“This kind of radio signal just wouldn’t exist unless material had completely left the star’s bubble of powerful magnetism,” Netherlands Institute of Radio Astronomy, Joe Callingham. The fact that this commentary is so struck resonates with the fact that the signal in question, being one of the signals that have been observed in archival records, is a solution to a long-standing issue in stellar physics: how to establish that other stars, not just the Sun, eject true coronal mass ejections (CMEs) into interplanetary space. In the neighborhood of a little red dwarf which is known as StKM 1-1262, that confirmation comes in the form of a short, sweeping radio feature which acts like a shock front drilling through a stellar corona.
This measurement is important to engineering-minded astronomy on a rather simple account: planets are hardware, and stellar space weather is their operating environment.
StKM 1-1262 is approximately 130 light-years and the Earth. With the Low Frequency Array (LOFAR) which is a distributed radio instrument which comprises thousands of antennas, researchers discovered a type II radio burst which is the same category of emission used in the study of the sun to determine a shock caused by a CME. The radio identification was combined with X-ray identification in the XMM-Newton observatory of the ESA that assisted to determine the fundamental characteristics of the star and to locate the eruption within a solar environment.
The burst seems to be extreme in terms of Solar System standards to the CME. It had a speed of 2,400 km/s, a figure that is only found during rare solar events and the magnetic field of the star was estimated to be 300 times stronger than that of the Sun. At such parameters, it is not about auroral spectacle, but mechanical compression, a thick enough, fast CME can compress the magnetosphere of a planet until the distance of “standoff” is shrunk to the atmosphere itself. Particles of charge and strong currents in that geometry are directly coupled into the upper atmosphere, increasing escape and chemical erosion.
Magnetospheres are not binary shields however, but systems of pressure-balance. The reason the nuance is important is demonstrated by recent modeling efforts on Earth-like planets in the M-dwarf habitable zones. In combining both the magnetic pressure and wind ram pressure, an Earth-sized magnetosphere is challenging to attain under typical assumptions and variations in the decay of stellar magnetic fields with distance can reduce magnetospheres by up to 56 percent in worst-case scenarios. Similarly in the same analysis, tidally locked likely habitable zone planets around M dwarfs are more numerous, also capable of changing atmospheric circulation, and may also complicate magnetic shielding due to the dependence of a dynamo with rotation.
That larger context is what makes what might seem at first as an isolated dramatic finding. M dwarfs comprise the most abundant stellar type in the Galaxy and with small habitable zones the potentially rocky planets are now near the origin of flares, winds, and eruptive plasma. Although there are relatively few eruptions on the human time scale, cumulative exposure over geological time is the appropriate measure of whether a planet is left with an atmosphere to be detected- or becomes a bare rock that passes through cleanly but exhales nothing.
At the same time the measurements in the atmosphere are converging on the same stellar activity in the opposite direction. Within the TRAPPIST-1 system, it has been demonstrated by attempts to measure the atmosphere of a small planet by transit spectroscopy how readily the spectral properties of a red dwarf star itself, as well as its variability, can confuse itself with planetary gases. The outcome is a two-way dilemma: space weather is capable of stripping away atmospheres, and stellar pollution can conceal or masquerade as the rest.
It is on that basis that the technical success of the StKM 1-1262 detection is also methodological: it connects a radio signature to an escaping CME beyond the Sun, providing a template on further surveys. As more sensitive arrays come into being, such as LOFAR-like methods higher in scale, the field will have a means to transition toward anecdote to statistics, and to relate the distances in the “habitable zone” to the more practicalities of magnetospheric compression, atmosphere loss and the actual survivability of exoplanet sky.
