It's amazing to think that just a few years ago we had no clue about planets around other stars. Now we know of over 300, and we're getting an idea of how they form, where they form, how they behave, and whether there's a chance of any being like home, our home. Not only that, we're learning whether they can form around stars that are different than the Sun: more massive, less massive, hotter, cooler, whatever. And new Spitzer Space Telescope results show that when conditions to form planets are different, the chemistry is different as well.
Artist's view of a planet forming around a cool star. Note the dark disk partially covering the star.
Planets form from disks of rock, metal, and ice surrounding young stars, accreting material much like a snowball rolling down a hill. When they get big enough from random collisions, their gravity takes over, pulling in far more material, and a proper planet can form. During this process, we can point telescopes at the disk, and by breaking the light up into a spectrum -- think of it like a rainbow with thousands of colors instead of just seven -- we get all sorts of diagnostic info about the material, including its composition. Spitzer does this in the infrared, where lots of interesting molecules give off light. And when astronomers observed the disks of material surrounding 44 young stars about as massive of the Sun, and compared them to 17 disks around smaller, cooler stars (all aged between 1 - 3 million years), they found a surprise: cooler star disks showed no indication of the presence of hydrogen cyanide (HCN) around them. Given that HCN is a deadly poison to humans -- not to Godwin myself, but Nazis used it in WWII, and it's on a list of potential chemical weapons -- you might be relieved. However, if you take five of these little guys and let them dance for a while, they'll combine to form adenine, a nucleobase amino acid that is a basic component to life as we know it. That's interesting -- planets that form around such cooler stars will have a different mix of prebiotic chemicals brewing in them. This might make life more difficult to get an initial toehold (or tentacle hold or pseudopod hold), or it may just mean life will take a different path than it did here on Earth 4 billion years ago. We don't know enough to say yet. But what this does mean is that we have to be careful about generalizing our knowledge to different environments. Spitzer observations like this one tell us more and more about these prebiotic materials in cosmic environments, opening the door to understanding how life originates yet another crack. And in a few years the giant James Webb Space Telescope may kick that door wide open: equipped with a mirror 8 times wider than Spitzer's, it will give us vast amounts of data about such organic materials. It may be a long, long time before we know if life exists Out There, but in the meantime there's still much to be learned. Image credits: NASA/JPL-Caltech and NASA/JPL-Caltech/JHU