Catastrophic Cosmic Alignment?

Can the sun and planets line up across the solar system and cause disaster here on Earth?

For centuries disaster and calamity have been foretold whenever the planets of our solar system align. In the last few decades these ideas have found their way into print in books (making their authors good money) through predictions about the grave consequences of such an event. The book The Jupiter Effect predicted that California would be hit by major earthquakes set off by an 1982 alignment. Almost two decades later 5/5/2000: Ice, The Ultimate Disaster said that an alignment in May of 2000 would unleash increased solar activity, starting a chain of events that would cause the Earth's crust to slide and poles to shift. Many of these theories suggest that the tidal forces from these grand alignments can cause earthquakes, floods and disasters of all sorts. What does science tell us about these predictions? Can we associate past alignments with catastrophes? Should we expect disasters from future alignments?

First, let's define the term alignment. An alignment of planets and the sun, as seen from Earth, is simply a time when many of the planets in the solar system are together in a rough line on the other side of the sun from Earth. This would be visible as a conjunction of the planets in the sky, except that since the conjunction includes the sun, and the sun washes all other light sources out of the daytime sky, it renders the conjunction impossible to observe. Most disaster scenarios argue that the tidal forces unleashed by an increase in gravity in one direction will cause major problems on our planet. Some disaster theories even have gone so far as to suggest that the Earth might be torn in half.

Gravity is the force that pulls all objects toward one another. The amount of gravity an object exerts is proportional to the mass of an object. That's why a large object, like the Earth, pulls you toward it. With a slightly smaller object, such as the moon, there is less gravity because the moon is only a fraction of the mass of the Earth. Even small objects, such as you and the computer you are sitting in front of, have gravitational pull attracting you toward each other, but because your mass and the computer mass are so small the amount of gravity is negligible.

Compared to other forces gravity is one of the weakest in the universe, but what it does not have in strength it makes up for in tenacity. Gravity is effective over the distance of millions of miles between the Sun and its planets as well as the millions of light years between the stars in a galaxy and the billions of light years between one galaxy and another. While gravity can act at great distances, it does lose a lot of its strength. Every time you double the distance between yourself and another object, the force of gravity acting on you from that object drops by one quarter. If you put ten times the distance between you and the other object, the strength drops to one hundredth its original value (The strength falls by the square of the increase in distance).

Tidal forces are caused by the gravity of one large object acting on another. One example would be the moon's gravity pulling on Earth. Because Earth is so big and gravity's strength drops so rapidly with distance, the strength of the moon's pull on the side of Earth facing it is significantly more than the moon's pull on the far side of the Earth. This difference acts on the Earth to try and tear it in two. Fortunately our planet is strong enough to resist this pull. However, any liquid material on the surface of the Earth is drawn toward the moon by these tidal forces. That is the reason why our oceans have low and high tides.

Under the right conditions, tidal forces can become quite strong.. The 19th century French astronomer Édouard Roche calculated that if a moon gets too close in its orbit around its planet it will be torn apart by this force. Roche estimated this distance to be about 2 1/2 times the size of the planet's radius. This measurement had become known as the Roche Limit.

The rings around the planet Saturn are thought to be the remains of one or more moons that came within Saturn's Roche Limit and were shattered into the small rocks that now compose the rings. In 1992 the comet Shoemaker-Levy 9 passed within the Roche Limit of the planet Jupiter and was torn into at least 21 separate pieces. Two years later these pieces plunged into Jupiter's atmosphere in a dramatic collision that was observed by Earth's telescopes and was broadcast around the world.

Could the Earth come to the same fate as Saturn's moon or comet Shoemaker-Levy 9? Could an extreme planetary alignment bring us within some interplanetary Roche Limit? Physics says, "No."

While the gravity exerted by the planets Jupiter, Saturn, Neptune and Uranus is large, they are very far away. Thus the amount of gravity and tidal forces they exert on Earth are only a tiny fraction of the forces our much closer moon exerts even though the moon is much smaller. Astronomer Philip Plait (of the Bad Astronomy Page) has calculated the gravity and tidal forces for the planets at their closest approach to Earth and compared them to the same forces from the moon. According to Plait's calculations even the largest of the planets, Jupiter, exerts only one hundredth the force on our planet as the moon and only 0.000006 percent of the tidal force. Venus, our nearest planetary neighbor, has a gravity that affects us at a tiny 0.006 percent that of the moon with tidal force of only 0.00005 percent that of the moon.

Could the combination of all the planetary forces plus the sun and moon bring on disaster? It seems unlikely. The gravitational forces of all the planets together add up to less than 1.8 percent of the force of the moon (Even this 1.8 percent value is high since all the planets never get in perfect alignment and never pull in exactly the same direction). The moon, because its orbital path is not perfectly circular, varies its own gravitational force on Earth as much as 25% every two weeks with no obvious catastrophic effect on our planet. Scientists have tried to find a connection between the tides of the moon and earthquakes, but so far no definitive conclusions have been reached.

Perhaps the best proof that planetary alignments do not cause disasters can be found by simply looking at history. Neither the 1982 alignment nor the 2000 alignment caused any problems on our planet, though they did sell a lot of books.

So do we have to worry that an alignment of the planets will cause some sort of disaster on Earth? No, we don't. Planetary alignments remain a beautiful and interesting, but safe, curiosity in the sky.

Copyright Lee Krystek 2001. All Rights Reserved.