The Song of The Dunes

I’m really quite fascinated by singing sand dunes. Also known variously as whistling sand or booming dunes, this is a phenomenon observed in places across the world when the right set of circumstances cause sand to be a little noisier than usual.

What kind of sound does the sand make, you ask? Have a listen…

For a sand dune to be musical, there seem to be a few qualifications needed:

  • A dune should be at least ~45m high
  • Sand should be loose and dry
  • Sand grains should be rounded and 0.1 – 0.5 mm in diameter
  • Grains need to contain silica
  • There needs to be a harder layer underneath the sand

altyn-emel-dunesFrom what I can find out, the exact mechanism is apparently not well understood. It seems to be to do with a resonant frequency being set up between the surface of the sand and the harder layer beneath (either rock or a wet layer of sand). This effectively makes the entire layer of dry sand resonate, boosting the volume. Though no one’s quite sure if the sand comes from friction as the grains rub together, or air between the sand grains being compressed.

In most places where singing sand exists, it’s less of a deep rumbling noise and more of a squeaking which happens when you walk over it. The most common frequency emitted by squeaky sand is apparently around 450 Hz, which sounds like this. The big dunes, on the other hand, have a much deeper set of frequencies, with the loudest being around 90 – 100 Hz. That’s a deep, bassy sound. Additionally, the dunes have been found to sing notes of E, F, or G. In case you want to sing along.

el-dorado-marsAn interesting thought is whether sand dunes on other planets will also sing this way. Sand, of one form or another, is certainly common. So common that there’s an International Planetary Dunes workshop, which is the source of this handy little document, and the slides from a related talk.

Mars is our friendly neighbourhood desert planet. If I was to look for sand anywhere in the Solar System, Mars is where I’d start. Turns out, Mars doesn’t have as many dunes as you might think. Most are confined to sand traps and crater basins. The exception to this is a region near the North Pole of Mars called Olympia Undae – a dune sea which Star Wars fans would no doubt find quite familiar.

mars-sand-dunes-mro-editGiven our neighbouring world’s lower gravity, sand dunes there can grow quite sizeable. Many are a few tens of metres tall, with the largest being up to 600 m in height! Mars is also different in that it’s a very dusty place. Whether having so much fine dust around would allow martian dunes to sing is unclear. Similarly, without doing some experimentation, it’s hard to say if the lower air pressure and effectively zero humidity would have an effect too.

Of course, there are still other more alien places we could look. Around 15% of Titan’s surface is covered by dunes, making it the most dune covered object in the solar system. I’ll admit, I wouldn’t have guessed that. Being so tiny, Titan’s dunes can also be rather tall, with the tallest identified dunes being in the Belet Sand Sea, reaching 100 – 175 m in height.

Finally, there’s Venus. The only images we have from the surface of Venus are still from the Soviet Venera landers, which showed rocky basalt plains. But there’s more to Venus than volcanic rock. Earth’s tragically underexplored sister planet is home to the Fortuna-Meshknet dunes in a region called the Al-Uzza Undae. It’s thought that these may have heights of 40 – 80 m, meaning that the taller ones may be in the range to produce sounds. Of course, whether or not they do, and what effect the much higher pressure will have is another question.

Or perhaps singing dunes are unique to Earth, and found nowhere else in the Solar System. Currently, it’s impossible to say. Somehow, I doubt it’s a question we’ll be able to answer anytime soon.

martian-sand

Images:
Sand Dunes in the Altyn-Emel National Park, Kazakhstan – © Jonas Satkauskas
The El Dorado Ripple Field, photographed by NASA Spirit
Sand dunes in Olympia Undae, from NASA MRO
Martian sand, examined by the Curiosity Rover

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Antarctica is Melting

Apparently, yesterday was the warmest February day in the Northern hemisphere since records began over 100 years ago. The worst part is that this comes as no surprise in the slightest to anyone who’s been paying attention.

The British Antarctic Survey recently released an aerial video of a crack in the Larsen C ice shelf in Antarctica. The crack is currently 175 km long and nearly 500 m wide, and will ultimately cause an iceberg the size of a small country to break off and float away into the sea.

Meanwhile, politicians bicker, continue to deny climate change is even happening, and forcibly run oil pipes through lands owned by Native Americans. In short, we’re all in trouble.

The mechanism here is incredibly simple, and can be explained with these three gifs, created by meteorologist Ed Hawkins. Firstly, this one.

spiral-co2

This shows increasing atmospheric CO₂ concentration in parts per million (ppm). As is abundantly clear, since the 1960s, the amount of CO₂ in the atmosphere has increased substantially.

CO₂ is a strong greenhouse gas and is responsible for quite a lot of the warmth absorbed by Earth’s atmosphere. If you want an example of how good CO₂ is at absorbing heat and warming up a planet, well. Just take a look at Venus.

The result of this steady increase in CO₂ is a similarly steady increase in Earth’s overall temperature.

spiral-t

As you can see from this image, Earth’s average temperature is nearly 1.5°C above where it’s supposed to be. That may not sound like a lot, but it’s worth remembering that a change of 1.5°C can mean the difference between ice and not ice.

It’s important to remember here that this is about the planet as a whole. The effects on weather patterns locally are many and varied, and the effects can be entirely unpredictable. By which I mean, just because it’s a cold day outside where you are does not mean the planet is not warming. In the exact same way that just because you spilled a glass of water on the floor does not mean your entire house is flooding.

As any schoolchild knows, if you warm up ice, it melts. So…

spiral-ice

This shows the volume of sea ice in the Arctic, and make no mistake, there is no logical reason why the Antarctic should be any different. As should be painfully apparent, the amount of sea ice has dropped markedly over the past 40 or so years.

The thing is that yes, if things do not change, these graphs will reach their ultimate and frightening conclusions. We will end up living on an overheating little planet, heavy with carbon dioxide, and with no sea ice. When that ice melts, it will ultimately all go into the sea, and the sea will rise.

If this doesn’t sound like the kind of world you want to live in, then you should do something. Campaign. Protest. Call your politicians. Walk somewhere instead of driving. Fit your house with solar panels. Because we need to do something about all of this while we still have that option.

Otherwise, consider investing in a wetsuit. Like whoever wrote this.

global-warming-graffiti

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Earth-like?

In the world of exoplanets, Earth-like planets are what everyone’s most excited over. And for good reason. It sure would be great if we could get a close look at one, don’t you think?

I mean, we all grew up watching things like Star Trek which, obviously, is full of Earth like planets. Many of which look suspiciously like Southern California. Unfortunately, the chances of an actual exoplanet being like that are really quite unlikely (albeit impossible to predict), no matter how much you might want to battle a giant lizard. The thing is, going by the definitions the exoplanet hunters use, there’s an awfully convenient Earth-like planet right nearby. In fact, it’s actually the closest planet to Earth. Its name is Venus.

slice-of-venusIt feels a bit like we, as a species, haven’t quite forgiven Venus for not being the idyllic paradise planet that the sci-fi writers used to love telling us about. Or at least for not being a swampy dinosaurland.

No, sadly everything that we’ve discovered about Venus seems to be given by people as reasons not to go there. Just imagine if everything about you was considered a good reason not to visit? Besides, while exploring Venus is admittedly not as easy as exploring Mars, there aren’t any difficulties which are insurmountable.

Human technology has progressed greatly since the old Soviet Venera landers. Moreover, we now know what kind of conditions we’ll need our technology to stand up to, if we try sending robots to Venus.

Sulfuric acid? No problem. We can use high grade ceramics and fluorinated polymers which are resistant to acid attack.

High pressure? Venus has a surface pressure of about 9.1 megapascals, and we have deep sea submersibles which can comfortably survive ten times that much.

Furnace-like temperatures? Sure, most human made electronics use semiconductors which can’t function above 250°C, but we know how to construct electronics that can.

Hah! Your move, Venus!

Seriously though, Venus is tragically underexplored. It’s actually the most visited other planet in the Solar System, but sadly, that’s purely because it’s a convenient way to get a gravitational slingshot before continuing to go somewhere else. NASA doesn’t seem to want to touch Venus with a proverbial barge pole, having not sent any spacecraft there since Magellan in 1989. Since then, there have only been two craft sent specifically to study Venus – ESA’s Venus Express, and JAXA’s Akatsuki. Though ISRO are considering sending a craft that way.

It’s a pity, really. Because while exoplanet astronomers are busily finding Earth-like planets, our only real criteria defining them as “Earth-like” are that they are of a similar mass and equilibrium temperature to Earth. By that definition, Venus is most definitely an Earth-like planet. Which means we have two Earth-like planets which we can study up close, characterise, try to understand, and ultimately use in making predictions about exoplanets. And right now, we have no way of knowing if the planets we find elsewhere are going to be more like Earth, more like Venus, or altogether different. For all we know, the planets we’re discovering may actually be Venus-like, with genuinely Earth-like planets being an oddity.

With all this in mind, you’d think it might be a good idea to spend some time studying the only other Earth-like planet we’ll be able to actually visit in the near future.

I’m just saying!

salty-venus

It’s worth pointing out that by equilibrium temperature, I mean the temperature predicted for an object without an atmosphere. Equilibrium temperatures of Venus and Earth are roughly 260 K (-13°C) and 255 K (-18°C) respectively, which really does go to show what a huge difference a planet’s atmosphere can make.

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Model Planets

As I pointed out yesterday, the recently announced TRAPPIST-1 system is tiny. The little star itself is barely larger than Jupiter. But what about the system as a whole?

So I made a model. Behold!

model-planet-systems-screen1

This image shows all sizes to scale with each other and all distances to scale with each other, but not sizes to scale with distances (I’ve reduced the distances by 10x). It’s easier to display that way. You can see a larger version by clicking here, if you like.

So here are a few interesting things which you can pick out. The TRAPPIST-1 system is a similar size to the Proxima system. It’s a lot larger than the Kepler-42 system which is, to my knowledge, one of the most compact star systems we know of. It’s also about 3 times as large as the main Jupiter system, where Juno is currently doing its thing – but I also marked Juno’s apojove. This is the furthest point in Juno’s orbit around Jupiter. Turns out, a similar orbit around TRAPPIST-1 would give a great view of the whole star system!

If anyone does live on any of the TRAPPIST-1 planets, I must say I envy them. Exploring the rest of their solar system would be easy compared to the task we have here in ours.

Incidentally, I did make an image with everything to scale, and you can see it if you click here. Needless to say, trying to display that on this website was… not feasible.

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A tiny red sun with a sky full of planets!

Imagine if your sun was tiny and red. Imagine if you could see other planets in the sky as large as the moon appears from Earth. Imagine if all the planets orbiting your star were roughly the same size as the planet you lived on. Now imagine that the world you’re imagining really exists and is in orbit around a star called TRAPPIST-1.

This was the news shared by NASA this afternoon (depending where you are) in a press conference – a preprint of the accompanying journal paper can be downloaded here. Honestly, this is pretty big news. Firstly, we’ve never seen so many terrestrial planets crowded together in a single star system before. They are all roughly Earth sized, and three of them appear to be in the star’s habitable zone. What a find! And it’s only 39.1 light years away. Which is right in our back yard, astronomically speaking!

I’m not going to rattle off the same thing in the press release, because it’s busily being talked about all across the internet right now. But I will do a little musing and point out a few cool things.

trappist-1-size-comparison

One interesting thing is that TRAPPIST-1 is tiny. Really tiny! It’s a class M8V ultracool red dwarf, which really is about as small as a star can get while still being a star. Much smaller and it wouldn’t be able to even fuse hydrogen. I’ve put it side by side with a few other familiar celestial objects in this image. As you can see, it’s a little bigger than Jupiter. It’s actually roughly the same size as HD189733b, a much studied hot jupiter, and noticeably smaller than Proxima, our friendly neighbourhood red dwarf. Lalande 21185 is on the larger end of the scale of red dwarfs, and is also one of the few you can actually see in the night sky (though you’ll need a dark sky to find it).

Ultracool red dwarfs really are tiny, but they’re also extremely long lived. Quietly burning stellar embers which exemplify the old saying that slow and steady wins the race. Because these little stars don’t burn their fuel too quickly, and because they’re low enough in mass to be fully convective, they can burn for trillions of years. Long after the Sun exhausts the fuel in its core, flares into a red giant and then cools silently in the darkness, TRAPPIST-1 will still be burning, providing warmth for it’s little planetary entourage.

Not much warmth, mind you. TRAPPIST-1’s handful of planets are huddling around their parent star as if it were campfire on a cold night. The entire star system would fit inside Mercury’s orbit and still have cavernous amounts of room to spare. So close are those planets, that they have years which pass by in mere Earth days. The shortest has a year which is just 1.5 Earth days long. The longest year length in the system is still less than a month.

aureliaOf course, I say Earth days, because these planets don’t have days as such. They’re so close to their parent star that they’re certain to be tidally locked. The gravitational forces are sufficiently different that they cannot rotate at all. One side constantly faces the tiny red sun in the sky, and the other side constantly faces outwards towards the cold night. It’s quite likely that the night sides of these planets may be frozen in a permanent winter night, never gaining enough warmth to thaw. Half a planet of permanent Antarctica.

On the side of the planet facing the star, it’s hard to say what might be. Some models suggest constant storms, driven by unflinching starlight. But in between the two extremes, planets like these could be quite comfortable.

We have no idea what these planets may be like. But with a star that can keep them warm for trillions of years, if there’s even a remote possibility of life forming on any one of them, it’ll have all the time in the Universe to do it. Life can evolve at a leisurely pace, nurtured under a sun which will outlive most others in the galaxy. Of course, this is largely speculative. We don’t have the first idea how long a planet can continue to support life. For all we know, these planets don’t even have atmospheres. But the drive to find out is exciting.

I’ve written about red dwarf planets on this blog several times before, as it happens. In 2008, I speculated about red dwarfs carrying miniature solar systems, and the possibility of life on them. In 2009, I wrote about the idea that red dwarf stars can have a very different chemistry to yellow stars like our own, and what implications there may be for astrobiology. And in 2010, I gleefully wrote about one of the first exoplanets to be found inside the habitable zone of a red dwarf. I revisited several of these ideas in 2013 in a summary article. Honestly, this is one of the best things about keeping track of these things for so long. After a while, you get to see things come to fruition. You see which ideas were right, which were wrong, and which remain uncertain.

Anyway, there’s a lot to think about with this discovery. I have a feeling I may be writing about this tiny star system again in the near future. In the meantime, here’s an image of the planets we’ve just discovered. If you want a better view, you should click to embiggen it.

trappist-1-planets

Images:
Stellar size comparison – created by me, including images from Galileo and SOHO
Aurelia from the National Geographic series Alien Worlds
NASA JPL visualisation of the TRAPPIST-1 planets

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A City on Mars

On Valentine’s Day, Sheikh Mohammed bin Rashid Al Maktoum, Vice President and Prime Minister of the UAE and Emir of Dubai, made an official statement about an audacious plan. The plan, officially dubbed Mars 2117, is to construct a small, functioning city on Mars within the next 100 years.

And he gave a statement on Twitter, in 6 brief tweets. Because, apparently, that’s just the kind of world we live in now.

I always admire an audacious plan.

The thing is, the UAE is currently an outsider in the world of space travel. While NASA is the kindly old grandfather who used to do amazing things and still does when he can remember where he left his wallet, UAE is more like the starry eyed little child who stares out of the window and wishes she could go to Mars someday. Something I’m sure many of us can relate to.

uae-mars-hopeEven so, the UAE is home to its own fledgling space agency, formed in 2014, with current plans to launch its first mission to our neighbouring planet. The Hope spacecraft is scheduled to arrive in orbit around Mars in 2021, coinciding with the 50th anniversary of the formation of the UAE.

But the question which I’ve seen a lot of discussions focus on is simple. With so little experience in spaceflight, does the UAE stand any chance of actually accomplishing a feat like this? They do plan to include an international team of scientists, so assuming they choose their employees well, there should be at least some knowledge and experience to go around.

And all too often, one of the biggest problems with space travel is funding – or a lack thereof. NASA, as a shining example, has been plagued by repeated setbacks in recent years due to a simple lack of funding. NASA’s ill-fated Constellation program, for example, was supposed to herald a return to the surface of the Moon. At least that was the plan when it was proposed in 2005. Due to politics and money, it was cancelled in 2009. Plans from Constellation were salvaged for the Orion spacecraft which was proposed in 2011, development for which is ongoing.

jerrie-cobb-mercuryConsider as well, that the Apollo program only took 8 years from its inception in 1961 to Neil Armstrong’s first steps on the Moon in 1969. NASA itself was formed in 1958, launching the Mercury program shortly afterwards.

The Mercury capsule, infamous for being little more than a tin can with an astronaut inside, made its first uncrewed flight in 1959, and its first crewed flight in 1961. In 1962, it made John Glen the first of NASA’s astronauts to make an orbit of planet Earth.

In other words, NASA went from having no orbital spaceflight experience at all to sending humans to the Moon in just 11 years. Of course, this was the Cold War. I could make valiant statements about how all it took them was willpower, a sense of purpose, and sufficient amounts of money… But more candidly this was about competing with the Soviet Union, and one of the only times in history when a country has put the level of resources usually reserved for war towards other purposes.

klaus-burgle-marsAll the same, it served to show us, as a species, what we’re capable of when we actually put our minds to it. It also left us full of dreams and ambitions which have yet to be realised. Despite 60 years of artwork envisioning cities on Mars and astronauts visiting Jupiter, none of this has been accomplished. I remember dreamily looking at pictures like those in books when I was just a kid, wondering when they might finally become reality.

Romantic visions aside, Sheikh Mohammed and his predecessor Sheikh Maktoum have shown talent in conceptualising ambitious projects and bringing them to fruition – The Palm Islands and the Burj Khalifa being notable examples. Dubai itself has made a dramatic transformation from a fading fishing town to a prosperous international city in a remarkably short time. The Al-Maktoum dynasty certainly has no shortage of money and the Sheikhs seem unlikely to give up on a project once they’ve set their minds to it.

The bottom line is, do I think that Sheikh Mohammed stands a chance at constructing the first human city on Mars? In only 100 years? Yes I do. NASA made a colossal accomplishment in space travel with only 11 years of hard work. Even if they only worked half as hard as they did then, if they’d simply been given enough money to continue, there would probably be humans on Mars right now.

Ultimately, I think what we need to lift our species off just one planet is simple. We need people who aren’t afraid to keep spending money working towards it. We need sustained effort that doesn’t vanish after only 4 years. We need to not be afraid to take a few necessary risks.

And we need to remember that it wasn’t actually very long ago that NASA had no experience in spaceflight either. That fact did not stop them from trying, and it should not stop others either.

mars-valley-foothills

In 2016, NASA was given a budget of $19.3 billion. Which seems like a lot until you realise that the US military was given a budget of $596 billion, which accounts for over a third of the total world military budget. I’m presenting these facts without comment.
I originally wrote here that the first US “astronauts” to fly above the Kármán line made their flights in 1959 in the experimental X-15 aircraft. Turns out, I was mistaken and that actually there were no X-15 flights above the Kármán line until after Glenn made his orbits of Earth in 1962! In any case, if you’re interested, there’s still a transcript of an interview with Neil Armstrong about the X-15 online to read.
And as Robert Heinlein once said, “The Earth is just too small and fragile a basket for the human race to keep all its eggs in.”

Images (excluding those in tweets):
UAE Space Agency Mars Hope – artist’s impression
Aviator Jerrie Cobb standing next to a NASA Mercury capsule
Artwork by Klaus Bürgle of a city on Mars
Panorama of martian hills taken by NASA Curiosity

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So many planets…

I love planets, don’t you? Being all… round. With their… Atmospheres. Very gaseous. What’s not to love? Actually, as I’m writing this, there are 3449 confirmed planets in our galaxy. 544 of the planetary systems we’ve seen are multi-planet systems. And our galaxy is so vast, we’re barely even scratching the surface!

To give you some idea of the speed with which most of these planets have been discovered, here’s a nicely constructed animation, courtesy of exoplanet hunter Hugh Osborn, showing 300 years of planetary discoveries.

hugho2-planets

Unfortunately, the resized gif may make the text a little small, so click the image to see a glorious full size version. The different detection techniques are in different colours. Green are detections using the radial velocity method, red with transits, yellow through gravitational microlensing events, and the cyan points were found by direct imaging. The blue spots show the planets known in our own solar system. If you watch carefully near the lowest end of the mass scale, you’ll notice that this doesn’t stay constant – both Ceres and Pluto have been considered planets and then not planets at different points in history.

You may also notice that the final number on this image is 2954, not 3449. That’s because we’re discovering exoplanets so rapidly, it’s difficult to keep up. Turns out, all the sci-fi I used to enjoy as a kid was right. Our galaxy really is full of planets!

Pretty cool, huh?

Full credit for this image goes to Hugh Osborn.
So if you like it, then you should go and buy him shiny objects.
Yes.

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8 Things About Uranium

As is fairly obvious, the recently inaugurated President of the USA, Donald Trump, has no idea what uranium is. To quote him directly:

“You know what uranium is, right? S’thing called nuclear weapons and other things and lots of… things are done with uranium including some BAD things.”
Donald Trump

Very… astute. And eloquently put. Reminded me of something I’d seen before. Needless to say, “s’thing called nuclear weapons and other things and lots of… things” is not a particularly good description of uranium. Despite its understandably bad reputation, it’s quite an interesting element, for a number of reasons. So for anyone else who’s a little hazy on what exactly uranium is, here are 8 things about it.

1. Uranium makes excellent fuel

Fission energy is the thing everyone will know about uranium. Being unstable and consequently radioactive, uranium’s atomic nuclei tend to fall apart when bombarded with neutrons, releasing prodigous amounts of energy. The actual physics behind this were first understood in 1939 by Lise Meitner, who also realised the dangerous potential behind it.

xkcd-energy-densityWhen discussing fuels, many scientists talk about energy density – which just means how much energy any given fuel contains, per kilogram. It’s often measured in megajoules per kilogram (MJ/kg). Atomic nuclei contain a massive amount of energy, and nuclei which can be split are the densest source of usable energy of any fuel, by quite a long way.

The petrol which you put in your car has an energy density of 46.4 MJ/kg. Uranium, on the other hand, contains 79,390,000 MJ/kg. That’s 1.7 million times as much energy! This xkcd comic explains that rather nicely.

2. Uranium has several isotopes

Isotopes are different forms of any chemical element. An element’s identity is defined by it’s protons but the number of neutrons it has can vary, so any atomic nucleus with 92 protons will always be uranium, with the rest of the mass being made up by neutrons. Most uranium atoms have 146 neutrons, making uranium 238 (or U-238 for short).

U-238 is relatively stable, with a half life of 4.468 billion years (I’ll come back to that later) and accounts for over 99% of the uranium on our planet. The other most common isotopes are U-234 and U-235. The one to be aware of here is U-235 which is “fissile”, meaning that it can sustain a chain reaction and can therefore be used in nuclear reactors to generate energy. In fact, U-235 is the only fissile atomic nucleus to be found naturally in any significant amount.

3. Uranium contains stored energy from a supernova

crab-nebula-sliceThis one’s pretty cool. Uranium is the heaviest element to occur naturally in the universe (unless you count the stuff that happens in neutron stars, but they’re weird). Atomic nuclei have what we call a valley of stability. Elements of a certain mass range are the most stable, and natural nuclear processes occurring in unstable nuclei are constantly trying to move towards that mass range. At the bottom of this valley is Iron-56.

Much heavier than this, and elements are radioactive. The nuclei shed fragments as alpha particles to try and get back to a more stable place on the periodic table. The heaviest naturally occurring elements can only be created in supernovae.

Any star is in a constant battle between gravity pushing everything inwards and the energy created by nuclear fusion pushing everything outwards. In the most massive stars, fusion in the star’s core creates heavier and heavier elements. The process keeps going because fusion gives out more energy than it takes in. That is, until iron is formed

Iron is the first element which needs more energy to fuse than it gives back. Once the star has no choice but to fuse iron, gravity wins the fight. Rapidly. The star’s entire mass starts to fall inwards, compacting the material in the star’s core. The outer layers, full of unreacted material, continue to rush in and a gargantuan flurry of fusion creates an immense explosion. The supernova that results is bright enough to be seen halfway across the universe.

The mindbending temperatures and pressures in supernovae create a huge array of heavy but unstable elements. Some fall apart nearly instantly, existing for millionths of a second. But the more stable ones persist. The energy which forged them was the energy released by an exploding star, which they’ll slowly release over millions, or even billions of years.

4. Uranium can help us work out the age of minerals

Uranium dating might be a good name for a website where you can meet singles, but it’s actually the name of a technique used by geologists in a study known as geochronology.

ancient-zirconAs I said before, U-238 has a half life of 4.468 billion years. When it does decay, it fragments into a chain of other isotopes, one of which is Thorium-230. Essentially, the older a rock is, the more uranium will have transmuted into thorium, and the ratio of the two can be used to find the age of the rock you’re looking at. This is known as uranium-thorium dating and can determine ages up to 500,000 years.

Older and more refined is uranium-lead dating. Lead-206 is the ultimate product of uranium decay, and looking at the ratio of the two in any mineral, geologists can tell you the age of that mineral, if anywhere from 1 million up to over 4.5 billion years, with precision of around 0.1-1%.  Given that Earth itself is only 4.543 billion years old, this lets us identify some of the oldest rocks our planet has. Like the blue crystal fragment in that picture there which, at 4.4 billion years old, is perhaps the oldest mineral ever found.

5. Nuclear reactors aren’t all created by humans

oklo-fossil-reactorSince our species discovered nuclear chain reactions, nuclear power has been a significant, albeit controversial, source of energy. It’s typically much cleaner than using coal, but if catastrophic circumstances occur, the end result is dramatically worse.

The interesting thing is that nuclear power is not new. In the small country of Gabon, on the west coast of Africa, are the Oklo fossil reactors. Mineral deposits showing what used to be a total of 16 nuclear reactors which occurred entirely naturally (one of which is shown here in this photograph). U-235 has a half life of roughly 704 million years. There’s not much around today, but 1.7 billion years ago about 3% of uranium on Earth was U-235. With the right conditions, this is enough U-235 to sustain a nuclear reaction to generate energy – which is exactly what happened in the Oklo fossil reactors.

They didn’t generate much energy, but the nuclear reactions in them were self-sustaining for a few hundred thousand years.

6. We’ve known about uranium for over 200 years

uraniteUranium was first discovered in 1789 in a mineral called pitchblende. Now more commonly known as uranite, this mineral is actually uranium oxide – mostly UO₂, but with some amounts of U₃O₈.

It’s a black mineral, as its name might imply, and given uranium’s tendency to decay and spontaneously transmute into other substances, it contains a host of other elements too, including thorium, radium, promethium, and the curious and ultra-rare technetium. You’ll also find lead, the end product of uranium decay, and helium from alpha particles. In fact, after helium was discovered in the spectrum of the Sun, it was first observed here on Earth in uranite.

7. It’s been used in glassware

Uranium glass is glass made with uranium oxides. It has an unusual lime green colour and used to be quite popular. It goes by a number of different names, including vaseline glass, Burmese glass, and custard glass.

While typically made with about 2% uranium, there were some pieces of uranium glass made in the 20th century containing up to 25% uranium! Uranium glass only fell out of fashion due to the cold war, when uranium became significantly more difficult to buy.

 In fact, using uranium in glassware dates back as far as the Ancient Romans. Nearly 2000 years ago, it was used in ceramic glazes to give a yellow colour, and glass containing 1% uranium was discovered in a Roman villa in Naples.

Another fun thing is that uranium actually fluoresces. Shine a UV light on some uranium glass and it’ll glow with an eerie green colour not unlike comic book depictions of radioactive materials.

uranium-glassware

8. Uranium has found a few other surprising uses too

uranium-denturesOne interesting use which people have found for uranium was actually in early photographic chemicals. Uranium nitrate in particular, was used as a toner to adjust the final colour of photographic prints.

Other odd uses for uranium in the past have included lamp filaments for stage lighting, as stains and dyes for wood and leather,  and in mordants for fixing dyes in wool and silk. It was also once used in dentures, to improve their appearance! I promise I’m not making this up.

In more modern times, the organo-uranium compounds uranyl acetate and uranyl formate have been used as stains in electron microscopy, where they can increase the contrast in ultrathin sections being studied, and for small, isolated subjects like viruses and organelles.

Posted in astronomy, chemistry | Tagged , | 3 Comments

Tarry Tarry Night

Ceres is a fascinating little world. The Empress of Asteroids. The little planet that couldn’t. A tiny, primordial remnant from the early days of the solar system, full of answers to questions, and new questions to be answered. And now, carbonaceous material has been discovered there! I’m quite enamoured with Ceres, as I am with discussions about astrobiology. However, that doesn’t change one big fact – discussions of life on Ceres are vastly premature.

It's an funny old world...In a feeding frenzy of the kind which should surprise absolutely no one who understands how the news media works, the past several hours have seen numerous reports from sources across the globe about how Ceres “contains the building blocks of life.”

Of course, this is something we’re always excited about. Another object in the solar system added to the list of things which might support life would be quite a discovery. That said, I’m loath to be the burster of bubbles but, to me, making claims like that seems to be quite an excessive leap in reasoning. It’s far too early to be able to speculate.

The thing is, chemically speaking, what we’ve found on Ceres is about as far from being the building blocks of life as a bucket of molten plastic is from being a set of Lego bricks. But that doesn’t make it any less interesting.

NASA’s Dawn spacecraft has been busily surveying the surface of Ceres with spectrometers to see what delicious molecules it can find lurking on the surface. I haven’t found a copy of the journal paper to read yet, but as far as I can tell, Dawn found alkanes. A kind of hydrocarbon made up of long chains – shorter chains are found in things like petrol, longer chains are found in things like candle wax. New Scientist lays the facts out quite cleanly:

The identity of the tar-like minerals can’t be pinned down precisely, but their mineral fingerprints match the make-up of kerite or asphaltite. The constituents and concentrations of these organic materials suggest that it’s unlikely they came to Ceres from another planetary body.

Now for a start, tar-like substances make up a huge amount of the carbon-containing material we’ve seen on other planets. It’s either that or carbon dioxide, typically. Tholin, for instance, is a tarry substance which is found everywhere from Titan to comets. But what we have here are minerals. Asphaltite is bitumen impregnated rock and kerite is a rubbery material made from bitumen and sulfur (I’m not a geologist, so if I’m wrong here please do correct me). Bitumen is the heavy tarry stuff to make roads – American English speakers probably have instantly recognised the word asphalt.

No, we did not find alien roads either. No matter how cool that would be.

At least it'll be easy to build a car park on CeresAdmittedly, this is less exciting than “the building blocks of life” for most people. Though bitumen does contain a fairly interesting collection of organic compounds. Mostly saturated hydrocarbon chains, but with an eclectic assortment of aromatic hydrocarbons and heterocyclic compounds. And given that things like DNA do contain heterocyclic aromatics, yes these are what we could consider to be prebiotic molecules – in other words, while we have no idea how life formed in the first place, we think that if you take molecules like these and leave them in the right place for a few million years, life might happen.

There is mounting evidence that the clays and carbonate minerals found on Ceres were processed in warm water at some point in the distant past. They’ve certainly been chemically altered by water – hydrated minerals actually contain chemically bound water molecules. And yes, this does suggest that the bitumens we’ve seen on Ceres may have been processed the same way. Given how little we know about the way life formed, it’s impossible to say what may have formed on Ceres, or how long it was simmering. Unfortunately, we need more evidence before we can place too much confidence in our speculations. It’s still a long stretch from prebiotic molecules to Cerean microbes in the same way that finding iron ore in the ground is not evidence of cars.

The fact that Ceres is full of carbonaceous mineral goo is still rather interesting. In a sense, I suppose it’s a gargantuan carbonaceous chondrite meteor. Chondritic meteors have long been known to contain prebiotic molecules. Even amino acids, though these have not yet been seen on Ceres (at least, to my knowledge). So an interesting fact we can learn here is that the solar system appears to be full of prebiotic molecules. That does suggest the inevitability of life, given the right conditions.

The biggest news here, to me, is that Ceres is far from being just a boring round rock. It’s a complex little world, with deposits of various raw materials. We’ve found mineral deposits, water ice, and now hydrocarbon deposits.

This is also the first time carbonaceous material like this has been found on an object in the asteroid belt, but it suggests we may be able to find more elsewhere. This kind of thing is very promising if we’re looking at the future potential for constructing habitats in the asteroid belt, or mining asteroids for resources – two things which may ultimately be a good idea if we’d like to ensure the continued survival of our species.

The sweet spot where they found all this carbonaceous material was Ernutet crater, which seems to have an abundance of it.

Have to wonder what else is waiting on Ceres for us to find

Personally, I’d love it if they were to find some actual evidence of life on Ceres. That would be wonderful, wouldn’t it? But I’m not overly fond of jumping the gun. I’m sure talking about life gets news pages a lot more clicks than talking about minerals, so I can see why this happens, but in a way that’s a little sad. Discoveries should be interesting because of what they are, not because of what they aren’t yet.

Interestingly though, while we haven’t found life just yet, technically we did strike oil. Bitumens are made of very similar stuff to tar and crude oil found here on Earth – though the stuff on Ceres didn’t come from long dead animals. Being essentially a big collection of heavy petrochemicals, bituments can be refined into synthetic crude oil. Whether telling the US government that there’s oil on Ceres will encourage them to send people there remains to be seen.

Posted in astrobiology, space | Tagged | 1 Comment

Save the Planet

It is my informed opinion that Donald Trump, with his government of the USA, is one of the greatest threats to the continued survival of our species. Unfortunately, the reason is climate change – and simply upon hearing that, some people are going to stop reading this.

our-pale-blue-dot

Still with me? Thanks. I appreciate it. Look, I’m going to be straight with you. I know you’re sick of hearing about climate change – but how do you think I feel? It’s 2017 for Foxe sake! It’s the 21st century! I literally grew up hearing phrases like “greenhouse effect”, “global warming”, and “climate change”. The fact that this is happening is a truth I’ve known for my entire life. Scientists have known about since long before I was born. We’ve made some progress, certainly, but not enough. Things are still getting worse. I have to wonder why I’m still needing to say all of this.

After decades, politicians finally started paying attention and telling people, and the first thing that people did was to start saying “No, I don’t believe you, I know better!” for some reason. There aren’t many professions which have to deal with someone telling you how to do your own job. You don’t argue with an electrician about the voltage of your house. You don’t argue with your mechanic about the reason why your car broke down. But apparently, people just love to argue about scientists about peer reviewed scientific research.

a-crack-in-the-worldOur planet is at a tipping point. 2016 was the warmest year on record. Over the past 400,000 years, carbon dioxide levels had never been higher than 300 ppm. Earth’s atmosphere currently contains 404.48 ppm of CO₂. Earth’s polar ice caps are melting. Quietly and without even realising, we are destroying Antarctica and its ice shelves. One of those shelves currently has a gigantic crack in it (in the image to the right here), which is threatening to cause a chunk of ice the size of a small country to break off and float away into the sea. As anyone who likes ice in their drinks may realise, it will melt. When it does, our sea levels will rise.

Consequently, our already overcrowded planet will lose vital coastal habitats. I’m not just talking about wildlife – Miami is going to be submerged into the Atlantic Ocean, together with most of Florida. Meanwhile the haywire weather we’ve been seeing over the past few years is set to intensify. Expect the wildfires in California to get worse as the global temperature rises. Expect tropical storms to intensify as climate systems are disrupted and become more unpredictable. Expect winters in the Northern hemisphere to get colder as reduced temperature gradients between the polar and equatorial regions cause weakened air currents and allow Earth’s polar vortices to bring more snow to the Sahara.

Honestly, I don’t know how many “once in a lifetime” weather events need to happen over the course of 5 years for people to start paying attention, but I’ve lost count of how many we’ve had now.

2013-co2-by-countrySo why is Trump so dangerous? Well, the USA is the second biggest producer of greenhouse gas emissions. The only country worse in China. Interestingly, China’s CO₂ emissions are falling as the country moves away from using coal.

Meanwhile, Trump intends to “embrace the shale oil and gas revolution” and is “committed to… reviving America’s coal industry“. Which, from a climate perspective, is horrifying. This is the exact opposite of what we need to be doing if we actually want our planet to remain habitable to humans.

America has already spent far too much time sitting on its hands and pretending everything is fine under the Bush Administration, who surreptitiously hid clear evidence of global warming from the world. By which I mean these satellite images showing obvious differences in sea ice off Alaska. These images, in fact:

alaska-sea-ice

With Trump, we’re not just in for more of the same. It’s going to get worse. Trump is a demagogue who’s shown every indication that he’s only in this for himself. He’s hired a team of billionaire supervillains to run America, complete with ties to Russian oil companies. There’s no reason to believe that they won’t chase profits even if they happen to ruin the planet in the process.

The worst part is that the Trump Administration is not just denying climate change – it seems to be actively censoring the discussion of it. Employees of the Environment Protection Agency (EPA) have been ordered to remove pages from the web, and researchers there are busily safeguarding their data – they have been for weeks now. Their grant programs are also being frozen, and they’re being instructed not to talk about it.

The most recent affront was the Badlands National Park twitter feed. 2 days ago, whoever manages the account tweeted several climate change facts, such as this one:

badlands-tweet

Shortly afterwards, all of these were deleted, apparently by instruction from someone at a higher level. And that’s horrifying. Speaking the objective truth should never be an act of courage or defiance. A society in which it is, is going down a very dark path indeed.

Trump is making his intentions clear. He is staging an assault on objective truth. He is actively hampering science and fact from reaching the public. He seems to be attempting to wage a war on science. And in doing so, he threatens to destroy the environment of the planet we’re all living on – and it simply cannot take much more.

This is an affront to all of us. Every human living on this planet. Not to mention the billions of other species we share it with. And I, for one, don’t think we should all just sit back and let an angry orange man with tiny hands ruin our planet for us.

Posted in Environment | Tagged | 1 Comment