Life on Mars? Only sample return missions will tell us
From Ed Prior, Williamsburg, Virginia, US
Your review of astrobiologist Steven Benner’s book, which reanalyses measurements from the Viking probes in 1977 that appeared to find biological evidence for life on Mars, was excellent. It reminded me of the controversy back then and the seeming reluctance of many in the space arena to attempt another such project. Twice in the years since, NASA has announced missions to Mars that would bring back samples to test on Earth for any hints of biology, but both were unfortunately cancelled (1 August, p 26).
Benner has examined the data in detail and concluded that Mars is “alive again”. I hope the 2031 Chinese sample return mission is successful (though I would much prefer NASA to try again before 2031) so that we can finally and carefully 鈥� without letting unknown biological molecules escape into our atmosphere 鈥� answer the question, “Is there life on Mars?”
Whatever the answer, I am sorry that the many talented engineers, scientists and technicians behind the Viking mission, including Gil Levin and Gerry Soffen, are no longer with us to see this resolved.
Kenneth Craik’s short life was full of brilliance
From Peter Brooker, London, UK
It was great that Kenneth Craik, one of the pioneers of cognitive science, modelling and risk analysis, got a mention in your piece about developing AIs that understand the world around them. He made huge contributions in a career lasting just a few years. Craik’s death was tragic, mundane and touched by irony given his work. He was cycling along King’s Parade in Cambridge, UK, when someone in a stationary car opened their door, knocking him into the path of a lorry and causing fatal injuries (8 August, p 30).
Climate crisis requires global economic change
From Peter Brown, Pickering, North Yorkshire, UK
The root cause of climate change is surely the market system that has become dominant. It has created modern civilisation, but takes no account of Earth’s resources, the damage from the exploitation of energy sources or the fate of products at the end of their lives. We must modify our economies so they benefit humanity and our planet. The market is a global system, so requires a global effort to change it. We need disincentives to all damaging activities, and subsidies for mitigation of adverse impacts and for attempts to reverse the damage (Leader, 8 August).
The questions raised by a heterogeneous cosmos
From John Wallace, Liverpool, UK
I enjoyed Leah Crane’s rundown of the cosmological principle, the idea that our universe is broadly homogeneous when viewed at a very large scale, particularly her admission that she doesn’t really believe in it: “We can accept something as close enough to truth to be useful, while knowing it’s not quite all the way correct (8 August, p 19).”
I sometimes wonder (and perhaps somebody can clarify this) whether similar assumptions were used in calculating the age of the cosmos. Observed on a large-enough scale, I think we picture the universe as something like a 3D web of superclusters, where most matter is concentrated and hence gravity is slowing time, with immense voids in between. Where there is little or no matter, time will have been running faster. When cosmologists claim that the big bang happened about 13.8 billion years ago, whose time are they using?
How should we eat in our 50s and beyond?
From David Jockelson, London, UK
In the article on what to eat from midlife onwards, JoAnn Manson says “you’re not going to achieve optimal health by throwing a multivitamin at an unhealthy lifestyle”. But her own COSMOS-Web trial found significant benefit from multivitamins, as Graham Lawton’s article in the same issue (p 18) confirms (1 August, p 30).
However, the participants were self-selected, being both interested enough in their health to volunteer and able to commit to a lengthy trial. They were probably already eating a reasonably good diet. So the real question is whether people with a poor diet would benefit far more from a multivitamin than the trial’s relatively well-nourished cohort.
From Robin Jacob, London, UK
The insights in “Eat your age” were foreseen in William Shakespeare’s play Much Ado About Nothing: “A man loves the meat in his youth that he cannot endure in his age”.
Stone Age fish transport is full of potential surprises
From T. E. Reimchen, University of Victoria, Canada
Reports suggesting that ancient hunter-gathers in what is now Norway transported fish to fishless mountain lakes, therefore allowing for summer fishing opportunities, are interesting and important. But this isn’t the only explanation for how the fish could have arrived there (25 July, p 7).
On the Haida Gwaii archipelago in western Canada, birds called red-throated loons, which nest in numerous fishless lakes, forage for their young in adjacent ocean habitats and carry fish (some of which are still alive) to the lakes to feed them. This occurs daily over the birds’ 50-day pre-fledging period, and by each nesting pair each breeding season.
Norway happens to have large numbers of red-throated loons too, and it isn’t improbable that the colonisation of fish in these lakes was mediated through transfer by these avian piscivores. I suspect that human transport is the more probable explanation, but the very common fish-transfer behaviour of these loons cannot be ignored. Finding out just how the fish got in the lakes might be possible by using genomic techniques on surrounding fish populations.
From Graham Parkinson, London, UK
After reading about the Stone Age Norwegian trout farms, I was excited to realise that my walk home from the fishmonger was a contemporary example of “human-mediated translocation of fish”. I thought I was just shopping for my supper.
For the record
Pig eyes have been kept active outside the body for up to 10 hours after death (18 July, p 11).
Charles Darwin’s book On the Origin of Species was published in 1859 (15 August, p 15).
The first letter in the section addressing new battery technologies was written by Christopher Jessop (Letters, 15 August).
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