Space geology?

Ken Tapping, 21th October, 2015

In the sky this week…

  • Saturn lies low in the sunset glow.
  • Venus rises before 4am, with Jupiter and Mars behind, very close together.
  • The Moon will reach First Quarter on the 20th and be Full on the 27th.

Some time ago I sent an image of a rock outcrop to a good friend who is a geologist. It showed alternating layers of different rocks. I did not give him any other information. I got a report back saying that the rocks were formed of sediments from the bottom of a fairly still, large body of water. He described how the lake had shallowed and deepened periodically, and then dried up sometimes. This happened increasingly often until the water vanished permanently. He then asked where this outcrop was located. I told him – Mars. It was one of the images from the Curiosity rover, currently exploring the surface of the Red Planet. What we are learning about the other bodies in the Solar System and beyond shows how much astronomy has changed and continues to change.

Astronomy is one of the oldest sciences. However, for most of its history, all that could be done was to measure the positions of things in the sky and how those positions changed, such as the apparent movement of the Sun, Moon and planets against the stars. It became apparent early on that what is going on up there looks very different from what seems to be going on down here. An eclipse of the Sun could be predicted years in advance, but forecasting next week’s weather was hard, and still is. The sky was different, ordered, regular, with an occasional comet sent by the gods as a warning of bad things on the way. This is probably how astrology came about. However, as astronomy crystallized as a science, astrology was left behind as a remnant of the old superstition.

For thousands of years the only planet available for detailed study was ours, so we came up with sciences such as geology, geography, geophysics and so on. The word "geo" means pertaining to the Earth. Even geometry, a branch of mathematics, means "measuring the Earth". Inchworm caterpillars, also called "loopers" because of the way they move, are also called geometers – Earth measurers, because of they look as though they are carefully pacing out a distance.

In the 1960’s astronomy started to change dramatically. Until then astronomy remained different from the Earth sciences in that even through our best telescopes, planets were distant discs showing either cloud belts or subtle surface markings. We knew little about the surfaces of those worlds and even less about what lay beneath. The only body we could see in detail was the Moon. Even then scientists were arguing as to whether the craters on the Moon are due to volcanism or impacts. In 1969 astronauts first walked the lunar surface, and we started seeing the Moon in detail, close up, as we see the Earth. Over following decades, space probes, orbiters, landers and rovers gave us the same views of other planets and moons. Now there are books on the geology of the Moon, Mars and other worlds. We will soon have detailed descriptions of the geologies of Pluto and Charon – Pluto’s largest moon. There are also "geographic" maps of those worlds too. On my bookshelf I have a book titled "Planetary Science – the Geological Perspective". These days "geo" in the name of a science may not mean a focus on the Earth at all, but more that it refers to any sort of body, including planets, asteroids, moons or comets. Geology now just means the study of the materials and processes that make a world, and geography the nature of a world’s surface. This is a good thing, since we now see what our planet is like in comparison with other worlds – one planet among many.

This means that astronomy is now something different from what it was. It is now not so much a traditional science, but more something encompassing the application of all the other sciences to objects beyond the Earth.

Ken Tapping is an astronomer with the National Research Council's Dominion Radio Astrophysical Observatory, Penticton, BC, V2A 6J9.

Telephone: 250-497-2300
Fax: 250-497-2355

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