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Friday, March 7, 2008
Thursday, February 21, 2008
Monday, February 18, 2008
In a NASA press release yesterday, two teams of astronomers announced complimentary research that suggests that earth-like planets around sun-like stars may be common.
The first team used the Spitzer space telescope to survey a bunch of sun-like stars of varying ages. They were looking for evidence of dust kicked up by the collision of planetesimals. Planets form in a disk of debris around their star. As smaller rocks collide, they stick together to form larger rocks. With more gravity, the larger rocks attract more mass, and you get runaway growth. It's a messy process though, and many of the collisions create small particles even as they add most of their mass to the growing planetesimals. It is these small dust particles that the Spitzer team searched for. Warmer dust is associated with formation of planets close to their star, like the earth. The astronomer found that 10 to 20 percent of young sun-like stars have warm dust, but stars older than 300 million years don't. This suggests that planet formation is common and that it runs to completion within the first couple hundred million years.
The second study is based on theoretical models of how planets form. They confirmed that dust is a by-product of rocky planet formation and offer up two ways of interpreting the dust observed by the Spitzer team. First, it is possible that the dust lingers for a while, so that even if planet formation happens in only ten million years, the dust sticks around and you see it even for older stars that have finished forming planets. If this is true, then about 20% of sun-like stars have planets. Another possibility is that big disks form planets fast and their dust gets eaten up, while less massive disks take longer, so their dust persists. Interpreted this way, the Spitzer dust observations could mean that up to 60% of sun-like stars form planets.
In reality, it is probably some combination of the two effects, which means that the likelihood of forming planets is somewhere between 20 and 60 percent. Pretty good odds, if you ask me.
For the original press release, check here.
Sunday, February 17, 2008
I collect quotes. To see the full collection, check my website. Yesterday, while reading some short stories by Ray Bradbury, I came across two passages that I thought I would share. The first is often partially quoted and it was nice to finally see it in its full context. It, like much of Bradbury's best writing, is almost like poetry:
"What are we? Why, we are the miracle of force and matter making itself over into imagination and will. Incredible. The Life Force experimenting with forms. You for one. Me for another. The Universe has shouted itself alive. We are one of the shouts. Creation turns in its abyss. We have bothered it, dreaming ourselves to shapes. The void is filled with slumbers; ten billion on a billion on a billion bombardments of light and material that know not themselves, that sleep moving and move but finally to make an eye and waken on themselves. Among so much that is flight and ignorance, we are the blind force that gropes like Lazarus from a billion-light-year tomb. We summon ourselves. We say, O Lazarus Life Force, truly come ye forth. So the Universe, a motion of deaths, fumbles to reach across Time to feel its own flesh and know it to be ours. We touch both ways and find each other miraculous because we are One."
-Ray Bradbury, in his short story "G.B.S. - Mark V"
The second quote needs a little explanation. The story is about a race of robots in the distant future, when all life has been exterminated. The second speaker, Ultar, is a robot scientist who has just created a human from the "protoplasm" and is reflecting on the differences between humans and robots:
Kront said, "Why did you do it? Why have you made this thing of flesh and imperfection?"
"Why?" Ultar turned to the box. "Look at him, this creature, this man, so small, so vulnerable. His life is worth something because of his very vulnerability. Out of his fear and terror and uncertainty he once created great art, great music and great literature. Do we? We do not.
"How can a civilization create when it lives forever and nothing is of value? Things only take value from their evanescence, things are only appreciated because they vanish. How beautiful a summer day is that is only one of a kind; you have all seen such days --- one of the few things of beauty that we know, the weather, which changes. We do not change, therefore there is no beauty and no art.
"See him here, in his box, dreaming, about to wake. Little frightened man, on the edge of death, but writing fine books to live long after. I've seen those books in forbidden libraries, full of love and tenderness and terror. And what was his music but a proclamation against the uncertainty of living and the sureness of death and dissolution? What perfect things came from such imperfect creatures. They were sublimely delicate and sublimely wrong, and they waged wars and did many bad things, which we, in our perfectness cannot understand.
"we cannot understand death, really, for it is so rare among us, and has no value. But this man knows death and beauty and for that reason I created him so that some of the beauty and uncertainty would return to the world. Only then could life have any meaning to me, little as I can appreciate it with my limited faculties.
"He had the pleasure of pain, yes, even pain a pleasure, in its own way, for it is feeling and being alive; he lived, and he ate, which we do not do, and knew the goodness of love and raising others like himself and he knew a thing called sleep, and in those sleepings he dreamed, a thing we never do, and here he is now, dreaming fine things we could never know or hope to understand. And you are here, afraid of him and afraid of beauty and meaning and value."
-Ray Bradbury, in his short story "A Blade of Grass"
Friday, February 15, 2008
If you haven't heard yet, here's the deal: a week or so ago, it was announced that the spy satellite USA 193 is disabled and will come streaking down to earth in a fireball some time in March. Needless to say, that could be cool to see, but it could also be dangerous.
Now the twist: MSNBC reports that the pentagon is going to blast the satellite with a missile before it re-enters to "minimize the risk to humans from its toxic fuel". Really? The toxic fuel is the problem? It's not that they don't want the remains of advanced technology falling into the wrong hands? It's not that they want to show that China is not the only nation that can blow a satellite out of the sky?
It will be interesting to see the repercussions this has on US space policy. Weapons and space together in any form are generally seen as a bad thing, unless, apparently, there's a spy satellite full of toxic fuel.
Thursday, February 14, 2008
Since it is Valentine's Day, I thought it would be fitting to post some spacey valentine images. Of course, the Bad Astronomer beat me to the punch, but I have one more to add.
A Rose by any other Name...
This one is an image of a reflection nebula taken by the Spitzer infrared space telescope. It was also, incidentally, taken by my first research advisor, Tom Megeath.