I've been keeping up with all the exo-planet news and have been particularly interested in the news of the asteroid belts found around Vega which appear to be in the same orientation around Vega as around our sun, with size scale differential of course. This is leading astronomers to believe there is a solar system of planets around Vega which may be similar to our own system of 8 planets, but we don't know yet.  I have 2 questions, 1) Why can't Spitzer, Kepler before it broke down, or the VLT determine the presence of planets around a star as close as Vega? and 2) will the Magellan or James Webb be able to answer the question burning in so many astronomers minds about Vega's likely planets?

(1) Kepler detected possible planets by looking for changes in the brightness of a star as a planet passed in front of it. That requires the orbit of the planet to be edge-on to our line of sight. The belt found around Vega is face-on. That is, we are looking at it from above or below the plane of the planetary disk, so there is no possibility of any of Vega's planets passing in front of it.

(2) That remains to be seen. I'd say it's more likely than not, but it depends upon how big the planets are, how close to or far from the star they are, and how reflective their surfaces are.
You might imagine that you could find the planets by looking for the light reflected off them from Vega, but that would be at least billions of times fainter than the light of Vega, which could completely drown out the image of any planet. Aside from that, seeing them from above means they reflect only a small percentage of the light falling on them in our direction. As an example, a quarter moon is something like 10 times fainter than a full moon, even though it has half the lit area, because more light is reflected back toward its source than to the side, which is where we are in comparison to any planets orbiting Vega.

I should note that although it would be interesting to know whether Vega has planets and what they are like, it will be much harder to observe them and even harder to determine what they are like than if they were orbiting "edge-on", as planets found by Kepler are. For planets with edge-on orbits, we can (at least in some cases) observe light passing through their atmospheres, and with luck, determine any number of things about the planets that would be well-nigh impossible to determine for planets observed from "above", as in the case of Vega.

Finally, although it is exciting to be living in an age when we can finally observe that other stars have planets, it has been known for many years that most stars should have planetary systems. The only question was how similar to or different from our planetary system they are. Are planets like the Earth as common as dirt, or a rarity? The former seems a more likely possibility, but selection effects in the methods used to observe exoplanets have made the detection of Earth-like planets far more difficult than the detection of strange things we might never expect to exist, save for having had a chance to observe their existence.


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Courtney Seligman


I can answer almost any question about astronomy and related sciences, such as physics and geology. I will not answer questions about astrology and similar pseudo-scientific rubbish.


I have been a professor of astronomy for over 40 years, and am working on an online text/encyclopedia of astronomy, and an online catalog of NGC/IC objects.

Astronomical Journal, Publications of the Astronomical Society of the Pacific (too long ago to be really relevant, but you could search for Courtney Seligman on Google Scholar)

I received a BA in astronomy and physics and a MA in astronomy, both from UCLA. I was working on my doctoral dissertation when I started teaching, and discovered that I preferred teaching to research.

Awards and Honors
(too long ago to be relevant, but Phi Beta Kappa and Sigma Xi still keep trying to get me to become a paying member)

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