Sceientist Warn Us About Danger From Space

Sceientist Warn Us About  Danger From Space

Tokuhiro Nimura is a researcher at the Japan Spaceguard Association, which was formed to monitor near-Earth objects that might strike the planet. In March 2016, Nimura and his coworkers suggested that the extinctions, global cooling and iridium layer might have been caused by the Solar System passing through a molecular cloud: one of the great clouds of gas and dust in space from which stars form. As dust accumulated in the atmosphere, it would have formed a haze that reflected sunlight and cooled the planet.

The basic idea goes back to a 1975 suggestion by British astronomer William McCrea. He thought that if Earth passed through an interstellar "dust lane" it could cause an ice age. At the time, astronomers Mitchell Begelman and Martin Rees pointed out that such dust might instead affect the way particles streaming from the Sun impinge on the Earth’s atmosphere and expose the planet to high doses of radiation, causing extinctions as well as climate changes.

The event 66 million years ago is just one of several known "mass extinctions", in which many species worldwide seem to have died out suddenly.

The biggest was at the end of the Permian period 252 million years ago, when no less than 96% of all life on Earth seems to have died out. All life today is descended from the surviving 4%, so it is easy to see that evolutionary history would have been very different if this extinction had not happened. When species die off, those that survive get opportunities to expand and diversify that they would not otherwise have had.

Our galaxy is shaped a bit like a plate. As it rotates, the Sun rises and falls in the galactic plane, rather like a merry-go-round horse. These shifts in position could change the amount of cosmic rays that stream through the Solar System and hit Earth.

Cosmic-ray collisions could also change the chemistry of the atmosphere. They might produce electrically-charged particles that affect cloud formation and thus climate, or they could destroy the ozone layer that protects the Earth from the Sun's harmful ultraviolet rays.

Stars explode as supernovae all the time; when they do, they can temporarily outshine their entire host galaxies. Many are seen every year in other galaxies, but the most recent one known to have happened in our own galaxy became visible about 140 years ago. Another in our galaxy that appeared in 1572 was so bright, it was visible to the naked eye and was seen by the astronomer Tycho Brahe.

But he adds that, while it is far from clear that our galaxy really has a disk of dark matter, "we know so little about the distribution and make-up of dark matter within the galactic disk and halo that the premise is certainly viable within our present uncertainty."

At this point that might be a rather too-familiar refrain: "interesting idea but it's all speculation". Should we believe any of these notions?


Full Article From BBC