Five small planets have been discovered around an ancient star.
Baby Picture
Every now and then in astronomy we’ll get an image that lets us actually see phenomena we have previously just deduced from other observations. The image above is one of them. It was taken by the Atacama Large Millimeter/submillimeter Array (ALMA), and shows an exoplanetary system in the process of forming. This isn’t an artistic rendering, it’s an actual image.
Diversity of Worlds
Although we’ve found planets in binary star systems, it isn’t clear how they could have formed. But new observations of a binary system provides a clue.
Gravel Road
We have a pretty good idea of how planets form around stars. We know that dust is formed from the remnants of supernovae, that protoplanetary disks of dust form around young stars, and that dust grains can clump together to form pebbles. We also know how larger planetoids can drive the formation of planets, and how planets can migrate from their point of origin to their stable orbits. But there are still gaps in our understanding.
Snow Queen
Kepler-421b is a cold world orbiting a star about 1,000 light years away. At least according to a new paper announcing its discovery. This work hasn’t yet been peer reviewed, but it looks quite promising. What makes the discovery a big deal is that it is the longest period planet to be discovered by the transit method.
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.
Water World
Venus and Earth are quite similar in many ways. The diameter of Venus is about 95% of Earth’s, its mass is about 80% of Earth’s, it has a similar geological make up, and surface gravity. Where they differ greatly is in their surface temperature. Venus has a surface temperature of over 800 degrees Fahrenheit, while Earth’s average temperature is around 57 degrees (460 C vs 14 C for you science types). They also differ in the amount of water they have. Venus has almost no water, while Earth is a watery world.
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.