Can an astronaut throw a ball to the Earth? The answer is Yes, and No. Depends what you mean by hitting the Earth.

First, if you throw a ball towards the Earth - yes it's traveling that way when you throw it. So, it is natural to think that no matter how slow it is, it would get there eventually. However, we aren't used to throwing things in orbit, and our intuitions can often lead us astray.

This is a particularly silly story about Nibiru, published today (in the Daily Telegraph): The end of the world now predicted for December say doomsday groups: "Terrifying stuff. Apparently, the planet due to collide with us is often visible, you may have seen it already. If you spot a blob next to the sun when you take a photograph, it could be the deadly planet, not a reflection."

If there were humans on the Moon - would we see the settlement lights from the Earth? For instance during a thin crescent Moon - could we see the lights of civilization in the parts of the Moon in darkness? 

It's a fun question to answer I think, so let's give it a go.

We can work it out backwards from the brightness of the full Moon.

Looking out on the lunar surface from inside a Moon city, frame from the 1965 Russian film Luna

(You can get this article as a kindle ebook)

Now we know, it's the second of those "Three mysteries" which they solved - by detection of water in the RSLs.  However, they didn't directly detect flowing water. Instead, they found hydrated salts. So let's look at this a bit more closely - why are they so confident this is evidence for flowing water? And what next - is there any way to follow it up, and what about the other mysteries?

The Indian ISRO space agency was going to announce the result of their first year of observations in Mars orbit - the Indian Times said - on Thursday.  But it didn't happen - seems it has been delayed! I look forward to hearing what they found - but seems that we have to wait some more.

We can't really make any deduction about what they will say, as their research is embargoed until then - they can't say anything about it. But we should hear whether or not they have detected methane from orbit so far.

The internet is buzzing with the announcement from NASA that they are going to announce the solution of a longstanding Mars mystery on Monday. at 11.30 am EST. That's 4.30 pm BST. Then, as many of the news stories have pointed out, the list of speakers includes Lujendra Ojha, a Nepal born researcher from Katmandu who discovered the "Warm Seasonal Flows" as an undergraduate back in 2011. It would be surprising to include him unless the solved mystery is something to do with these streaks. now often called Recursive Slope Lineae. So, what are they, and what are the main mysteries about them?