Will comet Elenin destroy us?
And: What about the planets lining up in the sky?
NASA/JPL-Caltech
by Dr Jonathan D Sarfati
Published: 4 August 2011(GMT+10)
Quite a number of readers have written to us about the comet Elenin. A number of
websites are preaching doom and gloom about this, as they have done with planetary
alignment. Dr Jonathan Sarfati demolishes these claims with real physics
and astronomy.
What is a comet?
We have addressed the issue of comets in detail in
Comets—portents of doom or indicators of youth? Readers may like to study
this, especially for the strong evidence they provide against millions of years.
This also points out that comets have widely been regarded as indications of looming
disaster. Now the sensationalism has a pseudo-scientific gloss involving the actual
comet.
My subcompact automobile exerts a greater influence on the ocean’s tides than
comet Elenin ever will.—Don Yeomans, of NASA’s NEO program.
But in reality, the comet itself is a ‘dirty snowball’ only a few km
across. And when it is close to the sun, then some of this material evaporates and
forms an ion tail and a dust tail. These can dominate the sky. However, the actual
material of the tail is even thinner than our best laboratory vacuums. So there
is no way the tail can hurt us in the slightest—there is almost nothing there!
Indeed, Earth passed through the tail of
Halley’s Comet in 1910 and barely noticed.
A direct comet impact would certainly be damaging to life. Because of their enormous
speed relative to the earth (11 to 74 km/s, 25,000 to 166,000 mph), their kinetic energy is huge as shown
by the standard formula E = ½mv². Because of the likely damage of an
impact,
NASA is tracking Near-Earth Objects (NEOs).
A small comet about 50 m across has been proposed as a cause of the 1908 explosion
in Tunguska, Siberia, a ~10 megaton blast which flattened over 2,100 km² (800
sq. miles) of forest. But this caused no loss of human life, since there were no
human habitations close by; there was no global effect. In fact, as explained in
this 2008 feedback,
impacts from far bigger comets would barely make a detectable difference to Earth’s
axis, rotational speed or orbit.
What about Elenin itself?
Photo: www.nasa.gov Loke Kun Tan (StarryScapes)
Comet C/2010 X1 was named after Leonid Elenin (Леонид Еленин), a Russian amateur astronomer who
discovered it on 10 December 2010. He was remotely using the International Scientific
Optical Network’s robotic observatory near Mayhill, New Mexico, USA. It is
not a very spectacular object: even at its brightest, it will be 25 times too faint
for the naked eye to see. It is probably only about 3–4 km in diameter. It’s
most likely a lot smaller than the famous Halley’s comet, which has a mass
of 2.2×1014 kg. This sounds a lot, but the earth’s mass (M⊕)
is 5.9722 × 1024 kg—27 billion times more.
Furthermore, its
closest approach to Earth is 34.4 million km (21.4 million miles) on 16
October 2011—this is about the same as the closest approach of
Venus. Venus has 81.5% of the mass of the Earth, and poses not the slightest
threat. So a fortiori, how much less will a little pipsqueak snowball at
about the same distance, with only 0.000,000,003% of the earth’s mass?
Tidal forces
Understanding the inverse cube law of tidal forces should immunize readers against
any sensationalist nonsense.
Actually, the biggest effect of any heavenly object on Earth, outside of an actual
collision, is tidal: the difference in gravitational attraction between
different parts of the Earth. As explained in
The moon: the light that rules the night, the
gravitational force between two objects is given by F = Gm1
m2 /R², where G is the gravitational constant, m1 and
m2 are the masses of the objects, and R is the distance between their
centres of mass—an inverse square law. Thus it is highest on the
part of the earth closest to the object, and lowest on the opposite side. This difference
is the tidal force; and this drops off with R³—an inverse cube
law.
The strongest tidal forces on Earth are exerted by the moon, with a mass of 7.35
× 10²² kg (1.23% of Earth’s) and distance of 384,404 km (239,000
miles). And the moon is very ineffective at producing serious earthquakes or supertides.
But compare Elenin: the moon is 334 million times more massive, as well as almost
90 times closer. This means that its tidal effect on Earth would be 240 trillion
times weaker than the moon’s! Disastrous? No, totally undetectable!
Don Yeomans, of NASA’s NEO program,
made the pithy comment, “my subcompact automobile exerts a greater
influence on the ocean’s tides than comet Elenin ever will”.
Planet alignment disasters?
From time to time, we receive queries about pending disasters when the planets are
aligned in the sky. First of all, ‘aligned’ to a solar system astronomer
usually means ‘in the same quadrant of the sky’, not ‘in a straight
line’ as many think. But this is not the main issue. Understanding the inverse
cube law of tidal forces should immunize readers against any sensationalist nonsense.
The sun is much further
away than the moon (400 times), so has a much lesser effect despite being 333,000
times Earth’s mass, or 27 million times more massive than the moon. The inverse
cube law means that this is more than countered by a factor of 64 million
(400³) due to the greater distance. Overall, this means that the sun’s
tidal effect on the earth is less than half the moon’s.
But because the sun is so massive—over 99% of the total mass of the solar
system—its effect is far bigger than all the planets combined could ever be.
The sun’s effect can be seen by comparing spring tides, when the sun and moon
are aligned, with neap tides when they are perpendicular. Clearly the most important
alignment in the solar system—as far as the earth is concerned—is far
from catastrophic.
To show the fallacy of sensationalist claims, we can compare the effect of a planetary
alignment with alignment of the sun. Since the sun’s effect is the difference
between the spring and neap tides, what is the effect of the other planets?
The closest planet is Venus.
It has only 1/400,000th the mass of the sun. However, at its closest
point, it is almost four times closer. So, to a good approximation, its tidal effect
on Earth compared to the sun’s is 4³/400,000, or 0.003%. I.e. it might
add this much effect to the spring tide—not noticeable.
Jupiter is the biggest planet, 2.5 times more massive than all the other
planets combined. But it is still less than a thousandth of the mass of the sun,
and it is more than four times further away from Earth at its closest approach.
So its tidal effect is only 1/12,000th that of the sun, or 0.008%.
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Readers’ commentsBrian and Maria S., New Zealand
Thank you for your clear explanation of gravitational laws. I am now at peace about not being destroyed by either a global deluge or Comet Elenin. Shalom
Hans G., Australia
Beautiful article explaining the senseless sensationalism about this event.
Keith C., UK
Your website is a wonderful resource! I just wish I had time to read lots more of it!! But isn’t it the suggestion that Elenin is a Brown Dwarf i.e. much greater mass than a comet, that threatens catastrophe on Earth—and not addressed by Dr Sarfati as far as I saw? Jonathan Sarfati responds:
Dear Mr C.
Thank you for your kind words about our site. With over 8,000 articles, I am not surprised that you haven’t read them all.
There isn’t the slightest chance that Elenin is a brown dwarf. This is a failed star, between about 10 and 60 times the mass of Jupiter, in turn over 300 times the mass of Earth. It stretches credibility to think that the mass has been so mismeasured for Elenin, and how it would escape detection from the enormous perturbation of planetary and moon orbits. So there was no point in addressing this suggestion in the article, as opposed to assuming that the comet identification was right.
Regards
Jonathan Sarfati
Ronald M., Australia
Once again, Dr Sarfati’s brilliant mind at work. His logic is catastrophic to old-earthers. BTW, I had a discussion at work the other day about the age of the earth. When I mentioned 6000 years one man scoffed. Another couldn’t believe I said it, but listened. I explained to him about his faith position in regard to evolution, and he realised what I said was true. I gave a few examples of evolutionary frauds and evidences for creation. He seemed quite impressed that I could defend my position from an intelligent viewpoint. Thanks to Creation Ministries, and all glory to God!!! |
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