twice each orbit the two spacecraft will be ideally located to view both northern and southern hemisphere auroras simultaneously. One spacecraft will always be in a position to monitor the plasmasphere and ring current, and twice each orbit stereoscopic views will enable reconstruction of 3D plasma structures. Ravens will be supported by a suite of ground-based observatories, both north and south, and computational physics-based modelling of the magnetosphere, providing a systems level approach to magnetospheric sensing and understanding.
Shown below is a simulation of the view-points of the two Ravens spacecraft from one part of the orbit as they encircle the Earth. [Click here for a movie - or right-click on the link to download the file to open in Quicktime.]
As well as the Earth and the average location of the auroras (red), the image shows the plasmasphere (blue) and ring current (orange) regions surrounding the Earth that are key observables for Ravens.
The Ravens mission will provide a step-change in our understanding of our immediate space environment and address fundamental problems in magnetospheric science, including the following key questions:
How does the global magnetosphere respond to incoming solar wind disturbances?
- How do geomagnetic storms propagate through the magnetospheric system, from dayside coupling region to magnetotail, to inner magnetosphere, ionosphere and atmosphere, and how and where is energy dissipated?
- How is plasma accelerated to form the enhanced plasma pressure in the ring current and how does the associated 3D pressure-driven current system control space weather in the inner magnetosphere?
- How does the plasmasphere erode and refill through the course of storms?
- What internal feedback mechanisms modulate the magnetospheric response to the solar wind, including plasmaspheric plumes and ring current modification of the magnetotail?
Why are the northern and southern hemisphere auroras not symmetric?
- Are auroral signatures of solar wind-magnetosphere coupling at the dayside magnetopause symmetric, and what are the ramifications for magnetic reconnection geometries?
- How and when are magnetotail signatures of energy unloading asymmetric, and what are the ramifications for magnetospheric and ionospheric structure?
- During periods of complicated magnetospheric topology, how are the northern and southern hemispheres magnetically connected, and what creates this topology?
- What do asymmetries in the conjugate auroras imply for the global interhemispheric current system?