Dark Matter and Dinasours

 Dark Matter and the Dinosaurs by Lisa Randall. As of November 2014 there are 5,253 known comets. The word "comet" comes from a Greek word that translates as 'wearing long hair.' Some are believed contain to components of DNA and RNA:

"Comets originate well beyond Jupiter in the outer regions of the Solar System, where water and methane remain cold and frozen. In these very cold regions far from the Sun, ice doesn't turn to gas. Ice remains ice. Only when com­ets pass into the inner Solar System where they are closer to the heat of the Sun do the volatile materials in the comet vaporize so that they stream out, along with some dust, creating an atmosphere around the nucleus called the coma. The coma can be much bigger than the nucleus -- thousands or even millions of kilometers across, sometimes even growing to the size of the Sun. Bigger dust particles remain in the coma whereas lighter ones are pushed into the tail by the Sun's radiation and charged particle emissions. A comet consists of the coma, the nucleus it surrounds, and the tail that streams away. ...

"Comets are among the most spectacular objects we can witness overhead with the naked eye. Most are very faint, but ones such as Halley's, which are visible without a telescope, pass by perhaps a few times a decade. Comets orbit the Sun with bright ion tails and sepa­rate dust tails that generally point in different directions. These trails of brightly shining dust and gas are the origin of their name, which comes from a Greek word that translates as 'wearing long hair.' Whereas the dust tail generally follows the comet's path, the ion tail points away from the Sun. The ion tail forms when solar ultraviolet radiation hits the coma, tearing off electrons from some of the atoms there. The ionized particles create a magnetic field in what is known as a magnetosphere. ...

"When in the 1950s the German scientist Ludwig Biermann (and indepen­dently another German, Paul Ahnert) made the extraordinary ob­servation that the bright ion tail of a comet always points away from the Sun, Biermann proposed that the Sun emits particles that 'push' on the comet tail, making it point this way. In a metaphorical sense, the 'solar wind' 'blew' the ion tail there. Understanding this process taught scientists about both comets and the Sun. ...

A comet's orbit showing the different directions of the gas and dust tails as the comet passes the Sun

"Comet tails can extend up to tens of millions of kilometers. ... The exact chemical makeup of comets is even harder to observe than the objects themselves. Meteorites found on Earth give us some clues by conveying some of their actual material to our home turf. ... Using ... sparse clues, sci­entists have concluded that the nucleus consists of water ice, dust, pebble-like rocks, and frozen gases including carbon dioxide, car­bon monoxide, methane, and ammonia. ... One further fascinating compositional feature of a comet is that it contains organic compounds, such as methanol, hydrogen cyanide, formaldehyde, ethanol, and ethane, as well as long-chain hydrocar­bons and amino acids, the precursors of life. Meteorites on Earth have even been found to contain components of DNA and RNA that presumably came from either asteroids or comets."