By Jane Houston Jones

Are you eager to see the annual Perseids meteor shower tonight? You’ll have to wait until near midnight to see it, so why not pass the time by viewing Venus, Saturn and Mars right from your doorstep? Step outside for the planetary warm-up act just as soon as the sun sets. (Viewing times will be best over the next week. By August 20, the planets set lower on the horizon and are harder to see.)

All you have to do is look towards the west for bright Venus to appear. Now hold your clenched fist up to the sky, covering Venus. To the right of Venus, about half of a clenched fist away, is a second planet: That’s Saturn! And to the upper left of Venus is another planet: Mars!

That’s not all you’ll be able to see. Look below Venus for the slender crescent moon. If you don’t see the moon, look again on the night of Friday, August 13 — it will be a larger crescent to the left of Venus.

Though the three planets appear together in our line of sight, they are really far apart from each other. Mars is about 300 million kilometers (about 185 million miles) from Earth, while Venus is 112 million kilometers (about 70 million miles) away. Saturn? It’s 1,535 million kilometers (about 954 million miles) from Earth. And finally, the moon is only 363 thousand kilometers (about 225 thousand miles) away. It’s fun to compare the size of the moon and Mars, especially if you received that annual email incorrectly stating that Mars will be as big as the moon this month.

Donald Yeomans

With the recent discovery of the amino acid glycine in the comet dust samples returned to Earth by the Stardust spacecraft, it is becoming a bit more clear how life may have originated on Earth. Water is a well-known ingredient in both comets and living organisms, and now it appears that amino acids are also common to comets and living organisms. Amino acids are used to make proteins, which are chains of amino acids, and proteins are vital in maintaining the cell structures of plants and animals.

Amino acids had previously been identified in meteorite samples, and these samples are thought to be the surviving fragments from asteroid collisions with the Earth. So now it appears that both comets and asteroids in the Earth’s neighborhood, the so-called near-Earth objects, delivered some of the building blocks of life to the early Earth.

Asteroid Eros - Mosaic of Northern Hemisphere. Image Credit: NASA/JPL/JHUAPL
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Impacts of comets and asteroids with the early Earth likely laid down the veneer of carbon-based molecules and water that allowed life to form. Once life did form, subsequent collisions of these near-Earth objects frustrated the evolution of all but the most adaptable species. The dinosaurs checked out some 65 million years ago because of an impact by a six mile-wide comet or asteroid off the coast of the Yucatan peninsula. Fortunately, the small, furry mammalian creatures at the time were far more adaptable and survived this impact event. Thus, present day mammals like us may owe our origin and current position atop Earth’s food chain to these near-Earth objects, one of which took out our dinosaur competitors some 65 million years ago.

Today, most of the attention directed toward near-Earth objects has to do with the potential future threat they can pose to life on Earth. However, the recent Stardust discovery of a cometary amino acid reminds us that, were it not for past impacts by these objects, the Earth may not have received the necessary building blocks of life, and humans may not have evolved to our current preeminent position on Earth. While giving thanks to these near-Earth objects, we still need to make sure we find the potentially hazardous comets and asteroids early enough so we don’t go the way of the dinosaurs.

For more information on near-Earth objects, see: http://www.jpl.nasa.gov/asteroidwatch/index.cfm