The Universe in 101 words: Where's the oldest water?

Sea water is old – it arrived as part of the planetesimals that formed the Earth.

But it isn’t the oldest water there is.

In 1998 a meteorite landed in Texas which was once part of a protoplanet - one warm enough for water to flow beneath it’s surface. The water left behind purple salt crystals and, inside them, some of that 5 billion year old water was trapped. When the meteorite was studied, the trapped water was found – and so we know what those alien waters were like, even though they dried up millions of years before Earth was born. 

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Above: The trapped bubbles of water, as imaged by microscope.

The Universe in 101 words: Where's the loneliest place in the Universe?

Above: A map of part of the web of galaxies that fills our Universe.

If it seems far to our nearest stellar neighbour, Proxima Centauri, remember: Some star systems wander between galaxies, millions of light years from anything. The loneliest are probably somewhere in the Bootes void, a huge gap in the web of galaxies that spans our universe. 

The sky of a world in such a void would be very strange: Devoid of stars, but against the darkness distant galaxies would be visible. The dim glows of spiral arms and halos would surround their bright, star like, cores, covering as much sky as a full moon, even from millions of light years distance… 
 

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Above: The Amdromeda galaxy, which is 2.5 million light years from Earth - but so big it's faint spiral arms cover as much of our sky as a full Moon.

What if I drop Boris Johnson into Jupiter's atmosphere?

Before the police come knocking on my door, I should be clear: This is not a bizarre death threat against the former London mayor. I'm going to sketch out what a probe or astronaut falling into Jupiter's incredible atmosphere would see and making a well known person the star of that gives it a certain je ne sais quoi.

That's my story. I'm sticking to it. Officers.

You'll be fine Boris. Well. No, you wont.

So, beyond the asteroid belt lies the biggest giant planet, Jupiter - a huge planet the size of a small star. Although only 1/13th the weight of the smallest things that might be called stars, it’s made mostly out of the gasses hydrogen and helium, like a star. But, because it lacks a star's searing heat, some of the trace components of it's atmosphere - like water, ammonia, and methane - can condense into cloud droplets and ice particles, giving Jupiter complex and colourful cloud systems.

Oooh, colours.

If we were to drop Boris Johnson, former mayor of London into that churning atmosphere – what would he experience? 

Being the inventive sadists we are (or at least, I am ) let’s imagine we can equip him with a suit that will keep him alive as long as possible. 

At first the fall will be silent, and seem almost motionless – we’re starting Boris a thousand kilometres above the level of Jupiter that has an air pressure of one Earth atmosphere. Here the atmosphere is thin to the point of being not much better than space. The gravity is two and a half times that of Earth but, in freefall, Boris won’t feel that. He will, however, easily exceed the speed of sound on this portion of is fall.

A bit better than this, at least.

That is, until he gets deeper into the outer layers of the atmosphere. As the atmospheric density climbs, reaching and passing a tenth of an Earth atmosphere (50 km above the 1 atmosphere level), Boris will slow, until he reaches a stable terminal velocity. His parachute opens and suddenly his plummet becomes a gentle drift.

Ahem. Relatively gentle  The wind speeds here, in Jupiter's upper atmosphere, are easily over 300 kilometres per hour. At the one tenth of an atmosphere level the air is too thin to carry much force, but as the astronaut drops and the pressure rises the winds increase in power, battering the politician turned astronaut savagely. To get a rough idea of what it'd be like, follow this link to the tale of a fighter pilot who had to eject from his plane inside a thundercloud.
 
At pressure levels of 1-4 atmosphere’s the wind speed increases, then levels off at over 610 kilometres per hour. The temperature has been bitterly cold up to this point – over 150 degrees Celsius blow freezing – but as our intrepid ex-mayor is finding out, once you pass the one atmosphere point it begins to rise. 

The one atmosphere point is also the top of the clouds: They’re about 50 km (31 mi) from top to bottom, and begin with hazes of ice crystals and organic compounds. They’re hardly visible to Boris, but they give way to thick white ammonia ice clouds, that block out the light. The thick ammonia ice cloud layer gives way to a layer of ammonium hydrosulphide droplet clouds (at a pressure of 1 to 2 atmospheres), then a lower layer of water clouds (at 3 to 7 Earth atmospheres) – it probably all takes at least an hour for the parachuting Boris to drop through. 

In the water cloud layer he’ll hear the occasional crack-rumble of huge lightening bolts  - these are infrequent, but thousands of times more powerful than Earth’s.  

Above: Lightening storms on Jupiter, photographed from orbit.

 
There might be something else in the water clouds: Life. Since the discovery of microorganisms that can live inside cloud droplets on Earth, any planet with a layer of water clouds has become a potential home for life.

Of course, given the weather conditions Boris may shortly be making a return to the upper cloud layers, as there are immensely powerful updrafts which occasionally bring water clouds to the upper levels. This could go on for a while - Boris being blown up and down the clouds by the immense winds.

But eventually gravity will win. 

The intrepid Johnson will break through the bottom of the water clouds, and as he does he may be getting pelted by high gravity rain. Because of the high gravity the droplets will fall at a smaller size than on Earth, and travel faster – although the increasingly thickening atmosphere will lower the droplets  velocity, so he needent worry too much. 

The other reason not too worry too much about the high gravity rain is that the temperature is rising rapidly, and the droplets are evaporating even as they fall: It’s 60 or 70 degrees Celsius as he exits the cloud deck. 

Although, as the temperature will only keep rising, he should probably be worrying about that.

Boris is now falling (and slowly cooking) through a world of hazes and mists, with an unbroken ceiling of lightening streaked clouds. They stretch away to a vague horizon that seems much too far away to Boris’s Earth adapted eyes. 

As the air pressure climbs towards ten or twelve atmospheres, the temperature exceeds a hundred degrees Celsius. How long Boris lasts will depend on how good his fictional suit is, but the Galileo space probe, which parachuted into Jupiter's atmosphere, finally gave up at 132 km below the clouds at temperature of 150 degrees Celcius. By that point the probe was entering the layer at which the pressure and temperature were so high the atmosphere became a supercritical fluid – like the atmosphere of Venus it’s too thick here to be called a gas, but doesn’t act like a liquid either. It is however, quite clear – Boris, assuming he's still alive, can see that there’s still a very long way still to fall below him. 

It's nothing but down, all the way down...

By now hours have passed since the former London Mayor began his drop. As falls from grace go it is at least spectacular, and he is entering a truly strange realm. Surrounding Jupiter's core is a vast ocean of 'liquid metallic hydrogen' - a strange, electrically conducting, form of hydrogen that happens under immense pressures.
There’s no definite surface to the liquid hydrogen sea, but Boris is heading into it. There's not much to see here, aside from the very distant flashes of lightening from the cloud deck - it's a long way up to sunlight, and everything here is pitch black. Sadly, neither Boris nor any probe we can currently build will reachthe ocean intact. 

• About another 40 minutes descent after the point where the Galileo probe died any aluminium components of Boris’ protective suit will start to melt. 
• If we built the suit out of titanium it will fare better – after falling into the ever thickening gasses for an astounding 6 and half hours, it would finally give up. 
• Incidentally, since Tony Stark’s Iron man suit is made from a titanium alloy, this is how far it could get – although it’s doubtful any amount of insulation and cooling could keep the occupant from being cooked. 
• The droplets of metal would keep falling for around another two and a half hours, before vapourising. 

By this point Boris' remains are well into the dark liquid metallic hydrogen ocean, well over a thousand kilometers below the relatively friendly cloud layers. The dwindling droplets of the suit have company here, on the last leg of their journey: It’s raining again. The rain drops are made of liquid neon, which is condensing under the bizarre conditions down here, producing a last rain of bright red droplets which fall until the still rising temperatures evaporate them. 

And then our adventurer is totally gone – dissolved into the liquid hydrogen with 75% of Jupiter’s depth still below. In the depths of that ocean very strange things – like massive bergs of crystallised carbon (diamond) are speculated to lurk – but with temperatures climbing to 24,000 degrees Celsius, before the theorised solid core is reached, we may never know...

'Bye Boris...

Above: The roiling, politician eating, lightening filled clouds of Jupiter.

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The Universe in 101 words: Could we see back in time?

One type of time travel that happens daily is seeing into the past: Light’s speed is limited, so the Universe is full of images from distant eras. A few of everyday examples are:

• We see the Moon as it was 1.5 seconds ago. 
• We see the Sun as it was eight minutes ago.
• We stars as they were up to 13 billionyears ago.

So here’s a thought: If we could locate a huge reflective surface 32.5 million light years away*, and focus an incredibly powerful telescope on it, we could see the dinosaurs.

Although re-watching Jurassic Park would be simpler...

*32.5 million yars for the image of Earth to reach it, and 32.5 million years for the light to be reflected back  equals 65 million 

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The Universe in 101 words: What's lightening like on Jupiter?

Above: Jupiter - still owning it.

The biggest lightening storms are found on Jupiter, the biggest planet in our solar system. 

Well, I guess that makes sense. 

Jupiter's bolts are ten times more powerful than terrestrial bolts. With no surface they simply strike within the clouds, like sheet lightening on Earth - so you'd seldom see the whole bolt, just a diffuse flash. They spring from Jupiter's water cloud layer, below its clouds of ammonia. 

Below the clouds the hydrogen atmosphere gets hotter and thicker, becoming an ocean of ‘supercritical fluid’. Over that 'ocean' the clouds form an immense roof, punctuated by the lightening...

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The Universe in 101 words: Could anything live in Venus' clouds?

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Although it's named after the brand of skincare products*, Venus'  clouds would remove your face, not moisturise it – they’re made of sulphuric acid, and punctuated by lightning. 

But that might not stop exotic microbes calling them home: In principle life might use sulphuric acid instead of water, and on Earth some microbes live in cloud droplets. Venus' endless yellow-white cloudscape has mysterious chemical imbalances, and strange UV absorbing pattern in it. 

Could these be signs of microbes floating in the relatively Earth-like layer between the blue sky, acid rain, and scalding surface? We can't say, but unless we explore those clouds...

*Yes, that's a joke. They're actually both named after Venus Williams, who was named after the brand of razors (citation needed).

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What is the Milky Way? And how is pizza involved?

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Given how many people live in and around cities these days, you may not have seen this:

Image courtesy of Stephane Guisard

I mean the Milky Way not the cactus.

The reason why a lot of people won't have seen it (including me - at least for a while) is that it doesn't really look anything like that bright. That picture is taken with a camera that was left to gather light for minutes or hours, turning a faint band of fuzz running across the sky into a glistening river of starlight.

To see anything like that picture you'll have to go well away from civilisations lights - then, in night sky, you'll see a band of stars. If you went into space, well away from Earth and the Sun**, you'd see that band actually running all the way around the sky. 

But, even if you did, the Milky Way still wouldn't be giving you the whole story.
 
It looks like a band of stars, but it’s actually a disk of them – it's a galaxy, a two hundred thousand light year wide disk of stars. The reason why it looks like a band running across the night sky is that we’re inside the disk – Earth is located about two thirds of the way from the middle, which it circles every 250 million years. 

Above: A map of the Milky way, showing the position of Earth.

Not convinced? To get a visual and tasty idea of how this works, cook yourself an extra large pizza. 

If you have no pizza in this is an excellent opportunity to order a take away pizza – tell your waistline a mad scientist made you do it – but ask them not to slice it. 

Once you have your large pizza take it into the kitchen*. Now slice out some of the pizza – enough that you can get a camera, iphone, or your head, inside the pizza. I’d go for a couple of traditionally shaped wedges taken centre to rim, but if you’re hell bent on scientific accuracy (and a monster) you could slice an appropriately sized circular chunk out, centred on a spot two thirds from the middle. Take the remaining pizza, and put your image-making thing inside the gap in the pizza. 

A cat is not an imaging device, although this is hilarious.

If you are using your own eyes and went for the scientifically accurate circular chunk removed two thirds from the centre... you are probably now wearing the pizza on your head. But as funny as that is it doesn’t affect the outcome.

Anyway, get your eyes or lens precisely on the level of the pizza, and take a picture (or just look through the scalding sauce now dripping onto your face): You can see that the disk shaped pizza is a band stretching across the 'scamera picture. 

Now imagine that your pizza is two hundred thousand light years wide and faintly glowing, and you’ll understand how the gigantic, disk shaped Milky Way galaxy can look like a band of light. 

You also have a fair bit of mess, but at last you have (slightly mutilated but hopefully still edible ) pizza. 

* This is not actually necessary, but ...I'd recommend it. 
**When I say get away from cities... that's a bit excessive, but you could. 

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Answers for Authors: What's the view like from other parts of our galaxy?

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To answer this we first need a quick bit of galactic geography:
Go out on a really dark, clear, night, far from any artificial lights, give your eyes time to adapt to the darkness, and look up. You will probably see many more stars than you’re used to and, stretching across the sky from horizon to horizon, a long band of faintly lowing fuzziness: That's the Milky Way, the galaxy that our Sun, our solar system, and this planet are part of.
 

This thing - although this is a long exposure that intensifies the light in the image. It doesn't look much like a swirl of stars from Earth, as we're inside the disk

It’s a collection of hundreds of billions of stars, at least that many planets, comets, nebula, and much weirder things with names like ‘magnetars’, ‘pulsars’, ‘white dwarfs’ that sound like they came straight out of an early draft of superhero comic. It's actually shaped like the swirl of cream in a coffee mug - and we can divide it into three bits:

• The central bulge / galactic core: The centre of the swirl, the core is made of a mix of stars of all ages. It's also one of the oldest neighbourhoods, and has both a lot of old stars and clusters of very young stars, and gas clouds primed for new star growth. Everything is very close packed (less than half a light year between stars on average, often much closer). The bulge is about 5,000 light years in radius, and has at least two gigantic black holes in the centre, one of which is the supermassive Sagittarius A* black hole, our galaxy's central black hole which weighs as much as 4,300,000 Suns. 
• The disc/arms: The arms of the swirl. About 60,000 light years in radius, and around 1,000 light years deep where the Sun is, it's mainly made of young to middle age stars. Beyond the edge of the disk is a mysterious ring of stars and gas surrounding it, with a radius of 75,000 to 80,000 light years, called the Monocerous ring. 
• The galactic halo: This is where my coffee metaphor runs out completely, unless you’ve brewed your coffee in weightlessness and then spilled it – these are, well, wispy bits outside the main galaxy. They are made of widely spaced gas and stars, floating above or below the plane of the disk in a rough ball, stretching to a radius of 130,000 lightyears. Although the stars and gas are incredibly sparse there, set within the halo are locales called globular clusters: Round clusters of hundreds of thousands of ancient stars, which are often separated from each by less than the width of our solar system.

Let’s assume I’ve got a ship fast enough, and well supplied enough, to go around the galaxy and stop in each section. What would my human eye see? 

The galactic disk: 

A map of the galactic disk, showing the spiral arms. Courtesy of Universe Today.

The nice thing about figuring out the view from the galactic disk is I live in it: Earth is located in the 'Orion spur' - a sub arm of the disk about 25,000 light years from the galactic centre. So there's lots of information to go on...

After my eyes have some time to adjust to the darkness the Milky way is a rough, very broad, band of faintly glowing fuzz stretching across the sky. In the direction of the constellation Sagittarius I can see a bulge in the band, with dark gaps in it - that's the direction of the galactic core. The gaps are dark nebula, blocking light from that direction out. 
I can't actually see the galactic core - there's too much gas, dust,and intervening stars in the way. What I see is the result of the disk getting slightly thicker in that direction.
If I look about with care I see the occasional dim fuzzy blob of a star forming nebula (like the one on Orion’s belt), and glittering collections of blue stars - open clusters. 

Above: The Pleiades, a cluster of young stars still wearing the remains of the nebula that created them.

The stunning colours I've seen in pictures from space telescopes are nowhere to be seen because, well, my eye isn't a space telescope. But it's good enough to make out some things: Above and below the plane of the galaxy I can see the Magellanic Clouds - smaller galaxies that orbit the Milky Way - as broader fuzzy patches well away from the galactic centre.


The galactic centre: 

Above: Incredibly densely clustered stars near the galactic core, Courtesy of the European Southern Observatory.

The stars of the core are densely packed, often living within fractions of a light year of each other, and many of the biggest and brightest are either huge, ancient, red stars or clusters of equally bright, young blue ones. The bright, close clustered, stars around me stop anything outside the galactic centre being  visible - the core seems to be the whole universe.

The sky is much, much brighter than on Earth: A lot of these stars are as bright as Venus from Earth – some are as bright as a full moon all by themselves. How bright is that in total? It’s very had to tell exactly, because clouds of gas and dust keep us from getting a really good count and the brightest stars wash out the fainter ones… but a back of the envelope calculation suggests the sky would glow with at least 1/300 the the brightness of the Sun from Earth**.

If that doesn’t sound so bright – the full Moon is juist 1/400,000 the as bright as the Sun, so the sky in the galactic core would be over a thousand times brighter than the full moon. Switching the lights off on my spaceship would still leave me with the equivalent light of bright sunset.

But!

If I head deeper into the core, eventually I come to the heart of darkness: Sagittarius A*, the 4.3 million solar mass black hole our galaxy is centred on. The vast black hole is 'only' as wide across as the orbit of the planet Mercury, but for half a lightyear around it is a swirling doughnut of superhot gas that X-ray telescopes can pick up even from Earth -
the graveyard of stars and planets that passed too close to the hole.

The galactic halo: 

Above: The Andromeda galaxy, in a long exposure photograph that brings out otherwise invisible details. Our galaxy might look similar, from outside. Courtesy of Brian Snyder.

The galactic halo is pretty lonely place. I’m well outside the galactic bulge and the disk, which are stretched out below me. 

I might have expected to see something like a celestial fried egg in an infinite black frying pan - but then I’m not remembering the view from Earth: There the galaxy is a dim fuzzy band across the night sky, even though I was looking lengthwise through it, with all the accumulated light of the  galaxy on my line of sight. Up here, looking down on the relatively thin galactic disk from a great distance, the only part that is very bright to the human eye is the galactic central bulge: A twinkling, fuzzy edged, blob of a billion stars – from here it’s easily brighter than the full Moon. 

Around it is an ethereal, almost invisible swirl of mist. That’s the galactic disk. You don’t need to take my word that it would be virtually see through: The Andromeda galaxy, that is regularly in the night sky from most locations, and it’s bigger than a full Moon. 

Ever seen it hanging in the sky? 

Above: The Andromeda galaxy, in a long exposure shot that makes it's outer regions brighter, and easier to see. Courtesy of Ted Van.

Probably not – even through a telescope, the only really visible bit is it’s galactic core. The spiral arms are vast, but too thin for our eyes to really make out.  

That said, it’s a dark sky out here: Rather than being separated by five or six light years, as in the spiral arms, the stars out here are separated by hundreds or thousands of light years. For that reason, if you turn so the bright core is behind you, it’s possible to dimly make out the structure of the spiral arms. Other galaxies are also more visible than from Earth, even through the disk of the Milky Way.

Globular cluster: 

A globular cluster - a vast ball of ancient, close packed stars.

 The last stop on our galactic whistle stop tour: These are huge collections of ancient, red stars floating in the galactic halo. Mostly they're located in a shell around the galactic core - and the stars are, if anything, even more tightly packed – big, bright old stars, dating from when the rest of the galaxy was just a huge cloud of gas. I can't see much outside of the cluster, except maybe the galactic core. 
Although this place is as bright as the core, the quality of the light is different: Orange-white, as every star is an ancient red giant or dwarf.
The close stellar quarters means that any planets will have been stripped away from their solar systems - not that there will have been many: Globular clusters are incredibly poor in heavier, planet forming, elements. This is a place where no new stars have been formed for billions of years - in many ways it's a tiny, zombie galaxy in it's own right.

And, finally, I can turn and head back to Earth. Hopefully I didn't leave the oven on... 

**The back-of-an-envelope calculation went: The very central cubic parsec (1 parsec = 3.26 lightyears) of our galaxy is estimated to contain 10,000,000 stars. To get a rough lower limit for how bright that would be, lets assume all those stars are as bright as the Sun (in reality many of them are far, far brighter), and arrange them in a sphere with a radius of 0.825 light years - the average distance from the centre assuming the stars are evenly spaced. Earth is 8 light minutes – 0.000015 of a light year, from the Sun. That means our hypothetical stars are each 55000 times further away from the centre of the sphere than the Sun is from Earth. Luminous intensity decreases with the square of distance, so each of those stars is delivering 1/ 3,025,000,000th of the Sun’s intensity at Earth. Multiplied by 10,000,000 that givs a total brightness, across the whole sky, of 1/302th the brightness of the Sun from Earth. 

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