6 October 2012 | NewScientist | 17

Mammal ancestor not quite so puny

THE common ancestor of modern mammals was tiny and shrewlike, living unobtrusively in the shadow of the dinosaurs – or so we thought. A genetic analysis now suggests it may have been more like a small monkey in size.

Fossils indicate that some larger mammals shared the dinosaurs’ world, but palaeontologists think they all disappeared at the same time as the giant reptiles. Only tiny mammals survived, giving rise to all modern forms.

Nicolas Galtier of the Institute of Evolutionary Sciences in Montpellier, France, begs to differ. With colleagues, he used common features in the genomes of 36 modern mammals to sketch out the genome of the creature from which they descended.

Galtier’s results suggest that the common ancestor of all living mammals weighed about a kilogram (Molecular Biology and Evolution, doi.org/jfk).

Michael Novacek of the American Museum of Natural History in New York is sceptical, given what the fossil record tells us. But Galtier points out that the fossil record is incomplete. A large mammal ancestor might simply have failed to fossilise.

Exoplanets form never-seen-before celestial alignmentTHE heavens have aligned in a way never seen before, with two exoplanets overlapping as they cross their star. The phenomenon is so new it doesn’t have a name.

Teruyuki Hirano of the University of Tokyo, Japan, and colleagues used data from the Kepler space telescope to probe KOI-94, a star seemingly orbited by four planets. A planet passing in front of a star causes the star’s light to momentarily dim: that’s how Kepler spots exoplanets. Two planets crossing at the same time dim the star even more, but if they

also overlap there is a momentary increase in brightness as the planets cover less of the star.

This latter light pattern is exactly what Hirano’s team saw. It seems that one planet candidate, KOI-94.03, passed in front of the star and then the innermost candidate, KOI-94.01, passed between the two (arxiv.org/abs/1209.4362).

As both candidates must still be confirmed, another explanation for the light show is that a single planet passed in front of a dark starspot. But there is no evidence

MOTHERS always have their children in the back of their minds – now it seems that this is quite literally true. Fetal DNA can enter a mother’s brain and remain there for decades, according to autopsy data.

During a pregnancy, cells from mother and fetus can cross the placenta and survive for decades in the skin, liver and spleen – a phenomenon known as fetal microchimerism.

Fetal DNA can also cross the blood-brain barrier and enter the brains of pregnant mice. To see whether the same is true in women,

Lee Nelson of the Fred Hutchinson Cancer Research Center in Seattle and her colleagues autopsied 59 female brains. They found the male Y chromosome in 63 per cent of them (PLoS One, doi.org/jfq).

Nelson says that pregnancy is the most likely explanation for the presence of male DNA, but having an organ transplant or an older brother, for example, could also be a factor.

Such foreign DNA may be one explanation for why certain brain disorders, such as Alzheimer’s disease, are more common in women who have had children.

Son’s DNA found inside mum’s brain

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for spots on the surface of the star.The uncertainty hasn’t stopped

speculation over what to call the event. Hirano favours “planet-planet eclipse”, but that implies the total covering of one body by another: KOI-94.01 is thought to be larger than KOI-94.03, so parts of all three bodies were visible. Another option is “double transit”, but that can include cases where two planets don’t overlap. Other options are “overlapping double transit” or “exosyzygy”, a play on the general term for any three celestial bodies in a row, “syzygy”.

Nazi Buddhist deity is space rock

ONE religious statue has a stronger connection than most to the heavens. An 11th-century carving from Mongolia of the Buddhist god Vais’ravana was fashioned from a meteorite fragment, a chemical analysis shows. Its extraterrestrial origins make it unique in both religious art and meteorite science.

The 24-centimetre-tall statue was apparently brought to Germany in 1939 by a Nazi-backed archaeological expedition searching for the roots of Aryanism.

An analysis of the carving by Elmar Buchner at the University of Stuttgart, Germany, and his colleagues shows that the concentrations of metals – including iron, nickel, cobalt and chromium – match those for the Chinga ataxite, a meteorite that fell to Earth between 10,000 and 20,000 years ago near the border between Siberia and Mongolia.

The meteor fragmented as it fell, and just two pieces heavier than 10 kilograms were known previously. The “Space Buddha”, as Buchner’s team has dubbed the statue, is the third such piece, at 10.6 kilograms.

Other ancient venerated objects are thought to be meteorites, but they have never been analysed scientifically. Also, none has been carved into religious statuary, making the Space Buddha one of a kind.

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