beccastareyes (![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png)
beccastareyes) wrote2008-11-13 08:07 pm
beccastareyes) wrote2008-11-13 08:07 pm
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Holy shit!
Okay, so I knew this one was coming a bit -- rumors and all. Prepare for SCIENCE!
How many planets can you see?
Well, most of us, aside from the blind-from-birth, have seen the Earth. I'd dare say that most of you have seen at least one other planet -- Venus, Jupiter and occasionally Mars are all pretty remarkable. There are five planets outside of Earth (Mercury, Venus, Mars, Jupiter and Saturn) that can be seen with the naked eye -- maybe Uranus at a good site and if you know which of the barely visible stars is which. Uranus can be seen in binoculars or a small telescope and Neptune in a larger telescope. (For completeness, I'll note that of the dwarfs, Ceres is visible in a small telescope, and Pluto, Eris, Naumea and Makemake all take equipment that only professionals or amateurs with large amounts of dedication and money have.)
Now, we know about about three hundred more planets. Most of these we haven't seen -- for all of you who have seen, say, Jupiter, consider how much fainter it was compared to the Sun -- the Sun is a star, and Jupiter is only reflecting a tiny bit of its light. Now, imagine that the Sun is one of the stars in the night sky. And Jupiter is right next to it. Yeah -- it's like trying to tell if you left your nightlight on when your house is on fire.
So, most of the planets we found -- certainly the first found around 'normal stars'* -- were found by looking for the reflex motion of the stars. Think of it this way -- imagine twirling a yoyo (or any type of 'weight on a string') around in a circle above your head. (Don't do this near breakable objects, unless you are really certain of your grip.) The yoyo is making a wide circle, but your hand also has to circle to make the motion, though much less. Now imagine the yoyo is a planet, your hand is a star, and gravity is the string. And you can't see the yoyo or the string, only your hand. An observer can tell that your hand is doing something, because it is moving in a circle. Since stars on their own don't generally do this, there must be something orbiting the star. What it is depends on the mass, which changes the reflex motion of the star. Astronomers can do this two ways -- look to see if the star is moving in the towards-away direction by how its light changes (like the way you can tell a train is moving towards or away by the pitch of its whistle), or by tracking how the star moves on the sky. Needless to say, since planets are small, this takes a great deal of precision, but several teams have it down to a science.
Still, it's not very exciting is it? All you know about the planet is a mass (or in some cases, only a minimum mass), and a distance. The next most exciting thing to come along are transits -- in some cases, planets pass in front of their stars, and we see a slight dip in their light thanks to the dimmer planet blocking part of the star's surface. If the data are really good, you see an even smaller dip when the star passes in front of the planet, and we can no longer see the planet's face. This can give you a diameter to your planet. The fact you can observe the star with and without planet lets you do more like subtract the starlight off to look for traces of what's in the planet's atmosphere. I've even seen a couple of attempts to track how heat flows on such a planet by watching the brightness change in the infrared -- the planet was close enough to its star (so a nice and toasty 1,000 degrees at its cloudtops) that the Spitzer Space Telescope could see that it was glowing in the infrared.
But this and this is even fricken cooler!
So, Formalhaut is a bright semi-young star (say 200 million years old, which is about 20-25 times younger than our Sun) and rather bigger than our Sun (2.3 times the mass, 15 times the brightness). You can see it low in the southern sky in fall -- it's a pretty bright star, since it's close (about 25 light years). We knew it has a debris disk orbiting it -- they aren't unusual in young stars, which is good since that's where planets come from. Formalhaut's is more like our Kuiper or Asteroid Belt, though -- more the junk left over from making planets than something that is making planets. We've known about it for a while, since the first infrared measurements showed Formalhuat was brighter than expected, and Hubble and ground-based telescopes have taken pictures of it. Some years ago, dealing with taking a picture of a faint thing near a bright thing (which is part 'put something in front of the bright thing' and part of 'figure out what the star is doing and subtract it from the image'**, with a dose of black magic) got the fact that the disk is more of a donut, with a clear center. Astronomer Paul Kalas suggested that maybe this was because a big planet was sculpting the inner edge, like Neptune does with the Kuiper Belt, and Jupiter does with the Asteroid Belt.
Well, they found it.
It might not look like much, but it's moving with Formalhaut around the galaxy, and it's been there for two years. I've seen reports of its mass as being anywhere from one to three times Jupiter's, and its orbit is about 900 years long (it orbits out at 100 AU, about 10 times farther than Saturn, or 3 times father than Neptune).
And not to be outdone, the fine astronomers of Christian Marois's team published this picture, of a star named HR8799 that they took with the Gemini North Telescope (in Hawaii). HR8799 is moderately farther away than Formalhaut (130 light years), a bit more massive and brighter than our Sun (five times brighter and 1.5 times more massive), and pretty young (60 million years -- our Sun is 4.5 billion years old).
See 'b' and 'c'? Planets. Using the Keck telescope in Hawaii, they spotted a 'd' even closer to the planet. They just released this, but again, they've been watching these for a while, to make sure they are actually orbiting the star. 'd' orbits at 25 AU, 'c' at 40 AU, and 'b' at 70 AU -- so 'd' would be between Uranus and Neptune, 'c' out by Pluto, and 'b' much farther out. The press release says that HR8799 also has a debris disk, interior to 'd's orbit, like our Asteroid Belt. The reason we can see these is because they are so young -- they're hot from forming, so they look much brighter (especially in the near infrared, where this picture was taken) than Jupiter would. All three are also more massive than Jupiter -- 'b' is probably 7 Jupiters, and 'c' is around 10. (Strangely enough, for reasons of physics, all would be about the same diameter as Jupiter.) These are getting into big for planets range -- normally astronomers place the cut off around 13 Jupiters, but one could quibble about models.
Now, why is this important? First off, you can do a lot more if you have actual photons of a planet -- you can do things like learn what it's made of. Our guess is probably mostly hydrogen and helium, like our big planets, but some of the tracers would be interesting. Plus, based on our other methods, we never would have found these -- the motion they set up in their stars is too small, plus young stars are very problematic to study precisely, since they do inconvenient things like spit off flares.
There's also the fact that this is Just Plain Cool! See those little specks? Those are planets orbiting another star! How cool is that?
* I have to say this as a member of Cornell University's Astronomy Department, but the first extrasolar planets were found orbiting a pulsar, the dead remains of a star that went supernova, at Arecibo Radio Observatory. They don't get much love outside of people who want to know how the heck you get planets that either survive a supernova or form after one since they are oddballs.
** One of my projects involves doing this on images of the Sun to look for haloes made by sand-sized particles in Saturn's rings.
How many planets can you see?
Well, most of us, aside from the blind-from-birth, have seen the Earth. I'd dare say that most of you have seen at least one other planet -- Venus, Jupiter and occasionally Mars are all pretty remarkable. There are five planets outside of Earth (Mercury, Venus, Mars, Jupiter and Saturn) that can be seen with the naked eye -- maybe Uranus at a good site and if you know which of the barely visible stars is which. Uranus can be seen in binoculars or a small telescope and Neptune in a larger telescope. (For completeness, I'll note that of the dwarfs, Ceres is visible in a small telescope, and Pluto, Eris, Naumea and Makemake all take equipment that only professionals or amateurs with large amounts of dedication and money have.)
Now, we know about about three hundred more planets. Most of these we haven't seen -- for all of you who have seen, say, Jupiter, consider how much fainter it was compared to the Sun -- the Sun is a star, and Jupiter is only reflecting a tiny bit of its light. Now, imagine that the Sun is one of the stars in the night sky. And Jupiter is right next to it. Yeah -- it's like trying to tell if you left your nightlight on when your house is on fire.
So, most of the planets we found -- certainly the first found around 'normal stars'* -- were found by looking for the reflex motion of the stars. Think of it this way -- imagine twirling a yoyo (or any type of 'weight on a string') around in a circle above your head. (Don't do this near breakable objects, unless you are really certain of your grip.) The yoyo is making a wide circle, but your hand also has to circle to make the motion, though much less. Now imagine the yoyo is a planet, your hand is a star, and gravity is the string. And you can't see the yoyo or the string, only your hand. An observer can tell that your hand is doing something, because it is moving in a circle. Since stars on their own don't generally do this, there must be something orbiting the star. What it is depends on the mass, which changes the reflex motion of the star. Astronomers can do this two ways -- look to see if the star is moving in the towards-away direction by how its light changes (like the way you can tell a train is moving towards or away by the pitch of its whistle), or by tracking how the star moves on the sky. Needless to say, since planets are small, this takes a great deal of precision, but several teams have it down to a science.
Still, it's not very exciting is it? All you know about the planet is a mass (or in some cases, only a minimum mass), and a distance. The next most exciting thing to come along are transits -- in some cases, planets pass in front of their stars, and we see a slight dip in their light thanks to the dimmer planet blocking part of the star's surface. If the data are really good, you see an even smaller dip when the star passes in front of the planet, and we can no longer see the planet's face. This can give you a diameter to your planet. The fact you can observe the star with and without planet lets you do more like subtract the starlight off to look for traces of what's in the planet's atmosphere. I've even seen a couple of attempts to track how heat flows on such a planet by watching the brightness change in the infrared -- the planet was close enough to its star (so a nice and toasty 1,000 degrees at its cloudtops) that the Spitzer Space Telescope could see that it was glowing in the infrared.
But this and this is even fricken cooler!
So, Formalhaut is a bright semi-young star (say 200 million years old, which is about 20-25 times younger than our Sun) and rather bigger than our Sun (2.3 times the mass, 15 times the brightness). You can see it low in the southern sky in fall -- it's a pretty bright star, since it's close (about 25 light years). We knew it has a debris disk orbiting it -- they aren't unusual in young stars, which is good since that's where planets come from. Formalhaut's is more like our Kuiper or Asteroid Belt, though -- more the junk left over from making planets than something that is making planets. We've known about it for a while, since the first infrared measurements showed Formalhuat was brighter than expected, and Hubble and ground-based telescopes have taken pictures of it. Some years ago, dealing with taking a picture of a faint thing near a bright thing (which is part 'put something in front of the bright thing' and part of 'figure out what the star is doing and subtract it from the image'**, with a dose of black magic) got the fact that the disk is more of a donut, with a clear center. Astronomer Paul Kalas suggested that maybe this was because a big planet was sculpting the inner edge, like Neptune does with the Kuiper Belt, and Jupiter does with the Asteroid Belt.
Well, they found it.
It might not look like much, but it's moving with Formalhaut around the galaxy, and it's been there for two years. I've seen reports of its mass as being anywhere from one to three times Jupiter's, and its orbit is about 900 years long (it orbits out at 100 AU, about 10 times farther than Saturn, or 3 times father than Neptune).
And not to be outdone, the fine astronomers of Christian Marois's team published this picture, of a star named HR8799 that they took with the Gemini North Telescope (in Hawaii). HR8799 is moderately farther away than Formalhaut (130 light years), a bit more massive and brighter than our Sun (five times brighter and 1.5 times more massive), and pretty young (60 million years -- our Sun is 4.5 billion years old).
See 'b' and 'c'? Planets. Using the Keck telescope in Hawaii, they spotted a 'd' even closer to the planet. They just released this, but again, they've been watching these for a while, to make sure they are actually orbiting the star. 'd' orbits at 25 AU, 'c' at 40 AU, and 'b' at 70 AU -- so 'd' would be between Uranus and Neptune, 'c' out by Pluto, and 'b' much farther out. The press release says that HR8799 also has a debris disk, interior to 'd's orbit, like our Asteroid Belt. The reason we can see these is because they are so young -- they're hot from forming, so they look much brighter (especially in the near infrared, where this picture was taken) than Jupiter would. All three are also more massive than Jupiter -- 'b' is probably 7 Jupiters, and 'c' is around 10. (Strangely enough, for reasons of physics, all would be about the same diameter as Jupiter.) These are getting into big for planets range -- normally astronomers place the cut off around 13 Jupiters, but one could quibble about models.
Now, why is this important? First off, you can do a lot more if you have actual photons of a planet -- you can do things like learn what it's made of. Our guess is probably mostly hydrogen and helium, like our big planets, but some of the tracers would be interesting. Plus, based on our other methods, we never would have found these -- the motion they set up in their stars is too small, plus young stars are very problematic to study precisely, since they do inconvenient things like spit off flares.
There's also the fact that this is Just Plain Cool! See those little specks? Those are planets orbiting another star! How cool is that?
* I have to say this as a member of Cornell University's Astronomy Department, but the first extrasolar planets were found orbiting a pulsar, the dead remains of a star that went supernova, at Arecibo Radio Observatory. They don't get much love outside of people who want to know how the heck you get planets that either survive a supernova or form after one since they are oddballs.
** One of my projects involves doing this on images of the Sun to look for haloes made by sand-sized particles in Saturn's rings.