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• We misidentified a photo as showing the Microscopy, Electrochemistry and Conductivity Analyzer from the Phoenix Mars spacecraft (28 July, p 45) . It actually shows part of the mass spectrometer for another instrument on Phoenix. Also, we said that Viking 2 landed on Mars on 3 September 1996: it was in 1976. • We …

Richard Findlay's enthusiasm for fire (28 July, p 23) leads him to repeat the common error that it satisfies all seven criteria necessary to be considered alive. Alas, fire does not display irritability, neither here nor on Mars: if one pokes a flame with a stick it will neither run away nor turn around to …

James Hansen forecast that sea level will rise by 5 metres by 2100 and, in support, referred to the end of the last ice age when sea level rose by 1 metre every 20 years (28 July, p 30) . I forecast effectively the same thing for the same reason more than 20 years ago …

Ivan Semeniuk is wrong to say the "Viking landers surprised researchers when they discovered that the top 10 centimetres of Martian soil contain oxidants that would sterilise any life there by breaking down organic molecules" (28 July, p 42) . They discovered no such thing. This idea was put forward to explain the contradiction between …

The only human clones known are monozygotic twins: so it is understandable that Hugh McLachlan turns to them for a reassuring analogue to cloning by somatic cell nuclear transfer (21 July, p 20) . Such reasoning by analogy can be useful, but you must take care to note any particular model's weaknesses, as well as …

Thank you for the excellent article by James Hansen (28 July, p 30) . Science can never eliminate all doubt, but policy advocates, whether environmental pressure groups, political parties or corporations, often indulge in spin and gross oversimplification to get a clear message across. Of course, climate change sceptics use the uncertainty of science as …

The feature "Building for a cooler planet" conflated energy saving with reducing carbon dioxide emissions (28 July, p 8) . Yes, reducing CO 2 will certainly help to save the planet from global warming, but energy reduction is a different kettle of fish. Unfortunately, many economists propose that energy reduction leads to economic growth, and …

You quote a researcher as saying that when the US Food and Drug Administration stopped the sale of the potential anti-cancer drug dichloroacetic acid (DCA), it "is doing the absolutely right thing to help protect vulnerable cancer patients" (28 July, p 7) . Another way of looking at it is that they are doing absolutely …

Najmedin Meshkati asserts that Iran is prevented from having access to "the independent safety review, knowledge and practices" of the IAEA's technical cooperation programme (14 July, p 46) . This is incorrect. In accordance with the relevant resolutions of the IAEA board of governors and the UN Security Council, the agency continues to assist the …

I found your editorial on nanotech safety misleading (14 July, p 3) . Considerable effort is being expended in meeting regulatory and research needs. As you mention, the Royal Society's 2004 report looked at possible ethical, social or health and safety issues raised by nanotechnology that were not covered by existing regulations. The UK government …