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First Image of Extrasolar Planet Confirmed
An anonymous reader writes "The year-long controversy about whether the European Southern Observatory had indeed captured the first picture of an extrasolar planet has apparently been resolved. Journal publication today of a fuzzy image of this Jupiter-sized, extrasolar planet led Christophe Dumas, a member of the discovery team, to say enthusiastically: 'The thrill of seeing this faint source of light in real-time on the instrument display was unbelievable. Although it is surely much bigger than a terrestrial-size object, it is a strange feeling that it may indeed be the first planetary system beyond our own ever imaged.'"
Here's the mirrordot link for the "picture" page in the story.
The actual page has started showing signs of fatigue due to slashdot effect, so use the above link.
It's actually (according to the BBC and eso.org) 5x the size of Jupiter, or about half the size of our sun
Remember that when astronomers talk about "size", they are actually talking about mass. Our sun is 1000x the mass of Jupiter, so this planet is still 200x smaller.
The minimum mass to call a big planet a "star" is about 70 times Jupiter (that's the minimum mass to start nuclear fusion).
Wrong, this planet is *not* 5x the size of Jupiter. It has a *mass* 5x that of Jupiter. Due to gravity etc no planet can grow much beyond the size of Jupiter. Don't remember the exact size but it was some 10-30% larger that was the limit.
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The reason why they are called failed suns is because they are. Gravity pulls the matter in towards the center of the planet. This makes the center hot and dense (think ideal gas law). If there is enough mass in the planet, the gravitational attraction is strong enough that it forces the pressure and temperature at the planets core to exceed the thresholds required for nuclear fusion (hydrogen to hydrogen) to occur. If the body is massive enough to do this it is a bona-fide star. Stars slightly less massive are known as brown dwarfs (there are technical reasons why they are not called planets), and bodies even less massive are planets.
Jupiter is giving off heat because the gravitational attraction is causing the temperature and pressure inside the star to be relatively high -- just not high enough for fusion.
When considering density you must also consider the pressure. The earth for instance is denser than its composition would be at sea level because of the tremendous forces resultant from its own mass.
It is suspected that the core of jupiter is metallic hydrogen, a phase that occurs only at extreme pressures.
As an aside: The earth is also a net "producer" of energy if you look at luminosity alone. All of the energy from solar radiation must be radiated away or we'd become very hot very quick. In fact, it's a bit worse than that since some heat is also escaping from the core. Evidence: volcanoes. so the total amount of energy leaving the earth as light must therefore be greater than the total amout of energy intercepted by earth as light.
I think most of us would agree that the earth is not "generating" heat, but rather just slowly dissipating the heat that's already there. from the formation of Earth. Io on the other hand is generating heat (or rather heat is being generated as a result of jupiter's tidal forces.)
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My guess would be that by "bigger" they actually mean more massive.
Yes. And IIRC, the threshold is something like 15-20 Jupiter masses. So that is why this one is "definitively" a planet.
Well, actually lots of people working in that area asked themselves the same question :)
Yes, there are non-stars that dont support "normal"fusion but still create energy by deuterium fusion. But even for this a limit can be calculated.
Normal Hydrogen burning stars start at around 7% of the mass of the sun, deuterium burning ones are normally called brown dward and start around 1.5% of M_sol. So still about 3 times that of this planet here.
You have to understand that those fusion processes are EXTREMELY temperature sensitive (we are talking about T^18 for pp, and it only gets worse for heavier fusion reactions, CC should be around T^50). So a star thats just a little smaller and thus cooler in the core than the limit already has nearly zero activity.
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From the article on Jupiter
...)
A. Composition of Jupiter
The fact that Jupiter's radius is 11.2 times larger than Earth's means that its volume is more than 1,300 times the volume of Earth. The mass of Jupiter, however, is only 318 times the mass of Earth. Jupiter's density (1.33 g/cm3) is therefore less than one-fourth of Earth's density (5.52 g/cm3). Jupiter's low density indicates that the planet is composed primarily of the lightest elements--hydrogen and helium.
The computer models predict that Jupiter's outer layer, composed of a gaseous mixture of hydrogen, helium, and traces of hydrogen-rich compounds such as ammonia, methane, and water vapor, is about 1,000 km (about 600 mi) thick. Beneath this layer, the pressure is so great and the atmosphere is so hot and compressed that the hydrogen and helium atoms do not behave as a gas, but as what physicists call a supercritical fluid. Supercritical fluids form at high temperatures and pressures and have properties similar to those of both gases and liquids. The supercritical zone extends 20,000 to 30,000 km (12,000 to 19,000 mi) into Jupiter, which is about one-fourth to one-third of the radius of the planet.
Beneath the supercritical fluid zone, the pressure reaches 3 million Earth atmospheres. At this depth, the atoms collide so frequently and violently that the hydrogen atoms are ionized--that is, the negatively charged electrons are stripped away from the positively charged protons of the hydrogen nuclei. This ionization results in a sea of electrically charged particles that resembles a liquid metal and gives rise to Jupiter's magnetic field. This liquid metallic hydrogen zone is 30,000 to 40,000 km (19,000 to 25,000 mi) thick--about half the radius of the planet--and extends to the molten rock core at Jupiter's center. The molten rock core occupies a sphere with a radius of about 10,000 km (about 6,000 mi)--about one-fourth of Jupiter's total radius--and has a mass perhaps 10 to 15 times the mass of Earth.
In order for a cloud of hydrogen gas to form a star, both gravity and pressure have to overcome the various fundamental forces that prevent atoms from fusing together,/a> (weak, electromagnetic).
In ratio to the "strong force" which holds the nucleus of the atom together, the electromagnetic force is 1/137, the weak force is 1/(10^6), and gravity is 1/(10^39).
Thus gravity is 10^37 times weaker than the electronmagnetic force, and 10^33 times weaker than the weak force. So you are going to need a considerable amount of mass to overcome these forces.
Another factor is Newton's Universal Law of Gravitation:
F = G . m1 . m2 / ( r^2)
where G is the Gravitational constant
m1 and m2 are the masses of two objects (eg. hydrogen atoms, dust, asteroids,
and r is the distance between the two objects
The implication of this equation is that gravitational forces become greater the closer the two objects are. So the gas cloud has to pull itself together from gas to liquid (a liquid cannot be compressed any further). At this stage, pressure is created, and gets converted into heat (electromagnetic force)
If there isn't enough mass, a sufficiently deep gravity well won't form, and you will end up with a superhot liquid gas planet - which is more or less what Jupiter is.
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You're thinking of Saturn. Jupiter is more dense than water.
http://www.solarviews.com/eng/saturn.htm
http://www.solarviews.com/eng/jupiter.htm