(Submitted October 29, 1996)
Is it possible that on May 5, 2000 the alignment of the planets can have
enough gravitational effect on the earth to cause it to tip slightly
causing mass destruction.
I have tried to find this answer from many, but everyone refuses to
respond. Please help.
We are not solar system astronomers. So we don't know which, if any,
planets align on May 5, 2000. But we know for sure that what the other
planets in our solar system do cannot have any profound effects on the motion
of the Earth. Let us explain.
Long ago Sir Isaac Newton gave us a mathematical description of how one
object affects, and is affected by, the gravitational force of another object.
Many, many years of observations have proven this description to
be accurate (at least for masses like those of the planets).
Newton's Law of
Gravitation states: The force between any two objects having masses
M1 and M2 separated by a distance R is an attraction
along the line joining the objects and has a magnitude
F = (G x M1 x M2) / (R x R)
G is the universal gravitational constant which has a value of
6.6732 x 10-11 newton-meters2/kg2 for all
pairs of objects. A "newton" is a unit of force that physicists
use. It is defined to be the amount of force needed to accelerate a 1 kg
mass at 1 meter per sec2. The important thing to remember here is
that a newton, as a unit of force, is fairly small... like a millimeter is a
small unit of distance or a microsecond is a small unit of time.
So let's examine the pull of the planets on the Earth.
We know the following:
|Planet||Planet Mass||Minimum Distance from Earth|
|(Earth Masses)||(106 km)|
|Venus ||0.807|| ||41|
|Mars ||0.106|| ||79|
|Jupiter ||314.5|| ||629|
|Saturn ||94.1|| ||1,277|
|Uranus ||14.4|| ||2,720|
|Neptune ||16.7|| ||4,346|
|Pluto ||0.00218|| ||5,751|
The Earth has a mass of about 6 x 1024 kg.
So... let's hypothesize that we can miraculously put all the planets at
their minimum distances from Earth, all in a straight line in one
direction -- so their gravitational forces add. This, of course, can never
actually occur, but it will give us the maximum possible gravitational pull
of the other planets on the Earth. So let's pretend that we can do this. What
do we get?
If you put all the numbers in Newton's law (and make the units compatible),
you get that the maximum force that all the other planets can exert on the
Earth is roughly 3 x 1018 newtons. What sort of result will this
have on the Earth... well, we use Newton's First Law which says that if a
force F is applied to a mass M, the mass is accelerated by a value A.
(This is the famous equation F=ma). A force of 3 x 1018 newtons
acting on the Earth causes the Earth to accelerate by 5 x 10-7
meters per second per second. In other words, the planets in our solar
system -- aligned or not -- cannot cause a shift in the movement of the Earth
which will lead to mass destruction.
To compare, let us look at the gravitational force that the Sun exerts on
the Earth. The mass of the Sun is about 329,400 times that of the Earth. They
are separated on average by approximately 149,000,000 km. Thus, the Sun
exerts a force of ~3.5 x 1022 newtons on the Earth. So you see,
that the other planets in our solar system don't matter at all compared to the
To be entirely correct, we must tell you that the laws of physics involved
actually show that the Moon is the one of the most important objects to the
Earth... gravitationally speaking. It is the Moon which is responsible for
things like ocean tides and such. All the other planets in our solar system
added together do not have as large a gravitational effect on the Earth as
the Moon does.
Here is a table of tidal forces of the Sun, Moon, and Planets. With the
Sun's tidal force equal to 1.00, the following values are given in
A last thought: alignments of various planets in the solar system occur all
the time. It seems that every time one comes along, doom-sayers arise to cry
that this is the end of life on Earth as we know it. The laws of physics,
however, cannot be denied in this Universe of ours. If life on this Earth
ends, it will not be because of planets aligning in our solar system.
Questions on this topic are no longer responded to by the "Ask an Astrophysicist" service. See http://imagine.gsfc.nasa.gov/docs/ask_astro/ask_an_astronomer.html
for help on other astronomy Q&A services.