Compared with their cosmologist（宇宙学家) colleagues, cosmogonists（星源学家) can sound a l

Compared with their cosmologist(宇宙学家) colleagues, cosmogonists(星源学家) can sound a little old-fashioned. Edgar Allen Poe turned to the mysteries of cosmogony in an 1848 public lecture, just reprinted by Hesperus Press. And we encountered a reference to cosmogonists most recently in a new edition of Poe's prose poem Eureka.

What's the difference between cosmologists and cosmogonists？ Just two letters and a few billion light years. Cosmologists worry about where the Universe came from, cosmogonists with how the Solar System formed. The interesting thing is that one-and-a-half centuries after Poe, they still can't reach agreement on what happened in the nearest 5 light years of space.

What's the problem？ It turns out that there are a couple of competing explanations for why our neighbourhood is the shape it is, as well as several bizarre anomalies in the data. Cosmogonists know that the Solar System is essentially flat. With the exception of two tiny outliers, Mercury and Pluto, the orbits of all the other planets lie in very nearly the same plane. And most cosmogonists agree that this is because the planets themselves formed from a nebular(星云状的)disc orbiting the early Sun, which had itself coalesced out of the same cloud of gas and dust.

But there's a catch. If the planets and the Sun came from the same nebular disc, then the Sun's equator should lie in the planetary plane. It doesn't. The Sun leans over at an angle of 7.25° The majority of cosmogonists insist that the angle is so close to zero that it really doesn't matter. Anyway, they add, the Sun has been losing mass for most of its life, and may have slipped a little.

The remaining minority aren't having this. How can 7.25° be the same as zero？ The Sun and the planets did come from cosmic dust, they say, but not from the same cloud of material. The Sun took shape somewhere in the Galaxy. Then it sailed along and picked up the planets—or perhaps the gas and dust that gave birth to them—elsewhere.

Is a tilting Sun the cosmogonists' only headache？ Not at all. It's also hard to agree on how the outer planets formed. Far out in the nebular disc, matter would have been so spread out that it couldn't quickly have dumped together. Some suggest planet-sized gravitational instabilities, others can find no reason for Uranus and Neptune to have formed yet.

The closer you get to home, it seems, the deeper the mysteries.

What is the best title for the passage？

A．Difference Between Cosmologist and Cosmogonist.

B．Where the Universe Came From.

C．How the Solar System Formed.

D．The Titling Sun.