Lithium pollution of a white dwarf records the accretion of an extrasolar planetesimal

Potassium and lithium on a white dwarf

White dwarfs are dense stellar remnants left when a dying parent star throws off its outer layers. The high gravitational fields should cause heavy elements to rapidly sink below the white dwarf surface. Nevertheless some “polluted” white dwarfs have evidence for those materials on their surface, which is thought to be due to the recent accretion of rocky bodies from a surrounding planetary system. Kaiser et al. report a white dwarf with pollution by potassium and lithium. This observation provides a record of the composition of the accreted rocky bodies and of the Galactic lithium abundance when the planetary system formed, billions of years ago.

Science, this issue p. 168


Tidal disruption and subsequent accretion of planetesimals by white dwarfs can reveal the elemental abundances of rocky bodies in exoplanetary systems. Those abundances provide information on the composition of the nebula from which the systems formed, which is analogous to how meteorite abundances inform our understanding of the early Solar System. We report the detection of lithium, sodium, potassium, and calcium in the atmosphere of the white dwarf Gaia DR2 4353607450860305024, which we ascribe to the accretion of a planetesimal. Using model atmospheres, we determine abundance ratios of these elements, and, with the exception of lithium, they are consistent with meteoritic values in the Solar System. We compare the measured lithium abundance with measurements in old stars and with expectations from Big Bang nucleosynthesis.

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Aussie grapes could be on the shelves year-round thanks to 20-year-old dwarf grape gene

Spring picnics are back on the menu as the weather heats up, but the grapes you’re filling your picnic baskets with at the moment are likely from overseas.

The Australian climate sees table grapes in peak production between November and May, but new research from the CSIRO hopes that could move to year-round production in the future.

About 20 years ago scientists discovered a dwarfing gene in an old French champagne variety, Pinot Meunier.

And now from bottles to tables, the CSIRO is using that gene to develop new grape varieties to grow in Australian conditions all year round.

The new varieties are small enough to be grown in pots, but still need summer like conditions to keep fruiting.(Supplied: CSIRO)

Small genes, big gains

The new dwarf varieties are small enough to be grown in a pot, but they will yield the best results for commercial growers in a hydroponic setup.

“Unless you’re living in the tropics, it will still go through a dormancy period as a normal grapevine would do,” the CSIRO’s Dr Ian Dry said.

The dwarfing gene sees the microvine skip its juvenile stage and fruit much earlier than many current grape varieties, and for longer.

“It now goes from seed to fruit within six months, whereas a normal grapevine would take two to three years,” Dr Dry said.

“Most grapevines produce only one or two bunches at the base of a growing shoot, whereas a microvine shows flowering and fruiting continuously along that shoot.

Dr Ian Dry is part of the team of researchers working with the 20 year old gene mutation to benefit Australia growers.(Supplied: Ian Dry)

With the mutation coming from a wine grape, these new varieties do not taste like what we are used to on the fruit platter.

“It has small berries, it has seeded berries, and it’s not a taste that one would normally associate with table grapes,” Dr Dry said.

Work over the past four years to change that is progressing well, with the CSIRO now looking for commercial-scale greenhouses to expand the research and move one step closer to releasing the new variety to Australian growers.

A bunch of green grapes hang from a vine.
Taste, size and seeds are the main differences between wine and table grapes — and something researchers have been working to change with their new microvines.(Supplied: CSIRO)

Reduced reliance on juicy imports

In 2019, Australia’s table grape exports tipped $500 million with Asia one of our biggest buyers, but through the cooler months, much of what’s on our supermarket shelves is imported.

“From about June up to [nearly] December again we rely entirely on imports, mainly from the United States, because we can’t produce those grapes locally,” Dr Dry said.

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