The search for life beyond that of our planet is a complicated one. As it stands we only know of life arising in a particular way, one we can’t be sure isn’t unique in the universe. Still it’s the best model we have to go by and so when we search for life we look for all the same signs as we do for anywhere here on Earth. The one constant that binds all life on Earth is water and so that is why we search so fervently for it anywhere in the solar system. Surprisingly there are many places to find it but none are more spectacular than Saturn’s moon Enceladus.
Enceladus is a strange world, truly unlike anything else in our solar system. Its surface is incredibly young, mostly devoid of the numerous pockmarks that are common among other atmosphereless celestial bodies. This is because it’s in a constant state of change, it’s icy surface splitting and cracking open to reveal a new unsullied surface. Enceladus is like this because Saturn’s massive girth warps the tiny moon as it makes its orbit, generating incredible amounts of heat in the process. The same process is responsible for the amazing cryovolcanoes that dot its south pole, spewing forth tons of water per day into the depths of space. Whilst it’s easy to confirm that there’s liquid water somewhere on Enceladus (those cryovolcanoes aren’t magical water spouts) the question of where the reservoir is, if there even is one, has been the subject of much scientific study.
It has long been thought that Enceladus was host to a vast underground ocean although its specifics have always been up for debate. Unlike Europa which is thought to have a layer of liquid water underneath the ice (or a layer of “warmer” ice) the nature of Enceladus’ ocean was less clear. However data gathered by the Cassini spacecraft during its flybys of the moon in 2010~2012 show that it’s very likely that there’s a subsurface ocean below the area where the plumes originate. How they did this is quite incredible and showcases the amazing precision of the instruments we have up in space.
The measurements were made by using the radio communications between Cassini and Earth. These stay at a relatively fixed frequency and thus any changes in the craft’s speed will manifest themselves as slight Doppler Shifts in the frequency. This is the same principle behind how the sound of an approaching ambulance changes as it gets closer and farther away and it allows us to detect even the smallest changes in Cassini’s speed. As it turns out when Cassini flew over Enceladus’ south pole, which has a great big depression in it (meaning there’s less gravity at that point) the change in speed was far less than what we expected. What that means is there’s something more dense below the depression that’s making up for the lack of matter in the depression and, since water is more dense than ice, a giant hidden sea is a very plausible explanation.
There may be other explanations of course, like a giant deposit of heavy elements or just plain rock, however the fact that there’s water gushing up from that location gives more credence to the theory that it’s an ocean. The question now turns to nailing down some of the other variables, like how big it actually is and how the water gets to the surface, which I’m not entirely sure the Cassini craft is capable of determining. Still I wasn’t completely sure it was capable of doing this before today so I’m sure the scientists at NASA have some very interesting ideas about what comes next for Enceladus.
One of the strangest phenomena I’ve ever read about in our solar system (and there are many, like Venus spinning in the opposite direction to everyone else, but that’s a story for another day) none are more perplexing than the hexagon atop of Saturn. It’s strange because shapes like that don’t typically appear in nature, especially at scales of that magnitude. The question of how it came to be, and more importantly why it keeps sticking around, was an interesting one and whilst there’s a sound scientific explanation for it a video shared to me by a friend showcases how the effect can come about.
You can see the effect most strongly at around 2:30 where he starts moving from the center of the spinning disk back towards the outer edge and, lo and behold, suddenly we have a hexagon shape created by a simple motion on a rotating disk. It’s easy to make the comparison between the spinning disk and the incredible winds that sweep across Saturn’s surface, but what about the artist’s arm motion? We can see it’s a simple periodic, much like a pendulum, but the scale of which these two forces act on would almost preclude any kind of relationship. As it turns out there are in fact some similarities but the mechanisms of action are far more complex.
The current theory is that the hexagon isn’t created by the wind currents per se, as the original spinning a bucket of water experiment would lead you to believe, instead its created by the differing wind speeds that are present throughout Saturn’s atmosphere. These differing wind speeds buffet against each other creating vortexes, eddies and waves. As it turns out Saturn’s north pole has the steepest wind gradient which gives rise to the hexagon. With this in mind the researchers created a system whereby they could spin a cylinder and its base at different speeds creating a gradient similar to that on Saturn and, with a little tweaking, a hexagon appeared.
Now you know all that you should take a look at the latest movie of Saturn’s north pole from Cassini showing the speed gradient in effect. Absolutely incredible, don’t you think?
It’s almost scary how similar Earth and Venus are in some respects. We’re roughly the same size, with Earth edging Venus out by 300KMs in diameter, and consequently roughly the same mass as well. The similarities end when you start looking further however with Venus being the hottest planet in our solar system due to its runaway greenhouse effect, it’s atmosphere a choking combination of carbon dioxide, nitrogen and sulphur. If there was ever a warning about the devastating potential about greenhouse gases it is our celestial sister Venus, but in that chaos lies an abundance of scientific data that could help us better understand ourselves and, hopefully, avoid the same fate.
Studying Venus’ atmosphere isn’t an easy task however as those extreme conditions have meant that the longest our probes have managed to survive down there is a couple hours. We can still do a lot of good work with satellites and spectral analysis but there’s really no substitute for actually being in the atmosphere for an extended period of time. Strangely enough whilst Venus’ atmosphere might be one of the most unforgiving in our solar system its composition, made up primarily of heavy than air elements, provides an unique opportunity that an atmospheric study craft could take advantage of. A concept craft that does just this is called the Venus Atmospheric Maneuverable Platform (VAMP) by Northrop Grumman.
The VAMP is part airship, part traditional aircraft which would spend the majority of its life high in Venus’ atmosphere. To do this the VAMP craft is extremely light, on the order of 500kgs, but it has a wingspan that exceeds that of a Boeing 737. The craft itself would be inflatable, allowing VAMP to cruise at altitudes between 55KM and 70KM above Venus’ surface. It can do this because of the incredible density of Venus’ atmosphere which makes even regular breathable air from Earth a powerful lifting gas. The only limit to its lifespan in the Venusian atmosphere would be its power source and since it could take advantage of the freely available sun a platform like VAMP could run for an incredibly long time.
The concept is actually a rework of another one that was designed to fly through the atmosphere of Saturn’s moon Titan, a mission many have wanted to undertake since the Huygens probe landed there a decade ago. The challenges of flying an aircraft there are far greater than that of Venus, primarily due to the much thinner atmosphere and huge drop in solar radiation to take advantage of. It would still be doable of course, however the mission profile you’d have to go with would have to be much less ambitious and the time frames much shorter. Still it surprises me that the concept didn’t go the other way around as putting balloons in Venus’ atmosphere has always been a concept that many wanted to explore.
Northrop Grumman appears to be quite serious about the VAMP project as they outlined many objectives they wanted to achieve for it back in 2013. I can’t seem to find much more on it unfortunately which means it’s likely still in the concept phase, hoping for a mission profile to come along that suits it. Considering how many incredible envelope pushing missions we’ve had of late I don’t think something like VAMP is too far out of left field, especially considering that it’s based on already proven technologies. Still it doesn’t seem like it will be too long before we have a plane soaring through another world’s atmosphere, another science fiction dream becoming a reality.