The Solar System: An Insider’s Guide Friday! What Lies Beyond? Small Bodies and Extrasolar Planets

Craters: Here, there, and everywhere Calisto Crater Chain Craters in Chad Craters on Ganymede Meteor Crater, AZ We’ve seen many examples of cratering on numerous bodies throughout the solar system. The Moon and Mercury were each covered in craters of various sizes. Other bodies in the SS whose surfaces are solid and fairly unchanging also show evidence of bombardment. Things smack into planets often. Asteriods, meteors and comets.

What is doing all this cratering? Option 1: Asteroids They are mostly located beyond Mars and before Jupiter. They range in size from tiny pebbles to nearly 600 miles across (Ceres). They collide with each other and break apart: there are many more smaller asteroids than larger ones. Their size distribution roughly mimics the distribution of crater diameters on solar system bodies. But why are they here? Perhaps a planet that didn’t or couldn’t form. Perhaps a planet that was broken apart by a huge impact?

Amazing: Bode’s Law … __________________ The asteroids are right where a planet should be, according to Bode’s Law.

Gaps and Resonances, Trojans The trojans occupy a position making an equilateral triangle with the Sun and Jupiter. The Kirkwood gaps in the asteroid belt occur at locations where the period of the asteroid is an integer multiple of the period of Jupiter. The resonance kicks them out!

Terminology meteoroid - asteroid which enter Earth's atmosphere usually pretty small (grains of sand, pebbles) meteor - streak of light from meteoroid burning up in Earth's atmosphere most burn up miles above surface of Earth meteorite - solid debris that reaches Earth's surface must start out greater than basketball size to reach Earth's surface

Comets Could the existence of Jupiter, with a mass large enough to divert large comets to impact with it, save us from potentially harmful impacts?

Don’t Panic No one should be overly concerned about an Earth impact of an asteroid or comet. The threat to any one person from auto accidents, disease, other natural disasters and a variety of other problems is much higher than the threat from NEOs. Over long periods of time, however, the chances of the Earth being impacted are not negligible so that some form of NEO insurance is warranted. At the moment, our best insurance rests with the NEO scientists and their efforts to first find these objects and then track their motions into the future. We need to first find them, then keep an eye on them.

Hale-Bopp

Comets Overview The total mass of comets in the Oort cloud is estimated to be 40 times that of Earth. This matter is believed to have originated at different distances and therefore temperatures from the sun, which explains the compositional diversity observed in comets. Recently, about two dozen EKOs that may have formed closer to the Sun but subsequently were scattered by Uranus and Neptune (called "Centaurs and scattered disk objects") have also been discovered in highly inclined, elliptical orbits extending as far out as 200 AU. Indeed, Pluto and Charon are suspected as being among the larger examples of these icy worlds of the outer Solar System, and there may be as many as 100,000 EKOs with diameters greater than 100 km (62 miles) -- as well as a billion or more kilometer-sized comets -- orbiting within 50 AUs of the Sun. By late 2000, over 300 EKOs had been discovered. However, none were found to be currently orbiting farther from the Sun than 55 AUs, despite recent surveys that were capable of detecting objects out to 65 AUs out.

Kuiper Belt: Home to Pluto…?

Extrasolar Planets

More beyond the Sun

Will we ever see other planets?