Shark embryos alert to danger

Adult sharks have highly sensitive receptors that can detect electric fields emitted by potential prey and predators. And now it turns out that at least in one species, their unborn offspring do too. “It’s the equivalent of a baby inside a mother responding to external stimuli before it’s born,” said Ryan Kempster, a marine neuroecologist from the University of Western Australia, who along with colleagues reported the findings in the journal, PLoS One.

The team studied the eggs of brownbanded bamboo sharks in an aquarium. To record the embryo activity, they scraped off the external layer, allowing them to view the transparent inner layer of the egg case when it was held in front of fibre-optic light.
Embryos that had completed about 90 per cent of their physical development — meaning they still had about one to two months remaining in their egg cases — were able to use electrical receptors to detect the signals of predators.

These embryos responded to predators’ electric fields by stopping all gill movements. Such information can help in developing better shark repellents, said Kempster, who is also the founder of the conservation group, ‘Support Our Sharks’.   
                                                                                                                     Sindya N Bhanoo, NYT

An asteroid’s brush with earth

On February 15, an asteroid orbiting the earth, called 2012 DA14, will pass extremely close to our planet. However, it won’t slam into our planet, say researchers. The asteroid, which astronomers estimate to be about 150 feet (45 meters) across, will give the earth a close shave. Two astronomers in Spain discovered 2012 DA14 at La Sagra Observatory, Granada in late February last year. The asteroid’s closest brush with earth will again come in 2020, but then the odds of an impact will be less than the chance of being hit by lightning in our lifetime – 1 in 1,00,000. The nearest 2012 DA14 can get to us next year is 12,680 miles (20,406 km). The asteroid will pass by satellites in geostationary orbit about 35,800 km (22,245 miles) above the equator.

A pair of good binoculars or a telescope are needed to view the flyby since the asteroid will appear faint to the naked eye. Predicting where an asteroid will be at some future time depends on a lot of things, including how good the observations are now and how long we’ve been watching it. When we observe an asteroid with a telescope, we can measure its position, but not with perfect accuracy. The earth’s atmosphere blurs the image a bit, and other factors make it impossible to get an exact measurement.

So we observe it many times, over as long a period as possible, to hammer down those uncertainties.
S A Mohan Krishna

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