The 2004 Venus in situ exploration mission aimed to collect information about the extreme atmospheric conditions that render the planet very different from Earth.
Credit: NASA
ASHLAND, OREGON: The difference in the escape velocities of ions may help to explain why Venus isn’t more like Earth, scientists say, and it may come down to a planet’s core.
Oxygen and hydrogen ions in Venus’s atmosphere do not behave the same when exposed to the solar wind, according to scientists at the Finnish Meteorological Institute in Helsinki.
“An oxygen ion is 16 times more massive than a hydrogen ion,” said lead author, Riku Jarvinen. “We found that the mass difference between the two ion species makes them move very differently from each other in the electric and magnetic fields created by the solar wind around Venus.”
Ions ‘blown’ to higher velocities
In the upper atmospheres of planets, particles are ionised by the sunlight, which is how planetary ionospheres are created, said Jarvinen of the study published in Geophysical Research Letters.
In Venus’s case, the uppermost planetary ions are in contact with the solar wind flowing close to the planet. When this occurs, the ions get energy from the solar wind and are accelerated, as though ‘blown,’ to velocities higher than the escape velocity of the planet and are lost from the atmosphere.
Magnetic fields generated in the planet’s core determine the ways in which its atmosphere reacts to the solar wind, said Jarvinen.
The difference between Venus and Earth
Planets with strong magnetic fields tend to repel the particle stream.
“The Earth has a strong intrinsic magnetic field. This means that the solar wind ‘feels’ the planet from very far (almost 100,000 km above the planet).
At Venus the story is different. Venus has no detectable intrinsic magnetism and the solar wind comes very close to the planet (altitudes as close as 1000 km). One important consequence of this is that the solar wind gets in direct contact with the uppermost parts of the Venus atmosphere.”
One of the greatest riddles of the universe
This, in turn, is what causes the acceleration of the ions and is what may have 'blown' away a possible ocean.
“We did the study by using a computer simulation which models the solar wind interaction with Venus' atmosphere,” Jarvinen said. “The simulation mimics the electric and magnetic fields and the solar wind around Venus.”
Added Larry Paxton from the Johns Hopkins Applied Physics Lab in Laurel, U.S., “One of the great riddles of the universe is whether there are other planets like the Earth… how important is the presence of a strong, intrinsic magnetic field to preserving the possibility of life on a planet?
This together with the work of many others helps us to build up a picture of what makes a world hospitable to life.”
