So yesterday I got all the nitty gritty of how scientists observe planets outside of our solar system out of the way. In short, there are several methods, including:

• Direct imaging
• Watching the change of light as planets pass in front of stars aka, the transit method
• Gravitational Microlensing
• Observing the wobbles of stars as planets affect their orbits slightly
• Other innovations on them.

One particular thing about the 'transit method' and 'direct imaging' is that not only can they detect that a planet exists, but they're also quite good at detecting its size, distance from the star, speed and, most interesting of all, chemical composition. using spectroscopy, we can determine what colour those planets would be if we were floating around at a moon's distance.

Some of those 3,000 discovered exoplanets look frankly wonderful, and others evil. I'll let you decide which, then I'll discuss how this can help us search for life.

GJ 504b: The Pink Planet

As far as planetary hues go, pink is a winner if you ask me. But why? Simply put, it's hot.

The planet happens to have been the first exoplanet directly imaged, which is one of the most difficult methods to see planets at all. The atmosphere was seen to have methane, and it was approximately 45 times further from its star than the Earth is from the Sun. That's way beyond Neptune's orbit, at merely 30 AU.

Hang on...If it's so far away, how is it so hot, I hear you ask. After all, its sun is less luminous than our own. Well, although it's one of the oldest planets discovered by this direct imaging method, it's still pretty young, somewhere between 100-500 million years old. It's still hot from its very formation, around 250°C.

That being said, the planet poses some conundrums about how it exists in the first place, since its distance defies our understanding of how gas giants form within the dense clouds of gas much closer to their stars.

55 Cancri e: The Diamond Planet

Yes, a planet of diamond. This poses some problems for humanity. If we manage to easily mine this and similar planets, our engagement rings will become worthless!

I doubt we will harvest such a planet though, as it is an extreme super earth. 8 times as massive yet only twice the size of Earth, it orbits its sun-like star in barely 18 hours. That means its so close to its sun that it's tidally locked, with a facing temperature of around 1,700°C.

Not very welcoming.

It does have as slight sunny atmosphere of Hydrogen and Helium, and its thought to be made up of 30% carbon. When carbon falls under intense heat and pressures, you get diamond, and a planet 8 times more massive than Earth has plenty of heat and pressure.

Oh, it's also actively volcanic. I like to think it spits out diamond rings.

TrES-2b: The Planet of Darkness

This planet is quite literally darker than coal. A deep black that reflects almost no light whatsoever, despite its blistering 1,200°C climate. To compare, Earth reflects about 37% of light. Jupiter, 52%. TrES? around 0.04%.

Part of this is due to it being too hot to have any reflecting cloudy atmosphere but that doesn't explain it entirely. Mercury isn't that dark. We're talking blacker than black paint. The true answer is still unknown, but it's theorized that there's some exotic chemistry going on in its thin atmosphere, such as the light-absorbing components of vaporized sodium, potassium, and gaseous titanium oxide.

How colour can help us find life

Earth-like planets could be green, Water worlds (as discussed in an earlier episode) are blue, others are red, pink, black, brown, and so forth. They kinda look like these petri dishes full of microbes

The theory goes that by looking at the hue of colourful planets, we could quite literally be staring at a microbial-dominated world. The chances are much slimmer that we'll be finding giraffes and snakes compared to that of much hardier microbes that have been found thriving in the most extreme conditions here on Earth; undersea volcanoes, oversea volcanoes, icy tundra, thousands of metres underground, covered in sulphur, desolate deserts, deep space and so on. Even the most toxic, acidic lakes and uninhabitable salty seas have been found with thriving bacteria, some of which have even mutated to chomp away on plastic.

Earth reflects infra-red light from the view in space, which is bouncing off chlorophyll from all our luscious plants. This could also be a result in exoplanet discovery.

So next time you want to look for life outside of our own, look for the pretty colours out there in the vast, darkness of space.

Thanks for reading!

Image Sources:

Pink Planet
Diamond Planet
Black Planet
Microbes
Green Planet Art

Previously:

Water World
Eyeball Earth
Extreme Exoplanet Weather of Death and Doom
Planet as old as the Universe
Strange Star Systems
Mystifact - What is a planet?
How to Find Exoplanets