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Top Document: [sci.astro] Solar System (Astronomy Frequently Asked Questions) (5/9) Previous Document: E.18 What's the difference between meteoroids, meteors, and meteorites? Next Document: Copyright See reader questions & answers on this topic! - Help others by sharing your knowledge [This question comes up most frequently with reference to ALH 84001, the Martian meteorite that has been suggested as carrying evidence of past Martian life.] Most meteorites are thought to originate from collisions between asteroids in the asteroid belt. However, a small number have characteristics suggestive of a Martian or lunar origin. Why do we think this? The short explanation is that we can compare the composition of a meteorite to what various space probes and missions have told us about the composition of Mars (or the Moon). Moreover, in the case of a candidate Martian meteorite, it may have small pockets of gas trapped within it, which can be compared to the Viking measurements of the Martian atmosphere. Finally, it is possible to simulate launching a small piece of rock from Mars or the Moon (say, from an asteroid impact) and determine its path through space. Because of gravitational perturbations from other planets (notably Jupiter and the Earth), such a small rock could find its way to Earth, on fairly short time scales even (a few million years or so). For more details, see "On the Question of the Mars Meteorite," <URL:http://cass.jsc.nasa.gov/pub/lpi/meteorites/mars_meteorite.html> and Michael Richmond's archive of postings by James Head (from the Lunar and Planetary Institute) on this topic, <URL:http://a188-l009.rit.edu/richmond/answers/martian.html>. Finally, the meteorite Northwest Africa #11 (NWA011) has a composition similar to that of many Martian and lunar meteorites, but some important differences as well (notably in the amount of oxygen). This has led some to speculate that NWA011 might be from Mercury(!). User Contributions:Comment about this article, ask questions, or add new information about this topic:Top Document: [sci.astro] Solar System (Astronomy Frequently Asked Questions) (5/9) Previous Document: E.18 What's the difference between meteoroids, meteors, and meteorites? Next Document: Copyright Part0 - Part1 - Part2 - Part3 - Part4 - Part5 - Part6 - Part7 - Part8 - Single Page [ Usenet FAQs | Web FAQs | Documents | RFC Index ] Send corrections/additions to the FAQ Maintainer: jlazio@patriot.net
Last Update March 27 2014 @ 02:11 PM
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with stars, then every direction you looked would eventually end on
the surface of a star, and the whole sky would be as bright as the
surface of the Sun.
Why would anyone assume this? Certainly, we have directions where we look that are dark because something that does not emit light (is not a star) is between us and the light. A close example is in our own solar system. When we look at the Sun (a star) during a solar eclipse the Moon blocks the light. When we look at the inner planets of our solar system (Mercury and Venus) as they pass between us and the Sun, do we not get the same effect, i.e. in the direction of the planet we see no light from the Sun? Those planets simply look like dark spots on the Sun.
Olbers' paradox seems to assume that only stars exist in the universe, but what about the planets? Aren't there more planets than stars, thus more obstructions to light than sources of light?
What may be more interesting is why can we see certain stars seemingly continuously. Are there no planets or other obstructions between them and us? Or is the twinkle in stars just caused by the movement of obstructions across the path of light between the stars and us? I was always told the twinkle defines a star while the steady light reflected by our planets defines a planet. Is that because the planets of our solar system don't have the obstructions between Earth and them to cause a twinkle effect?
9-14-2024 KP