Friday, March 22, 2013

Malice on the Moon

kw: book reviews, science fiction, astronomy

Many years ago I read the compilation Venus Equilateral, by George O. Smith. For the first time I felt a strong disconnect between the wonder of the technical ideas and the overdone social duality between the "good guys" and the "bad guy". The notion of using the L-4 and L-5 points in the orbit of Venus as communications relay stations was enthralling. But the badness of the bad guy, in particular, was too melodramatic and rung false. I may have been socially backward and awkward at age 22, but even I already knew that people are complex creatures, a mix of good and bad. However, it served a purpose for me: I began to consciously expand my social horizons, to grow out of my youthful nerdiness.

Reading Farside by Ben Bova, I felt a sense of déjà vu, a kind of "here we go again" feeling. In the midst of a wonderful setting—the creation of a large optical interferometer on the outward-facing side of the Moon—the human story is a jarring contradiction. As the drama of politics-of-revenge, fueled by sexual jealousy, played out, I felt it was just too much. There has to be a better human story for Bova to put in this setting. But I thought over his prior novels, and I realized it is the only kind of politics he uses, perhaps the only kind he understands. So let's put all that aside and glance at the interesting ideas:
  1. An astronomical puzzle: A planet has been found circling Sirius A, the Dog Star, a class A star about 8 light years distant. Single-instrument observations have yielded tantalizing hints of an atmosphere, and it is a twin of Earth in size, in the habitable zone about its central star. The puzzle? Sirius B, now a hot white dwarf, is known to have novaed in the last few thousand years. It ought to have stripped off any atmosphere from Sirius C, as the planet is being called. The "hints" come from observations of transits; the orbit of Sirius C is lined up so that it transits Sirius A, and the shadow disk has an unexpected fuzziness. More about this momentarily.
  2. An interferometer of three 100-m diameter telescopes placed at many km distance, in an equilateral triangle I presume, around Farside Station, located as exactly opposite Earth as possible.
  3. Traditional methods of mirror-building have produced one mirror as the story opens, but it has been damaged. The option is explored of using nanotechnology to either repair or replace this glass dish quickly. By the end of the book, nanotech has triumphed, and the observatory is in operation.
  4. Nanotech plays a bigger rôle than this, however. For the chief of the nanotech operations, nanomachines in her body are keeping her healthy, and a chief engineer who must spend much of his time outside, where radiation exposure is damaging, is offered the chance for nanotech repair. That he takes the offer could have become a more interesting story than what we have in this novel. Instead it becomes a red herring during detective work to uncover who is using nano-gobblers to sabotage the telescope-building operation.
  5. The goal of the interferometer is to image the planetary surface of Sirius C and get spectra of its atmosphere, to determine just how Earth-like it may be.
I just had to figure out what it takes to observe details on a planet that is 8 light years distant. Let's first remember that the moon's diameter is 3,476km, so an interferometer has to be smaller than that. A part of the story in which it takes about 30 hours to drive from Farside Station to one of the mirror locations in some kind of Moon buggy sets the scale at about half that, maybe more. One crater identified is Mendeleev, from which I conclude that the size is about 2,500 km, each telescope about 1,250 km from Farside Station. The triangle configuration makes the effective diameter closer to 2,000 km.

Eight light years is about 76 trillion km. A telescope that can see Sirius C (diameter close to 13,000 km) as something more than a 1-pixel dot at such a distance must be at least 3.3 km in diameter. There goes the hint about fuzziness during a transit, using a single telescope of more "ordinary" size such as 20-40m (what we might expect in a few decades). Also, the transits would be 10 years apart. Sirius A is a hot class A star, so the habitable zone is quite a distance away, 8-9 AU.

To see features as small as 10 km on Sirius C, the interferometer's effective diameter must be 4,160 km. With about 2,000 km, the smallest features visible would be a bit over 20 km across. If the full lunar circle were used, you could get below the 15 km range. That's it. It isn't too bad; it works out to a planetary image 600-800 pixels across. This image of Earth is about 800 px across, though this presentation is about half that; click on the image to see it full size.

That is actually an impressive amount of detail. If we could see detail like this on a planet 8 light years away, we'd have a good first impression of its habitability. The biggest clue would be the presence of water and oxygen, or perhaps a different indicator of an atmosphere strongly out of chemical equilibrium. Equilibrium equals sterility.

Just to be a squidge about it, though, we'd really like to see such images out to much greater distances. At 80 light years rather than 8, the earth would appear like this to the Farside observatory. At 800 light years, the image would be a mere 6-8 pixels across. Of course, farther out than about 20 light years, if we were to find a sister Earth, and it were inhabited, conversation with the inhabitants would be a decidedly long-term matter, with decades between "Hello, I am John of Earth" and "Hello, I am Rover, how are you?".

Bova's writing skills are great enough that the book is a quick read, in spite of my discomfort with the melodrama. I keep hoping we, or someone, will regain the gumption to return to the Moon and set up a more permanent presence there. Perhaps someday a Farside Station Observatory will become a reality.

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