In brief–Research news and discovery

EACH winter, humpback

whales travel from the Antarctic

to the northern tropics to find

warm water in which to raise

their young. The migration is

the longest documented for

any mammal.

Kristin Rasmussen of Cascadia

Research Collective in Olympia,

Washington, and her colleagues

photographed the tails of

humpbacks wintering off the

“Wintering areas occur where

waters with temperatures

between 21 °C and 28 °C are

found,” says Rasmussen. This

supports the idea that the long

migration saves the whales

energy in the end.

Rasmussen says that Japan’s

proposed annual “scientific”

catch of 50 humpbacks makes it

important to understand whale

migration. “Killing whales in one

area could potentially impact

their population halfway around

the world,” she says.

Caribbean coast of Costa Rica.

From their individual tail patterns

they identified seven of the same

animals after they had returned

to the Antarctic. One mother and

calf made the 8300-kilometre trip

in 161 days (Biology Letters, DOI:

10.1098/rsbl.2007.0067).

Using satellite data, the

team also recorded sea-surface

temperatures for the sites where

humpbacks spent the winter.

A long way to go for a warm bath

TREATING women who become

clinically depressed during

pregnancy could prevent

thousands of premature births.

Veronica O’Keane at the

Institute of Psychiatry in London

and her colleagues have found a

link between clinical depression,

levels of stress hormones and

premature birth. They found that

pregnant women suffering from

severe depression had higher

levels of the stress hormones

cortisol and corticotrophin-

releasing hormone (CRH) in

their blood than healthy women.

They also found that pregnancies

were shorter on average in the

depressed women. Preterm

delivery is the leading cause of

infant illness and death.

“Depression is a major

cause of preterm birth, and

overstimulation of stress

hormones is at least one cause

of this,” concludes O’Keane,

who presented the results at a

conference in London this week.

Stress warning

THERE’S no need to invoke dark

matter to explain why nearly

80 per cent of spiral galaxies have

a bar of stars or dust running

through them. A tweaked version

of Newton’s law of gravitation

does the job better.

Olivier Tiret and Françoise

Combes of the Paris Observatory

used computer models to

compare how the bars form,

either with dark matter or

modified Newtonian dynamics

(MOND), in which gravity changes

character as you get further away

from a galaxy’s centre (www.

arxiv.org/astro-ph/0701011 ).

Bars formed in a billion years

in MOND models, but much more

slowly with dark matter. Both

models give roughly what is seen

today, but MOND matches the

frequency of bars more closely.

Modified gravity

reigns in star bars

CHINESE purple, the pigment found on the 2000-year-old

Qin terracotta warriors unearthed in the 1970s, turns out to

be a genuine Chinese invention.

This ancient pigment is one of only three not based on

natural dyes. Another is Egyptian blue, and until now it

was thought that the Chinese learned how to make their

purple pigment from the Egyptians. However, Chinese

purple contains barium in place of the calcium in Egyptian

blue, and the higher melting point of barium would have

made the Chinese pigment harder to synthesise.

Zhi Liu’s team at the Stanford Synchrotron Radiation

Laboratory in California has now probed the microstructure

of Chinese purple with X-rays. Their scans suggest that the

pigment was an all-Chinese invention, manufactured using

a glass-making technique perfected by Taoist monks.

From about 450 BC to AD 220, the monks made a glass

tinted with barium to imitate jade, and added lead to

lower the melting point. Liu’s team found that Chinese

purple was made in a very similar way, using lead to grow

the barium crystals, which suggests that Taoist monks were

responsible for it as well. Bolstering this theory is the fact

that as Taoism declined in China, so did the use of Chinese

purple (Journal of Archaeological Science, DOI: 10.1016/

j.jas.2007.01.005).

IMAG

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A touch of Taoist alchemy gave warriors their purple patches

18 | NewScientist | 14 April 2007 www.newscientist.com