Sunday, 15 June 2014

WHY ISN’T THE ASTEROID BELT A PLANET? by Fraser Cain on June 11, 2014

It seems like there’s a strange gap in between Mars and Jupiter filled with rocky rubble. Why didn’t the asteroid belt form into a planet, like the rest of the Solar System?
Beyond the orbit of Mars lies the asteroid belt its a vast collection of rocks and ice, leftover from the formation of the solar system. It starts about 2 AU, ends around 4 AU. Objects in the asteroid belt range from tiny pebbles to Ceres at 950 km across.
Star Wars and other sci-fi has it all wrong. The objects here are hundreds of thousand of kilometers apart. There’d be absolutely no danger or tactical advantage to flying your spacecraft through it.
To begin with, there actually isn’t that much stuff in the asteroid belt. If you were to take the entire asteroid belt and form it into a single mass, it would only be about 4% of the mass of our Moon. Assuming a similar density, it would be smaller than Pluto’s moon Charon.
There’s a popular idea that perhaps there was a planet between Mars and Jupiter that exploded, or even collided with another planet. What if most of the debris was thrown out of the solar system, and the asteroid belt is what remains?
We know this isn’t the case for a few of reasons. First, any explosion or collision wouldn’t be powerful enough to throw material out of the Solar System. So if it were a former planet we’d actually see more debris.
Second, if all the asteroid belt bits came from a single planetary body, they would all be chemically similar. The chemical composition of Earth, Mars, Venus, etc are all unique because they formed in different regions of the solar system. Likewise, different asteroids have different chemical compositions, which means they must have formed in different regions of the asteroid belt.
In fact, when we look at the chemical compositions of different asteroids we see that they can be grouped into different families, with each having a common origin. This gives us a clue as to why a planet didn’t form where the asteroid belt is.
If you arrange all the asteroids in order of their average distance from the Sun, you find they aren’t evenly distributed. Instead you find a bunch, then a gap, then a bunch more, then another gap, and so on. These gaps in the asteroid belt are known as Kirkwood gaps, and they occur at distances where an orbit would be in resonance with the orbit of Jupiter.

Jupiter’s gravity is so strong, that it makes asteroid orbits within the Kirkwood gaps unstable. It’s these gaps that prevented a single planetary body from forming in that region. So, because of Jupiter, asteroids formed into families of debris, rather than a single planetary body.

Saturday, 14 June 2014

Hubble Hubba: Stars Are Being Born Around A Black Hole In Galaxy’s Center by ELIZABETH HOWELL on JUNE 13, 2014

Let’s just casually look at this image of a galaxy 86 million light-years away from us. In the center of this incredible image is a bright loop that you can see surrounding the heart of the galaxy. That is where stars are being born, say the scientists behind this new Hubble Space Telescope image. “Compared to other spiral galaxies, it looks a little different,” NASA stated. “The galaxy’s barred spiral center is surrounded by a bright loop known as a resonance ring. This ring is full of bright clusters and bursts of new star formation, and frames the supermassive black hole thought to be lurking within NGC 3081 — which glows brightly as it hungrily gobbles up in-falling material.”
A “resonance ring” refers to an area where gravity causes gas to stick around in certain areas, and can be the result of a ring (like you see in NGC 3081) or close-by objects with a lot of gravity. Scientists added that NGC 3081, which is in the constellation Hydra or the Sea Serpent, is just one of many examples of barred galaxies with this type of resonance.
By the way, this image is a combination of several types of light: optical, infrared and ultraviolet.

Thursday, 5 June 2014