At the same time, the layers affected by the meteoroids on Earth are very narrow, maybe only a mile or two wide, while Venus and Mars both have layers stretching six to eight miles.
According to Withers, the difference may come from the presence of Earth's strong magnetic field, a feature lacking on the other two planets. But scientists aren't certain how much of a role the field actually plays.
Finding the source
To study Earth's ionosphere, scientists can launch rockets to take measurements in the region. But the process is more complicated for other planets.
As a spacecraft travels through the solar system, a targeted radio signal sent back to Earth can be aimed through the ionosphere of a nearby planet. Plasma in the ionosphere causes small but detectable changes in the signal that allow scientists to learn about the upper atmosphere.
This process — known as radio occultation — doesn't require any fancy equipment, only the radio the craft already uses to communicate with scientists on Earth.
"It's really one of the workhorse planetary science instruments," Withers said.
Because it is so simple, the process has been applied to every planet ever visited by spacecraft.
Only in recent years has enough data come back on Venus and Mars to seriously examine their upper atmospheres. As of yet, no numerical simulations have been created to explain some of the differences, but Withers expressed hope that this would change in the near future. Such simulations could help answer some of the questions that the observations have raised.
Withers also hopes that, in time, a detailed understanding of the ionosphere could even help scientists engage in a kind of "atmospheric archeology" for Venus and Mars.
One day, scientists may be able to track the history of comets in the solar system by measuring how planetary atmospheres have been affected by the icy wanderers' shed dust and gas. But conclusions drawn by this sort of sleuthing are probably a ways down the road, Withers said.
- Spectacular Perseid Meteor Shower Photos of 2011
- 7 Biggest Mysteries of Mars
- 2012 Meteor Shower Skywatching Calendar
Copyright 2012 SPACE.com, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.