Many people worry about the possibility of the end of all life on our planet. However, the Earth is by far the most habitable planet in our solar system and there's no reason to expect that to change for hundreds of millions of years.

The Earth may become uninhabitable between 500 million and a billion years from now. That may seem a short time, when you compare it with the billions of years the Earth has evolved for. But compared with the length of time there have been humans on the Earth it's a very long time.

To get an idea of who may need to deal with this issue, the idea is, to look at the last billion years. And then think about where we or our evolutionary cousins might be after another billion years after that. First some background though.

When Curiosity's successor and the ExoMars rover land on Mars around 2021, we will see two different approaches to the search for life on the planet side by side. NASA's mission is the first stage of a sample return program. The ESAs ExoMars rover (in partnership with Russia) will explore Mars in situ for biosignatures as well as drill two meters below the surface. Which is the best approach? 

A sample return would be great for geology. But would it help with the search for life on Mars? Or is it more of a technology demo for this?

One day you feel a strange stinging, biting or crawling sensation beneath your skin, which just won't go away. Then fibres begin to protrude from the skin or you may see red or blue lines below the surface of your skin. Eventually sores erupt all over your body, including in places you can't reach such as the middle of your back. You go to the doctor - and - after doing tests to rule out many other similar conditions, he finds that you fit the symptoms of a very rare condition, popularly called "Morgellons". He or she then tells you that this is not a real disease, but rather is a delusional condition. There is nothing physical causing this. It's just something going on in your mind which leads to all these symptoms.

This is a question that is frequently asked on Quora, with a different date each time. We get a fair number of quite worried people asking this question, in all seriousness, concerned that Earth is about to be hit by a giant impactor. Sometimes they have read sensational stories by online papers that should know later.

It is easy to keep up to date with potential impact dates by visiting this page, automatically updated for the Sentinel program: Current Impact Risks. Just look and see if there are any entries coloured orange or red. Then look for the predicted date of impact. So far this has never happened.

This is a question which was asked recently on quora: Is it possible to have a moon so reflective that when it reflects the light of the sun, it will be as if it is daylight? Anyway it is a rather fun problem, easy to work out by "back of the envelope calculations", and the answer takes us to some interesting areas of planetary physics.

So, you think you know what a planet looks like? A sphere, perhaps flattened at the poles? But if you've been following recent discoveries of dwarf planets, you may know that rapidly spinning dwarf planets like Haumea typically are rugby ball shaped (triaxial spheroids), rather surprisingly perhaps. So, what other shapes can a planet have? Theory, and experiment with droplets in simulated zero g suggest several exotic possibilities.