Planets have held fascination in human conscience ever since our ancestors started looking at the night sky with any kind of consistency. In the sea of seemingly unchanging “fixed” stars, a handful of heavenly objects moved across the sky, and did so in a consistent and predictable kind of way. It is of little surprise that these “wanderers” had been accorded mythical, or even divine, status. The status of planets, however, was forever altered with the invention of telescope and the realization that they are entire “worlds” in their own right. In many respects much different than the Earth, but still familiar enough that they can be (for the most part) understood in terms of atmospheric and geological processes that are similar to those we are familiar with on our own little rock.

The interest in planets was recently revived after Pluto was demoted from their ranks. This short introduction aims to explain what we mean by the word “planet” today, and why the inclusion of Pluto in that category would open the door for dozens, or perhaps hundreds, similar objects in the future. The planets of the Solar System are thus divided into four smaller “rocky” ones (Mercury, Venus, Earth, Mars) and four large gaseous giants (Jupiter, Saturn, Uranus, Neptune). The book does a great job of explaining why each one of these planets has the characteristics that it does, and how the extreme temperature and pressure conditions on many of them create features that are as far removed from our notion of hospitable environments as they come. And yet, because of these extremes each of the planets is a unique world that is immensely fascinating to explore and continuously keeps disclosing more of its secrets. Despite centuries of investigation, planetary science still feels like a very young scientific discipline and almost each year there is a new attention-grabbing headline describing yet another fascinating discoveries.

The book briefly deals with the possibility of life on other Solar System planets. As we know more about the conditions on these planets we get renewed hope that in some corner of one of the planets or its moons life might have independently originated. However, the kind of life that would thrive under those conditions is very far removed from anything that we had come across on Earth, and at this point such prospects seem more like wishful thinking than a realistic possibility.

The book concludes with a chapter on planets surrounding other stars. Beginning in the early 1990s such planets were discovered using some very sophisticated indirect methods, and by now we know of hundreds extra-Solar system planets. Most of these are Jupiter-like planets, but in recent years some “rocky” ones have been discovered as well. It is certain that in the upcoming years we will learn even more about these distant worlds, and they will help us get an even better picture of our place in the Universe.

Whether you are looking into brushing up on your knowledge of planets or want to learn about them for the first time, this is an excellent informative short introduction to the subject. It is very well written, it doesn’t require much in terms of technical knowledge, and yet it provides meaningful and educational information. It is popular science writing at its best.