Text 7. What size collision formed the moon.

The favourite theory to explain the origin of the Moon is that a large, rogue planetoid about the size of Mars collided with Earth some 4.5 billion years ago. An 'oblique impact' or sideswipe by the intruder would have vaporised the upper regions of Earth's crust and mantle, spraying the material out into space. From a gaseous disk, the material slowly formed a series of hot moonlets which eventually came together into the single, large Moon we see today.

The main problem with this theory seems to lie with the size of the original impactor. New modelling work at the University of Colorado in Boulder suggests that a Mars-size intruder would be too small to create the required volume of material. Instead, the team suggest that the Earth collided with an object 2.5 to 3 times the mass of Mars, leading to the formation of the Moon just 15,000 miles above our planet.

There is, however, still a problem with this scenario. The larger impact results in an Earth that is spinning too quickly. The new model produces a system with roughly twice as much rotational spin as the Earth-Moon system exhibits today. The older version provides the right amount of spin but not enough raw material. It seems that our nearest neighbour is determined to hold onto its secrets for a while longer.

Peter Bond

ASTRONOMY NOW / SEP 1997

I. Read the text and note the important details.

II. Identify the sentences:

1. with the Subjunctive Mood;

2. with the Infinitive Construction.

III. Make a written translation of the text.