From rockets to rickets?

May 27, 2017 12:52 PM

If we moved to another solar system, could we still make our own vitamin D?

As you all probably know, our bodies make vitamin D when our skin is exposed to sunlight -- specifically, to UVB rays. Would the light from another star contain as much UVB as light from our sun? Could other factors, such as the planet's atmosphere, affect vitamin D synthesis? Thanks!

posted by Perodicticus potto to Science & Nature (2 answers total)

Best answer: Most stars emit something similar to a blackbody radiation spectrum. The amount of radiation emitted at a given frequency in the spectrum (such as the UVB region, which is centered around 0.3 µm in that graph) is very dependent on the temperature of the star. The Sun's radiation is pretty close to that of a blackbody at about 5800 K, but there are smaller, cooler, redder stars that have a significantly lower surface temperature than the sun. As you can see from the graph, the amount of UVB emitted by a star that's 1000 K or so cooler than the sun is significantly lower.

This would be mitigated somewhat by the fact that a habitable planet would need to be closer to a cooler star than the Earth is to the Sun, but the overall effect (I'm pretty sure) is that the overall intensity of UVB radiation hitting the planet would be noticeably lower for a cooler star.

As far as stuff in the atmosphere absorbing the UVB level, it's certainly conceivable; but I'll leave the exact details to any chemists who might decide to answer this question, as it's not really my area of expertise.
posted by Johnny Assay at 1:57 PM on May 27, 2017 [3 favorites]

Best answer: Page 8 of these lecture notes has info on absorption of UV by various (Earth) atmospheric gasses. They say "Absorption of UV radiation in the gaseous atmosphere is primarily due molecular oxygen O2 and ozone O3." So presumably, all else being equal an atmosphere with a lot more O2 or 03 would transmit less UV from a sun-like star to a planet's surface, compared to our Earth. Of course there are many variables, type of star, closeness of orbit, size of planet (depth of atmosphere), YMMV, etc etc. I'm sure there are other gases that could be in an atmosphere that absorb much more UV than O2 does, but this at least shows that composition of atmosphere is certainly a factor.
posted by SaltySalticid at 2:40 PM on May 27, 2017 [1 favorite]