EXOPLANETS 101 – Learning the basics

Steph P. Bianchini May 28, 2014 3 Comments

I have already spoken a few times here about the challenges of worldbulding in SF, both in terms of designing working planetary systems – around a single or binary star – and imagining celestial bodies where life is at least theoretical possible. However, since 1991 when the first exoplanet has been identified, news about discoveries are becoming increasingly frequent. The last time I have checked the records – earlier this month, at http://exoplanet.eu/catalog – I have found about 1106 planetary systems, 1786 planets and 460 multiple planet systems. Most of them, thanks to the NASA’s planet-hunting Kepler space telescope mission (http://kepler.nasa.gov/). A huge lot and an amazing variety, in terms of shape, composition and motion.

This makes life of an attentive SF writer a lot easier. What you need to do is just looking around and shopping for some ideas: at least, you can be sure that your planet will manage to hover in space in some kind of orbits and not imploding or disintegrating because you haven’t respected some elementary law of physics. 

Now let’s see what is around. You know you can expect gas giants (Jupiter style), ice giants (like Neptune) and small rocky ones. You are also aware  that planets in the so-called HD or Goldilocks Zone are more likely to host some forms of life; and that they are to be found around one but also two stars, given the relative abundance  of binary systems in space. But there’s even better: some of the things in outer space are so weird that they beat all creativity you can summon.

Before talking about the strangest creatures out there, I will start with the normal ones, ie, the ones closest, in shape and characteristics, to our Earth. There are a few candidates for the title of Earth Twin (see chart), and the ESI, the similarity index, gives a good synthetic measure of it.

 You can also notice that Gliese 581 star system hosts a few suitable planets. One of them, Gliese 581 d, may be the most potentially habitable alien world known so far, 8 times the Earth’s mass, with an atmosphere and conditions for liquid water to exist on its surface (yes, water is a necessary ingredient for life – at least the one we are familiar with). Gliese 581 itself is a red dwarf star relatively close to our system, around 20-22 light-years away, in the constellation of Libra, with at least four confirmed planets and six suspected.

But wait: it seems that one even more suitable has been recently (only last month) found by Kepler, and it is Kepler-186f, with  a diameter of 8,700 miles – just 10% larger than Earth, and well within the HD zone. 

http://www.space.com/25531-new-earth-size-planet-could-have-water-video.html

However, located about  490 light-years from Earth, it is certainly difficult to glimpse any direct image, so we can’t be sure which planet qualifies the most. For the moment.

So far, nothing strange, isn’t it? Wait and see, next time strange objects are coming on stage…