Mars is the most studied planet other than our own, currently playing host to no less than 7 different craft currently operating both in orbit and on its surface. It’s of interest to us due to its similarity to Earth, giving us an insight into how certain processes can affect planets differently. Mars is also the easiest of our sister planets to explore, being relatively close and having an atmosphere that won’t outright destroy craft that dare land on it. Still for all that research it still manages to surprise us, most recently by revealing the fact that liquid water still flows on it. We’re still far from done with it however and the MAVEN craft has just revealed some key insights into Mars’ atmosphere and the history behind its current state.
Mars’ atmosphere is extremely thin, over 100 times less dense than the atmosphere here on Earth. To put that in perspective that’s about the same density as the air here is on Earth at an altitude of about 30KM, or about 3 times as high as your typical jet airliner flies. It’s also almost all carbon dioxide with a small smattering of nitrogen and other trace elements. However it wasn’t always this way as numerous studies have revealed that it must have held a much thicker atmosphere in the past. What has remained something of a mystery is just how Mars came to lose its atmosphere and whether those same processes were in effect today. MAVEN, a craft specifically designed to figure this out, has made some key discoveries and it seems that the long held belief that the sun is to blame is true.
For a planet to lose its atmosphere there’s really only two places it can go. In some cases the planet itself can absorb the atmosphere, driving chemical reactions that pull all the gases down into more solid forms. This specific scenario was investigated on Mars however the lack of the kinds of minerals we’d expect to see, mostly carbonates given Mars’ mostly carbon dioxide atmosphere, means that this was unlikely to be the case. The second way is for it to lose the atmosphere to the vacuum of space which can happen in a number of ways, usually through the planet being unable to hold onto its atmosphere. This latter theory has proved to be correct although it’s far more interesting than Mars simply being too small.
In the past Mars would have looked a lot like Earth, a small blue marble wrapped in protective gases. Back then the core of Mars was still active, generating a magnetic field much like that on Earth. However, after a time, the core began to cool and the engine behind the giant magnetic field began to fade. As this field weakened the solar wind began to erode the atmosphere, slowly stripping it away. Today Mars’ magnetic field is around 40 times weaker than Earth’s, no where near enough to stop this process which is still continuing to this day. For Mars it seems that its diminutive core was what sealed its fate, unable to sustain its protective magnetic shield from the relentless torment of our sun.
Whilst this has been the prevailing theory for some time its good to get confirmation from hard data to support it. Our two closest solar relatives, Venus and Mars, provide insights into how planets can develop and what changes produce what outcomes. Knowing things like this helps us to understand our own Earth and what impacts our behaviour might have on it. Mars might not ever see its atmosphere again but at least we now know what it might have looked like once, and where it has gone.
MESSENGER was a great example of how NASA’s reputation for solid engineering can extend the life of their spacecraft far beyond anyone’s expectations. Originally slated for a one year mission once it reached it’s destination (a 7 year long journey in itself) MESSENGER continued to operate around Mercury for another 3 years past its original mission date, providing all sorts of great data on the diminutive planet that hugs our sun. However after being in orbit for so long its fuel reserves ran empty leaving it unable to maintain its orbit. Then last week MESSENGER crash landed on Mercury’s surface putting an end to the 10 year long mission. However before that happened MESSENGER sent back some interesting data around Mercury’s past.
As MESSENGER’s orbit deteriorated it creeped ever closer to the surface of Mercury allowing it to take measurements that it couldn’t do previously due to concerns about the spacecraft not being able to recover from such a close approach. During this time, when MESSENGER was orbiting at a mere 15KMs (just a hair above the max flight ceiling of a modern jetliner) it was able to use its magnetometer to detect the magnetic field emanating from the rocks on Mercury’s surface. These fields showed that the magnetic field that surrounds Mercury is incredibly ancient, dating back almost 4 billion years (right around the creation of our solar system). This is interesting for a variety of reasons but most of all because of how similar Mercury’s magnetic field is to ours.
Of all the planets in our solar system only Earth and Mars have a sustained magnetic field that comes from an internal dynamo of undulating molten metals. Whilst the gas giants also generate magnetic fields they come from a far more exotic form of matter (metallic hydrogen) and our other rocky planets, Venus and Mars, have cores that have long since solidified, killing any significant field that might have once been present. Mercury’s field is much weaker than Earth’s, on the order of only 1% or so, but it’s still enough to produce a magnetosphere that deflects the solar wind. Knowing how Mercury’s field evolved and changed over time will give us insights not only into our own magnetic field but of those planets in our solar system who have long since lost theirs.
There’s likely a bunch more revelations to come from the data that MESSENGER gathered over all those years it spent orbiting our tiny celestial sister but discoveries like this, ones that could only be made in the mission’s death throes, feel like they have a special kind of significance. Whilst it might not be the stuff that makes headlines around the world it’s the kind of incremental discovery that gives us insight into the inner workings of planets and their creation, something we will most definitely need to understand as we venture further into space.
Magnetic fields permeate our entire existence. The Earth’s molten iron core generates a gigantic magnetic field that shields us from the harsh solar winds that our Sun blows forth and, when it momentarily fails, generates the beautiful aurora seen at the more extreme latitudes. They’re also behind some of the greatest technological advances in modern times from things like the humble hard drive that’s in the vast majority of computer systems to the first television screens that were driven by cathode ray tubes.Visualizing a magnetic field is somewhat difficult though as whilst may things react to them they don’t really show you their beautiful field lines. Ferrofluids however are one material that showcases them quite distinctly and they’re quite beautiful:
You can actually purchase both of the sculptures in the video from here and whilst they would make an awesome little art piece on their own I think they’d also be a great little educational tool. Magnets and iron fillings get you part of the way but ferrofluids like this give you a much better view of how the fields interact with each. Most importantly they show them in 3D space, something that’s incredibly hard to grasp when you demonstrate magnetic fields the old fashioned way.
Now if only someone would chuck one inside an MRI machine, I’m sure that’d make for quite a display.
Superconductors are an incredible scientific discovery and not just because they have the oh-so-nice property of having 0 electrical resistance. They also have the peculiar property of ejecting all magnetic fields from within them, an interesting phenomena considering the duality of electromagnetism. Unfortunately traditional superconductors required extremely low temperatures to exist, usually not far off absolute zero. This made them impractical for the many uses we could think of for them as whilst the lack of resistance would prove a boon for power transmission the ongoing maintenance would prove to be far too costly. However recent materials advancements have given rise to what we call high temperature superconductors which has opened up many new avenues of research.
Don’t let their moniker fool you though, the temperatures that most of these operate at are still well below freezing, however they do become superconducting at temperatures that are achievable using coolants like liquid nitrogen rather than exotic solutions relying on cryogenic fluids like liquid helium. This has lead to a lot of research with these particular kinds of superconductors and interestingly some demonstrations that almost appear like magic when you first see them:
As I mentioned earlier superconductors expel all magnetic fields from within them, however when the superconductor is thin there will be little areas of weakness where the magnetic field can get through. Since the superconductor is trying its darnedest to expel those fields it locks them in those small areas allowing the superconductor to levitate on the field. The locking happens in the direction of the magnetic field which actually allows you to do some very interesting things (as demonstrated in this video). The effect only lasts as long as the cooling however and once that’s gone the levitation effect disappears instantly.
Really hammers home Arthur C. Clarke’s quote: “Any sufficiently advanced technology is indistinguishable from magic.” doesn’t it?