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Planets: Terrestrial

Terrestrial planet, or rocky planet,

is a planet composed primarily of silicate rocks or metals. Within the Solar System, the terrestrial planets are the inner planets closest to the Sun.

The terms “terrestrial planet” and “telluric planet” are derived from Latin words for Earth (Terra and Tellus), as these planets are, in terms of composition, “Earth-like”.

Terrestrial planets have a solid planetary surface, making them substantially different from the usually larger gas giants, which are composed mostly of some combination of hydrogen, helium, and water existing in various physical states.

{adapted from Wikipedia, Terrestrial Planet }

Many large moon exist in our solar system, which are made of the same materials as terrestrial plants:


The Grand Texture of Planets

By Caleb A. Scharf , March 30, 2015

In an idle moment, while staring at a set of solar system data, it occurred to me that it might be interesting to display a set of planetary surfaces on an equal footing, where the overall texture of these worlds was visible (although topography is probably a more accurate word on these scales) – and decided it was worth sharing as a brief piece of solar system trivia.

In the images below I’ve collected a set of planetary maps with the same cylindrical projection, and with their grayscale adjusted to a similar range. I’ve cheated a bit by including Ceres, Europa, Ganymede, and Titan because I wanted a comparison across a wider range of surface environments. I’ve also cheated by using some data that is based on radar reflectivity (Titan, Venus).

For a first pass I simply scaled the x-axis to be the same for all objects (the equatorial circumference). Below these individual images is one where I merged the maps by scaling the x-axis according to the true physical equatorial circumference. Since these are cylindrical projections that’s a slightly odd thing to do – but it does give an idea of the relative scale of each body.

What is, I think, quite striking, is how different each map is – there are very specific characteristics to each world. Even Ceres, which you might say looks a little like Mercury, reveals its diminutive size by virtue of its cratering – the scale of most of the stuff that has hit Ceres is clearly much larger compared to the size of this world than most of the stuff that has hit Mercury (and the impactors on both should share a common size distribution).

The Earth displays a clear dichotomy between continental crust and oceanic basins – and while this may be exaggerated in these particular datasets, there’s no doubt that Earth would always stand out when compared to its planetary siblings.

Mars, for example, looks more warty than crusty. Venus is perhaps the most similar in character, but a bit wrinkly, while Ganymede definitely has ‘plate’ like coverage, but on this moon the regions look fragmented and cracked rather than raised or embossed.

In the last panel, with the worlds gathered together, I think Earth’s richness of form really shows – even in dull gray it appears sculpted to a different degree.

Here’s the gallery: Stepping outwards from the Sun, first up is Mercury as seen by NASA’s Messenger probe.

Next comes Venus, this is a map shaded to indicate topography rather than being a pure radar reflectivity map.

And now an odd-looking world, a topographic map stripped of atmosphere and surface water. I’ve also made a horizontal flip, in order to try to see the Earth through a stranger’s eyes.

Mars rounds out the terrestrial worlds.

Little Ceres – the map is not yet very high resolution or complete, but it displays a distinct character.

Europa is up next, ice-coated and very different than a rocky surface.

The grand Jovian satellite Ganymede has a truly striking surface patterning.

And finally, here is much of the surface of Titan, recorded as a radar reflectivity map, showing dark zones of liquid hydrocarbons.

Putting all of these together, scaling by the x-axis and re-arranging, I got a nice mosaic. The sheer grandeur of the Earth is very apparent.

Caleb A. ScharfAbout the Author: Caleb Scharf is the director of Columbia University’s multidisciplinary Astrobiology Center. He has worked in the fields of observational cosmology, X-ray astronomy, and more recently exoplanetary science. His books include Gravity’s Engines (2012) and The Copernicus Complex (2014) (both from Scientific American / Farrar, Straus and Giroux.) F


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