http://www.bbc.co.uk/news/science-environment-31519875

70,000 years is yesterday in astronomical time!

This is a diagram of our local system:

1. Heliosphere (0 - 100AU)
   This is filled with the influence of our Sun, which pours out massive amounts of all kinds of electrical & magnetic radiation (far more than just visible sunlight).
2. Heliopause (100AU)
   The edge of the bubble of the Heliosphere; outside is the radiation from the Galaxy (our Milky Way, the Galaxy that our sun is within), and it is the point where the pressure within from our sun is equated by the pressure without from the Galaxy.
3. Oort Cloud (1,000 - 100,000AU)
   A region filled with trillions of comets, each a mile or more across.
4. α-Centauri
   Proxima Centauri (at 4.24 light-years away, the star nearest to our own) forms a triple-star system with α-Centauri A+B.
5. AC +79 3888 (1,000,000AU)
   This catchily-named star, 17.6 light-years away from Earth, is the next star that will be visited by Voyager 1 (about 40,000 years hence).

A team of astronomers led by Eric Mamajek at the University of Rochester, New York, have been investigating Scholz’s star and have discovered that, just 70,000 years ago, that it came within 0.8 light-years of the Earth (damn close! and closer than any other), which means that it passed within the outer reaches of the Oort Cloud.

Scholz’s star is a Red Dwarf / Brown Dwarf binary:

Red dwarfs are by far the most common type of star in the Milky Way, estimated to constitute ¾ of all the stars. As the name suggests, they are small (at maximum, just half the size of our sun) and not very bright, so hard to see from the Earth. However, they are heavy enough to have ignited a thermonuclear hydrogen-hydrogen fusion reaction, and thus they shine.

Brown Dwarfs are even smaller than Red Dwarfs. Indeed, they are too small to sustain hydrogen-1 fusion, which is what defines the main-sequence stars to be stars. The very interesting feature is that they need to be bigger than Jupiter but, in addition, it is known that Jupiter radiates more energy than it absorbs (which means that some form of nuclear fusion/fission is occuring within the planet). If Jupiter had ended up a bit bigger, then ours would have been a binary star system.

Comets from the Oort Cloud: Scholz’s star is currently about 20 light years away, which indicates a relatively fast velocity. One interesting feature concerns current theories on gravitational effects from nearby stars disturbing comets within the Oort cloud & sending them our way into the inner solar system. Dr Mamajek believes that this did not happen with Scholz’s star, as it is both too small & too quick to have caused much disturbance.

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Alex Kemp