We get many sensational news stories, saying a giant asteroid will hit Earth, or will nearly miss us. Several so far this year. Many of us worry about these things. So what is the truth behind them?

Actually astronomers have this well in hand for the largest asteroids. They have found 90% of the largest asteroids likely to hit Earth. This is mainly due to Pan-STARRS, which takes a 1.4 gigapixel image of a three degrees span of the night sky several times a minute. It continues to find a new large asteroid about once a month, and will find most of the remaining 10% by the 2020s.

Is anything going to happen on September 24th? Well, the astronomers say, no. It is an ordinary day in space, nothing remarkable of note at all on that day by way of asteroid flybys.

Yes, it's true, as some news stories say, there is a distant flyby by a rather unremarkable asteroid. It is one of dozens that pass by Earth every month. It's not especially large as asteroids go. Indeed there's one more than double its size, passing closer, at a faster speed, on October 4th that nobody is interested in except perhaps a few astronomers.

This story has recently hit the news. I think it is reasonably clear he was not putting forward a serious worked out future plan for Mars. But is there any potential in the idea?

This is just for fun. At first sight this seems impossible - the smallest stars are heavier than the heaviest planets, and how can something heavier orbit something that is lighter? But what if you have a very dense star and very large very low density planet? And if you interpret "orbiting it" as "having barycenter (the "center of mass of the system") within the planet"?

Also, could a star sometimes be lighter than a planet, is that possible at all? I'll also describe a way that a heavier object can, in a way, "orbit" a lighter one - a way to get a heavier star move in such a way that the barycenter of the system lies within a large low density planet - can you figure out how, before I get to it?

Perhaps you saw the news recently about astronauts in the International Space Station eating their first home grown lettuce? It's just a beginning, but in the future, could they grow all their own food and get all their oxygen from plants?

Is the ISS the most expensive single human artifact ever, after adjusting for inflation? Well, to start with, it's a whole lot more expensive than a medieval cathedral anyway. First we need an estimate of the cost of the ISS, and this article in the Space Review estimates the total cost up to 2015 as $150 billion (in 2010 dollars). That's the total cost including all the international partners. So, how much did it cost to build a medieval cathedral?