Unfortunately... A little late & sort of an urban legend

Sounded interesting...so I looked it up to get more info and was planning to put it on my calendar.  Doh!    Here is what I found:

It happened 4 years ago - August 23, 2003.
http://www.space.com/scienceastronomy/mars_amateurs_030624.html

But there has been an email about it circulating for years.
http://www.snopes.com/science/mars.asp
http://urbanlegends.about.com/library/bl_mars_encounter.htm

Sonya, I will attempt to briefly answer your questions.

Possibly the most important difference between Earth and Mars is that Mars is only about half the diameter of the Earth and only about 11% as massive. Mars has much less gravity. It is thought that this is why Mars lost its water and atmosphere and Earth hasn't. Today Mars is cold, dry and (probably) dead, but it is very likely that it was much more earthlike in the past.

Venus is the planet that makes me very nervous about the near term future of the Earth. It is only slightly smaller than the earth and has a surface temperature of 900 degrees Fahrenheit. Although somewhat closer to the Sun the main reason for the high temperature is that the atmosphere is almost entirely carbon dioxide.

Although the Sun is very slowly getting brighter most estimates are that we have another six billion years or so before it uses up all its hydrogen, swells to a red giant, sheds its outer layers, and ends up as a white dwarf.

Long before the Sun uses up its hydrogen the future of the Earth gets pretty grim as the amount of solar energy hitting the planet rises. (We are talking a few hundred million years.) I recommend the book "The Life and Death of Planet Earth", by Peter Ward and Donald Brownlee, Owl Books, 2004, if you want the gory details.

Unfortunately, things get grim much sooner than a few hundred million years. Ward and Brownlee feel that the present Interglacial period is an anomaly in the history of the earty. Over a few tens of thousands of years they think the earth will reabsorb all the carbon dioxide we are putting into the atmosphere and humans will see much of the earth covered in ice again.

Ice ages can come quickly. I've seen estimates that if the melting ice in Greenland deflects the Gulf Stream that Europe could be plunged into a new ice age in only a few years. See Gulf Stream near the bottom of the following page: http://www.geol.umd.edu/~jmerck/geol100/lectures/33.html .

I'm not convinced we can avoid a runaway greenhouse effect, but one can argue about that and I'm not an expert in this field anyway. However, as climatologist Stephen Schneider put it (speaking about the concentration of carbon dioxide in the atmosphere): "The ever rising curve from Manuna Loa has taken on the characteristics of a cobra poised to strike." (Filters against Folly, by Garrett Hardin, Penguin Books, 1985, p. 148)

Incidentally, if you are interested in astronomy there is a coffee table book with lots of information and gorgeous illustrations that I will recommend: "The Illustrated Atlas of the Universe", by Mark Garlick, 2006. It was orignially published in Australia. Borders was remaindering it for about $10.00 the last time I looked.


-- Modified on 8/21/2007 12:00:32 AM