Why is Earth so dry?

A new analysis of the common model explaining how the planets formed around our Sun uncovers a possible reason for Earth's comparative dryness.

By STScl, Baltimore, Maryland — Published: July 17, 2012

This illustration of two different disk models shows overhead views of the structure of the protoplanetary disk that encircled the newborn Sun 4.6 billion years ago. The Sun's family of planets agglomerated from dust and ices within the disk. Credit: NASA/ESA/A. Feild (STScI)

With large swaths of oceans, rivers that snake for hundreds of miles, and behemoth glaciers near the North and South Poles, Earth doesn't seem to have a water shortage. And yet, less than one percent of our planet's mass is locked up in water, and even that may have been delivered by comets and asteroids after Earth's initial formation.

Astronomers have been puzzled by Earth's water deficiency. The standard model explaining how the solar system formed from a protoplanetary disk (a swirling disk of gas and dust surrounding our Sun) billions of years ago suggests that our planet should be a water world. Earth should have formed from icy material in a zone around the Sun where temperatures were cold enough for ices to condense out of the disk. Therefore, Earth should have formed from material rich in water. So why is our planet comparatively dry?

MORE: http://www.astronomy.com/en/News-Observing/News/2012/07/Why%20is%20Earth%20so%20dry.aspx

Sources: Space Telescope Science Institute, Astronomy Magazine

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