The Cosmic Background Microwave Radiation is the oldest light in the universe. 

Light travels at a finite speed. So, believe it or not, when you turn on a light in a dark room it takes a (very tiny) amount of time for the photons (light particles) produced by the bulb to fill the room. It's just that this happens so quickly, we can't see it.

The Cosmic Background Microwave Radiation is an echo of when the first photons could travel freely, shortly after the universe's creation (about 380,000 years, which isn't very long in a universe's lifetime).

This radiation marks the moment where the lights went on in the universe. It's just that the universe is a lot bigger than your living room, so this light has taken a lot longer to reach us.

The Cosmic Background Microwave Radiation is the furthest back in time we can explore using light. It's a snapshot in time and can reveal a lot about the initial conditions for the evolution of the universe.

​For example, it gives us hints as to how and why the stars and galaxies formed and was also provides one of the key pieces of evidence that the universe started with a Big Bang.

As the universe expanded, the wavelengths of the Cosmic Microwave Background photons have grown (or have been ‘redshifted’) to 1mm. Their effective temperature has also decreased to just 2.7 Kelvin, or around -270ºC, just above absolute zero.

And these photons fill the Universe today. There are roughly 400 in every cubic centimetre of space.

The Cosmic Background Microwave Radiation creates a background glow that can be detected by far-infrared and radio telescopes.

The Cosmic Background Microwave Radiation was discovered completely by mistake in 1964. Arno Penzias and Robert Wilson were using a large radio antenna in New Jersey when they picked up an odd buzzing sound coming from all parts of the sky.

They tried to remove the source of this (assumed) interference, and even removed some pigeons that were nesting in the antennae!

"When we first heard that inexplicable 'hum,' we didn’t understand its significance, and we never dreamed it would be connected to the origins of the universe," Penzias said in a statement. "It wasn’t until we exhausted every possible explanation for the sound's origin that we realized we had stumbled upon something big."

They were awarded the Nobel Prize in Physics in 1978 for the discovery.

The European Space Agency (ESA) is investigating the Cosmic Microwave Background Radiation with the Planck spacecraft to study this ancient light in more detail than ever before. NASA's Wilkinson Microwave Anisotropy Probe (WMAP), which launched in 2001 and stopped gathering data in 2010, and its COBE (COsmic Background Explorer) craft both provided early images of the Cosmic Background Radiation.

The Cosmic Microwave Background Radiation also provided evidence of primordial gravitational waves - which is the "smoking gun" to support the theory that the universe expanded in a cosmic inflation.

I've attended many talks during my 15 years as a science and tech writer and sometimes, when I look back on my reams of shorthand notes, I struggle to find an interesting angle.

Last week, I attended a symposium with Apollo astronaut Charlie Duke. And I'm struggling again with my notes. But only because there are so many wonderful snippets of information that I'm struggling to know where to start.

So, I'll start at the beginning and do my best to summarise what was the best talk I have ever had the privilege of attending, using a few of Charlie Duke's own words.

Charlie is a respectful man who commands great respect with his humble, yet engaging, manner. He struck down the well-pattered conspiracy theories around the moon landings with the same amount of considered respect throughout his talk.

Another wonderful nugget of information also came to light, as Charlie explained why the US flag appears to 'flutter' on the lunar surface: "It was vacuum packed for six months and I could not get the wrinkles out."

So, there you go. The flag is not blowing in the breeze of whatever desert people claim the lunar landings were filmed. It was just wrinkled. (And, if you take a look at the Apollo 16 shots, the same pattern of wrinkles appear in the flag at all times - it's not moving.)

But this rebuke around the nine lunar landings is my favourite. Charlie was involved with five out of nine of the Apollo moon programs. He's formed part of the astronaut support crew and worked as CAPCOM (the Capsule Communicator who communicates directly with the crew of a manned space flight).

He was CAPCOM during the Apollo 11 landing. It was a particularly tense and long landing that almost expended all of the Lunar Module Eagle's fuel. Duke's first words to the Apollo 11 crew on the surface of the Moon (when a safe landing was confirmed) were flustered: "Roger, Twank... Tranquility, we copy you on the ground. You got a bunch of guys about to turn blue. We're breathing again. Thanks a lot!"

Just to give you an indication of Charlie's character, he also repeated that famous phrase when asked in front of the entire auditorium in his distinctive Southern drawl that made him familiar to audiences around the world in the 1960s and 1970s. Fantastic.

The glamour of the space program was also quickly refuted by Charlie. From tales of sharing a 300 cubic foot space with two other astronauts to spending 1,000 hours in a simulator or 500 hours in the hot Florida sun practising the aforementioned rock picking, Charlie is quick to point out: "A space flight is not a guaranteed route to fame and fortune."

The Apollo 16 mission collected nearly 213 pounds of rock and soil samples and, despite extensive geological training, Charlie admitted they chose to "pick up one of every colour" on the lunar surface. He also claims he broke the lunar land speed record using the mission's rover (something other moonwalkers dispute!) and that parking on the moon is pretty easy because "you can just pick up your car and put it in a different spot".

But one of my favourite stats comes around the budget for flying three men to the moon. According to Charlie, the Apollo 16 astronauts received $25/day for the trip, so that's $275 for the 11-day trip. Charlie said: "I could buy, maybe a new golf bag with that. So, I filled out a travel voucher instead."

"Unfortunately, meals and quarters were deducted. I got $13.75 in expenses for the moon landing."

This is Charlie's impression of space. The strikingly simple phrase perfectly sums up what (I can only guess) it must be like to peer out of your window and see nothing, yet everything.

It's not just space that's vividly black, so is the dark side of the moon, according to Charlie. Apparently, later Apollo programs were interested in landing on the dark side, but Mission Control refused this request. And, after passing on the dark side, Charlie said: "​It was so black, you'd think it was space. But it was the moon that was black. It looked really, really rough and I'm glad we did not land there." 

The broad and fine details of Charlie's time in space and on the moon are fascinating. From seeing Earthrise to dropping a $10 million science experiment on the lunar surface (it was fine), Charlie and fellow astronaut John Young spent a record-breaking 71 hours and 14 minutes exploring the moon. ​"Every time we crossed a ridge, we did not know what we would see," he added.

The dusty surface of the moon also has a very familiar (but unexpected) smell, according to Charlie. When dust transferred from their spacesuits and gained moisture in the spacecraft: "We had a strange feeling that it smelt like gunpowder."

Charlie also thought he'd try his hand at the high jump on the team's very own version of the Olympics (his lunar landing happening in 1972 ahead of the Munich games). He lost his balance and landed on his back, which was no laughing matter as such an impact could have fatally compromised his space suit. "That ended the Moon Olympics. Mission control was very upset," he added.

Charlie remains optimistic that we will see a Marswalker in the future and the nature of the human spirit means: "We will figure it out." 

But, how are we going to figure it out? There are only six moonwalkers left on Earth and Charlie also made a very pertinent point about the space program. While some are swift to argue the money would be better spent here on Earth fixing our (somewhat mounting) problems, the ROI of the Apollo mission is ten-fold, with some studies estimating a $7 to $14 return for every $1 of NASA expenditure.

So, I hope that we will  start to see a new wave of moonwalkers. Not just because of the wider benefits such programs bring to society thanks to the employment and innovation they create, but because of the spirit of discovery they nurture in the human race.

If there was ever a time to look up to the stars instead of inwards, it's now.

Because we also need more Charlie Dukes. We need more advocates for science, exploration and innovation for the human race to thrive and survive.

Charlie repeatedly called his time on the space program "a privilege". Well, it was a true privilege to hear him talk.

Thanks to the Armchair Astronaut for organising such a great event! I may have missed a few key points as I was too enthused to make really detailed notes. So, if you were at the talk and want to share your experiences - please do so in the comments below.

Last week, I looked at the electromagnetic spectrum. At the one end of this continuous band of electromagnetic radiation, we have radio waves.

​Radio waves cannot be seen with the human eye. They carry the least amount of energy and have the longest wavelengths of all the electromagnetic wave categories. They're also incredibly useful in the field of astronomy.

Simply put, radio astronomy studies objects in the sky that give off radio waves. In our Solar System, the Sun and Jupiter give off radio waves. And, further away, the centre of our galaxy (the Milky Way), giant explosions called supernovae, and exotic celestial objects call pulsars and quasars are all radio sources.

Radio astronomy allows us to probe regions of space that cannot be seen using visible light. This is because radio waves can pass through dust, so radio astronomy has unmasked previously invisible regions of space. 

It also means that, unlike optical telescopes, radio telescopes are not hampered by clouds or poor weather.

​Radio telescopes are massive structures because they have to capture the long wavelengths of the radio spectrum. The largest radio telescope in the world as a single dish, is the Arecibo telescope. It was featured in the movie Contact, and is located in a natural hollow in Puerto Rico, South America. You may also be familiar with the Lovell radio telescope at Jodrell Bank (which is also one of the favourite places on planet Earth - I'd highly recommend a visit).

This huge white bowl of Lovell (and other radio telescopes) reflects incoming radio waves into the focus box mounted on top of the central tower. Here, at the focal point of the reflector, a small aerial picks up the waves and feeds them into a sensitive radio receiver where the signal can be transported and analysed.

To make a clearer (or higher resolution) radio image, radio astronomers often combine several radio telescopes into a pattern called an array. Together, these dishes act as one large telescope whose size equals the total area occupied by the array. This is a technique called interferometry.

The Very Large Array (VLA) in New Mexico consists of 27 radio telescopes, arranged in a Y-shaped configuration. Each telescope is 25 metres in diameter. All 27 telescopes are used simultaneously to observe a target, then their observations are added together.

To get an in-depth view of radio astronomy, the National Radio Astronomy Observatory is a great place to start and Jodrell Bank's website is a mine of useful information. Also, check out this page if you want to find out more about radio interferometry.

​It's not just the radio spectrum that you can use to probe the universe. You can also use gamma rays, X-rays, ultraviolet radiation, infra-red and microwaves.

This is a wonderful talk from radio astronomer Natasha Hurley-Walker too:

Hello. I’m the freelance writer who gets tech. I have two degrees in Physics and, during my studies, I became increasingly frustrated with the complicated language used to describe some outstanding scientific principles. Language should aid our understanding — in science, it often feels like a barrier.
​
So, I want to simplify these science sayings and this blog series “Sunday Science” gives a quick, no-nonsense definition of the complex-sounding scientific terms you often hear, but may not completely understand. 

If there’s a scientific term or topic you’d like me to tackle in my next post, fire an email to [email protected] or leave a comment below. If you want to sign up to our weekly newsletter, click here.
​

Twinkle, twinkle little star, how I wonder what you are? Well, the stars and other celestial objects we "see" are not just emitting visible light, they are also emitting a huge range of wavelengths across something called the electromagnetic spectrum.

The electromagnetic spectrum is a continuous band of energy that's radiated (travels out) of an object. 

Depending on its wavelength (typical values are shown in brackets below), the different portions of the electromagnetic spectrum can be used for very different things:

• Radio waves (1,000m) - TV and radio signals
• Microwaves (0.01m or cm) - Cooking and mobile phones
• Infrared (0.00001m) - Optical fibre communication
• Visible light (0.0000001m) - Seeing
• Ultraviolet (0.00000001m) - Detecting forged bank notes
• X-rays (0.0000000001m) - Medical imaging of bones and tumours
• Gamma radiation (0.000000000001m) - Killing cancer cells

Electromagnetic radiation is created when a particle, such as an electron, is accelerated by an electric field and this causes it to move. As the electron moves, it produces oscillating (moving back and forth in a regular rhythm) electric and magnetic fields. 

Electricity and magnetism are not separate entities. Electricity can cause magnetism and vice versa. The electric field and magnetic field contained in electromagnetic radiation travel at right angles to each other in a bundle of light energy called a photon.

The photon is both a particle and wave. It's a confusing concept and it's further discussed in this previous Sunday Science post.

Every photon travels at the same speed (the speed of light) and moves energy from one place to another. In the electromagnetic spectrum, long wavelengths have the lowest energy. So, radio waves have the lowest energy, and gamma rays have the highest.

The range of the electromagnetic spectrum is used in astronomy to detect and investigate some pretty amazing phenomena. This post provides a great introduction to the topic - and I'll be delving into radio astronomy in the near future.

And if you'd like an introduction to the equations behind the electromagnetic spectrum, check out this video:

Over the summer, Sunday Science has tackled the planets of the Solar System. It's remarkable the number of emails I've had asking me to include Pluto in the list - even though it was demoted to  "dwarf planet" status more than 10 years ago.

There are five officially recognised dwarf planets in our Solar System: Pluto, Eris, Ceres, Haumea and Makemake, but astronomers predict there could be hundreds more. (Check out the end of this post for a pretty cool animation.)

The fundamental difference between a planet and a dwarf planet is to do with what else is in its orbit around the Sun.

​Because Pluto shares its orbital neighbourhood with other dwarf planets and other objects in an area of space called the Kuiper belt, it's not classified as a planet.

The International Astronomical Union (IAU) has three criteria for a full-sized planet:

1. It is in orbit around the Sun.
2. It has sufficient mass to assume hydrostatic equilibrium (in other words, it can form a nearly round shape).
3. It has "cleared the neighbourhood" around its orbit.

​So, Pluto and the other dwarf planets fail on the last point. There are too many other objects sharing this orbital path.

Of the five dwarf planets, Ceres is the odd one out because it is located between in the asteroid belt between Mars and Jupiter. So, it's the closest dwarf planet to the Sun - and also the smallest with a mere 590-mile diameter.

Haumea has an elongated shape (a bit like a rugby ball), which is believed to be the result of its rapid rotation. It's named after the Hawaiian Goddess of childbirth (which is a nice contrast to Pluto - the Roman God of the underworld) and has two moons. 

Makemake​ was first observed in 2005 and is named after the god of fertility in Rapa Nui mythology. It's also the second brightest object in the outer Solar System and, despite sharing a lot of Pluto's characteristics, it does not have an atmosphere.

Eris is named after the Greek Goddess of discord and strife, which is quite fitting for a dwarf planet that's shrouded in controversy. When it was first discovered in 2005, Eris was thought to be larger than Pluto and it was submitted as the tenth planet in our Solar System. However, its discovery was one of the reasons Pluto was demoted in 2006 to dwarf planet status.

Yes. NASA's New Horizons probe flew past Pluto in 2015. The probe took multiple snaps of Pluto, including images of its icy mountains and a new view of its largest moon Charon.

​New Horizons is currently in hibernation mode before it prepares to fly past an icy body on the edge of our Solar System called 2014 MU69 on 1st January 2019.

Here's an animation I took from this fascinating Reddit post. The visualisation is from the simulator Universe Sandbox, which is based on the list of 'possible' dwarf planets from Caltech professor Mike Brown.

You can try this simulation yourself in Universe Sandbox by selecting home > Open > Solar Sys > Solar System All "Possible" Dwarf Planets (the author of this video also turned on view > Orbits).

And here's quite an extensive video all about Pluto:

Want more Sunday Science? I've just started the Sunday Science Facebook Group. If you've got a question about science, want to see more science on your news feed or just want to keep up to date with the latest on the blog, it would be great to welcome you to the group!

A friend once told me that I was "living the dream" as a professional freelance writer. When asked what they meant, they simply said: "Because you're your own boss, you work the hours you want and you get to see your children."

It's an interesting set of assumptions - because they're all completely wrong.

While I am (technically) my own boss - I'd argue that a boss (in the conventional sense) has been replaced by the fleet of customers I have on my books. They're all my bosses now. I suppose the one advantage is that the tables have been turned. I can choose whom I work with and "fire" any one my "bosses" if I want to.

And, yes, I do get flexibility in my hours. But I just worked for most of the bank holiday weekend as I listened to my children playing outside. So, that's points two and three of my friend's statement scuppered too. But, to be completely objective, I do get to pick my children up from school every day - I just have to work until 1am most nights to make up the hours.

Now, please don't think this is going to be a big rant about the woes of freelance writing. If you're thinking about a career as a freelance writer, I ABSOLUTELY recommend it (I even used capital letters to emphasise this point, which means I'm REALLY serious about this).

The best and worst part of my work is: I love it. Why's that a bad thing? Because I can't say no to the flurry of fascinating work that comes my way - so I always end up with too much on my plate.

Boo hoo. Poor me. What a chuffing first world problem.

​I could write a very smug and self-indulgent piece on why I LOVE my job. (Yes, capital letters again. I know you noticed.) But I don't think you'd want to read that. And I don't think I'd want to write that. (Which breaks the golden rule about only writing stuff you'd want to read.)

Anyway, the assumptions people make when I say I'm a freelance writer are intriguing. (My favourite question so far from someone I'd only just met is: "Are you writing the next Fifty Shades of Grey then?" No. I'm more geek than grey.)

So,  I was particularly fascinated by this white paper on The State of Freelance Writing in 2017 by the bods at Freelance Writing. It gives a fascinating insight into life as a professional freelance writer. Here's a synopsis of the findings:
​

• Most freelance writers earn $10,000 or less annually
• Most freelance writers work less than 20 hours a week
• Those who earn 40K+ work full-time
• Most writers gained specialised expertise in previous jobs. This expertise then allowed them to be better freelance writers.
• Writers predict the industry will become more competitive
• Writers also predict they will continue on in the field for the foreseeable future

The full infographic is at the end of this post if you want to see all of the stats.

I was quite disheartened by the findings of this white paper. It seemed, on first inspection, to paint freelance writers as a struggling bunch of workers with a below-par income.

But, the middle sentence, really stuck a chord with me: Most writers gained specialised expertise in previous jobs. This expertise then allowed them to be better freelance writers.

And I think that may be the thing no one tells you about freelance writing:

I'm quite flattered when people ask me for advice on following a career as a freelance writer. I'll be honest, it's more luck than judgement that has led me to "living the dream".

But the one bit of advice I give time and TIME again (see, capital letters, this is important) is to (drumroll please): HAVE A SPECIALISM.

I've touched on the importance of a specialism before, and it's absolutely vital if you want to thrive and survive as a professional freelance writer.

Throughout my 10+ years as a writer, I've always focused on science and technology. After all, I have two degrees in physics, I've worked as a research scientist and software developer (amongst other things) and have an unhealthy obsession with Brian Cox. I write about the stuff I love and know about.

That's not all.

If you really want to succeed as a writer, you need to give your clients real value in everything you write. No one wants to read another listicle about the top 10 ways you can do XYZ - people want real insights from real people.

So, make sure you find your niche and work hard to become an expert in this area.

​Before I came up with the (dubious) tagline that "I'm the freelance writer who gets tech", I was part of the below $10K salary demographic identified in the Freelance Writing survey.

As soon as I started shouting about my expertise in science and technology, the work snowballed.

So, if you want to "live the dream" - you have to invest the time in that dream. You have to work out what you want to write about. Then, work your socks off to achieve that dream.

And try hard not to punch anyone in the face who claims you're "living the dream" as a freelance writer as you work until the wee small hours to make another ridiculous deadline.

After all, you're you own boss, right? And you can work your own hours, right? And when did you last see your children?

The real truth about freelance writing is: it's a tough job.

​But it rocks.

Here's the full infographic from Freelance Writing:

Neptune is the furthest planet from the Sun - but it may have formed much closer to the Sun before moving to its present position.

Neptune rotates on its axis incredibly quickly - its equatorial clouds take only 18 hours to make one rotation - and it's also the smallest of the class of planets known as the "ice giants". Despite being smaller than Uranus, Neptune has a greater mass.

It also has a very thin collection of rings and has 14 moons. One moon, Triton, is a volcanic icy world and was recently discovered to have seasons.

Neptune's atmosphere is made up of hydrogen, helium and methane gases. Methane absorbs red light, so the planet has a rich blue hue. Below its atmosphere, you'd find a layer of water, ammonia and methane ice and the inner core is made up of rock.

The planet also has a very active climate. A large storm was recorded on its surface in 1989 (and can be seen in the above image) - it was called the Great Dark Spot and lasted approximately five years. 

The Great Dark Spot was discovered by the Voyager 2 spacecraft, which is the only craft to have flown by the planet. The Hubble Space Telescope has also studied Neptune, as have many ground-based telescopes. In fact, a strange storm that's as wide as the Earth has recently been spotted on Neptune by the Keck Observatory in Hawaii.

Believe it or not, scientists have theorised that Neptune and Uranus could produce "diamond rain" thanks to the combination of the high temperatures and pressures, and the hydrocarbons present on both planets.

It may sound a bit far-fetched, but this process has recently been reproduced in the lab. Unfortunately, the lab-produced diamonds were only a few nanometres thick - but Neptune and Uranus's diamonds could be far bigger.

And here's a great video on the blue planet from Astrum:

Right. Before I start writing this post, you can stop sniggering at the name of this planet. Uranus is the name of the Greek god of the sky. Although, it was almost called "Georgium Sidus" (after King George III) by the planet's discoverer - William Herschel.

Anyway, Uranus is the seventh planet from the Sun. One year on Uranus is equivalent to 84 Earth years and a day is only 17 hours and 14 minutes long.

​Uranus is also the third largest planet in the Solar System. Here's a quick scale reference where Ironman is the Earth and Uranus is a Galia melon. You could fit 63 Earths in Uranus.

Uranus was the first planet to be discovered using a telescope back in 1781. Herschel originally thought his discovery was a comet or star, before the observations of fellow astronomy Johann Elert Bode confirmed it was indeed a planet, and subsequently named this planet Uranus.

Uranus is an "ice giant" planet with 27 small moons and 13 faint rings of rock and ice debris. The planet is mostly made up of a hot and dense fluid of "icy" materials including water, ammonia and methane. There's no solid surface to land on and it also has a small rocky core that heats up to almost 5,000 degrees Celsius.

Its unique feature is that it orbits at almost 90 degrees from the plane of its orbit. In other words, Uranus looks like a ball rolling around the Sun.

Only one spacecraft has ever visited Uranus, which is almost three billion km from the Sun: Voyager 2.

It took the craft nine years to get there, before gathering a huge amount of information on the planet in just a six-hour flyby. The craft found that the temperature of the planet's Sun-facing pole is the same as the temperature at its equator and that there may be an ocean of boiling water about 800 km below the cloud tops.

Voyager 2 also discovered 10 news moons, two new rings and a strong, tilted magnetic field on Uranus.

If you're ever in the beautiful city of Bath in the UK, then check out the Herschel Museum of Astronomy. There's not just some great information on the discovery of Uranus, but the work the Herschels did on astronomical instruments and the mathematics of astronomy is fascinating. William worked alongside his sister Caroline, who helped him to develop the modern mathematical approach to astronomy.

The Hubble Space telescope also spotted a huge shimmering region on Uranus earlier this year, which is believed to be caused by powerful bursts of solar wind.

​And here's a great video on Uranus from Altrum:

The Cassini space probe will begin to spiral to its death tomorrow after giving us some of the most spectacular images of the planet Saturn - so this seems like quite a fitting Sunday Science post. More on Cassini later. 

​Saturn is one of the most recognisable planets in our Solar System thanks to its characteristic rings, which are made up of chunks of rock and ice.

​It's not the only planet to have rings (Jupiter, Uranus and Neptune do too) - but it is the second largest planet circling the Sun and farthest planet from Earth that can be observed by the unaided human eye.

Saturn is a gas giant planet, which means it is big and, um, mainly made up of gas. Just like Jupiter (another gas giant), Saturn is composed mostly of hydrogen and helium gases.

The centre of the planet is also remarkably similar to Jupiter's core, although it is slightly smaller. The core is a dense mix of ice, water, rock and other compounds, which are enveloped by liquid metallic hydrogen.

The days on Saturn are short (believed to be 10.7 Earth hours - but this is difficult to measure) but the years are long as the planet takes 29 Earth years to orbit the Sun.

Saturn also has seasons, just like on Earth, thanks to its tilt with respect to the Sun. 

And here's a fun fact - Saturn is the only planet in the Solar System that's less dense than water. So, you could float it your bath tub - if you could find a big enough one!

Oh yes. As mentioned, the Cassini spacecraft has been whizzing around the planet for 13 years. While the images are stunning and have revealed more detailed information about Saturn - there have been some interesting developments in the hunt for extraterrestrial life.

​One of Saturn's (confirmed) 53 moons - Enceladus - has a global saltwater ocean under its icy crust. Cassini has had Enceladus in its sights for some time - it first detected signs of an icy water plume in early 2005. Could the moon harbour life near hydrothermal vents? It's one of several ways life could exist on Saturn's moons.

Another one of Saturn's moons - Titan - has also just been added to the list of candidates for supporting life in the Solar System. And two other Saturnian moons - Dione and Tethys - could also be hiding liquid under their icy exteriors.

Saturn is a beautiful - and much photographed - planet. Check out NASA's image gallery here and you can see Cassini's images here. 

Here's an extensive list of facts about Saturn and a lovely 4K resolution video from Astrum:

Mars is a small, rocky world that's about half the diameter of Earth. Like our home planet, it has seasons, volcanoes, canyons, weather and polar ice caps.

The average temperature on Mars is minus 80 Fahrenheit. Red dust covers most of its surface and oxidised iron particles in the soil are responsible for this distinctive red colour.

​Mars has clouds and wind just like Earth, but its sand storms can cover the entire planet in a dusty haze for weeks.

The planet is also home to the largest volcanic mountain in the Solar System (Olympus Mons) and it has two small moons, Phobos and Deimos.

There are signs that huge floods once overcame the Martian surface some 3.5 billion years ago and this water may have pooled to form shallow oceans or lakes. It is still unclear where the floodwater came from and what happened to it.

However, Mars is now too cold and its atmosphere is too thin for liquid water to exist on the surface for very long. Findings from NASA'S Mars Reconnaissance Orbiter (MRO) suggest salty liquid water may still flow on Mars.​

Yes. NASA's Mars Exploration Rover Project landed twin rovers Spirit and Opportunity on Mars in 2004. Both missions were only meant to last three months but Spirit worked for six years, and Opportunity is still active.

Also, check out these amazing images from NASA's Curiosity Rover that's been scouring the planet's surface for more than five years.

Not all missions have been as successful, including the UK's Beagle 2 Mars probe and the Schiaparelli rover, which crashed into the Martian surface last year. But there are hopes for an upcoming rover, which should touch down on the Red Planet in 2020. Schiaparelli and the 2020 rover are part of the wider ExoMars mission from ESA (European Space Agency) and Russian space agency Roscosmos.

NASA has ambitious plans to get humans to Mars in the 2030s and the Mars 2020 mission also plans to answer key questions about the potential for life on Mars.

Here are 10 amazing facts you probably didn't know about the Red Planet and you can find out more about NASA's plans to get to Mars here, or find out more about all the Martian missions (past, present and future) here.

Here's a summary of all NASA's work on the Red Planet: