Jupiter Stuff
Published on Jun 4, 2006 at 10:40 am.
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Filed under planets.
Go out a bit after sunset and look to the Southeast (at least in the Northern Hemisphere). If you do that in the next few nights, you’ll see the Moon. You’ll also see what looks like a really bright star. That is no star! That is the planet Jupiter. You can’t miss Jupiter, since it is the brightest thing that you’ll see up there other than the Moon.
Currently Jupiter is moving into the constellation Libra. It takes just under 12 years for Jupiter to make one complete orbit, and thus it appears to move around the sky in about 12 years. Since it moves through about 12 constellations during those 12 years, that means that it will be in one constellation per year. To the Chinese, it was the “year star.” The Chinese calendar was based upon the constellation that Jupiter was in that year. So, if it was in the Chinese constellation of the Horse, then it was the Year of the Horse, and if it was in the Chinese constellation of the Rabbit, it was the year of the Rabbit, and so forth.
Jupiter is the largest planet in our Solar System. It has a mass of nearly 320 Earths, but it has a volume of over 1000 Earths. Clearly, it is made of lighter stuff! In particular, Jupiter is mostly hydrogen and helium. In fact, Jupiter probably has a composition very similar to that of the Sun. When I was taking astronomy classes, Jupiter was often called a “failed star.” This designation came from the realization that if Jupiter were larger, then it would be able to support nuclear fusion in its core, like the Sun. Well, if that is the case, then it is really a failure, since it would have to be nearly 85 times larger to be a minimal star. Since my days as a student, though, another category of object has been found, called a brown dwarf. Brown dwarves are more properly failed stars. These are bodies that form at just barely too little mass to sustain nuclear fusion. They likely do undergo a very limited fusion of the most easily fused isotopes, but they cannot sustain that fusion, and the energy so released is not a significant factor in their heating or equilibrium state the way it would be if they were really stars.
Jupiter and Saturn, the two largest planets in the Solar System probably formed directly out of the disk of dust and gas surrounding the protosun. The other planets likely were built up from smaller bodies. But, Jupiter and Saturn have moons that may have formed in the same manner that the other planets of the Sun formed, particularly the larger moons of Jupiter and Saturn. Jupiter has over 60 moons, but most are likely asteroids or comets that got caught by Jupiter’s gravity. The four biggest moons (Io, Europa, Callisto, and Ganymede) may have formed from the disk of material swirling together to make Jupiter. These moons are worlds in their own right. They are planet sized! Ganymede, in fact, is about midway between Mercury and Mars in diameter.
If you look at Jupiter in even a small telescope, you see that it has stripes. The light colored stripes are zones, and the darker stripes are called either belts or bands. Jupiter is composed mostly of hydrogen and helium, but its upper atmosphere has clouds made of ammonia, water, and ammonium hydrosulfide. The ammonia clouds are white, and the ammonium hydrosulfide clouds have color. So, the zones are regions where you see ammonia clouds, the uppermost cloud layer. However, the belts are places where the uppermost atmosphere is comparatively clear, and you are seeing deeper into the planet, where the ammonium hydrosulfide clouds are to be found. This has to do with how air circulates on Jupiter. Where the air is rising, you get clouds, and where the air sinks, it is more clear. The same works here on Earth. Where air is rising, then you have low pressure on the surface of the Earth, and where air is sinking, you get higher pressure. So, look at a weather map. Where the big “H” is located, the air is sinking, and it is normally clear. Where you see a big “L”, the air is rising and you get storms. (Rule of thumb here.)
So, if you get a change, to out and look for Jupiter. Even without a telescope, it is impressive as bright as it is.
-Astroprof
