Researchers from the Higher School of Economics and Space Research Institute (Russia) have calculated the main parameters that determine space weather close to the nearest Earth-like exoplanet, Proxima Centauri b. Such parameters include solar wind, as well as galactic and solar cosmic rays. The results of the research were published in Astronomy Letters.
Proxima Centauri b is the closest exoplanet to the Solar System where life might exist. The exoplanet is located in the circumstellar habitable zone of the red dwarf Proxima Centauri, which indicates that the temperature on the surface of Proxima b is suitable for the existence of liquid water.
British astronomer Mikko Tuomi discovered the exoplanet in 2013, but it took three years for the European Southern Observatory to announce its discovery. Since then, Proxima b has given researchers the opportunity to search for life in the universe. The exoplanet is located 4.25 light years from Earth, while other Earth-like planets are typically at least 11 light years away.
Over the last two years, a lot of research has been done on Proxima b’s potential for life. To determine if life can survive on the planet, it is not enough to know just the temperature on the planet’s surface; it is also important to study radiation conditions. The cosmic rays that determine these conditions, however, are no longer being discussed practically. Researchers from the Braunschweig University of Technology have looked at the impact of cosmic rays on exoplanets, but their research does not factor in the impact of solar wind. This is the task Russian scientists set out to solve.
In their calculations, the study’s authors used simple models developed to help understand the Sun in the 1950s-1960s, and for the first time ever they determined the radiation conditions near Proxima b.
‘Such simple models were used for one reason – our knowledge of other stars is on par with our knowledge of the Sun in the fifties and sixties. The advantage of these models is that they do not require a large number of input parameters,’ explains one of the study’s authors, HSE Physics Faculty Associate Professor Andrey Sadovski.
The input parameters used in these formulas include the star’s magnetic field, coronal temperature, and standard solar characteristics. The researchers used the Parker Model to determine that star wind speeds were 600-1,200 km/s, with density of around 1,000-4,000 particles per cubic centimeter. They also collected data on the activity and magnetic field of Proxima Centauri and calculated the possible flows and fluences (amount of protons flying in a particular direction) of galactic and solar cosmic rays.
The results of the research show that galactic cosmic rays should not exist near Proxima b up to energies of 1 TeV, as solar wind carries them away.
‘The cosmic rays (particles occupying interstellar space) that reach Earth have energies starting at 10 GeV, while they start at 1,000 GeV for Proxima Centauri. Accordingly, their quantity on the exoplanet should be a thousand times less, which might impact the atmosphere, climate, etc.’ Andrey Sadovski notes.
The researchers also assumed that solar cosmic rays might accelerate to high energies (3,150 αβ GeV) in stellar flares (occurrences similar to the Sun’s solar flares). Flares on Proxima Centauri are capable of speeding up protons and maintaining a constant intensity of solar cosmic rays in the atmosphere because of their high frequencies. In other words, the planet is still able to withstand a large amount of cosmic rays, but its climate will depend more on the star’s activity.
This is why it is so important to find out what is happening on exoplanets similar to Earth, particularly those like Proxima b, which is much older than Earth. According to researchers, this will help us better understand what is taking place on our own planet and possibly predict its future.