Solar Storms Strip Air From Mars, NASA Says
The air on Mars — what there is of it — is leaking away, about half a pound a second sputtering into space, scientists announced on Thursday.
The planet’s early atmosphere is thought to have been as thick as or thicker than Earth’s today, and even over the 4.5-billion-year history of the solar system, that slow leak would not explain how it atrophied to its current wisps.
But new readings from NASA’s Mars Atmosphere and Volatile Evolution mission — Maven, for short — show that when Mars is hit by a solar storm, the ferocious bombardment of particles from the sun strips away the upper atmosphere much more quickly.
That could help explain the disappearance of the atmosphere. The sun during its youth was more unsettled, with many more solar storm eruptions, and it shone brighter in the ultraviolet wavelengths that also help knock atoms out of Mars’ atmosphere.
from Carol's post
Such solar storms were stronger and more frequent about 4 billion years ago, and the sun's emissions in extreme ultraviolet (UV) light were more powerful back then as well, he added. The solar wind — the flow of charged particles from the sun, which is a major driver of Martian atmosphere loss today — was also more potent during the sun's youth.
"All of these [factors] point to the loss of the Martian atmosphere in the earliest stages," Jakosky said.
This all happened right after Mars lost its global magnetic field, which had protected the planet's air against solar-driven stripping, he added. (Earth, which is much larger than Mars, retains a global field to this day.)
That stripping would then have proceeded very quickly, "within a few hundred million years after the shutoff of the magnetic field," Jakosky said.
Now Venus reportedly has been in the same place for billions of years
it is even closer to the Sun than Mars (or Earth)
and would thus receive stronger solar winds
it does not have nor apparently ever had a global magnetic field
but it still has a dense atmosphere
so why if this worked on Mars, why did it not work on Venus?