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Episode 42: Our Solar System Is Not of This Galaxy!

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Recap: In 2003, scientists released a detailed map of the Sagittarius Dwarf Galaxy that's being ripped to shreds by the Milky Way Galaxy. In 2007, a few news outlets took this and used it to say that our solar system is not native to the Milky Way. Find out what the evidence shows in a, "Who's yo' mamma?" episode of intrigue.

Solution to Episode 40's Puzzler: There are really two parts to this. First is the fact that comets are less dense than asteroids. The average density of a comet is very very roughly around 1-2 grams per cubic centimeter. The average density of an asteroid is very very roughly 3-5 grams per cubic centimeter, which we'll call about twice that of a comet. This means that the MASS of the impactors that have the same diameter would be different by a factor of about 2, as well. Again, this number can vary from around 1.5x to 10x depending on exactly what densities and types of asteroids you're talking about.

The second part is that comets have a much higher velocity than asteroids when they are in the inner solar system, and this velocity is what they'd hit the moon or any other object with. There's a velocity distribution, just like there's a velocity distribution of asteroid impactors, but the average velocity is somewhere around 60-70 km/sec. The average velocity of an asteroid from the Main Belt when it gets to Earth is around 25 km/sec, so about 1/3 that of the comet.

The size of the crater formed, all other things being equal, is directly related to the energy of the impactor. Kinetic energy is 1/2*m*v^2, so the relative energy of both impactors is proportional to their masses times the velocity-squared. Their masses differ by roughly a factor of 8. Their velocities differ by roughly a factor of 1/3, which squared is 1/9.

Since these are all approximations, 2/9 is basically 20%, so the solution is that even though the asteroid has more mass, the greater velocity of the comet would result in a bigger crater ... assuming the comet holds together (material strength would be a factor but it's not really something you need to take into account for this puzzler).

No Puzzler for This Episode

Q&A: This episode's question is another crater one that comes from Chew who asks: "I've seen power-laws for meteor magnitude vs frequency and asteroid diameter vs impact interval but what's the law for dating a surface from craters? If one surface has 50 1-km craters and another has 100 1-km craters, how much older is the latter surface? How does throwing in a [sic] 8-km crater adjust the age?"

The answer to Chew's question is that it's complicated. If the impact flux - the number of impactors hitting per unit time - were the same throughout the solar system's history, then the answer would be that it's purely linear: If Surface A and B are the same area and A has 50 1-km craters and B has 100 1-km craters, then B would be twice as old 'cause it has twice as many craters.

Putting in an 8-km crater would probably not alter the age too much because it's only one crater. We also have a distribution of craters across all sizes, so you can't really get a surface that just has 50 or 100 1-km-diameter craters ... it just wouldn't happen. So in practical terms, you would likely do something that I talked about in the last episode where you used the sum of all craters larger than 1 km to get an age estimate.

Now, in actual solar system history, the rate of impacts has NOT been constant. We know that soon after solar system formation, it was much higher than it is now. This is where we have to go back to the lunar samples to rely on correlating number of craters on a surface with the age. Doing this, we get a function that we use to say that if a surface has this many craters, it's this old.

If the surface is fairly young, then the linear model still works. 2x as many craters means it's 2x as old. But, since early on there were many more impacts, then if a surface has, say, 2x as many craters as a 4-billion-year-old surface, then it's not going to be 8 billion years old. It might be more like 4.1 billion. This is why I said it's complicated.

But, it's also a bit more complicated. We know, for example, that asteroids have broken up into families and this likely sent an extra bunch of impactors our way. We don't know how to account for those now, and so they are not in that function. We also think there may have been a spike in the impact rate around 4 billion years ago called the Late Heavy Bombardment. That's also not factored into the function we use, though some people do have alternative models that use it.

Again, it's complicated. But, as I feel the need to mention on this kind of podcast that even the worst case corrections are not going to change the fundamental ideas that I talked about with crater age dating in the past two episodes.

Additional Materials:

Check out CosmoQuest's MoonMappers! Help us do crater science on the Moon.


Claim: The basic claim is that our solar system - from the sun to the planets to asteroids and comets - is not native to the Milky Way galaxy. Rather, we're from the Sagittarius Dwarf Galaxy which is currently being cannibalized by the Milky Way, and much like an adopted child when they turn 18, we're finally discovering that the Milky Way i'n't our real mommy.

Background: This was a story that really first came out in 2007, and since then it's been brought up and used by various pseudoscientists for their own particular purposes, and it's been picked up by random people as more an element of intrigue. Lately, I've generally heard it used in the context of 2012: [Coast to Coast AM clip from February 22, 2012, Hour 4, starting at 23:10]

The Paper Everyone's Talking About

The basis for this entire thing can be tracked back, at least as far as I can tell, to a 2003 paper in "The Astrophysical Journal," one of the main astrophysics journals in the world. The paper is by Majewski et al., and it's called, "A TWO MICRON ALL SKY SURVEY VIEW OF THE SAGITTARIUS DWARF GALAXY. I. MORPHOLOGY OF THE SAGITTARIUS CORE AND TIDAL ARMS."

Note: The paper is from 2003. The press release is from 2003. This story was first corrupted in 2007. Moving on ...

The paper did have a follow-up in 2004. Both I will link to in the shownotes for this episode because they're available online for free. The paper is pretty dense, and they're both long. In an attempt to summarize, there are two basic ideas here.

First, we know that the Milky Way, OUR galaxy, is fairly massive, and that there are several satellite galaxies around it. The Large and Small Magellanic Clouds are probably the best-known, but there are several other, much fainter galaxies. Many of them are in the process of being eaten by our galaxy because of the larger gravity. If you could be outside our galaxy and observe things over a very long period of time, you'd see the smaller galaxy orbiting ours and get shredded and eaten, and during that process it would be spread out into very long streams of stars due to tidal forces. We've known since 1994 that one of these galaxies is the Sagittarius Dwarf galaxy.

The second basic idea is that an all-sky survey at infrared wavelengths was completed around a decade ago, or shortly before this paper was written. The Sagittarius Dwarf galaxy has a lot of old, red stars in it.

Putting these two together, the scientists in the paper used the infrared survey to do the most detailed map of these stars and so were able to produce the most detailed map of the Sagittarius Dwarf galaxy to-date. In 2003.

Among other things, they found that one of the streamers of stars from the galaxy that's being ripped to shreds happens to pass through a region of our galaxy that we're currently in.

In 2003, the University of Virginia, where most of the authors on the paper were, put out a press release that simplified all the results and I'll link to in the shownotes.

The press release starts with typical news media verbage to get you interested: "NEW MAP OF THE MILKY WAY SHOWS OUR GALAXY TO BE A CANNIBAL" is the title with the subtitle "Study Shows the Milky Way is Out to Lunch." The article starts out with, "Chicken Little was right. The sky is falling. Thousands of stars stripped from the nearby Sagittarius dwarf galaxy are streaming through our vicinity of the Milky Way galaxy, according to a new view of the local universe constructed by a team of astronomers from the University of Virginia and the University of Massachusetts."

Another part of the press release has a quote from the lead author: "For only a few percent of its 240 million-year orbit around the Milky Way galaxy does our Solar System pass through the path of Sagittarius debris," Majewski said. "Remarkably, stars from Sagittarius are now raining down onto our present position in the Milky Way. Stars from an alien galaxy are relatively near us. We have to re-think our assumptions about the Milky Way galaxy to account for this contamination."

News Media Misrepresentation

Fast-forward four years, and a website called "CureZone" whose current tag-line is "Educating instead of medicating" came up with a page that claims that our solar system is not native to the Milky Way, but rather it's from the Sagittarius Dwarf galaxy. The website looks as though it was designed in the early 1990s so is difficult to read and figure out anything else.

Fortunately, or unfortunately depending on your point of view, another website called the ViewZone latched onto it and did an article that's readable. I should note that ViewZone's current top stories include, "Illuminati and Rap Music," "Vampires and the Bones of St. John the Baptist," and "Galactic Superwave and Expanding Earth Theory."

Anywho ... Dan Eden of this particular illustrious site started out his story with this: ""Imagine the shock of growing up in a loving family with people you call "Mum" and "Dad" and then, suddenly, learning that you are actually adopted! This same sense of shock came as scientists announced that the Sun, the Moon, our planet and its siblings, were not born into the familiar band of stars known as the Milky Way galaxy, but we actually belong to a strange formation with the unfamiliar name of the Sagittarius Dwarf galaxy!"

As Phil Plait summarized at the time, Eden's article tries to take the following steps:

  1. The Milky Way is currently eating a smaller galaxy, one that's called the Sagittarius Dwarf galaxy.
  2. The Milky Way's gravity has spread out the dwarf into long streamers of stars.
  3. This stream is at an angle to the plane of the Milky Way, and it intersects the Milky Way.
  4. The sun is near one of the places that it intersects, and the odds of this happening are low.
  5. Therefore, the sun originally came from the dwarf galaxy, not the Milky Way.

To say that this is an incredible leap between steps 4 and 5 is putting it mildly.

Evidence? - Angle of the Milky Way in Our Sky

One of the alleged lines of evidence is that the Milky Way is at an angle in our sky: [Coast to Coast AM clip from November 12, 2009, Hour 1, starting at 32:25]

"The fact that the Milky Way is seen in the sky at an angle has always puzzled astronomers. If we originated from the Milky Way, we ought to be oriented to the galaxy's ecliptic, with the planets aligned around our Sun in much the same angle as our Sun aligns with the Milky Way. Instead, as first suggested by researcher Matthew Perkins Erwin, the odd angle suggests that our Sun is influenced by some other system. Together with data from the Two-Micron All Sky Survey we now know what it is. We actually belong to the Sagittarius Dwarf galaxy." --ViewZone (NOT read during the podcast)

I'll get to Whitley Strieber's whole 2012 plasma dense bad stuff thing in a bit. But regarding the angle ... I don't know what astrophysicists he thinks he's been talking with, but no astrophysicist is intrigued by the question of why the Milky Way appears tilted in our night sky. It's random. Our solar system may seem big to us, but as a whole compared with the rest of the galaxy, it's like saying that a small current of water isn't flowing in the exact same direction of the rest of a lake, therefore it's not part of the lake. We're less than 0.005% the size of our galaxy in length, and less than 0.00005% in volume. The plane of rotation of our solar system is not expected to be aligned with the plane of the galaxy.

And no, all of the other stars are NOT aligned with their rotation axis perpendicular to the plane of our Galaxy.

Independent Ways to Show We're Native to the Milky Way

If we want to talk about ways to show that we ARE native to the Milky Way, there are three lines of evidence.

Solar System's Orbital Dynamics

One that may sound familiar from Episode 15 on the non-galactic alignment in December of this year: Astrometry. Astrometry is the measurement of star positions and velocities and is an incredibly delicate field.

As I have said before, all of the astrometrical observations show that our solar system's main proper motion is with the motion of the rest of the stars in our vicinity, around the Milky Way, not through it. When you subtract out that main motion, we are traveling upwards out of the plane of the galaxy a bit, but we'll slow down in a few million years, reverse direction, and come back through. I'll note that this direction of "up" is opposite to the direction that the Sagittarius Dwarf galaxy stars are moving through our Galaxy at our present location.

Location Coincidence is 1 in >1 million

A weaker line of evidence is probability. People who believe that we're not part of the Milky Way point to the coincidence that the solar system happens to be at one of the intersections of the Sagittarius Dwarf galaxy with the Milky Way at the moment. Yes, it's a coincidence. They say it's too much of one to be a coincidence, therefore we're from it.

What they don't look at is even the MUCH smaller probability that we'd be where the Milky Way intersects the Sagittarius Dwarf galaxy. The Milky Way is large, yes, and it takes 240 million years for us to orbit it once. But because the Sagittarius Dwarf has been spread out so much, its path is much larger than the circumference of our galaxy. It would take over a billion years to complete one orbit, and the amount of time we'd spend plunging through the disk of the Milky Way would be maybe a million years, and the time just spent in the thick disk, where we are now, even less.

So if you want to just argue probability-wise based on the intersection, then it's MORE likely we're from the Milky Way than the Sagittarius Dwarf.

Types of Stars and Metallicity

Another way, besides location and motion, of telling if one star belongs to a certain population, is to look at its metallicity. Mainly we measure the ratio of iron in a star to hydrogen.

The sun has a lot of iron, relatively speaking. Stars in the Milky Way, on average, have less iron, but our sun would not be abnormal and it fits reasonably well with other stars in our vicinity.

The Sagittarius Dwarf stars, however, are mostly MUCH lower iron than our sun. Indicating, again, that we're more likely a member of the Milky Way population than the Sagittarius Dwarf galaxy population.

Revised Press Release

One last thing before I briefly address the new agey claims related to this. After all this stuff came out, the scientists who wrote the original journal article decided to amend their press release. At the top now states, in big red bold capital letters: "IF YOU ARE LOOKING AT THIS WEBPAGE BECAUSE YOU HAVE HEARD FALLACIOUS NEWS REPORTS ABOUT THE SUN BEING FROM THE SAGITTARIUS DWARF GALAXY:"




4. This web page contains the original press release text from 2003(!) that has been corrupted/misinterpreted to "support" the incorrect conclusion that the Sun did not originate in the Milky Way galaxy. Read carefully and you will see this press release only details the characteristics of the Sagittarius galaxy and nothing more. All astrophysical evidence points confidently and indisputably to the fact the Sun is now and has always been a part of the Milky Way.

So, yeah, you'd think at this point that people would know this isn't the case. But as most of us know by now, it's much easier to make a claim than to stop it. That Coast to Coast clip I played at the beginning of the episode is from February 2012.

New Age, Show Thineself!

Now, as promised a little about the New Age stuff that's come out of this.

Almost everything that I've heard or read tries to tie this into 2012 either doom and gloom or joy and hope and consciousness and love.

As you heard in the clip with Whitley Strieber, he's tying it into denser plasma. Earlier in that interview he was implicating this for more asteroid hits and global warming across the solar system ... but that's a future episode.

The ViewZone article tries to tie this into global warming, dark spots on Pluto, pole shifts on Uranus and Neptune, and other things. And it notes that "Readers may also be interested to read about Doomsday: The Mayan Prophecy."

The ViewZone article concludes with: "In our movement through space, our Earth has now fully begun to respond to the more powerful galactic energies and electro-gravitational bias of the massive Milky Way. We have reached the higher energy equatorial disc region of the massive spiral arm. We have now been "adopted" by a new system, a stronger and more powerful system, and we can expect changes on almost every level of energy. Whatever these changes are, they are all part of the natural birth, death, rebirth and transformation of the cosmos. As our knowledge of the universe grows, we cannot but understand how much we do not understand. Such is life."

But ... no. There is no evidence we're from the Sagittarius Dwarf galaxy, there is evidence we're from the Milky Way. There's no evidence of any of the doom and gloom of 2012 stuff - and I will have more episodes on 2012 stuff coming up - and the solar system wide global warming stuff will be the subject of a future podcast episode.

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