The orbits of three of the moons of Jupiter (Io, Europa and Ganymede) have an interesting pattern. For every time Ganymede orbits Jupiter, Europa orbits twice, and Io orbits four times. In other words, the periods of their orbits follow the ratio of 1:2:4. This is known as an orbital resonance, and it occurs a number of times in our solar system. Saturn’s moons of Hyperion and Titan have a 3:4 resonance, and Pluto and Neptune a 2:3.
True Blue
One of the cool things we’ve been able to do is determine an exoplanet’s color. The planet is known as HD189733b, and as seen in an article published in Astrophysical Journal Letters, it has a blue color. This does not mean this planet is Earth-like in any way. Neptune is also blue, and it is hardly a paradise world. I’ve written about this exoplanet before, where it was found that the hot Jupiter-type planet has atmospheric winds of over 6,000 miles per hour. We now know that its atmosphere contains silicates which give it a blue color. It seems its atmosphere is filled with small droplets of silica that scatter blue light, giving it a blue color.
Vanished Planet
Gliese 581 is a red dwarf star with 6 planets, two of which happen to fall within the star’s habitable zone. At least that was one possible conclusion. The 6-planet solution to the data is actually a bit controversial (http://goo.gl/whWWRh), and other astronomers preferred a 4-planet solution. The difficulty in determining the number of planets is due to the challenge of finding the signal in the noise.
The Red Zone
Recently there’s been news of the discovery of the closest potentially habitable exoplanet yet. Named Gliese 832 c, it is a “super-Earth” orbiting in the habitable zone of a red dwarf star. In April of this year, there was news of the “most Earth-like planet yet”. Named Kepler 186 f, it is a super-Earth orbiting a red dwarf star. In 2012, there was an announcement of the “most habitable exoplanet yet” named Gliese 581 g. It is a …wait for it… super-Earth orbiting a red dwarf. Whenever a new potentially habitable world is announced, it will likely be a super-Earth orbiting a red dwarf. But why?
SEO Astronomy
SEO, or Search Engine Optimization, is a method of trying to game search engines in order to raise the impact of your website or post. One of the common ways has traditionally been through the use of keywords. In astronomy a similar method is used to raise the impact of new research. One of the most effective methods is to use the keywords Exoplanet, Earth, and Habitable. If you can add a nice concept sketch of a watery landscape with double suns, that’s good too.
Round Round Worlds
We often talk about discovering exoplanets, or planets around other stars, but simply stating the number of confirmed planets doesn’t really press home the idea that we are discovering entire worlds, and entire solar systems around other stars.
It’s a Trap!
We now know that planets are relatively common in the galaxy. So common that most Sun-like stars (using that term loosely) likely have planets. We also know that young stars commonly form with protoplanetary disks. We have observed clumps within these disks that indicate planets are forming. So we have a good handle on how planets form, and that this process is fairly common.
Mega
A super-Earth is an exoplanet that is rocky like Earth and other terrestrial planets, but more massive. Typically they are around 5 – 10 Earth masses. Anything much more massive than that, so it was thought, would be massive enough to hold a thick atmosphere, and would likely be a small gas giant. Uranus and Neptune, for example are about 15 Earth masses. But recently we’ve discovered a planet as massive as Neptune that is decidedly rocky like Earth. It has sometimes been referred to as a mega-Earth.
Testing Metal
When it comes to planetary systems, it’s generally been thought that planets would tend to form around stars with a higher metallicity. At a broad level that makes sense because rocky planets such as Earth can only form in a system where there are enough metals like iron, silicon, carbon and the like. You can’t make a terrestrial planet out of just hydrogen and helium. But now that we’ve discovered lots of exoplanetary systems, we can actually put this idea to the test. A recent paper in Nature has done just that, and they’ve found something rather interesting.