Why is Venus so hot?

Venus, the second planet from our Sun is a hellish place. Despite being further away than Mercury, the planet is several hundred degrees hotter. At 735K (that’s 462ºC or 863F in old money) the air is hot enough to melt lead and once you start looking at the planet a bit more closely, the reason becomes clear.

Venus's thick atmosphere

Venus’s thick atmosphere prevents astronomers from seeing the planet’s surface. Credit: NASA

Venus’s has one heck of an atmosphere. The surface pressure is around 92 times that found on Earth and it’s made out of some pretty nasty stuff: 96.5% carbon dioxide, 3.5 nitrogen, laced with sulfur dioxide,  sulphric acid and a few other trace elements.

It’s no great secret that carbon dioxide is a green house gas – it lets light and heat in, but not out again. Venus is an example of what can happen if you let carbon dioxide build up in your atmosphere to ridiculous levels.

But what I always wondered was why does Venus have such a thick atmosphere in the first place? In most respects the planet is much like Earth. It’s slightly smaller, with around 80% of Earth’s mass, meaning its gravity is pretty much the same. It’s at 0.7 AU, one AU being the distance between the Earth and the Sun, so it’s not that much closer and from most observations seems to be pretty similar to the Earth. At first glance its warmer atmosphere and lower gravitational pull should mean atmospheric molecules are more likely to escape. So what the hell happened?

The surface of Venus

Using radar, scientists have managed to get a good idea of what Venus’s surface looks like. Credit: Venus

The answer is all to do with that magical substance that has defined the hunt for life in the Galaxy: water. Venus doesn’t have any, or at least not much. It has trace amounts in the atmosphere, around 20 parts per million, but compared to the 40,000 parts per million of water found in our atmosphere it’s practically nothing.

But it used to. As I said, Venus is very similar to Earth and almost certainly formed in much the same way. The Earth has water, as did Mars in the beginning for that matter. It stands to reason that Venus had its fair share too, though we don’t currently have any evidence as no Venusian lander has lasted longer than two hours on the surface.

At some point though the temperature on the planet reached a tipping point and it began to lose its oceans. The Sun has been warming at a rate of a few percent every billion years. On Earth this hasn’t appeared to have effected us too much, but Venus receives twice the energy from the Sun. The change in temperature was too much, eventually the oceans began to evaporate and as that happened, things began to go oh so terribly wrong.

Water’s of Venus

The evaporating water saturated the atmosphere. In the high atmospheric levels the Sun’s radiation started to break apart the water into hydrogen and oxygen. The light hydrogen floated away into the deep dark depths of space while the heavier oxygen does what oxygen always does, and reacted with absa-bloody-everything, most notably any carbon hanging around to create carbon dioxide.

Not only that but as the water evaporated the planet’s mantel began to dry out. Plate tectonics require liquid water to absorb minerals, act as a lubricant and so on. Without it, everything just seizes up, and that’s exactly what happened on Venus. Volcanic activity is another way that carbon dioxide gets sucked up and stored in rocks, being re-released when volcanoes do their thing.

All of this lead to rising carbon dioxide levels in the atmosphere, which caused the planet to begin heating causing the oceans to evapourate and eventually boil. To make matters even worse, water vapour is itself a green house gas, insulating a planet. Once the water began to be lost, Venus never stood a chance. On Earth the interaction between water, rock and carbon dioxide help to regulate our nice, temperate climate [1]. With this thrown out of kilter, everything went awry. The end result is a planet no one ever wants to go on holiday to.

Venus surface by Venera 13

The Russian Venera programme has sent several probes to Venus, including several landers. The missions were the first to land on another planet, but none lasted longer than two hours. However they did manage to send back several images of the planet surface, including this image taken by Venera 13. Credit: Roscosmos

[1] The Earth is pretty good at regulating its temperature. It does this through the interactions of volcanism, carbon dioxide and water. Volcanic activity is constantly catching and releasing carbon dioxide in the Earth’s crust. If the global temperature drops, water freezes, stopping it from absorbing carbon dioxide, which creates a green house effect, which heats the planet and melts the ice. Global temperatures get too high, the ice caps melt, the atmosphere becomes more humid and all that lovely liquid water sucks up the carbon dioxide and temperatures drop again. It should also be noted that while the planet is doing this, there are colossal civilisation ending, mass extinction educing storms and weather pattern shifts, which is why ‘global warming’ does not mean ‘a bit sunnier in the Summer’.

 

Did you know…

1994 Solar eclipse

The light of the corona is usually only visible on Earth during a total eclipse. It can be seen with specialist equipment though. Like a space telescope. Credit: Luc Viatour

The Sun’s corona, this aura of plasma that surrounds the main star, is many hundreds of times hotter than the photosphere, the surface that we see. While the temperature of the Sun’s surface is only 6,000K the corona can reach up to 1,000,000K.

All hail hypnothread. ALL HAIL.

Simulation of a cross section of a thread of solar material. All hail hypnothread. ALL HAIL.
Credits: NAOJ/Patrick Antolin

No one is 100% sure why this is, though the current leading theory is that it’s probably magnets… or rather that magnetic waves generated by the motions of matter inside the star. These oscillate through the Sun and cause the plasma in the corona to move in a turbulent motion (queue mesmerising gif to left) and the friction heats up the corona.

Exploring the Universe with the At-Bristol 3D Planetarium

Sitting under the dome of At-Bristol’s new 3D planetarium, I stared up at what looks like the night sky. There are a few stars I recognised but mostly there was familiar orange glow of light pollution circling the horizon. The presenter leading the show asked us all to close our eyes for a moment.

“Now,” she said. “Open your eyes.”

Credit: Tim Martin

Credit: Tim Martin

In front of my eyes was a sky covered in stars, the Milky Way streaking across the centre. For many people who lived in and around Bristol, this was the first true representation of a dark sky they had ever seen.

Credit: Tim Martin

Credit: Tim Martin

“There was one lady who came out of that show who was buying lots of astronomy books because she wanted to find out more,” said Lee Pullen, Planetarium Manager when I interviewed him later. “She confessed that she’d found the experience so emotional that she’d wept tears of joy in the show. Often people are just amazed. They had no idea there was so much out there to be able to find.”

The show in question was Summer Stargazing, a seasonal show highlighting the landmarks of the night sky at this time of year. We flew to distant stars, searched the sky for various asterisms like Cygnus and Lyra, though the highlight for me was taking a swooping journey through the rings of Saturn. The sight of ice particles jumping out of the screen all around me is something I won’t be forgetting.

An environmental perspective

The planetarium shows don’t just look up at the sky. Their environmental show, Blue Marvel, casts its gaze back downwards to our own fragile planet. Here the 3D really came into its own. The Earth became the canvas on which to paint humanities impact in a very tangible way. Deforestation was projected across the globe and oil consumption per capita jumped out from every country*. But perhaps the most striking moment was when the sea levels were made to rise 20m, flooding the world, including the place where I live.

The show was an excellent way to show the strain we humans are placing on the world, but also rather depressing. There was little indication of what we could do to prevent what seemed like the inevitable destiny of our civilisation.

Bristol is open to technology

But it is projects like this, beyond its main use as a planetarium, that the dome was upgraded for. The funding for the project came in part from the Bristol Is Open project.

“The Bristol Is Open Network is a high speed network that runs all around under Bristol,” says Seamus Foley, the planetarium’s media production officer. As part of this network the Planetarium goes by the moniker ‘the At-Bristol Data Dome’. “The idea is that in the future we might be able to stream 4K frames down the pipe in real time so you can have a supercomputer processing visualisations of molecular simulations, for example, and it turns up in the planetarium.”

The planetarium aims to be more than just a fancy screen for showing astronomy films, and the team are currently working at ways to make the dome earn its keep, including some intriguing ideas such as putting on music concerts and introducing interactivity.

At-Bristol Planetarium & Millennium Square

Credit: Tim Martin

“One of the experiments that we’ve done is dropping a buggy onto scans of the Tycho Crater and driving around it like a computer game,” says Foley. “We want to make it more than just a cinema experience. We want it to be an interactive and engaging, let people can take part and take control of the experience.”

Whatever comes next, I’m sure it will put the planetarium to its best use. I look forward to finding out what At-Bristol has in store.


* – Luxemburg was the real surprise here. It practically hit you in the head with it’s oil consumption the spike was so huge. Apparently it’s due to people nipping across the border to fill up on cheap petrol.

For those of you with a family At-Bristol is open most days between 10am-5pm on weekdays, and 10am – 6pm on weekends. They also regularly puts on After Hours and Planetarium Nights to allow adults to use the planetarium and have a look round.

 

The Perseid meteor shower

Meteor showers are probably the easiest astronomical events to see, and the Perseids is one of the most spectacular. This year the shower will be in our skies from 17 July to 24 August, it will peak on 12-13 August. So how do you go about watching the show?

Perseid meteor shower

Credit: Fred Bruenjes

How to watch a meteor shower

The first thing you need to work out is where to look. The place where the meteorites originate from is called the radiant and for the Perseids this is found, as the name would suggest, in the constellation of Perseus. It’s near the ‘W’ shaped constellation of Cassiopeia if that’s a more recognisable landmark. At this time of year you can see both Perseus and Cassiopeia in north to north east of the sky, but as meteors appear over a wide area of the sky there’s no need to locate either constellation exactly. Now you’re ready to settle in for a night of meteor watching.

Perseid Sky Chart

Credit: Sky and Telescope

The great thing about meteor showers is that they are best viewed with equipment no more advanced than your eyes. You don’t even need particularly dark skies. I’ve seen them while lying down in the middle of a city (in my back garden I should add, not the middle of the road which is a terrible idea – too many street lights). All that you need is a place you can get away from direct sources of light, such as streetlamps and the moon. Luckily the Moon is a few days off new, as the light from our nearest celestial neighbour can sometimes put a dampener on things.

Once you’ve found your spot I suggest making yourself comfortable – you’re going to be there for a while. Find a place to sit down, but make sure you have some decent insulation, it can take your eyes up to half an hour to adapt and it gets cold much faster than you think. Soon enough you’ll start seeing those few flecks of light as they streak across the sky. Try and keep count of how many you see and how fast they come.

How many Perseids can I expect to see?

You may have heard a number being bandied about in the press claiming that the rate of meteors is around 100 per hour. That’s not exactly true. That number is what is called the zenithal hourly rate (ZHR). This is the number of meteors you would see if conditions were perfect, if the radiant was directly overhead at a dark sky site and if you could see the whole sky at once. Unless you are a fish (which I doubt if you are reading this) or have some very strange glasses on you cannot see the whole sky at once. For most people observing from an urban setting you’re more likely to see a third to a half of this rate. Still that will mean you’re going to see one shooting star every minute or so, which isn’t exactly shabby.

What are meteors?

So now you’ve seen a couple of shooting stars, what are they? Dust and debris from the Solar System hit our atmosphere all the time, about 100 tons every day. Most of this is dust and rocks the size of gravel that burn up * before they reach the ground without much ceremony. Some burn with a light bright enough to be seen from the ground and it’s these we see as shooting stars. However much of this is just stuff that’s floating around our planet or in its orbital path and hits our atmosphere pretty randomly.

Meteor showers a bit different in that they happen regularly. In most cases it’s caused by the Earth passing through the trail of debris left behind by a comet. In the case of the Perseids this was the comet Swift Tuttle which passes through the Earth’s orbit every 133 years, the last time in 1865. As the Earth’s orbit shifts slightly every year we haven’t managed to completely clear a path through the debris field and so we are left with the glorious sight that is the Perseids meteor shower.

So I hope that helps you some, and I hope you manage to get out there and see a few shooting stars for yourselves!

 

*: Technically the glowing isn’t caused by the meteor ‘burning’ but because it’s travelling so fast. The friction between it and the air causes the air to super heat and it’s this air that stars glowing. Of course this then melts the meteor, and there’s probably some oxidisation going on somewhere so you could say the rock is burning, but it’s not the flaming rock that you can see streaking across the sky.