Brahma Blogs

This team blog is designed to allow a group of friends who have known each other for 20+ years to share their thoughts on culture, politics, religion, relationships, etc.

Sunday, May 01, 2005

A New Planet?

posted by Edith @ 8:20 AM  

3 Comments:

  • At 8:23 AM, Blogger Edith said…

    Let's try that again...

    "New images taken of an object five times the mass of Jupiter confirm that it is a giant planet closely orbiting a distant star, an international team of astronomers reported"

    So what's the story beyond what CNN has published?

     

  • At 9:04 PM, Blogger Unknown said…

    The story is that, for the first time, an image of a planet orbiting a distant star has been made.

    Many an extrasolar planet has been detected in previous observations over the past decade or so. The earliest detections, I think, involved in each case the observation of the motion of the star along the direction between the earth and the star. According to the physical theory, for example, the center of the sun is not the center of mass of our solar system, though the center of mass of the solar system is near the center of the sun. One can imagine that every object in the solar system---even the sun---orbits around the center of mass of the solar system. Most of the sun's motion in this model is due to the fact that the center of mass is located somewhere along the line between the center of the sun and Jupiter. Anyway, from the point of view of an observer in a distant solar system, our sun would appear to move closer to the observer and then farther from the observer in a cycle that lasts about one Jovian year. The cyclic motion of the sun due to Jupiter's gravitation effect might be detected by the distant observer in the doppler shifting of the light from the sun.

    Of course, we on earth might observe the same kind of cyclic motion of a distant star if there is a big planet tugging on the star as the planet goes around in its orbit. And I think that most of the planetary discoveries have been of this sort.

    Another way to discover an extrasolar planet is to look at the brightness of the distant star. If a planet happens to orbit the star so that the plane of its orbit is viewed edge-on by an earth-bound observer, then when the planet passes in front of the star, the star's light should diminish somewhat. That is, we could view an eclipse-like event. I think that a few of these have been observed.

    If the previous method is combined with spectroscopy, then any unique spectral features emitted by the planet should disappear when the planet passes behind the star. I think that this kind of observation was first made only a few months ago. In this case, one directly detects the light from an extrasolar planet, but one still does not have an image of the planet, because all of the light from the star and the planet is coming from what looks like a single spot on the sky. If we had a telescope with high enough spatial resolution, we could presumably resolve the single spot into a pair of spots (one extremely brighter than the other, and that's part of the problem), but this is really hard to do.

    The clearest indication of an extrasolar planet, however, is to resolve the light into two distinct spots, one for the star and one for the planet. The first such observation is what has made the news recently. (Actually, the clearest of all observations would actually resolve the angular size of each object, but that's beyond the capability of current technology at the moment. For now, we do well just two separate two spots, each of which is indistinguishable from the image formed by an infinitesimally small point in terms of angular size.)

     

  • At 5:45 AM, Blogger Unknown said…

    Of course, whether any extrasolar planets have actually been discovered, by any of the above means, depends on the definition of "planet". Clearly, if the mass of the candidate object were less than the mass of Jupiter, then we should have no problem calling the object a planet. Unfortunately, most of the objects so far discovered are much larger than Jupiter, and there is some debate about whether such a large object ought to be called a planet or a "brown dwarf".

     

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