Volume 548 Number 7669



News Features

News & Views

Cosmic exhumation p.526

Binary star systems known as cataclysmic variables can exhibit violent explosions called novae. Observations of a system hundreds of years after a nova reveal details about the long-term effects of such explosions. See Letter p.558

doi: 10.1038/548526a

The case of the mysterious messenger p.527

Bacteria and archaea use an innate immune system called CRISPR–Cas to combat viral infection. The identification of a family of molecules that play a key part in this system deepens our understanding of such immunity. See Article p.543

doi: 10.1038/nature23532

Food for early animal evolution p.528

A revised timeline for when algae became ecologically important among plankton in the ancient oceans reveals a link between chemical changes in those waters and the emergence of animals in marine ecosystems. See Letter p.578

doi: 10.1038/nature23539

Putative medicines that mimic mutations p.530

Molecules that block the activity or production of the protein ANGPTL3 have now been found to lower blood levels of lipoproteins and cholesterol in mice and healthy humans, mimicking the protective effects of genetic mutations in ANGPTL3.

doi: 10.1038/nature23544

Volcanism caused ancient global warming p.531

A study confirms that volcanism set off one of Earth's fastest global-warming events. But the release of greenhouse gases was slow enough for negative feedbacks to mitigate impacts such as ocean acidification. See Letter p.573

doi: 10.1038/548531a

A toxin that fuels metabolism p.533

Formaldehyde, a DNA-damaging agent formed in cells, has now been shown to support metabolic processes that involve molecular units containing a single carbon atom — linking metabolism to a DNA-protection mechanism. See Article p.549

doi: 10.1038/nature23541

The inflammasome turns 15 p.534

The discovery of the inflammasome protein complex in 2002 was a breakthrough in our understanding of how the immune system triggers inflammation. Now researchers are attempting to modulate its activity to treat disease.

doi: 10.1038/548534a



Proper-motion age dating of the progeny of Nova Scorpii AD 1437 p.558

‘Cataclysmic variables’ are binary star systems in which one star of the pair is a white dwarf, and which often generate bright and energetic stellar outbursts. Classical novae are one type of outburst: when the white dwarf accretes enough matter from its companion, the resulting hydrogen-rich atmospheric envelope can host a runaway thermonuclear reaction that generates a rapid brightening. Achieving peak luminosities of up to one million times that of the Sun, all classical novae are recurrent, on timescales of months to millennia. During the century before and after an eruption, the ‘novalike’ binary systems that give rise to classical novae exhibit high rates of mass transfer to their white dwarfs. Another type of outburst is the dwarf nova: these occur in binaries that have stellar masses and periods indistinguishable from those of novalikes but much lower mass-transfer rates, when accretion-disk instabilities drop matter onto the white dwarfs. The co-existence at the same orbital period of novalike binaries and dwarf novae—which are identical but for their widely varying accretion rates—has been a longstanding puzzle. Here we report the recovery of the binary star underlying the classical nova eruption of 11 March AD 1437 (refs 12, 13), and independently confirm its age by proper-motion dating. We show that, almost 500 years after a classical-nova event, the system exhibited dwarf-nova eruptions. The three other oldest recovered classical novae display nova shells, but lack firm post-eruption ages, and are also dwarf novae at present. We conclude that many old novae become dwarf novae for part of the millennia between successive nova eruptions.

doi: 10.1038/nature23644

Molecular machines open cell membranes p.567

Rotary molecular machines, activated by ultraviolet light, are able to perturb and drill into cell membranes in a controllable manner, and more efficiently than those exhibiting flip-flopping or random motion.

doi: 10.1038/nature23657

Very large release of mostly volcanic carbon during the Palaeocene–Eocene Thermal Maximum p.573

The Palaeocene–Eocene Thermal Maximum (PETM) was a global warming event that occurred about 56 million years ago, and is commonly thought to have been driven primarily by the destabilization of carbon from surface sedimentary reservoirs such as methane hydrates. However, it remains controversial whether such reservoirs were indeed the source of the carbon that drove the warming. Resolving this issue is key to understanding the proximal cause of the warming, and to quantifying the roles of triggers versus feedbacks. Here we present boron isotope data—a proxy for seawater pH—that show that the ocean surface pH was persistently low during the PETM. We combine our pH data with a paired carbon isotope record in an Earth system model in order to reconstruct the unfolding carbon-cycle dynamics during the event. We find strong evidence for a much larger (more than 10,000 petagrams)—and, on average, isotopically heavier—carbon source than considered previously. This leads us to identify volcanism associated with the North Atlantic Igneous Province, rather than carbon from a surface reservoir, as the main driver of the PETM. This finding implies that climate-driven amplification of organic carbon feedbacks probably played only a minor part in driving the event. However, we find that enhanced burial of organic matter seems to have been important in eventually sequestering the released carbon and accelerating the recovery of the Earth system.

doi: 10.1038/nature23646