Two Mars probes were launched this month. Both missions are significant for different reasons.
The MAVEN spacecraft from NASA will do something that no Mars probe has done before – study its upper atmosphere. This is important because most planetary scientists believe Mars once had a thicker atmosphere and flowing water on its surface billions of years ago.
Hold up, you say: if Mars lost its atmosphere, why didn’t Earth lose its own? That’s a good question, and the best answer we’ve been able to come up with is that Mars once had a global magnetic field like Earth’s that protected its atmosphere from the solar wind. Earth gets its magnetic field from the superhot liquid iron flowing around inside its mantle. This internal heat is left over from planetary formation. Depending on its size, a planet will gradually lose its internal heat over billions of years. A smaller planet has a greater ratio of surface area to volume than a larger one, so it will lose its heat faster. Think of a small ice cube versus a larger one – the smaller one will melt faster.
Mars is only half the size of Earth, so it likely lost its internal heat faster. Its core solidified as a result, and shut down its magnetic field. There is no magnetic field on Mars today, except for local areas of magnetism on the surface. Without a magnetic field to deflect them, the charged particles of the solar wind would have eroded away the atmosphere over billions of years.
Even though it’s the best theory we have of Mars’s demise, we have yet to confirm it. MAVEN will help us do that by studying how the solar wind interacts with the atmosphere, and how quickly the atmosphere is losing gases.
Mars Orbiter Mission (Mangalyaan)
MOM is the first Indian Mars probe. It is primarily intended as a technology demonstrator for India’s future space plans, but it will also take its own readings of the surface and atmosphere. Some of these readings may supplement MAVEN’s own and give us a better picture of how Mars got to where it is now.
However, I think this mission’s real significance lies in the shift of power in interplanetary space. If MOM reaches Mars safely, it would do what Russia could not with its Phobos-Grunt spacecraft, which failed after launch in 2011. Russia has been having problems with quality control in its space hardware, as exemplified by Phobos-Grunt and a few spectacular Proton launch failures. Whether this represents a decline in Russian space power remains to be seen, but it’s clear that India has space ambitions with the successes to back them up – witness its recent Chandrayaan mission to the moon.
As for me, I’m happy that another country is throwing its hat into the ring.