The Earth as a Distant Planet A Rosetta Stone for the Search of Eart
Is the Earth, in some way, special? Or is our planet but one of the millions of other inhabited planets within our galaxy? This is an exciting time to be asking this old question, because for the first time in history, the answer is within reach. In The E
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Observing the Earth
The planet Earth plays the leading role in this book. The detailed knowledge we have of it at present has been accumulated mainly over the last decades. Over the centuries, the task of producing the first maps of our planet’s surface has slowly and painstakingly been carried out. From our towns and villages, humanity has mapped the observable Earth, with the depths of the oceans remaining as the last obstacle. Simultaneously, human ingenuity has devised methods to measure its basic parameters. At present, we have already detected around 300 exoplanets and we are progressing in the characterization of their physical properties, including global maps of their surfaces. We are proceeding inversely to the way in which we observed the Earth, making first global observations and, step by step, increasing the observed level of detail. In the past, the Sun was our guide for interpreting the observations of other stars; now our planet will be the Rosetta Stone used to decipher the data from other planetary worlds. The proposed Earth–Exoplanets connection is based on the universality of processes leading to the formation of planets around stars. Thus, what we can learn by observing the Earth as a distant planet can be used to interpret the observations of future terrestrial planets. However, we must keep in mind that our reference is 4.6 Ga old, and has only one Earth mass and radius, while certainly other ranges of these parameters will be observed on exoplanets.
1.1 The Exploration of Our Planet For many centuries, the Earth was considered as something different from the rest of the Universe. This was largely a final consequence of a debate in classical Greece between two different models. Leucippus (first half of fifth century BCE) was the founder of atomism. His ideas are mainly known from Democritus (460–370 BCE),1 who suggested that the 1 No word written by Leucippus has survived. From Democritus we have only some fragments of his books, but a good description of his principles are included in the writings of Aristotle and Diogenes Laertius.
M. V´azquez et al., The Earth as a Distant Planet: A Rosetta Stone for the Search of Earth-Like Worlds, Astronomy and Astrophysics Library, c Springer Science+Business Media, LLC 2010 DOI 10.1007/978-1-4419-1684-6 1,
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1 Observing the Earth
Universe is composed of ‘atoms’ and ‘voids’. Both are infinite and constitute the primary elements of everything. Each atom is uniform, homogeneous and indivisible. To him is attributed the following sentence: There are innumerable worlds of different sizes. In some there is neither sun or moon, in others they are larger than in ours and others have more than one. These worlds are at irregular distances, more in one direction and less in another, and some are flourishing, others declining. Here they come into being, there they die, and they are destroyed by collision with one another. Some of the worlds have no animal or vegetable life nor any water. (Guthrie 1979, p. 405).
This theory was spread throughout Europ
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