This is part of my series where I read physics articles in Scientific American, and offer commentary as a former physicist.
I’ve had the June issue around for over a month, but I procrastinated too much and here we are in July. I’ll try to keep it short this time so I can move on to the next one.
The June issue is when COVID-19 really hits Scientific American. The cover says in big letters: “The Coronavirus Pandemic”. I already got the July issue, and the coronavirus is on the cover of that too. But, the cover notwithstanding, there are still physics articles, and that’s my area of expertise. This month’s article is “A Planet is Born“, by Meredith A. MacGregor. This one isn’t paywalled so you’re free to read it yourself.
Let’s try for a one-sentence summary. Astronomers used high-resolution millimeter-wavelength imaging to detect circumstellar disks analogous to our solar system’s Kuiper belt, and infer the presence of planets based on the effect they had on the dust rings.
I’ve discussed multiple times the mismatch between a scientific article’s hook, and what makes it actually scientifically exciting. Here, the hook is exasolar planets. But personally I think the more exciting thing is the circumstellar disks themselves. Merely detecting a planet is one thing, but it’s another to directly see the debris left over from the planet formation process, a process that I’ve been told is poorly understood. Rather than thinking of the circumstellar disks as a means to an end, I think they are a valuable end in themselves. I’d bet that the scientists working in this area privately agree.
High-resolution astronomy seems to be a theme among the astronomy articles I’ve reviewed. One of the neat things about reading science articles, is they eventually start to build on each other, each providing context for the others. This study has resolution of around 0.01 arc seconds, which is hecka small. But compare it to another study I discussed, about mapping the Milky Way, and that had 0.001 arc-second resolution. Or another study that imaged a black hole, using 0.00004 arc-second resolution.
Those other two studies used radio waves, where this study used millimeter wavelength (or far infrared) light. Using shorter wavelength light tends to improve the resolution; but where the other two studies used radar arrays spread across the globe, this study uses a radar array spread across a “mere” 16 km.
It’s a straightforward article, but there was one itsy bitsy grain of sand that puzzled me. It talks about small dust particles (microns in size) and larger dust particles (the size of sand). The small dust particles tend to get blown away by solar winds and other things, but the larger dust particles stick around as a record of planet formation. Astronomers can distinguish between large and small dust particles, because near-infrared light comes from small dust particles and far-infrared light comes from large dust particles. But why would that be? If you have any ideas, drop them in the comments.