NASA scientists are mystified by the appearance of a rock on the Martian surface that wasn’t there last time Opportunity rover passed by.  
 
Opportunity landed on Mars in January 2004 with an anticipated 3 month mission lifetime.  Ten years later it is still roving, and exploring the Martian surface. 
The second of the two images shown, in which the rock appears, was taken about 12 Martian days (each of 24 hours 39 mins) after the first.  At first I thought this was a hoax, but the truth of the matter is revealed on NASA’s Opportunity website:
 http://marsrovers.jpl.nasa.gov/mission/status.html#opportunity.

The ground operations team were genuinely surprised by the ‘sudden’ appearance of the rock, where there was none beforehand. Possible theories being suggested were that the rover may have flipped the rock into its new position as it passed by, or that it had just landed there after a meteorite impact nearby. Clearly there were other
ideas such as little green men (or Elvis?) throwing stones at the intruder.  Whatever the cause, NASA scientists now consider the rock worthy of further scientific scrutiny.

Over the last few months, Venus has been a very bright object in the evening twilight, but you may be forgiven for not noticing it (if you are UK observer) as it has been very close the the Western horizon for most of that time.  So, although it has been shining brightly, it has appeared against a twilit sky and also setting soon after the Sun.

Just now it is about to overtake the Earth on the 'inside track' in its orbit, so its evening sky apparition is about to end with 'Inferior Conjunction' on the 11 January 2014, when it will be directly between the Earth and the Sun. At the time of writing, it still shines brightly in the evening twilight, but it is rapidly getting closer to the Sun so it will soon be lost in the evening twilight.  After the 11th it will eventually establish itself (by the end of January) as a brlliant object in the pre-dawn sky.

However, a couple of days ago the moon and Venus were quite close to each other in the evening sky, both showing a very thin crescent phase, as show in the accompanying image (which incidently I did not acquire myself!).  On the left hand side, the image shows the actual distance between the moon and Venus on the evening of 2 January, and the larger right hand image shows a composite revealing the correct relative sizes and phase of each object - I emphasise that they were not as close to each other as the right hand image suggests.

However it was a note-worthy occasion, the like of which will not happen again for a year and half or so.