"When in doubt, make a fool of yourself. There is a microscopically thin line between being brilliantly creative and acting like the most gigantic idiot on earth. So what the hell, leap." -Cynthia Heimel Once every four years, the elusive entity that is today -- February 29th -- comes along. The historical origins and urban legends associated with it are incredibly interesting, but the reason there's any such thing as Leap Day at all is because of the physics of planet Earth.
(Image credit: Mrs. Snyder at the Seven Hills School.)
The Earth, of course, is rotating on its axis while simultaneously revolving around the Sun. Rotation, as we all learn, is responsible for sunrise, sunset, moonrise, moonset, the Coriolis effect, and the rotation of all the stars in the night sky about the poles. Revolution, on the other hand, is responsible for the seasons; when your hemisphere tilted away from the Sun, that's when you have your winter (and minimum daylight), and when your hemisphere is tilted towards the Sun, that's when you have your luminous summer.
And you probably learned that a day is 24 hours, due to the rotation, while a year is 365 days (with an occasional 366 for leap years), taking care of the revolution. It turns out it's a little more complicated than that, so let's dive in!
(Image credit: Larry McNish at RASC Calgary Centre.)
The Earth completes a full rotation in less than 24 hours: 23 hours, 56 minutes and 4.09 seconds, to be more precise. But even though we've spun around a full 360 degrees, we've progressed just a little bit in our orbit around the Sun. If we insisted on using the 23:56:04.09 figure as our day, the Sun would be out at midnight for half the year! To fix the motion of the Earth around the Sun, we need those extra 3 minutes and 56 seconds to orient ourselves correctly. That takes care of what a day is, but what about a year? A revolution -- for the Earth to return to the same position with respect to the Sun -- might be an interesting astronomical thing to mark, it isn't a useful definition for a year on Earth.
In order for the Earth to achieve the same seasonal position in its orbit around the Sun -- and trust me, if you live on Earth, you'll want to mark your calendars by the seasons -- you'll need for the Earth to be oriented the exact same way with respect to the Sun as it was exactly one revolution ago. We could do this from winter solstice to winter solstice, when the Earth's north pole (for me) points maximally away from the Sun, or any other arbitrary point in its orbit. This way of measuring the year, known as the tropical year, is actually a little shorter than the astronomical measurement of a year we might be tempted to make.
(Image credit: Greg Benson at Wikimedia Commons.)
Because the Earth only needs to revolve slightly less than 360 degrees around the Sun to make one tropical year. The difference is tiny -- 359.986 degrees instead of 360 -- but enough to make the tropical year about 20 minutes shorter than the sidereal (or astronomical) year. This difference is known as precession, and it explains why the pole star in the night sky appears to change very slowly over a period of about 26,000 years. (25,771 years, for the sticklers.)
(Image credit: retrieved from Tom's Astro Blog / Marian Ware.)
Combine all three of those effects together -- rotation, revolution, and precession -- and you can answer the question of how many days will it take the Earth to make a tropical year?
The answer, as precisely as we can figure for 2012, is 365.242188931 days. If we just had 365 days in the year every year, we'd be off by nearly a month every century, which is pretty lousy. Putting in a leap year (with an extra day) every 4th year gets us closer, giving us 365.25 days in a year. (This was how we kept time with the Julian Calendar, which we followed for 1,600 years!) Still, this difference was significant enough that, by 1582, we had put in 10 too many days. For this reason, October 5th through October 14th of 1582 never existed in Italy, Poland, Spain and Portugal, with other countries skipping 10 days at a later date. The Gregorian calendar, which we now follow, is exactly the same as the Julian calendar, except instead of having a leap year if your year is divisible by 4 (as 2012 is), you don't get a leap year on the turn-of-the-century unless your year is also divisible by 400! So even though 2,000 was a leap year, 1,900 wasn't and 2,100 won't be, but 2,400 will be again. When did your country make the switch?
The adoption of the Gregorian calendar gives us a calendar of with -- over time -- 365.2425 days in the year. In comparison with the present, actual figure of 365.242188931 days, it will take over 3,200 years for us to be off by a single day, which is certainly good enough for a little while.
But if we want to be planning for the long term, we shouldn't simply be thinking about this difference. We should be thinking about the fact that the Earth's rotation rate is changing, and over long enough amounts of time, so should our definition of what a "day" is!
What am I talking about? Two things happen that change the Earth's rotation rate, and they push the day in opposite directions.
(Image credit: USGS.)
Every time we have an earthquake, that's mass inside the Earth rearranging itself so that -- by the conservation of angular momentum -- its rotation speeds up a little bit. For instance, last year's Japanese earthquake shortened the day by 1.8 microseconds, and the 9.1 Sumatra earthquake in 2004 shortened the day by 6.8 microseconds. On the other hand, there are two bodies out there with large gravitational effects on the Earth!
(Image credit: Rick Taylor.)
The Sun and the Moon both exert gravitational pulls on the Earth, all while the Earth itself rotates. If the Earth were just a point in space, this wouldn't matter; the Earth would make its elliptical orbit around the Sun, the Earth-Moon system would orbit their center of mass, and nothing would change. But because the Earth is a sphere, both the Sun and the Moon exert greater gravitational pulls on the side of Earth that's closer to them than on the side that's farther away.
(Image credit: the COMET program. Registration required.)
(Image credit: Purdue University.)
The slow-down is small but pretty consistent, at an average of 14 microseconds per year, a much larger effect than the speedup due to earthquakes. And over geological times, this really adds up! If we go back to the daily patterns left in the soil from the tides -- known as tidal rhythmites -- we can calculate what the period of Earth's rotation was from it.
(Image credit: Touchet formation by Williamborg.)
If we look at the most ancient one we know of on Earth, from 620 million years ago, we find that a day back then was a little under 22 hours long!
If you extrapolate this tidal braking back to when the Earth was first formed, 4.5 billion years ago, you'll find that a day was originally only around 23,000 seconds, or six-and-a-half hours!
(Image credit: Primeval Earth by Don Dixon.)
And the best part about this is that the Earth continues to slow down! Every 18 months or so, because of the difference between 86,400 seconds and an actual day, we add an extra leap second to our clocks (for now). Wait around for around four million years or so, and the day will lengthen by about 56 seconds, enough that we won't even want leap year anymore; a year will have exactly 365 Earth days!
So appreciate this leap day and our attention to detail to getting the Earth's seasons to remain constant from year-to-year, but also be aware that our Earth, however imperceptibly, means that these leap days, too, shall pass.Read the comments on this post...
"One mustn't look at the abyss, because there is at the bottom an inexpressible charm which attracts us." -Gustave Flaubert The deepest depths of space, out beyond our atmosphere, our Solar System, and even our galaxy, hold the richness of the great Universe beyond. Stretching for billions of light years in every direction, there are structures large and small, dense and sparse, everywhere we've ever dared to look.
(Image credit: R. Jay GaBany, Cosmotography.com.)
In addition to the visible, luminous matter we see in the image above, there's both non-luminous normal matter and dark matter. The non-luminous matter is made out of protons, neutrons, and electrons, but doesn't emit light. This includes things such as gas, dust, planets, and astrophysicists: in other words, most normal matter in the Universe. But when we take everything we know about normal matter, including how much there is of it, how its pulls together under the force of gravity throughout the Universe, we find that there needs to be about five times as much dark matter as all the normal matter combined.
One of the easiest ways to figure this out and measure it is by looking at some chance locations in the Universe where there are two massive structures directly lined up, one-behind-the-other, relative to our line-of-sight.
(Image credit: ESA, NASA, K. Sharon and E. Ofek.)
Above is what happens when you have a galaxy cluster with both a quasar and a background galaxy directly behind it. This result -- of multiple images and/or distorted, arcing appearances of the background source(s) -- comes about because of gravitational lensing. This intervening mass bends and magnifies the light from the background source, allowing us to see incredibly distant objects that would be otherwise invisible.
It works the other way, too. From the light that we observe from these background objects, we can infer all sorts of things -- like the mass and how it's distributed -- of the intervening, foreground object, as well as how perfectly/imperfectly it's aligned with the background ones.
The results are often breathtaking and, at least to me, always spectacular.
(Image credit: ESA/Hubble & NASA, retrieved from APOD.)
The "horseshoe" above represents a nearly perfect alignment of two sources. Almost perfect, but not quite. If the background and foreground sources were perfectly aligned, the background source would be bend into a uniform-brightness circle -- a great cosmic rarity -- known as an Einstein ring.
If you could zoom into a nearly-but-not-quite-perfect Einstein ring that was lensed by a black hole, the sight would surely, for as long as you remained an intact being, blow your mind. For what you'd find would be an infinite sequence of these rings, progressively decreasing in brightness, as you approached the event horizon.
(Image credit: Public Domain image, retrieved from Wikipedia.)
But I digress. These Einstein rings are lensed by galaxies, not black holes. The circles they make are never exactly perfect, but some come close. In particular, here's a (falsely-colored) image of one that was recently discovered. This one is particularly interesting for the sheer distances involved: the foreground galaxy -- the one doing the lensing -- is a luminous red galaxy located 9.8 billion light years away. But the background galaxy, the one bent into the ring, is an even more spectacular 17.3 billion light years away. And as you'll notice, it forms a nearly, but not quite, perfect ring.
This system, known as JVAS B1938+666, is much more than just a pretty ring of nearly-perfectly aligned galaxies. You remember, when you form a ring like this, one of the things you'll learn is how the foreground mass is distributed. In addition to the central, luminous red galaxy, there's also a dark concentration of mass, a bit off from the center, of about two hundred million Suns.
Incorrectly reported by many as a purely dark matter galaxy, this is simply a standard dwarf galaxy, but it's so far away that the light from its stars are insufficiently bright to be seen, even with a ten-meter telescope!
(Image credit: David Lagattuta / W. M. Keck Observatory.)
So what's really going on here? You can take a look at the full paper (S. Vegetti et al., 2012) for yourself, but let's break it down in simple terms, and (hopefully) clear up the confusion surrounding this. Almost everywhere in the Universe, the structure you form is about 80-85% dark matter and 15-20% normal matter.
Everywhere. In our galaxy, in galaxy clusters, even in superclusters on the largest visible scales. In these large objects, the gravitational forces are huge, and the gas, dust, and all the forms of normal matter stay bound to their parent object, no matter what you do to it.
(Image credit: NASA, ESA, and A. Aloisi (ESA & STScI).)
But in dwarf galaxies, the little guys, large bursts of star formation can be so powerful that they can eject normal matter out of the galaxy itself! This allows them to, over time, become galaxies that are even more dark-matter-dominated than other, more massive objects in the Universe. In the image above, I Zwicky 18 is full of young stars, indicating an intense burst of star formation that's no more than 500 million years old. There are older stars in there, too, which are more like 10 billion years old, but this latest burst, as perhaps the image below shows even more clearly, will turn this galaxy into an even more strongly dark-matter-dominated object in the future.
(Image credit: Centro de Astrofísica da Universidade do Porto, retrieved from here.)
As this intense burst of star formation happens, bright, hot, young stars form, burn brightly, and die in spectacular supernova explosions. The radiation and outward flux from these objects can heat up and energize the normal, non-luminous matter so thoroughly that it can achieve escape velocity, kicking it out of the dwarf galaxy! What gets left behind are the relic, long-lived stars, the old stellar corpses, and the dark matter.
But what's really important here is that this is exactly what we know should happen! Despite what you may have read elsewhere, there's no reason to believe these objects are 100% dark matter, and there's definitely no reason to believe these observations pose a problem for structure formation. Some people argue that dark matter simulations predict a different density of dwarf galaxies than our Local Group has, and therefore dark matter is wrong. But we have to look at the entire Universe! This one fact does not mean that our Local Group is a good representation of the rest of the Universe; in fact we already know many ways in which it is definitely not! So we go to the paper itself, wherein they've found the most distant dwarf galaxy ever, which says: Our results are consistent with the predictions from cold dark matter simulations at the 95 per cent confidence level, and therefore agree with the view that galaxies formed hierarchically in a Universe composed of cold dark matter. And this is as close to a definite (12-σ significance!) detection as one could get: see for yourself!
(Image credit: S. Vegetti et al., Figure 3 in the pdf.)
You're always going to make waves by claiming that you've done something sensational, like disproven dark matter or found an object made out of 100% dark matter and 0% normal matter, but that's not what we have here.
We've just discovered, at nearly 10 billion light years away, the most distant low-mass, dwarf galaxy in the Universe. And that should be impressive enough; do you know how hard these things are to find?
(Image credit: NASA, ESA, and The Hubble Heritage Team (STScI/AURA).)
The closest galaxy to us, the Sagittarius Dwarf Galaxy, is about the same size: 1-200 million solar masses, and it took the freakin' Hubble Space Telescope to take this picture of it! Considering it's only seventy thousand light years away, maybe we can cut ourselves some slack for not being able to see the starlight from its twin ten billion light years away!
And despite the great cosmic distance, we are still able to find it, all thanks to gravitational lensing. Are you not impressed?Read the comments on this post...
Score!Read the rest of this post... | Read the comments on this post...
I'm home with The Pip today, so no extended typing for me, but I pre[ared for this by typing something up ahead of time, and getting John Scalzi to post it for me, as part of his Big Idea series:
In a way, a book about Einstein's theory of relativity is uniquely suited to a series about Big Ideas. Relativity, at its heart, is a theory built on a single Big Idea:
The laws of physics do not depend on how you're moving.
For all its fearsome reputation, everything stems from that single,simple idea. Whether you're moving or standing still, floating in space or on the surface of a planet, you will see the laws of physics work in exactly the same way.
There's a bunch more, but you can read it over at John's blog. And if you're sold on that, well, How to Teach Relativity to Your Dog is released today, so you can get it immediately.Read the comments on this post...
The Pip says, "Hi, folks. My daddy's book is released today, and he's shameless enough to use me to promote it:"
"I can't read it yet, because I'm just a baby, but I can report that it was very satisfying to drool on. So you should definitely buy a copy, maybe two."
"Also, dig the awesome stuffed alligator toy I got from my Aunt Erin and Aunt 'Stasia. It crackles, and it has a mirror! It's so cool!"Read the comments on this post...
If you have a few minutes to kill, go check out this podcast over at Sol Lederman's website “Wild About Math.” Laura Taalman and I discuss the BSB (by which I mean the Big Sudoku Book). We talk Sudoku, math, education and plenty of other stuff. We originally planned on talking for thirty minutes. but everything went so well that we ended up hanging around for fifty. So go enjoy and let me know what you think!Read the comments on this post...
If you're allergic to hype, you might want to tune this blog out for the next couple of days, because How to Teach Relativity to Your Dog is officially released tomorrow, so it's all I'm going to talk about for a little while. Because, well, I'm pretty excited.
And tonight's exciting finding is that it's mentioned in the Washington Post:
If "Physics for Dummies" left you baffled, maybe it's time to go a step further: Why not physics for pets? In "How to Teach Relativity to Your Dog," physics professor Chad Orzel attempts to explain Einstein's theory of relativity via a dialogue with his dog, Emmy. Orzel breaks down complex concepts -- time dilation, relative motion, black holes, the big bang -- by applying their physics to canine-friendly situations, like chasing rabbits and determining whether a dog can eat enough kibble to run at the speed of light. Rather than barking or growling, Emmy leavens the mood with requests for walks; and when the academics get heavy, she interjects to beg for clarification. Obviously, real-life dogs will not walk away from the book with a grasp of the universe's mechanics, but the human sort of non-scientist can get some benefit.
OK, that one paragraph is the sum total of the mention, and I'm not sure if that's in the print edition or just the web site (then again, who reads print newspapers any more?), but, dude! The Washington Post acknowledged my book! Woo-hoo!
"All right!," says Emmy. "The Post represents the conventional wisdom of political elites, so if they say nice things about our book, it's only a matter of time before Congress dishes me some of that sweet, sweet pork I keep hearing about. Mmmmm.... pork...."Read the comments on this post...
I know many of you enjoy discussing resonance. Check this out:Read the comments on this post...
We're in the home stretch of this term, and it has become clear that I won't actually be using the toy model of the arrow of time I've talked about in the past in my timekeeping class this term. These things happen. Having spent a not-insignificant amount of time playing with the thing, though, I might as well get a final blog post about it, with something that sort-of worked and something that shows why I'm not a computational physicist:
First, the thing that sort-of worked: in thinking about trying to use the code I wrote, I was struggling to come up with a way to quantify the apparent irreversibility of the evolution of my toy system for larger numbers of "particles" in a relatively non-technical way that might be comprehensible for non-physicists. After a bit of thinking, I realized that there's an easy-ish way to do this, because the system has an easily calculated maximum entropy, which it ought to converge to. And empirically, when I start it going, it shoots up toward the maximum, and then noodles around up there, with occasional downward fluctuations as more "atoms" randomly end up on one side or the other.
To quantify the number and amount of those downward fluctuations, I realized I could just use the number of points dropping below various fractions of the maximum entropy, once the system got close to the maximum value. Which led to this graph:
To get these, I ran for 100,000 time steps, throwing out the first 1000 (as the entropy climbed upward from the initial low-entropy state with all the "atoms" in the left half of the array), and set up some simple counters that recorded the number of time steps where the entropy was below 90%, 75%, and 50% of the maximum possible for that number of lattice sites and atoms.Read the rest of this post... | Read the comments on this post...
By Stacy Jannis
Exciting things are happening in 21st century classrooms all over our country. Teachers and students are using cutting-edge technology, working in teams, and connecting and sharing projects with classrooms all over the world. Innovative groups like the Concord Consortium , Promethean World , Project Lead the Way and Epals are at the forefront of creating the curriculum, software, tools and environment of tomorrow's classroom, today. A rich and exciting mix is brewing, one that combines multimedia, digital simulations, games, computer programming, inquiry and project-based learning, to accelerate our children's skills to think creatively, work collaboratively, and train to tackle 21st century problems.
Can we save the world through science and engineering? We think so! We are inspired by the excellence and passion for science and science education that takes place in innovative classrooms all over the country, every day.
A 6th grade classroom at Friends School Haverford took up this challenge as part of the Kavli Science Video Contest. As a class, they researched, brainstormed ideas, and focused on topics including energy, health, and the environment. Then they let their creativity go wild, including writing and recording original music, animations, and video. Here's what some of the kids said on the last day of the project:
"This project has changed how I think about science. I knew science could cure sickness and diseases, but I never realized science could save the world."
"I really got a better understanding of what science can do."
"I already thought [science] was fun and important but doing this project made me think about science as a way to change the world."
"Science isn't always just researching, working in the lab, or finding solutions to problems every day. Science can be fun and exciting."
The Kavli Science Video Contest challenges students to investigate how science and engineering saves our world, and answer the central theme creatively.
Grades 6-12 students compete for the chance to win $2000 (first prize) and a travel stipend to Washington DC to attend the festival. The winners are also honored in an awards ceremony, hosted by Bill Nye, as part of the festival.
Our central theme, or driving question, is how to "Save the World through Science and Engineering". Students make a short video( :30-:90) that shows how scientific discoveries and inventions can improve our lives and change our world, either right now or in the future. Enter by Mar. 21, 2012.
Click here to read more about the Festival and the Kavli Video Contest.Read the comments on this post...
Neil deGrasse Tyson has a new book out: Space Chronicles: Facing the Ultimate Frontier. It is (as one might guess) about space exploration, and assembles earlier speeches and writings with some new stuff. This is an interesting time to be talking about the space program, as NASA seems to be producing new results ever week, there are large and small space robots on their way to distant orbs, or soon to be launched, we are on the verge of understanding the potential of life on Mars on a basic level, we are finding more earth-ish Exoplanets and at the same time the sky is falling, or at least, trashed with litter from one of the most significant, direct and obvious side effects of the space program: We humans get to ruin not just the air and the sea and the land, but also, near space!
From a recent NPR interview:Read the rest of this post... | Read the comments on this post...
Hey, you might not know this, but I wrote a book...
The official release date for How to Teach Relativity to Your Dog isn't until Tuesday, but a friend reported buying a copy in Missouri, so when I was headed out to do some work this afternoon, I went to the cafe at the local Barnes&Noble so I could check for myself, and there it was:
That's How to Teach Relativity to Your Dog spotted in the wild. I'm not going to say "in its natural habitat," because it's really a domestic animal, which belongs in a loving home, with people to care for it. Copies in the bookstore are feral editions, which need to be tracked down, taken in, and adopted.
So, please, head down to your local store, and take one home, won't you? You could even arrange to have one sent directly to you, from one of the nice retailers linked at DogPhysics.com...Read the comments on this post...
Once again, Kate is running an auction to benefit the Con or Bust project providing financial support for fans of color(*) to attend science fiction/ fantasy conventions. The auction is run via LiveJournal, with a variety of cool items on offer in individual posts to that community, with an overall index here.
Among the items on offer are signed copies of How to Teach Relativity to Your Dog and How to Teach Physics to Your Dog (in your choice of several languages). You can also bid on some of our excess books.
Bidding ends at midnight Sunday, so you've got a little time left. Check out the lists of stuff, and get your bids in soon.Read the rest of this post... | Read the comments on this post...
The other controversial thing this week that I shouldn't get involved in is the debate over whether Brian Cox is talking nonsense in a recent discussion of the Pauli Exclusion Principle. Tom at Swans on Tea kicked this off with an inflammatory title, and Cox turned up in the comments to take umbrage at that. Sean Carroll provides a calmer and very thorough discussion, the comments to which include a number of well-known science popularizers duking it out.
My take on it is basically the same as Tom and Jim Kakalios in Sean's comments: unless the two particles you're talking about are within about a de Broglie wavelength of each other, Pauli exclusion doesn't really matter. This was actually a question at my Ph.D. defense, because a big part of my thesis was about quantum statistical effects in ultracold collisions, where Pauli exclusion forbids certain types of collisions from taking place. When we think about that sort of thing, we require that the two colliding atoms be in an overall antisymmetric wavefunction, but we don't worry about the state of other atoms of the same element elsewhere in the apparatus, because they're so far away that they don't change the energy states available to the colliding atoms in any significant way.
In Tom's comments, Cox insists that hes right, and says that the whole thing is worked out in detail in his new book. I haven't read the new book, though I've been offered a copy by a publicist, so we'll see. I think Sean and Matt Leifer at comment #6 have covered pretty much all of the bases, though, so I'm inclined to think that Cox is just wrong. There may be a narrow philosophical sense in which he's correct, but I don't think it's useful, and given that there are large numbers of people working scams based on woo-woo notions of quantum phenomena enabling paranormal abilities, I think this is a bad direction to take popular quantum mechanics.Read the comments on this post...
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Is approaching 1 per minute and accelerating.
It's not a good week for me to be writing about anything remotely controversial, but if I want to keep my physics blogging license, I need to say something about the latest fast neutrino news. This has followed the usual trajectory of such stories, with the bonus farcical element of people who blasted the media for buying into the initial release seizing triumphantly on an initial rumor in the press that was garbled into incomprehensibility. With a little more time, it's become more clear how their result has become less clear, and the best place to look for a description of this is Matt Strassler's blog, where he has not just one, not just two, but three excellent posts on the news, laying out what's really going on.
Having written at the time that "if something is wrong with their experiment, it's something pretty subtle, because they've checked all the obvious problem areas carefully," though, I probably need to say something about whether this counts as "subtle." Because "look for loose wires" might seem too obvious to count as subtle, at least if you're not familiar with experimental physics.
If you are familiar with experimental physics, though, this definitely would count as "subtle," because real experiments aren't like block diagrams, with single wires running in and out of a single detector. In an experiment on this scale, you're probably talking about hundreds of individual cables connecting different boxes, and checking all of them is a non-trivial matter. What's more, there's nothing about their measurement that suggests a bad connection as the first thing you would look for-- a loose cable, particularly a fiber-optic cable, shouldn't produce tens of nanoseconds of signal delay unless by "loose" you mean "on the other side of the room from where it's supposed to be."
What's more, as Strassler notes, there are actually two timing issues, moving the signal in opposite directions. Fixing one would tend to reduce the apparent speed, while fixing the other would increase it, making matters worse. So the whole situation is, as Strassler says in the third post linked above, completely confused. At this point, it's not clear what if anything they can say about the apparent speed, other than that it's worth testing again in a new data run, with more neutrinos and more detectors, coming later this spring.Read the comments on this post...
"Day after day, day after day,
We stuck, nor breath nor motion;
As idle as a painted ship
Upon a painted ocean.
Water, water, every where,
And all the boards did shrink;
Water, water, every where,
Nor any drop to drink." -Samuel Taylor Coleridge, Rime of the Ancient Mariner Despite the discovery of dozens of worlds -- planets and moons -- in our own Solar System, as well as hundreds (soon to spill into the thousands) of confirmed planets orbiting other stars, our Earth is still unique.
(Image credit: The Suomi NPP Blue Marble, NASA / NOAA.)
At least, it's unique as far as we know.
A smaller, dense rocky world with not just continents, but also oceans and life, Earth is the only one of its kind. So far, that is. And yet given the huge variety of stars and worlds found to date, it makes you wonder just what sort of unusual places this Universe contains.
(Image credit: NASA, ESA and G. Bacon (STScI).)
The first exoplanets found were Hot Jupiters: gas giant planets orbiting very close to stars even hotter and brighter than our own. And this is no surprise: it's much easier to detect large, heavy planets that are close to their parent star. Conversely, it's much more difficult to detect planets when they're any combination of smaller, lighter, or farther away from their parent star.
In the last few years, our technology has improved enough that we've found a vast variety of stars, from the smallest, coolest, reddest stars up through big, bright hot blue stars (and even a few red giants and supergiants) that have planets orbiting them. In the image below, all 2,326 exoplanet candidates discovered by the Kepler Mission are shown.
(Image credit: NASA's Kepler Science Team / Jason Rowe.)
Based on the temperature and luminosity of the star that's central to each of these solar systems, each planetary system has a region of space where -- according to our current knowledge of biology and chemistry -- life may be likely to arise. We call this region the Habitable Zone, and planets found within it are excellent candidates for the one Earthlike condition we prize over any other: liquid water.
Planets too close to their star, like Mercury in our own Solar System, are going to be too hot for this. Rocky worlds that are too far distant, like those out beyond Mars, will be too cold. We have reached the point where we've discovered solar systems other than our own that have planets in all three zones!
(Image credit: wikimedia commons user Henrykus.)
Like the vast majority of stars in the galaxy, the parent star of the exoplanet system above, Gliese 581, is a red dwarf star with less than 40% the mass of the Sun. While their habitable zones are tiny compared to the one around our Sun, there are already many excellent rocky planetary candidates found interior to and within their habitable zones.
In fact, the Kepler team has put together a tremendously illustrative video of all the candidate planets found. Have a look for yourself!
Now, if we were to rescale these raw distances, we'd find that there are a great number of planetary candidates closer to their star than Mercury is to the Sun that would be too cold to support life, but that -- by far -- the most common type of exoplanet found so far is still the one too close to its star to support Earth-like life.
But one of the most interesting things to consider is that not every solar system is going to have the same chemical composition as ours. How's that?
(Image credit: La Silla Observatory / MPG / ESO.)
The way you form stars -- as the star forming region NGC 3324 illustrates -- is by collapsing molecular gas clouds down into regions with a central star and a protoplanetary disk. Over time, the atoms in the disk accrete into planets, with typically the densest elements closest to the parent star and the least dense elements the farthest away. It is no coincidence that Mercury, Venus, and the Earth (and Earth's Moon) have significantly higher densities than all other planets, moons, comets and asteroids in our Solar System.
But the reason we have as many heavy elements as we do is because the molecular cloud that formed us had enough enriched elements from deceased, previous generations of stars to form us. Stars that were formed much earlier in the Universe, as well as stars that formed later in less enriched regions, would have solar systems containing planets with much lower densities. Even the innermost planets.
(Image credit: David A. Aguilar (CfA).)
And by measuring not just the mass and radius of the planet, but the star's light filter through the planet's atmosphere, we can measure the infrared color of "sunset" on the world, and hence determine the elemental composition of the planet's atmosphere!
What did they find? A thick, dense, featureless atmosphere composed primarily of water vapor! As the Harvard-Smithsonian Center for Astrophysics reports:
"The Hubble measurements really tip the balance in favor of a steamy atmosphere," said [Zachory] Berta.
Since the planet's mass and size are known, astronomers can calculate the density, which works out to about 2 grams per cubic centimeter. Water has a density of 1 g/cm3, while Earth's average density is 5.5 g/cm3. This suggests that GJ1214b has much more water than Earth, and much less rock.
As a result, the internal structure of GJ1214b would be very different than our world.
"The high temperatures and high pressures would form exotic materials like 'hot ice' or 'superfluid water' - substances that are completely alien to our everyday experience," said Berta. That strong signal favoring an atmosphere composed 100% of water vapor is definitely there, as the signatures of models with significant other atmospheric components are clearly disfavored in Figure 10 (thanks, Michael Richmond) from the paper:
(Image credit: Z. K. Berta et al.)
The conclusion that the planet has this uniform, thick H2O atmosphere around it indicates a large, watery chemical composition. The sheer amount of water indicated by this data -- combined with the information about the overall density of the planet -- renders a solid, rocky surface is inconceivable!
This world most likely is a waterworld, with a 100% oceanic surface!
(Image credit: retrieved from Steven Andrew.)
This planet is likely to be at very different temperatures and pressures from Earth, and so will likely have unusual states of water. It should be constantly boiling (at an average temperature of 450 degrees Fahrenheit (230 Celsius), and there should be strange states of matter, like "hot ice" or "superfluid water" composing the surface/atmosphere.
There are stranger worlds out there than most of us have ever imagined, and this one orbiting this star -- GJ 1214 -- just 42 light years away, is the first super-Earth that's ever had its atmosphere detected.
I can't help but look on with awe, and enjoy wondering what else is out there!Read the comments on this post...
Both Phil Plait and Sean Carroll are tentatively reporting that they may have an explanation for the recent anomalous report of neutrinos traveling faster than light: it may have been a case of a faulty connection in a timing circuit. If that bears out, it may be a bit embarrassing.
But it does suggest an important possibility. When we get around to building the first starship, don't have those fussy, punctilious physicists wire it up. Gather a gang of sloppy slapdash biologists to stick it together with spit and chewing gum. We'll have it going a heck of a lot faster than light than those experts can even imagine.
(Also on FtB)Read the comments on this post...
I'm grading exam papers at the dining room table when Emmy trots in. "Hey, dude," she says. "Where do we keep the superconducting wire?"
I'm not really paying attention, so I start to answer before I understand the question. "Hmm? Wire is in the basement, next to the--wait, what?"
"The superconducting wire. Where do we keep it?"
"We don't have any superconducting wire. And you're a dog. What do you need superconducting wire for, anyway?"
"I'm building a particle collider! I need superconducting wire for the beam-steering magnets."
How to Teach Relativity to Your Dog goes on sale next Tuesday, wherever you buy books. The above video is a dramatic reading of the dog dialogue that opens Chapter 8: Looking for the Bacon Boson; E = mc2 and Particle Physics. If you enjoy that, there are 11 more such conversations in the book, along with longer, more detailed explanations of the relevant physics.Read the comments on this post...
... Well, everything is in space, but I mean outer space!Observations by NASA's Hubble Space Telescope have come up with a new class of planet, a waterworld enshrouded by a thick, steamy atmosphere. It's smaller than Uranus but larger than Earth.
Zachory Berta of the Harvard-Smithsonian Center for Astrophysics (CfA) and colleagues made the observations of the planet GJ1214b.
"GJ1214b is like no planet we know of," Berta said. "A huge fraction of its mass is made up of water."
The ground-based MEarth Project, led by CfA's David Charbonneau, discovered GJ1214b in 2009. This super-Earth is about 2.7 times Earth's diameter and weighs almost seven times as much. It orbits a red-dwarf star every 38 hours at a distance of 1.3 million miles, giving it an estimated temperature of 450 degrees Fahrenheit.Read the comments on this post...