Planetary effects on Earth

By Dr Kavan Ratnatunga

The Gravitational effects of the Sun, Moon, and other planets in our Solar system on Earth is very simple to compute. Any A-level Physics student should be able to do so. The Gravitational Force is proportional to the Mass/(Distance)2 and the resulting tidal Force is proportional to it's first derivative i.e. Mass/(Distance)3. When dealing with such large quantities, it is more convenient to express Mass in units of the Mass of the Earth (approximately 6x1024 kg) and distance in Astronomical Units (AU) which is the average distance from the Earth to the Sun (approximately 150 Million km). Distance between the Earth and Planets varies depending on the location in orbit, but to maximize the possible effect of planet use minimum possible distance between Earth and Planet.

  ________ ____________ _____________ ____________ ____________ 
 |        | Distance AU|      Mass   | Gravity    |  Tidal     |
 |        | from Earth |      Earths | Factor     |  Factor    |
 |Moon    |min  0.0024 |      0.0123 |   2140.    | 890000.    |
 |        |max  0.0027 |             |   1690.    | 624000.    |
 |Sun     |min  0.9833 | 333000.     | 344000.    | 350000.    |
 |        |max  1.0167 |             | 322000.    | 317000.    |
 |Mercury |min  0.52   |      0.055  |      0.21  |      0.40  |
 |Venus   |min  0.26   |      0.815  |     12.5   |     49.1   |
 |Mars    |min  0.36   |      0.107  |      0.80  |      2.20  |
 |Jupiter |min  3.93   |    318.     |     20.5   |      5.22  |
 |Saturn  |min  8.03   |     95.1    |      1.48  |      0.184 |
 |Uranus  |min 17.4    |     14.5    |      0.048 |      0.003 |
 |Neptune |min 28.8    |     17.1    |      0.020 |      0.001 |
From this Table you see that the Tidal effect of the Moon is 2 to 3 times that of the Sun and more than 10,000 times the combined maximum perturbation of all of the Planets, which will be lost inside much larger tidal variations caused by the Sun and the Moon. Note the importance of distance. The Sun is about 27 Million times as massive as the Moon, but exerts less than half the tidal effect, since the Sun is 400 times more distant than the Moon. This is very well understood, simple physics, which any scientist should understand.

Energy of earthquakes are measured by magnitude known as the Richter scale. A unit increase magnitude is a Tenfold increase in energy of the earthquake. For example a magnitude 8 earthquake is a 1000 times more powerful than magnitude 5.

Recently in the news, there have been attempts to relate Planets to earthquakes. The Daily News on April 9 reported that a Peradeniya University Geologist had predicted an earthquake larger than 5, between April 5th and April 8th. They reported the success of this prediction after 7.1 earthquake of April 7th. What they did not report was that there were 5 Earthquakes larger than 5 during those days and 10 during the 4 days before and 12 during the 4 days after from the same area. After a Great earthquake like the 9.0 in Japan on March 11th, there are many smaller after-shocks for many weeks. Earthquakes are not uncommon. Recorded each year on average there is 1 Earthquake larger than 8, 16 larger than 7, 150 larger than 6 and about 1,500 larger than 5.

There were No earthquakes above 6 as predicted by the Geologist between April 10th and 20th and published in the Times of India on April 9 There has been little press about the failure of the predictions of which I am sure there would have been a lot, if it had randomly come true. None of the previous claimed success have a documented recorded of being predicted before the event.

In an interview by Nalaka Gunawardena with this Geologist, published in online in on April 19, he had claimed to have found a statistical correlation of 136 major earthquakes over last 100 years, with the planetary alignment of Mars, Jupiter, Saturn, and Uranus within a small angle, with the Sun and Moon close to the same line. He had not found any direct co-relation with the Sun and Moon.

There are few papers in the refereed scientific literature which discuss the possible Tidal effect of the Moon and Sun on Earthquakes. For example there is a 2001 paper published by Hu Hui and Li Xiaoming of Yunnan Observatory in China in Natural Hazards, Volume 23, Numbers 2-3, pages 339-348, with some possible correlations of Earthquakes with the approximately 18 year cycle of the Earth and Moon's orbit around the Sun. They state that the effect of Planets is negligible, as I have shown above.

In the interview with Nalaka, the Geologist had also suggested magnetic interaction with the molten core of the Earth. Magnetic fields are complex, but also decrease as inverse of the (Distance)3. Relative to their mass, the magnetic fields of the massive Gas Planets (Jupiter, Saturn, Uranus and Neptune) are much smaller than the less massive rocky planets with a molten core like Earth and Mercury. The magnetic fields of other planets at the Earth, are more negligible than that of their gravity. Earthquakes are clearly not caused by alignment of Solar system Planets, whatever misleading statistical correlation anyone appears to find. Any correlation that was seen must clearly be an error in the statistical analysis. To put in in more understandable terms, a bridge which can handle heavy Trucks, does not collapse by dogs or ants walking across it.

Prof Max Wyss of the University of Alaska in his 2001 review paper in Tectonophysics Volume 338, pages 217-233 says To make significant progress in earthquake prediction research, we must learn how to conduct rigorous science in a field where amateurs use a slipshod aproach with the dream of helping mankind quickly.

The Nation article on March 27 said the 136 earthquakes analyzed measured over 6 on the Richter scale. Since there have been about 15,000 earthquakes larger than 6 in the last 100 years, it is not clear how the subset of 136 was selected. When I spoke to the Geologist briefly over the phone on April 19th, he said, a random subset over selected regions. An analysis of over 15000, will be statistically more than 10 times better and also unbiased, than a selected 136. That should have been done, before speaking to the Press, which unfortunately resulted in scaring the public living along the coast of Sri Lanka, from a peaceful Sinhala and Thamil New Year.

Predictions when published by an academic who is an associate Professor of a reputed university are obviously taken seriously, by the public who may not understand the details of the Science. Statistics and Astrophysics are popular topics, since it is understood by even smaller fraction of the public. The speakers to the Press themselves probably unaware of the limits of their popular understanding of modern Astrophysics they abuse.

I hope the Sri Lankan University authorities will put in place a proper referee system to ensure that such non-science is not released to the press, and harm the reputation of the University. The Minister of Disaster Management has said that legal action will be taken against astrologers, academics or others who make predictions on natural disasters and thereby cause panic among the people (SundayTimes April 17). I hope the press in all local languages will also show restraint particularly as we approach 2012 and all that Mayan nonsense sweeping across the Internet, and even leaking to the local print and electronic media.

Writer is an Astrophysicist who has done 25 years of research in many leading universities in USA, Canada and Australia, after a Physics Honors degree from the University of Ceylon.
An edited version of this article By Dr Kavan Ratnatunga was published in Sri Lanka: Planetary effects on Earth in The Nation (§ Eye page 4) and translated into Sinhala in The Rivira (§ Rividahara page 22) on 2011 May 8th