Scientists studying the atmospheres of Mars and Venus claim that conditions on the two worlds are "surprisingly similar".
Planetary researchers used two European Space Agency craft to record the way in which the two planets' atmospheres are stripped away into space.
The simultaneous observations by Mars Express and Venus Express have given scientists the data they need to investigate the evolution of the two atmospheres.
The magnetic regions behind the planets are the predominant channels through which electrically-charged particles escape. They also present the first detection of whole atoms escaping from the atmosphere of Venus.
By observing the current rates of loss of the two atmospheres, scientists hope to turn back the clock and understand what they were like in the past.
The new observations show that Mars and Venus are "surprisingly similar" despite the differences in size and distance from the Sun.
Both planets have beams of electrically charged particles flowing out of their atmospheres. The particles are being accelerated away by interactions with the solar wind, a constant stream of electrically charged particles released by the Sun.
At Earth, the solar wind does not directly interact with the atmosphere as it is diverted by Earth's natural cloak of magnetism.
Neither Mars nor Venus have appreciable magnetic fields generated inside the planet, so each planet's atmosphere suffers the full impact of the solar wind.
"This is because the density of the ionosphere at 250km altitude is surprisingly similar," said Tielong Zhang, principal investigator for the Venus Express magnetometer instrument at the Institut für Weltraumforschung in Austria.
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