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Shooting star, seen from above

ISS image of a meteor

The bright streak of a Perseid meteor as it flashes into Earth's upper atmosphere. The image was snapped by an astronaut aboard the International Space Station.

THIS ASTRONAUT PHOTOGRAPH, taken from the International Space Station (ISS) while over China (approximately 400 kilometres to the northwest of Beijing), provides the unusual perspective of looking down on a meteor as it passed through the atmosphere.

Many people have spent time outdoors under a dark sky, watching for “shooting stars” to streak across the firmament. In some cultures, this event is an occasion to make a wish; in others it is viewed as a herald of important events, such as the birth of a future ruler.

While not actual stars, “shooting stars” do come from outer space, in the form of meteoroids entering the Earth’s atmosphere.

Meteor or meteorite?

Meteoroids are small objects moving through the Solar System that are attracted to the Earth by its gravitational pull.

These small objects—typically fragments of asteroids or comets, though they can also originate from the Moon or Mars—begin to heat and burn up as they collide with air molecules in Earth’s atmosphere, creating a bright vapour trail or streak.

At this point, the object is known as a meteor. If any remnant of the object survives to impact the Earth’s surface, it becomes known as a meteorite.

While most meteorites are natural in origin, on occasion manmade space debris can re-enter the atmosphere and also become a meteor or even a meteorite!

Comes from a comet

The image was taken on August 13, 2011, during the Perseid Meteor Shower that occurs every August. The Perseid meteors are particles that originate from Comet Swift-Tuttle; the comet’s orbit is close enough for these particles to be swept up by the Earth’s gravitational field every year—leading to one of the most dependable meteor shower displays.

Green and yellow airglow appears in thin layers above the limb of the Earth, extending from image left to the upper right. Atoms and molecules above 50 kilometres in the atmosphere are excited by sunlight during the day, and then release this energy at night, producing primarily green light that is observable from orbit.

Part of a ISS solar panel is visible at upper right; behind the panel.

Astronaut photograph provided by the ISS Crew Earth Observations experiment and Image Science & Analysis Laboratory, Johnson Space Centre. Text adapted from information issued by William L. Stefanov, Jacobs/ESCG at NASA-JSC.

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Made in Space – DNA building blocks

NASA-FUNDED RESEARCHERS HAVE UNCOVERED EVIDENCE that some building blocks of DNA—the molecule that carries the genetic instructions for life—found in meteorites, were likely formed in space.

The research gives support to the idea that a ‘kit’ of ready-made parts formed in space and delivered to Earth by meteorite and comet impacts, assisted the development of life.

Adapted from information issued by NASA / GSFC.

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Comet crash caused climate change?

Artist's impression of an asteroid or comet striking the Earth.

Artist's impression of a comet striking the Earth.

Earth was struck by thousands of cometary fragments over the course of an hour 13,000 years ago, leading to a dramatic cooling of the planet, according to astronomer Professor Bill Napier of the Cardiff University Astrobiology Centre.

The cooling, by as much as 8 degrees C, interrupted the warming which was occurring at the end of the last ice age and caused glaciers to readvance.

Evidence has been found that this catastrophic change was associated with some extraordinary extraterrestrial event.

The change is marked by the occurrence of a “black mat” layer a few centimetres thick found in rock layers at many sites throughout the United States containing high levels of soot indicative of continental-scale wildfires.

There are also microscopic hexagonal diamonds (nano-diamonds), which are produced by high-pressure shock events and are found only in meteorites or impact craters.

These findings led to the suggestion that the catastrophic changes of that time were caused by the impact of an asteroid or comet 4 km across on the Laurentide ice sheet, which at that time covered what would become Canada and the northern part of the United States.

The cooling lasted over a thousand years, and its onset coincides with the rapid extinction of 35 genera of North American mammals, as well as the disruption of the Palaeoindian culture.

The chief objection to the idea is that the odds against the Earth being struck by an asteroid this large only 13,000 years ago are a thousand to one against. And the heat generated by the rising fireball would have been limited by the curvature of the horizon and could not explain the continent-wide occurrence of wildfires.

Multiple comet crashes the cause?

Professor Napier has now come up with an model that accounts for the major features of the catastrophe without involving such an improbable event. According to his concept, the Earth ran into a dense trail of material from a large disintegrating comet.

Fragments of comet 73/P Schwassman-Wachmann 3

Comets sometimes break into many pieces, such as 73/P Schwassman-Wachmann 3, seen in this Hubble Space Telescope image from 2005.

He points out that there is compelling evidence that such a comet entered the inner planetary system between 20,000 and 30,000 years ago and has been fragmenting ever since, giving rise to a number of closely related meteor streams and asteroids known as the Taurid Complex.

In the course of the giant comet’s disintegration, the environment of the interplanetary system would have been hazardous and the Earth would probably have run through at least one dense swarm of cometary material.

The new model indicates that such an encounter would last for about an hour during which thousands of impacts would take place over continental areas, each releasing the energy of a megaton-class nuclear bomb, generating the extensive wildfires which took place at that time. The nano-diamonds at the extinction boundary would then be explained as having come in with the comet swarm.

One recent meteorite is known which may have come from this giant comet progenitor—the Tagish Lake meteorite, which fell over Yukon Territory in January 2000. It has the highest abundance of nano-diamonds of any meteorite so far analysed.

Professor Napier sums up his model: “A large comet has been disintegrating in the near-Earth environment for the past 20,000 to 30,000 years, and running into thousands of fragments from this comet is a much more likely event than a single large collision. It gives a convincing match to the major geophysical features at this boundary.”

Adapted from information issued by the RAS. Image credits: NASA / ESA / H. Weaver (JHU/APL) / M. Mutchler / Z. Levay (STScI) / G. Rhemann and M. Jager.