Launch Pad, Day One: Kevin R. Grazier on Solar System/Cassini

Rachel Swirsky • July 12th, 2010 @ 8:25 pm • Launch Pad

How many solar systems are there in the galaxy? One. One star is called sol. There is one solar system. It is a proper noun and should be capitalized. Solar System.

It starts with an exploding star. Stars of very large size live by the credo “live fast, die young, live a good-looking black hole.” A supernova can outshine the sum total of all other stars in its galaxy.

Fusion–fundamental energy creation process in our sun, a proton-proton chain. You slam hydrogen together, make helium and energy in the process.

Also, there’s a triple-alpha process, CNO cycle… sun makes elements and energy during its lifetime.

Our star doesn’t make much big stuff. When it dies, it will blossom out, and expand, and there will be a little more nitrogen, oxygen, and carbon, and that’s about it.

Big stars, however, at the ends of their lives are so big that the temps and pressures are so big that they’ll make iron. Iron is stellar toxin. When a star makes too much, it dies. Eventually, it explodes. When they explode, they populate the universe with heavier elements like aluminum, magnesium, iron, silicon–the kind of things that make planets.

Which is why you start with dead stars before you can make planetary systems.

A star explodes, an expanding cloud of gas, which becomes a solar remnant or nebula. It doesn’t have enough mass to recollapse into anything else. Within large nebulae, we see regions where there are planetary systems being formed.

(BTW, if you want to buy a telescope, start with binoculars. Then you can try out stargazing, and also it’s useful elsewhere.)

Star and planet formation begins when temperature overwhelms fragments. Gravity pulls in, but the temperature wants to expand. These two forces are a constant tug-of-war, keeping stars the size it are–and nebulae too. So, something will get these enriched nebulae to collapse, such as another supernova, which causes a shock wave to pass through the nebula and leaves the planetary system behind? Ish? The missing steps are the foundation of the rest of the lecture.

As the shockwave passes through, you get “blobs”… you have a big remnant of gas, spinning ever so slowly, as a conservation of angular momentum from the spinning star. It starts to collapse, moving more rapidly. The blobs left over, are the size of planetary systems, and they also spin. After 100,000 years as the cloud collapses under its own gravity, the potential energy converts to kinetic, causing it to heat up as it condenses. A proto-star forms.

This is a nice part of astronomy because we can see star formation and star phases and star death in different phases, rather than just hypothesizing.

As we get this spinning disk of gas and dust, there are sometimes chemical reactions, occasionally the grains of dust accrete, and after a while they accumulate a nontrivial amount of gravity and draw stuff in. In the middle, that’s where the early star forms,with a disk of glass and dust around it; within the disk there are planet-forming bits.

Planetary cores near the sun are rocky and volcanic. Ones beyond the frost lines are icy. This makes sense: the sun is hot. So, there tend to be ices: water, carbon dioxide, ammonia, methane. In the inner solar system, rock and metal condense first; this is also true in the outer solar system, but ices also condense out there. As you probably guessed, because only big stars make the metal and iron bits, it’s hard to make rocky planets.

The T-Taurus phase begins. Like any adolescent, the star becomes subject to mood swings, it release jets of material from north and south pole, and there’s energetic solar wind, which is a constant stream of charged particles that come off the star, which blows out the remaining gas in the inner solar system. The inner cores which had only rock and metal are probably pretty small. The outer cores which had rocks, metals, and ices,become more massive. We believe that Jupiter had 10-15 earth masses at the center. Also, in the outer solar system, things are moving less quickly, and so it’s easier for them to adhere to existing masses.

Mike asks, is there a specific calculation for figuring out where the frost line ends up in relation to the star? Probably, says Kevin, but I don’t know what it is; I imagine it would have to do with where the freezing points are. Strictly speaking, there would be more than one frost line, since each ice freezes at a different point, but water is the most ubiquitous, so we work with that.

This isn’t conjecture anymore, though they’re still filling in details. For instance, we know that sometimes things stick together when they collide, but we don’t know what causes that, or what causes them not to stick. (It’s being used by creationists as a GOTCHA.)

We’re left with terrestrial planets. (We have a better map of Venus than of Earth because we don’t have good maps of our ocean floor.) These have iron cores in rocky envelopes.

Earth is the densest planet in the Solar System, for reasons will come back to.

Jovian planets are much larger. The great red spot of jupiter is 2.5x earth. Saturn is the only panet with a density less than water. The other plaents (not Jupiter or Saturn) are ice giants.

How do you find the radius of a gas planet? When you reach the point where the pressure of the gas pressing you from above is about the same as the pressure at earth’s sea level, that’s where the diameter is marked.

The lone property that gives a star color, size, lifespan, method of death, etc., is mass. You can look at this with the HR diagram.There is almost a 1 to 1 correlation between color and temperature. Contrary to faucets, red means a cool star. It’s like metal being in a fire, it glows red, orange yellow, green, blue, white.

How many times have you heard “our star is an average star?” A zillion times? That’s flat out wrong. Our star is not average. That came about because our star falls in the middle of the HR diagram. Our star is more massive than 93% of stars out there. Stars bigger than ours are really, really enormous, but the bulk of stars are tiny, ad not much bigger than Jupiter, or the same size. If Jupiter turned into a star, it would condense and become a little smaller than Jupiter.

We can make the claim, talkin g about the planets, that if we ever find a plent with life, we can make a good argument that it will be on a planet orbiting a star similar to ours. Now I realie thorughout the history of astronomy there have been a lot of earth-=centric arvuments that have been overtunred. We’ve always wanted to consider ourselves special, though we’ve learned ove r time that we’renot.

Our star has some important properties based on where it is. It turns out that you don’t have to get a whole lot larger than our star before its lifetime is measured in billions, then millions of years. Not 10billion years (as some bigger stars are true) versus one billion. That’s how long it takes to form life, so we won’t find life there.

If you’re on procyon, some stars there live about a billion years. Habitable range around a star is bound to a star’s lifetime, not its size.

There are stars we expect might have life or might be hospitable to life.

You could find stars in the upper left part of the diagram (where there’s not much lifespan to the star), it’s just that it would have to be colonizing not have evolved there. Although even that’s a problem if the lifespan of the star is short enough because it takes a long time for a planet like earth to become habitable to us.

The first life on earth: cyanobacteria, 3.8 billion years ago. (Grazier wonders how many times things like cyanobacteria might have appeared just as a planet became habitable, and then been destroyed by stars that went boom. This was turned into a BSG episode, as Grazier was consulting for the series.)

How long would a red dwarf live? They could last trillions of years. We have no reason to believe that in the history of the universe, a red dwarf has ever ended its life. Fusion is dictated by pressure and temperature, but because of the astral mass, a larger star has greater temperature and pressure and much more comes into play during the fusion process. That’s why they live shorter spans, because a lot of them fuses, and they burn very brightly. Not much of a red dwarf is involved in fusion.

Every second, our sun converts 600mil tons of hydrogen into 596 tons of helium with the resulting 4mil tons being converted into energy. That takes place in the core. It takes about 1mil years before it’s radiated outward. Our light is a bit older than 1mil years old.

When you convert energy, you get gamma rays, which is a high-energy form of light, but not visible light.

Fusion and sunspots are largely unrelated. There are huge magnetic fields on the sun. Magnetic fields sometimes create a cool spot, or a sunspot. It’s still very bright, it’s just not as bright as the rest of the sun.

What creates the variability in the star clusters. Matter wasn’t evenly distributed, and here again we see that as mass begins to accrete, it becomes larger, and is more likely to continue accreting.

Density of planets is an important concept. I have listed just a few things that make a planet: metals (mostly iron), rocks, ices, and gas. If you can get the density of a planet or a satellite or comment or asteroid, you have a guess of what it’s composed of.

Why is earth the dentist planet? We’re fairly certain a planetoid bigger than mars collided with earth gave us a glancing blow. The resulting splatter coalesced to form our moon. This skimmed off some light material, and added some heavy stuff from the asteroid, which explains earth’s density.

Earth’s tilt, fast spin, isotope/O2 ratios, and the fact that the moon has no iron core unlike other rocky things in the solar system, suggest to us that the moon was a bit of earth. There were theories of moon formation that don’t work which had been conceived of before this, such as moon capture, which is enshrined in Mormon theology.

Other planets do have a tilt, and we think likely they were tilted by impacts. Venus, for instance, titls a LOT, and we think it was an impact. Jupiter is so big it doesn’t tip easily, so it’s been hit with a lot of big things, even recently, but does not tilt.

Debunked theories of moon formation: earth’s gravity capturing it, but an orbit involves energy between one thing and another, and you can’t capture something the size of the moon. Daughter theory, that earth was spinning SO FAST that the moon was shed. People argued that the moon came form the Pacific basin. Also, the sister theory, the moon formed in a similar orbit to the earth, and since it approached us slowly in its orbit, we captured it. It’s just that the earth has no iron core, so this seems unlikely.

Other moons have formed by capture, for instance because they collided with the planet, which made them move slowly, so they got captured. For instance, moons that are in backwards orbits are probably captures. Phoebe is likely one of these, but no one knows *how* the capture occurred.

Scientists and engineers think differently, to varying degrees. Engineers are narrow-focus, and detail-oriented. Scientists much more out-of-the box, right-brained, big picture. Scientists want to understand the problem, engineers don’t care about the big system, they want the answer for their current problem.

Can moons have moons? There’s no reason why they can’t, but they’re enmeshed in the gravitational field much larger than them, so unless they’re really small, they tend to get pulled away. IOW, you can engineer parameters to make it work, but it’s not common.

Spreadsheets are very valuable computation tools, particularly when you need answers fast. People underestimate spreadsheets. There’s a whole chapter in a book on Cassini called the science of spreadsheets. (This is not amazing astronomy info, re: writing, but it’s good cultural stuff.)

The collision of the moon and the earth happened at a minimum of 11.2 km/second.

There are different ways to observe planets. One is ground observation. Also, there are fly-bys that pass by, which see things, but may miss important stuff due to the angle of their pass, or due to ways the planet changes over time. There are also in situ craft that observe, and there’s human observation. A rover will do what you tell it to do, but only exactly what you tell it. Say today you take a panorama shot. You’re done with that, so you send rover to another place, and the rover won’t do one thing that a human will do as a matter of course–e.g. look around when not instructed to do that.

A rock is an aggregate of minerals.

Science is about the how and why, not the what, because the what will change as we discover new things. (Particularly, one assumes, in fields like planetary science). For instance, Jupiter has 64 moons, but it could have many more. We haven’t seen them all, and some of the ones we have seen, we’ve only seen once.

Therefore, science is not about counts: number of moons, etc. Except when it is–for instance, counting craters is important because it indicates the age of a body.

Earth has craters. From lots of things, like glaciers, and volcanoes, and impacts.

Form a planetary science standpoint, looking at the moon titan, when we see that it has no craters, we can tell that it’s an active object. We’ve discovered details about how it’s active subsequently: but the lack of craters already gave us that information before we knew.

Escape velocity is the velocity needed to literally escape. It’s a function of the mass of the object you’re leaving. It’s not a function of the mass of the object escaping. The escape velocity is the same for a rocketship or an atom. Titan has less mass than mercury, though it’s bigger (it’s density is lower), though it has an atmosphere when Mercury does not. Why? Titan is further from the Sun, so its temperature is a lot lower, so that’s a measure of the average kinetic energy of the object. So, the atoms in the atmosphere of Titan move slowly and cannot escape. The heated atoms in the atmosphere of Mercury move quickly, and can.

So, anyway, they find rivers on Titan! Ooo. Shiny. The surface of Titan looks much like the surface of Mars–the stones are smooth! But what’s in the river? What’s flowing? Not water, which is ice this far out.

Well, there seems to be volcanic action on Titan because of the way that the impact crater from our crashing vessel created an irregular, squared-off shape. They also found sand dunes, which are caused in places on earth by continental collision. Are these things evidence of tectonism on Titan? Yes, they imply it. And we do seem to be able to see a volcano.

We’ve also found lakes, the first open bodies of liquid we’ve found outside earth.

We now believe that like some other moons, Titan has an ocean in the subsurface, water beneath ice (with more ice below that).

Atmospheric dynamics of Saturn–suppose you want to know about atmospheres, but don’t want to know about anything else on a planet. You can’t study someplace like earth where all that other clutter affects the atmosphere. Studying a gas giant allows you to isolate atmosphere effects. So for instance, in Saturn, weather originates in the east in the lower latitudes, and in the west in the upper, as on Earth. There are also storms on Saturn (at least of one formed a hexagonal shape, which they don’t understand yet).

There’s an argument for some kind of internal heat to melt the ice that composes the rings, since the rings need to be replenished, as very very small bits of ice do not last long in space (they sublimate, etc)… could there be cold vulcanism, they wonder? With eruptions that provide material for the rings?

Enceladus: the stripes on the surface look like Earth’s mid-ocean ridges. A temperature map shows that the temperature on the stripes is higher than the area around it. We also see glassy ice near the stripes, and when there’s an eclipse blocking the sun, we can see there are geysers erupting from the stripes. We see lots of images of these, still continuing to erupt.

Europa: believed to be underneath its rocky/icy exterior, a liquid ocean, which might contain life. There is only one “crater” which is believed to be a sub-surface volcano.

Iapetus: you can see it on one side of saturn and not the other, so one person thought perhaps it was light on one side and dark on the other. And that turns out to be sort of true, according to the Voyager photographs. We see light and dark material on the planet, like a yin-yang, almost like a walnut with a bright side and a dark one. Because the moon is tidally locked with the same face always facing saturn, it always has a leading and trailing edge. So it could be sweeping stuff up, people thought, or it could be rising from inside, or that eruptions could spew material upward that then gets reabsorbed, or that a ring could have collapsed into the surface. Why is there a straight line on this equator (more or less, varying by altitude); this rarely happens in nature? (Some conspiracy nuts latched onto this.) Looking up close at the high latitudes of the bright material, it appears to be implanted, especially because the craters are dark inside. They don’t know where the bright material comes from, but the sunlight is preferentially absorbed by the dark material, making it hot, any ice in contact vaporized and goes away, making it even darker.

At least one moon has made a channel through Saturn’s rings, as predicted before we saw it.

We see waves and wakes in the rings.

The equinox is when the ring plane is perpendicular with the sun’s rays. We saw that upcoming because we knew we would have to eventually delineate between ring particle and moonlet. Over time, anything tall like waves or like moonlet will cast shadows at the right angle with the sun.

Why do we see the rings of saturn from one direction, and different rings (but not the originals) from another? (They used this in Battle Star Galactica when they needed a prophecy where the prophet would see a vision from one direction that would be accurate, but misleading, because the object looks different from the other direction.) The reason this happens has to do with backscatter, which happens when there are large objects close together. When you have small objects, far apart, then they forward scatter.

What’s the next big mission? Mars science laboratory which will be the size of a mini-cooper. They can’t use the airbag technique to land this one, but will need retro-rockets instead. Like Cassini, the MSL is powered by radio decayed plutonium. The cool thing is the previous explorers, Spirit & Opportunity, were only expected to move 90 days, and yet while one is stuck, the other continues to go. Why do they go? Dust on Mars gets everywhere; it’s corrosive and invasive. The dust is rust; Mars is red because it’s rusty. From a construction POV, we’ll just have to build as well as we can. But anyway, we knew that as Mars moved into Winter and dust covered the solar panels on Spirit and Opportunity, they’d eventually be unable to gather power to keep going. BUT dust devils have been cleaning the panels off, and the scientists are moving the craft to sunnier points, and not doing much with them, during the winter days.

3 Responses to “Launch Pad, Day One: Kevin R. Grazier on Solar System/Cassini”

  1. T. says:

    Actually, we have perfectly good maps of the ocean floors: it’s just that all the data are held by a) the navies with submarines and b) the resource exploration companies. What we don’t have is a coordinated database where these data get put after a proprietary period. Thank goodness there are civilian space agencies doing planetary exploration…

  2. Raphael Mccaulley says:

    Very clearly set.

  3. david bell says:

    I have come to the same conclusion that the earth can possess no iron core, based on surface gravity and the radius of the earth according to Newtonian gravity. The apparent density of the earth corresponds to that of the mantle and crust approximately. An iron core would make the earth too massive.

    Is this how you came to this conclusion as well?

    Have you examined the seismological evidence for a molten outer core? Do you believe this analysis has been incorrect? How?

    I am very interested in how you came to a similar conclusion.

Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>