Marissa Mayer has been appointed the next chief executive officer of Yahoo which is a bit like being given a red shirt and joining an away mission on Star Trek.

The life expectancy of Yahoo CEO's is proving remarkably short but Mayer so she will need to know which dark shadows are likely to have a person with a knife hiding in them fairly quickly. Apparently she applied for the job, rather than being press ganged while she was under the weather from a few shandies in a Calefornian bar. Yahoo managed to keep the news secret too probably because Mayer is working at its rivals Google, where she was a key player in Google's star chamber.

Yahoo has been in hot water for a while, the fact that she is the fifth chief executive in five years, is probably a bad sign. Yahoo said that Mayer's appointment "signals a renewed focus on product innovation", indicating that the company aims to compete on technology, and not just the content. Mayer, 37, has a degree in artificial intelligence and was the Google's 20th employee. She has been working there for 13 years.

She is six months pregnant with her first child, due in October, and said her maternity leave would be "a few weeks long and I'll work through it". Analysts say that Google should be a little concerned about the appointment. Mayer is very widely respected and she really knows the business. She also knows their business. At Google, Mayer had been responsible for many of the company's key products, including its famous search homepage, Gmail and Google News. More recently, she has taken on responsibility for location and local services, including Google Maps.

But it seems that Google made a mistake in 2010 by making another executive, Jeff Huber, senior vice-president of local and commerce, one level above Mayer's post. This effectively blocked her career.