Planet still missing

In the 18th Century, Johann Bode and Johann Titius came up with a strange procedure for predicting where to look for planets.

It seems more like a numbers game than a scientific tool.

Make a little table with four columns. A spreadsheet program provides a nice way to do this.

• In column 1, write the numbers 1 to 8.
• In column 2, put zero at the top, then a 3 below it, and below that just keep doubling the number above:
  3, 6, 12, 24 etc.
• In column 3, add 4 to the numbers in the second column: 4, 7, 10, 16, 28, etc.
• Divide the numbers in the third column by 10, and put the results in the fourth column, which gives:
  0.4, 0.7, 1, 1.6, 2.8, 5.2, 10, 19.6.and 38.8.

In order to make the distances in the Solar System easy to comprehend, we define the average distance between the Earth and Sun as 1 astronomical unit (1 au).

Using this convention, the distances of the planets from the Sun are:

• Mercury (0.4 au),
• Venus (0.7 au)
• Earth (1 au)
• Mars (1.5 au)
• Jupiter (5.2 au)
• Saturn (9.8 au),
• Uranus (19 au)
• Neptune (30 au).

That strange series of numbers concocted by Bode and Titius are either exactly or close to the actual distances the planets lie from the Sun.

Uranus was discovered after Bode and Titius put together their number series, and was exactly at the predicted distance. This gave that list of numbers huge credibility.

Fascinatingly though, the numbers also suggested there should be a planet orbiting at 2.8 au, between the orbits of Mars and Jupiter, and there wasn't one. The search was on.

Finally, in 1801 Piazzi found something. Initially it was believed to be the missing planet, and it was named Ceres.

However, it turned out that this new discovery has a diameter of less than 1,000 kilometres, which is far smaller than the Moon, and definitely not big enough to qualify as a planet.

A year later another object turned up. Named Pallas, it was even smaller, with a diameter of a bit over 500 km.

By 1807, the count was up to four, with Vesta and Juno added to the list. Vesta is about the same size as Pallas, and Juno a bit more than half the size.

Instead of a planet, there were multiple small bodies sharing similar orbits between Mars and Jupiter. These new objects came to be called planetoids, or, less accurately, asteroids. The less accurate name is the one that stuck.

As telescopes got bigger, and cameras started to be attached to telescopes, the number of new discoveries rocketed. Astronomers carefully stabilized their telescopes over hours to collect enough light to image distant galaxies, and then found asteroids had made unsightly tracks across the images as they drifted past.

Because of this, asteroids soon became known as the "vermin of the skies.”

However, until recently, nobody knew why, instead of a planet between Mars and Jupiter, there is an enormous collection of rubble, ranging from dust and gravel to a body the size of Ceres.

Today, we have a possible explanation. The story starts back when the Solar System formed.

A great cloud of gas and dust collapsed into a rotating disc, and then as the disc got smaller, denser and rotated faster, the core formed the Sun, and in the surrounding disc, "diskettes" formed, each of which formed a planet, except for one.

The problem was that one of those diskettes had accumulated a large amount of material and formed the giant planet Jupiter. Then, the strong gravity of that planet interfered with the neighbouring diskette toward the Sun, preventing it forming a planet, and leaving it as a huge collection of smaller bodies.

We have an explanation for the missing planet, but we still have no good explanation for that series of numbers Bode and Titius put together.

• Jupiter is conspicuous in the south overnight
• Saturn is to its left.
• Mars rises around midnight
• Venus, shining even brighter than Jupiter, appears shortly before dawn.
• The Moon will reach Last Quarter on the 11th.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.