Astronomy Cast » Our Solar System

Ep. 195: Planetary Rings

Astronomy Cast — Fri, 27 Aug 2010 16:17:28 +0000

Saturn is best known for its rings. This huge and beautiful ring system is easy to spot in even the smallest backyard telescope, so you can imagine they were a surprise when Galileo first noticed them. But astronomers have gone on to find rings around the other gas giant worlds in the Solar System – the differences are surprising.

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Ep. 194: Dwarf Planets

Astronomy Cast — Mon, 02 Aug 2010 21:45:17 +0000

In 2006, the International Astronomical Union demoted Pluto out of the planet club. But they also started up a whole new dwarf planet club, with Pluto, Eris and the asteroid Ceres as charter members. Let’s find out what it takes to be a dwarf planet, and discuss the current membership.

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Fraser: Astronomy Cast Episode 194 for Monday June 14, 2010, Dwarf Planets. Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos, where we help you understand not only what we know, but how we know what we know. My name is Fraser Cain, I’m the publisher of Universe Today, and with me is Dr. Pamela Gay, a professor at Southern Illinois University Edwardsville. Hi Pamela, how’re you doing?

Pamela: I’m doing well. How are you doing, Fraser?

Fraser: Good! I hear you’ve been infested with groundhogs.

Pamela: We have a giant (just one) rodent of unusual size eating in our backyard, and it’s really, really cute.

Fraser: Awww, it’s adorable until they tear your whole yard apart… make it unusable.

Pamela: Yeah, we’ve already got moles and squirrels and yeah, I’m not worried.

Fraser: Just give it back to nature. Alright, well, in 2006 the International Astronomical Union demoted Pluto out of the planet club. But they also started up a whole new dwarf planet club with Pluto, Eris, and the asteroid Ceres as charter members. Let’s find out what it takes to be a dwarf planet and discuss the current membership. Alright, well now the first episode of Astronomy Cast was us talking about why Pluto is no longer a planet. I was hoping we could do an update… you know, Pluto back in the planet club…

Pamela: Nope.

Fraser: Nope.

Pamela: Nope.

Fraser: So then it’s really kind of official… let’s follow it up, let’s set it in stone. Dwarf planets… there have always been dwarf planets… there will always be dwarf planets.

Pamela: Well, there haven’t always been dwarf planets, but…

Fraser: We’re rewriting the history books now… alright, well let’s not talk about the history… so let’s provide a shorter version of what happened in 2006.

Pamela: Well, at a meeting of the International Astronomical Union it was decided that they needed to figure out what to do with all of these giant icy bodies in the outer solar system.

Fraser: Right. This was really triggered by the discovery of Eris… which is bigger than Pluto.

Pamela: …which is bigger than Pluto. Even NASA called it the 10th planet. So there’s a lot of people up in arms… “No, there aren’t ten planets!” My favorite argument of all is if we start calling all of these icy bodies planets, then there’s too many planets for the children to memorize. I’m like… but there’s 26 letters in the alphabet, and we make them learn those… there’s 50 states in America and we make them learn those…

Fraser: But I can imagine with the success of the icy body finders… the Kuiper Belt object discoverers… there was going to be more and more of these objects, so you would have from 2006 to 2010 there were 10 planets, and then from 2010 to 2015 there were 11 planets…. As the telescopes get bigger… especially, you can imagine what James Webb might be able to turn up… so it’s just a matter of time before they find more and more and more… are there 15 planets… 20 planets…

Pamela: That starts to become a matter of what makes a planet a planet. And this is where you start to get to logical arguments. The “well we can’t have that many planets ‘cause the children can’t memorize them,” that’s not a rational argument, people. But saying, well Ceres in the asteroid belt was considered a planet for 50 years before we started turning up other asteroids and realized oh, it’s part of a family of objects… let’s call the whole family asteroids. Well, Pluto was the first one found in the Kuiper Belt, and now we’re finding all these other chunks of ice, and well it’s now the Kuiper Belt. Demoting Pluto is sort of like demoting Ceres, we just realized “oh, it’s not really a planet, it’s part of this family of specific objects.” The analogy I always use is that if aliens were cleaning up our solar system and sorting things into bins, Jupiter, Saturn, Uranus, and Neptune—they’d get thrown in a bin. Then all the rocky stuff would more or less get thrown in bins. And all the icy stuff would more or less get thrown in bins, and who knows what they’d do with Mercury, Venus, Earth, and Mars… but those’d probably get their own stand-alone bin as well. So, yeah… we have all this icy stuff… not really planets… no, not physically planets… but for a certain class of objects—they’re all round, they’re in hydrostatic equilibrium, and Haumea isn’t exactly round because it’s spinning wildly… but it could be round if someone stopped it spinning. So now we look at physical characteristics.

Fraser: Right, so in 2006 the IAU decided to do something about Eris, and once and for all… so they came up with their three rules for planets.

Pamela: Right… something has to be in hydrostatic equilibrium, which means the sucker is round.

Fraser: So it has to be a sphere… so something like the Mars moons, Phobos and Deimos, they’re not round… they’re asteroids… they’re, as you call them, spuds. So those, even if they were going around the sun, they would not count.

Pamela: And the way they make an exception for Haumea is they look at it and acknowledge that if it were left alone, the self-gravity of the object would cause it to collapse into a round shape.

Fraser: So that’s rule number one, right? It’s gotta be round.

Pamela: Rule number two… it needs to be orbiting the sun. So if you have a giant object, orbiting Jupiter, does not count as a planet.

Fraser: And we do… we have Ganymede which is bigger than Mercury. So were it orbiting the sun, it would be a planet.

Pamela: But it’s not, so it’s a moon.

Fraser: So it’s out. But it is in hydrostatic equilibrium… but it doesn’t orbit the sun, so it’s out…. not a planet. So the third rule… the kicker…

Pamela: The kicker is it needs to have cleared out its own orbit. And this is where a lot of the controversy comes in. If you took Earth and put it out at the distance of Pluto, the huge volume of its orbit… the earth just wouldn’t be able to clear that out. So even the earth, in the Kuiper Belt, wouldn’t count as a planet. So this is where folks like Alan Stern start looking at the definition we have for a planet and start saying… no guys, we need to rethink this. We need to start classifying things based on the characteristics of the objects. And here’s where a lot more controversy comes in… what do you start requiring? And no one really knows. And everyone’s just sort of grasping at straws at the moment. But we know that we need to change the definition because the whole “must be orbiting the sun” part kinda means that things orbiting Eta *?* and 51 Peg and all these other stars out there, they technically aren’t planets.

Fraser: But you can just change it to “orbiting their star.”

Pamela: Right, but still that’s a change in definition. So while we’re rewriting the definition, let’s start to consider what other things do we need to put into the definition to make planets incontrovertibly planets.

Fraser: Right. What if they orbit a pulsar, right? What if they orbit two stars in some strange way… anyway, yeah I can see that it might get more complicated. Ok, we’ve got the three rules… it’s gotta be a ball, it’s got to go around the sun, and it’s got to have cleared out its orbit. What are the current dwarf planets?

Pamela: Currently, there’s five known dwarf planets…. five acknowledged dwarf planets. We have Ceres hanging out in the asteroid belt, and then of course there’s Pluto and its demoted self in the Kuiper Belt. We have Haumea and Make-make, and then there’s Eris. These are five very, very different objects, and there’s two more that a lot of people group in, but we don’t know enough about them. There’s Quaoar, which is utterly unpronounceable, and Sedna; and we just don’t know if these objects are in hydrostatic equilibrium, so we need better data to figure these two out. But, they probably are.

Fraser: And these objects are actually quite different… especially Ceres compared to the Kuiper Belt objects. So let’s take a look at Ceres first.

Pamela: Ceres… it’s a rock. It’s nearby; it formed right along the frost line of the solar system. It’s on the inside of the frost line; so when it formed, it actually formed without any volatiles. It looks like a moon. It looks a lot like our own moon. It has craters, it has variations in color on the surface; but it’s hanging out in the asteroid belt, leering over all the potatoes in its sphericalness.

Fraser: Right. Ceres is the largest object in the asteroid belt by far… it’s got a third of the mass… but it hasn’t cleared out the space around it.

Pamela: No… no. And it’s not actually that big once you start comparing it to some of the other dwarf planets. It’s radius is 487-ish km. along the equator. It’s 455 along the pole. It’s a lot bigger than all the other asteroids, but it’s not the biggest thing out there.

Fraser: And the cool thing is that NASA’s Dawn spacecraft is going to be getting to Ceres in 2015 after it explores Vesta next year.

Pamela: Right. So this means that we’re going to have two more dwarf planets getting explored in the not too distant future. And we also have New Horizons, so apparently we’re focused on sunrises and sunsets and horizons with these missions. We have New Horizons going out to visit Pluto…

Fraser: Also in 2015…

Pamela: Yes.

Fraser: That’s going to be a big year.

Pamela: And they’re looking for another target for New Horizons to go to after Pluto, so hopefully we’re going to be able to get two icy bodies for the cost of one satellite.

Fraser: So then we talked about Pluto [Ceres?-ed.], so we can kind of jump out then to take a look at Pluto… which is very different from Ceres.

Pamela: So Pluto… it’s a system… it has moons… it’s surface is pretty much solid ice. This is an icy body… it’s atmosphere comes and goes. When it’s closest to the sun, it has a very, very diffuse atmosphere. Then that atmosphere snows out when it’s at its most distant, and then its a nice atmosphere-less icy blob. One thing that I heard Mario Livio say once that I’m never going to forget is you can’t call Pluto a planet because if you gave it… and I’m paraphrasing… you gave it the orbit of a comet, it would grow a tail in the inner solar system and that’s not the way a planet should behave.

Fraser: That’s just not civilized.

Pamela: No, not at all. So, it probably has a rocky core… It is denser than water… but it has this icy outer layer, and yeah, if you brought it close to the sun, the sucker would grow a tail. It’s density is only 2 x 103 g/m3. That’s twice the density of water, so it’s still not that rocky of a rocky body.

Fraser: And Pluto has a moon that’s a significant portion of its own mass. In fact, the two objects, Charon and Pluto, they orbit a common center of mass. And so for a while there, there was a possibility that Charon would be considered a dwarf planet all on its own.

Pamela: Right. That was part of the argument actually… what do we start calling all of these things? They were throwing everything in… if it’s round, we’re going to call it a planet. So all of these smaller bodies were also getting considered, and Charon, they kicked out. And, this is where they start looking at secondary parameters. They start looking at the densities, they start looking at the… well, is it round because it hasn’t been beaten up that much, or is it round because this is its default shape due to gravity. With Charon, if you beat it up enough, it would stay in a deformed state.

Fraser: Oh, ok… so it just hasn’t been beaten up enough and so it’s got a fairly circular shape.

Pamela: Right.

Fraser: Ok, and then the next object out is Haumea.

Pamela: Right, and this one is just interesting in so many different ways. So first of all, it’s not round, as near as we can tell. Now we don’t have any perfect images of it. Instead, what we look at is how does it’s brightness vary over time. It’s thought, based on watching light curves as it rotates, that it’s probably much longer on one axis than the other, and this implies fairly fast rotation. Now, at the same time, because we don’t have any direct images, it could also be just another one of these strange objects that has two extremely different albedos. We’ve seen this on some of the moons out there. But it’s thought, no, this is actually something that simply has very different dimensions in the two axes… almost a factor of 2 difference. So looking at it, we make this guess at the shape, we make this guess at its rotation period, and as near as we can tell it’s a fast-rotating oblong object, and it probably just got the tar knocked out of it in a collision early on in our solar system’s past. Now this was the second giant object found out in the Kuiper Belt. It also had a fairly controversial beginning. The people who are normally acknowledged for finding it are Michael Brown and his team. But if you actually look at the official notice for it, it’s kind of confusing because it’s acknowledged as having been discovered at Sierra Nevada Observatory in Spain, but then it’s given the name that was submitted by Michael Brown’s team. If you read back about what happened, Michael Brown had been observing it, along with the rest of his team, and as they were pulling together all of their data, they nicknamed it Santa Claus, and they observed it multiple times… they were holding back with it and some other objects to have a really big release. They’d written an abstract that was submitted to a conference, and somehow a Spanish team got wind of it. They looked at the conference abstract… they did some Googling… they found the observing logs, which give you a sense of where on the sky the telescopes were pointed. Apparently Michael Brown and his team didn’t know their observing logs were public. So the Spanish team, knowing an object had been discovered, knowing the rough area on the sky where it had been discovered, went back through some archival images… back to 2003 archival images… found the object in the archival images. They did follow-up observations based on the positions of Michael Brown’s team’s observing logs… rediscovered the object using the predictions and then sent in their results to the Minor Planet Center. Now this put the Minor Planet Center in a horrible position because… well, initially, Michael Brown sees a discovery of one of his objects, kind of does the “oh, no, other people are looking at the same things I am…” rushes Eris, which is bigger than Pluto and really important to him, to publication. And this was like on a Friday afternoon, and a bunch of us looking at the press releases were like, “Wait, huh? Press release Friday afternoon? This makes no sense, there’s some story behind this.” And Michael Brown… he took the high road… he congratulated the Spanish team. He admitted… Yeah, some folks looked at my observing logs and that’s why I rushed Eris to publication… really sorry to step on your thunder. But the Spanish team didn’t acknowledge that they were the ones who looked at his observing logs, and he figured that out later. He ended up lodging a complaint, and so the announcement and the naming of this object really got held up in the politics of trying to figure out who do we give credit to. They ended up giving credit to both teams by naming the observatory from the one team and using the name from the other team. It was David Rabinowitz who came up with the name. It’s the matron goddess of the island of Hawaii where Mauna Kea Observatory is, where their team was observing it. But it was just a political mess. As near as anyone can tell, having public data logs is a really bad idea when you’re discovering objects. The Spanish team read the observing log, realized that no one had published the discovery yet, and stole it.

Fraser: …is the allegation.

Pamela: Is the allegation.

Fraser: Right. We have no proof either way. So next is… so you’re saying it’s Makemake, or not?

Pamela: I think it’s Makemake… it rhymes with bake…

Fraser: Right. Makemake.

Pamela: Right, it’s not a fish dish… I keep trying to turn it into one…

Fraser: Mmmmm. This one was discovered by Michael Brown and team.

Pamela: Yes. This one was announced back in 2005. It’s the third largest known dwarf planet… it’s a big ol’ object. It’s on a really weird orbit… it comes in as close as 38 ½ AU and goes out as far as 54 AU, so it’s really elongated. It’s a rock… well, actually it’s a block of ice.

Fraser: It’s a block of ice… it’s a snowball.

Pamela: It’s a block of ice. Yeah, it’s not the most exciting of them…

Fraser: Yeah, there’s not a lot that’s very interesting… so let’s just move on…. to Eris.

Pamela: Well, Eris… this is where we get into the big controversy… For almost a year it got referred to as the 10th planet, even by NASA.

Fraser: Or Xena…

Pamela: Or Xena… that was the other one that was particularly cool… it’s code name was Xena and it has a moon, so it’s code name for the moon was Gabrielle. I think everyone was really hopeful that silliness would prevail, but…

Fraser: But it didn’t.

Pamela: No!

Fraser: Although the name that they came up with was pretty great.

Pamela: The name that they came up with was pretty great. It was almost kind of sad, though, because Michael Brown’s daughter was born at the same time, and her name was Lillith. Rumor has it that he wanted to name it after his daughter, but that wasn’t allowed. So the dwarf planet’s name is Eris. It’s moon’s name is Dysnomia, and we were lucky to be able to find it when we did. This is again an object that has an extremely elongated orbit, comes in to about 38 AU and then goes out to 98 AU, and it’s not visible out there. It’s orbital period is actually 557 years. Brown and company… Brown and Trujillo and Rabinowitz… they were lucky to catch it when they did… ‘cause it’s on its way in right now, it’s on some of its closest approach, and we get to observe it, and then it goes away for awhile.

Fraser: So it gets as close as 37 AU and as far away as 97 AU… that’s a big difference between its closest point and its most distant point.

Pamela: Yeah.

Fraser: And it’s got a moon, and it’s bigger than Pluto.

Pamela: And it’s a lot bigger than Pluto… that’s cool. It’s dense, it’s big, and it’s on a really weird orbit… this is one of those objects that leads people to really start trying to figure out what could cause these weird things. But there are weirder objects lurking out there still awaiting final classification.

Fraser: And so with the five dwarf planets, and 2 or 3 provisional ones… the two Sedna and Quaoar are pretty close. Maybe with better observations, seeing their orbits for longer, maybe discovering a moon… that’ll make a big difference.

Pamela: Right.

Fraser: But it really is just a matter of time before more of these large Kuiper Belt objects are turned up.

Pamela: And that’s what’s so amazing is so, for instance, Quaoar… it’s a rock. It’s a known rock. There’s a great post over on Emily Lakdawalla’s blog… The Planetary Society Blog… titled “Quaoar: A Rock in the Kuiper Belt” where she pulls a bunch of these images where they were looking to see its moon and trying to figure out its mass. It’s moon is named Weywot, which is just fun to say. So they’re out there, they’re trying to figure these things out, and as they look at them… Quarhar… we don’t know where this rock in the Kuiper Belt came from, and that leads to a lot of questions about dynamics. We look at Sedna that has this really weird orbital radius of 509 AU, this is another object we were lucky to catch when we did.

Fraser: That’s five times further away from the sun than Eris.

Pamela: Right.

Fraser: And more like ten times further away than Pluto, but happens to be at the closest point of this really elliptical orbit.

Pamela: And so we look at these things and start wondering well what gravitationally could cause something like this… and there’s some folks working on planetary orbits who figured out, well, there could easily be an Earth-sized object, a Neptune-sized object, a Jupiter-sized object, out thousands of AU from the sun just waiting to be found. And of course there’s the eternal search for Nemesis, a small dwarf star that’s orbiting our sun, waiting to be discovered. So there could be more things that we’d recognize as planets waiting to be discovered, just not reflecting a whole lot of light.

Fraser: So it’s really just a matter of time… so we’ll be updating this show, somehow, as we go… In ten years when we have episode 500 of Astronomy Cast… we’ll have probably more dwarf planets by then. Especially with the launch of the James Webb Telescope, so stay tuned. Alright, well thanks a lot, Pamela!

Pamela: Sounds great, Fraser. Talk to you later.

This transcript is not an exact match to the audio file. It has been edited for clarity.

Show Notes

Ep. 175: Mysteries of the Solar System, Part 2

Astronomy Cast — Wed, 03 Mar 2010 00:32:44 +0000

Apparently this is at least a 2 part series. This week we continue examining some of the baffling mysteries of the Solar System, where we fill your head with more questions than answers. Sometimes we’ve just got to share the enjoyment of not knowing the answer.

Download Ep. 175: Mysteries of the Solar System, Part 2 [mp3]

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Show Notes

Mysteries of the Sun’s corona – GSFC/NASA
Temperatures of the Sun’s corona – Hypertextbook.com
Warm Coronal Loops May Hold Key to Hot Solar Atmosphere – Universe Today (Ian O’Neill, 5.31.2008)
Tiny Flares Responsible for the Outsized Heat of Sun’s Atmosphere — NASA (8.14.2009)
Solar Dynamics Observatory

7. The Kuiper Belt Cliff

Kuiper Belt – Universe Today
Kuiper Cliff — Wiki
Patryk Lykawka and his research on the Kuiper Cliff

8. Why are there long period comets?

Long period comets — Wiki
Paper: Reassessing the Source of Long Period Comets — Science (7.30.2009)
The Problem with Comets -- Geocentricity
Paper: Long period comets and the Oort Cloud – Wiley
Evidence Mounts for Companion Star to our Sun — Science Daily (4.26.2006)
Niburu nonsense — Universe Today

9. Why does Enceladus have geysers?

Cassini Finds ‘Heat,’ More Geysers on Enceladus — Universe Today (2.23.2010)
Enceladus Supplies Ice to Saturn’s A-Ring-- Universe Today (2.5.2008)
Enceladus’ Tiger Stripes, Tidal Flexing, possible underground ocean — JPL
Misty Caverns of Enceladus — BBC
Enceladus — Cryvolcanism in Motion — NightSky (3.21.2010)

10. The Hexagon on Saturn

Saturn’s Hexagon May Be Solar System’s Coolest Mystery — Wired (12.9.2009)
Video of Saturn’s Hexagon — NASA
Saturn’s Hexagon Endures! — Universe Today
Standing Wave — Wiki

Transcript: Mysteries of the Solar System, Part 2

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Fraser: Astronomy Cast Episode 175 for Monday February 1, 2010, Mysteries of the Solar System, Part 2. Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos, where we help you understand not only what we know, but how we know what we know. My name is Fraser Cain, I’m the publisher of Universe Today, and with me is Dr. Pamela Gay, a professor at Southern Illinois University Edwardsville. Hi Pamela, how’s it going?

Pamela: It’s going well. How’s it going with you, Fraser?

Fraser: Good… ready for more mysteries. So apparently, this is at least a two-part series. We have no idea how many there’s going to be. But this week, we continue examining some of the baffling mysteries of the solar system… where we fill your head with more questions than answers. Sometimes we’ve just got to share the enjoyment of not knowing the answers. Alright Pamela, so we… when last we saw our heroes they’d covered Pioneer, Uranus, Europa’s seas, methane on Mars, strange atmosphere on Titan… so, mystery number six: How does the sun’s corona work? Why is it so hot? So what’s a corona?

Pamela: It’s the highest level where you start seeing the beautiful loops, the beautiful flares, all of the amazing activity that missions like STERO and… well, our new little SDO is going to be imaging these as well.

Fraser: Right, so these are all these crazy plumes and prominences coming out of the sun… that’s the corona. And it’s hot.

Pamela: It’s too hot. It’s pretty much the same temperature–like 15 million degrees-ish–as, well, the core of the sun.

Fraser: Right, so the corona–the outside of the sun–is the same temperature as the core of the sun… which is hotter than the surface of the sun, which is only like 5800 Kelvin.

Pamela: Yeah.

Fraser: So, how is it possible that you can have… I understand that the core of the sun is 15 million degrees Kelvin, the surface is only 5800 degrees Kelvin, and it keeps getting cooler from there… but, no, the corona is back to 15 million degrees.

Pamela: Yeah.

Fraser: Now it’s not like, you know… go out and roast in the 15 million degree temperature… I mean the pressure… there’s so little material out there that it’s not like fusion is taking place.

Pamela: So, here’s what’s happening. The material… it’s really, really thin. But when you start looking at it with missions with ever-so-boring names like the NASA-funded X-ray Telescope… very blandly named instrument, or the Extreme Ultraviolet Imaging Spectrometer, also very blandly named instrument, both of these on the Henoday spacecraft, you start seeing that there’s plasma that’s 10 million degrees Kelvin, there’s plasma in other places that’s 5 million degrees Kelvin… we’re looking at all the different loops and measuring the temperature… so the material tied up in the loops… and we can’t really explain what’s happening, and that’s never a good thing. It was originally thought… and Ian O’Neill who writes for Universe Today is one of the people who worked on this model… that perhaps there’s some sort of steady state heating where you have these giant loops and they’re able to conduct heat up, and it’s this conducted heat that’s steadily, steadily increasing the temperature, increasing the temperature, increasing the temperature. But the models that make those predictions predict that the loops are going to have a certain density, and they don’t. And that’s a bit problematic.

Fraser: So some process is boosting the temperature of this material back up again, and there’s no real good answer yet.

Pamela: So, the other thing that we blame it on is nanoflares, but we’re just starting to be able to observe nanoflares. So, we’re not sure if that’s right either. So this is one of those cases where we have more models than we have evidence. Hopefully soon we’ll know.

Fraser: So you just mentioned that the SDO has just launched…

Pamela: Yes.

Fraser: Is that going to help?

Pamela: Well, the one thing that it will be able to do is constantly monitor the sun’s activities at a cadence, a rate, that we’ve never seen before. It’s going to be taking image after image after image after image, firing them back to the planet Earth… tidal wave of data coming back at us in a resolution that we haven’t seen before. And hopefully, by getting flooded in data, somewhere in all this new information, the solution is going to be found.

Fraser: Question number seven: What is the cause of the Kuiper Belt cliff? So the Kuiper Belt is an area of icy objects surrounding the sun… starting from the orbit of Neptune and out… large objects in this group are Pluto and Eris… so, why does it start and why does it end?

Pamela: Well, the starting is a little bit easier. It couldn’t really have formed anywhere earlier in the solar system.. it was either too warm, and you ended up with an asteroid belt instead… too cleared out by Jupiter, which is very good at herding things into little pockets of Trojan objects, Saturn’s another object that’s pretty good at clearing up the space around it. So, where the Kuiper Belt starts is pretty much where you’d expect a belt of icy bodies to maybe start being able to exist. But the problem is, is that it’s thought that they should just keep going, and they don’t. We know that we don’t have them further in because of resonances, we know that there’s empty holes where the objects would be in resonances with some of the other planets that are emptied out. Then, suddenly, about 50 astronomical units away from the sun, they just drop off in number. And they shouldn’t… they should actually be increasing in number according to models. So, the idea of a planet being out there really isn’t one that we’re all embracing quickly, but it is one that’s been mathematically worked out by a researcher named Patryk Lykawka and if he’s right, then there could be another planet out there… something the size of Earth or Mars that’s responsible for clearing out this area of the Kuiper Belt.

Fraser: Where’s the planet?

Pamela: We don’t know…

Fraser: We would see it, right? If we’ve discovered Eris… it would be further out than Eris, right?

Pamela: It would be further out… so we’re looking for something that would be further out. We don’t know how dark it is, if you have something that big it’s probably… well, we don’t know… we can’t say anything about it, but it could be covered in substances that make it non-highly-reflective. It could just be we haven’t managed to stumble across it yet.

Fraser: But it would be… it would be pretty big.

Pamela: It would be the size of roughly Earth or Mars. But if you have something out there that’s slow-moving, and this would be slow-moving, that’s extremely faint because it’s not very reflective, it could’ve gone missed at this stage. So this is where the Large Synoptic Survey Telescope potentially will be able to start finding some of these really faint, really slow-moving objects that are out on the edge of the solar system while it’s turning up everything else.

Fraser: So, is it possible that the Kuiper Cliff is actually more of a divot, that we see the end of the cliff and there could be some great big planet orbiting in that spot, and then on the other side of that planet’s gravitational influence, there’s more icy objects.

Pamela: It’s entirely possible.

Fraser: And then we just can’t see them, we’re already working at the very limits of Hubble to even see some of these Kuiper Belt objects at all.

Pamela: Right. Right. And so the confusing thing that we’re in right now is, yeah… there could be a divot out there, and in fact, all of our theories suggested that the number of objects should increase by as much as a factor of two beyond 50 AU instead of dropping to zero. So, it could be that there is an object out there that’s dark and orbiting slowly that we just haven’t seen, and that there’s more objects hiding behind it.

Fraser: Hmmm… it’s a mystery. Who knows the answer? We don’t! Alright, number eight… Why do long-period comets come into the solar system?

Pamela: Yeah, we don’t know that one either.

Fraser: No… we have the short-period comets that are really just Kuiper Belt objects that have been shoved into a more… a different orbit where they come in, but they don’t go out too far. They come in to the sun and they don’t go in too far. But there’s this whole class of objects that come in almost like they’re coming in on a straight line… the size of their orbit is so big, and they can take tens of thousands of years, millions of years to make a trip around the sun. What on Earth… or what on space… where are they coming from? Why are they coming towards us?

Pamela: Well, we’re pretty sure we know where they are coming from. They seem to be originating from somewhere… probably between 20,000 and 100,000 astronomical units away from the sun. They’re starting really, really, really far away. But, what we don’t know is what sent them our direction. So, there’s this cloud of material that we call the Oort Cloud that we believe… and there’s some evidence based on looking at alterations to the cosmic microwave background that we can actually see what in some ways might be regarded as the shadow of the Oort Cloud… We’re pretty sure the Oort Cloud’s out there. We don’t have direct evidence, but we’re pretty sure it’s out there. Something is causing objects to get knocked out of the Oort Cloud and sent our direction, and it could be that we periodically pass close enough to other stars that objects get knocked in. It could be objects interact with one other periodically and something gets sent in, it could be there’s a giant planet on an elliptical orbit or a… maybe we have a brown dwarf or a red dwarf companion star that just hasn’t been found. And any of these additional bodies could knock things up in the Oort Cloud and send a rain of icy material into the inner solar system.

Fraser: And one of the theories is that it’s these rains… these periodic rains of comets that have caused some of the big devastation on Earth in the past, that seem to come every 65 million years or so, right? With the last one occurring about 65 million years ago…

Pamela: Exactly. But, even ignoring these giant infalls of material, we still get 5 to 10 fairly significant cometary bodies coming in to the solar system each year. So, yeah, we get giant influxes on a regular basis, but we’re also getting things on a steady lower level all the time.

Fraser: So the question is, what is the thing that kicks them out of their nice stable Oort Cloud. Why did they choose now… out of the 4.5… 4.6 billion years they’ve been orbiting the sun, why did they pick now or 10,000 years ago to fall into the inner solar system?

Pamela: And all different possibilities we have are ones that… if you generally see an article that says “Giant planet suspected to be orbiting edge of solar system,” you’d call the person a crazy… “Sun thought to have binary companion,” you’d think the person a crazy. But, the only way we can start to explain this is to invoke these theories, and it starts to get kind of uncomfortable. It’s almost like an angry gremlin kicking them into the inner solar system is just as valid a theory, but you can’t mathematically justify that. So, it looks at one level really like there could be something out there.

Fraser: But… it has nothing to do with this Nibiru nonsense… Planet X…

Pamela: No. Nothing. Nothing at all to do with any of that.

Fraser: So, mystery number nine: Why does Enceladus have geysers? And this is amazing. This is one of the big discoveries of the last 5 years… which is that Cassini has discovered these geysers of water-ice blasting out of the southern pole of Saturn’s moon Enceladus. So if there’s a geyser of water-ice, then does that mean that there is a hot bubbling water pool that’s spewing out water that’s turning into ice as it reaches space? So, what’s going on here?

Pamela: Well, what we know for certain… because we can image it… is that Enceladus has geysers, that they’re shooting sprays of water out of the surface with escape velocity. This is actually helping to feed into some of Saturn’s rings and to keep replenishing them with new material. And then trying to understand it, there are competing theories. There are groups saying that there are underground oceans that perhaps the pressure from the oceans… the water’s mist is coming up through the surface and sending out this high-powered mist in some ways.

Fraser: Right, but it’s the same situation… it’s a tidal flexing going on… an interaction between Saturn and Enceladus that is causing it to remain liquid inside and heating up the liquid, and then that liquid is being spewed out of these geysers. Sorry to derail you, but I think it’s kind of funny that one mystery about Saturn has been solved by this, and yet it creates a brand new mystery.

Pamela: I know, I love it!

Fraser: What is one of the possible sources replenishing Saturn’s rings? Oh, well it’s the geysers on Enceladus… the wha?! The geysers on Enceladus? Yeah, I know… that’s what it is. Sorry, so what’s the other… you said maybe it’s bubbling water?

Pamela: Maybe it’s underground oceans… there’s other groups that are claiming–well maybe there’s caverns where this is taking place… all sorts of crazy geometries of the underground geophysics are being invoked… and they’re not really crazy. They’re all
geophysics that exist here on earth.

Fraser: And I’ve seen some dry… some not-water… not-liquid solutions for it as well. Which are just ice being rubbed together… sublimated… and it’s just coming out as geysers. So it’s not actually liquid, it’s just ice, because Enceladus is almost entirely ice.

Pamela: Right, so you basically have cryovolcanism. But the real question starts to be that Enceladus, as far as we know, isn’t all that different from the other icy moons. Why don’t all of them have geysers? So this is really a two-sided problem. Not only why does it have geysers, but why don’t the others as well? And we don’t know.

Fraser: But they might… I know they’ve found like hints of some similar process going on with Rhea and Dione as well. So, they haven’t ruled it out yet. They’ve found particles. I forget what it is… like hydrogen atoms surrounding those moons, but not in the same way that you see it around Enceladus.

Pamela: So, we need to just keep looking, and keep trying to understand it. And maybe send another robot.

Fraser: But as I said, that is a classic example of like… one problem solved… ten! ten mysteries open up…

Pamela: And throw out one problem and get back ten theories.

Fraser: Yeah, exactly. Ok, mystery number ten: the hexagon on Saturn… hexagon on Saturn? What’s that?

Pamela: Right, oh… if you haven’t seen a video… any of you out there listening to my voice right now… if you haven’t seen a video of Saturn’s hexagon in motion…

Fraser: Google it!

Pamela: Yes, there’s examples of it on Wikipedia… easy to find. It’s this amazing structure that’s a perfect hexagon. It’s not something where you’re eye is tricking you into thinking… well, maybe there’s something vaguely stop-sign-shaped… but, no, it’s a perfect hexagon.

Fraser: There’s a bolt… there’s a great big bolt on the bottom of Saturn that you could take a great big wrench and crank it. That’s what it looks like.

Pamela: And the straight sides on this thing… they’re basically 14,000 kilometers long.

Fraser: That’s a big wrench.

Pamela: Yeah, you’d need a really big wrench… really big handle to turn it, as well. This entire thing is being turned by an invisible wrench at the same rate that the planet seems to be rotating… a little over ten hours. So, lots of people have been trying to figure out exactly what this is. It has basically a clearly-defined hurricane-like eye wall that’s a hexagon rather than the perfect circle that you get with a hurricane.

Fraser: It should be a circle… by every piece of physics that we know, and atmospherics, that should be a circle.

Pamela: Yeah. But it’s not. And so when you see things that you don’t understand that are waves that are not changing, you call them standing waves. So, it’s been possible in the laboratory to spin buckets of just the right fluids in just the right ways to get polygons. There’s all sorts of really cool experiments where they spin things under different conditions and sometimes they actually take giant globe… put giant globe over it and fill the space between the two giant globes with different fluids that mix in different ways, and they try and create planetary atmospheres this way, or at least the motions of planetary atmospheres. And we can get polygons, by spinning things in just the right way… but not hexagons… and we haven’t seen exactly this shape. There are some people that think this might actually be tied in somehow with Saturn’s aurora. So, time will tell… more observations are needed.

Fraser: Does it have one on the other hemisphere?

Pamela: No… at least not that we’ve imaged yet. So far in all the images–and this has been seen by both Cassini and by the earlier Voyager mission–there’s a northern pole hexagon.

Fraser: Do we see this on any of the other gas giant planets?

Pamela: There’s something similar on Venus, but it’s not identical. It’s another giant
hole through the atmosphere generated by the spinning winds.

Fraser: Right. But we don’t see an even bigger one on Jupiter…

Pamela: No.

Fraser: Jupiter provides the circle that we crave.

Pamela: Or at least behaves more rationally.

Fraser: Yeah, exactly. So, who knows why it’s there? We don’t know. It’s a mystery. Sorry… Well, I think we got through another set of five and who knows… to leave you with one more mystery… next week, will we continue on with mysteries 11-15? Or start our first set of mysteries about the Milky Way? Who knows?

Pamela: This is our mystery to you…

Fraser: Or to us… ’cause we haven’t figured it out yet…

Pamela: And one final announcement, though. We forgot to tell you at the beginning of the show… we have new toys for you in the Apple store.

Fraser: Oh, right! Yes… yes….

Pamela: Wizard Libsyn Systems… our hosting provider… put together for us an iPhone app. So, if you’re an iPhone owner, you can go out and buy an app that will bring to your phone the latest shows, and we’re going to be getting all of our transcripts into it. It’s $1.99 and we do get proceeds from this, so there’s yet another cool way for you to get and consume all of the Astronomy Cast content.

Fraser: Right. So this is like a separate app, apart from what you would download in iTunes. So, check it out, and if you want… yeah…. $1.99. Well, thanks a lot Pamela, and we’ll talk to you next week.

Pamela: Sounds great Fraser… talk to you later.

This transcript is not an exact match to the audio file. It has been edited for clarity.

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Ep. 174: Mysteries of the Solar System, Part 1

Astronomy Cast — Thu, 25 Feb 2010 06:51:19 +0000

We know a lot about our Solar System, but there’s an awful lot that’s a complete and total mystery. Today we’re going to begin a series of unknown length examining some of these mysteries, and explain the best theories astronomers have so far.

Download Ep. 174: Mysteries of the Solar System, Part 1 [mp3]

Jump to Shownotes

Jump to Transcript or Download

Show Notes

1. Pioneer Anomaly

Pioneer Anomaly overview — Universe Today
Pioneer Anomaly — several links from the Planetary Society
Investigation of the Pioneer Anomaly at ISSI

2. Uranus and Venus axial tilt

Tilt of Uranus — Universe Today
How Uranus got its tilt — Planetary Society Blog (4.28.2006)
Axis of Venus — Universe Today
Orbital resonance of Saturn and Jupiter — Wiki
A Planetary Migration? — Centauri Dreams

3. What is under the ice on Europa?

Europa — Solar Views
Ice on Europa -- GSFC/NASA
Europa: What Could Be Under the Ice — Science Daily (12.14.2007)
Unexpected Life Found Under the Ice in Antarctica (Video) — Universe Today (3.18.2010)
Europan Tidal Flexing Leads to Formation of Ridges, Possible Habitats for Organisms — Space.com (6.8.2000)
A Submarine for Europa — Universe Today (8.9.2007)

4. Methane on Mars

Large Quantities of Methane Being Replenished on Mars – Universe Today (1.15-2009)
New Findings Say Mars’ Methane Comes from Water or Life — or Both — Universe Today (12.8.2009)
Mars Methane Movies (listen to scientists discuss Mars’ methane) — Universe Today (1.19.2009)
Mars Science Laboratory (a.k.a. Curiosity) — NASA
Lava Tubes on Mars — ESA

5. Where does Titan’s atmosphere come from?

Titan’s atmosphere – Windows to the Universe
Titan’s Atmosphere and the Solar Cycle — Planetary Society (6.3.2009)
Does Titan’s Methane Originate from Underground? – ESA (3.1.2006)
Titan Has “Hundreds of Times More” Liquid Hydrocarbons than Earth — Universe Today (3.18.2008)

Transcript: Mysteries of the Solar System, Part 1

Download the transcript

Fraser: Astronomy Cast Episode 174 for Monday January 25, 2010, Mysteries of the Solar System, Part 1. Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos, where we help you understand not only what we know, but how we know what we know. My name is Fraser Cain, I’m the publisher of Universe Today, and with me is Dr. Pamela Gay, a professor at Southern Illinois University Edwardsville. Hi Pamela, how’re you doing?

Pamela: I’m doing well Fraser, how are you doing?

Fraser: I’m doing great! So this week… well, we know a lot about our solar system, and there’s an awful lot that is a complete and total mystery. Today we’re going to begin a series of unknown length examining some of these mysteries and explain the best theories that astronomers have so far. So I think that one of the problems that we do is that we kinda come up with an idea for a show, and we have a schedule, and I’m often rushing Pamela to kind of meet the schedule, meet the time. Well, I’m not going to be time’s slave anymore… so we have no idea how many part series this is going to be. Could be a one-part series… but, you know, more likely no… it’ll probably stretch on further. But, it’s so cool… and you know what’s kind of interesting is… now, I’m kinda going off on a tangent–sorry… my daughter is studying space and astronomy in her school, and I’m going to come in and give a presentation to her class that is essentially the podcast we’re going to do today, which is a collection of crazy mysteries in the solar system and the best ideas that we have. But I get to show pictures to the class… you’ll just have to use your imaginations… or follow along on the web as you go… so, let’s get on with it! These are big mysteries in the solar system… in some cases astronomers have some idea of what we’re talking about… in other cases–no idea. Should we start with the Pioneer anomaly?

Pamela: Let’s go ahead and start with that. It’s kind of the oldest of the mysteries, I think.

Fraser: Alright, let’s do it. So, in case you weren’t aware, there is a weird situation where the Pioneer spacecraft aren’t where they’re supposed to be. So what’s going on?

Pamela: Well, as they’re moving out towards the edge of our solar system, as they move out towards leaving our solar system we have calculations on how much they should be slowing down as they go because the sun and the solar system’s gravity is pulling on them, we have calculations on… ok, we fired the rockets here this amount… We should know everything about how these suckers are moving through space. We know that there might be some factors to correct for… they fire off radio transmissions toward Earth–that might have an effect. They get heated up by the sun–that might have an effect. And when you put all these pieces together and you figure out where they should be–they’re not there. It turns out that for reasons we can’t really explain–and this is true for Pioneer I and Pioneer II–both the missions seem to be slowing down more than they should be, and we can’t explain it.

Fraser: So, they’re not as far from the sun as we would expect them to be.

Pamela: Right.

Fraser: And even when you plug in Newton’s formulas for gravity and then you try Einstein’s formulas for gravity and you include all that stuff–the additional push of them using the radio transmitters… that’s a pretty weak amount of push that they must be getting–they’re still slowing down too quickly.

Pamela: Right. And the thing is, all of these things that we’ve tried to blame the Pioneer anomaly on–the fact that that they are using their antennae to blast radio signals… that should be accelerating them away from the solar system, the fact that the sun is heating them on one side and not the other… that should be pushing them away from the solar system… So, for some reason those things aren’t pushing them out of the solar system, or at least there’s something else keeping them in the solar system with an even stronger force. And all we can really do is go over the numbers again and start scrutinizing how we built the missions. And the crazy thing is, within error, it looks like we might have the exact same results for the Cassini and Galileo missions as well on their way out to Jupiter and Saturn.

Fraser: What about the Voyagers?

Pamela: The Voyager missions… and now we’re going to hopefully have New Horizons as another case study to look at. But we’re not sure how to explain how these different missions all have, with their different architectures, seemingly the same anomaly. Now the thing is so far, Cassini, New Horizons, and Galileo haven’t gotten that far out and we have a completely different design for those missions than we have for the older ones. And we also, more importantly, have a different way of transmitting and storing the data. And one of the things that’s being scrutinized is are changes in how we look at the data… are those differences over all the years and all the different format changes–are those the responsible party? Or does it actually have something to do with the spacecraft and its fuel cells perhaps giving off heat in one direction but not the other.

Fraser: And so it’s either a measurement error…

Pamela: Yep.

Fraser: It’s an unknown… sort of something going on with the spacecraft, some interaction that we’re not thinking of, like…

Pamela: One side is hot due to the fuel cell, and that side is the one that’s away from the sun and that heat from the fuel cell is creating a force.

Fraser: Or, it is deep and fundamental… that there is some understanding of basic physics of about how things move in space over long distances that we just don’t understand.

Pamela: And that’s the most painful one to deal with because when we look at the orbit’s of the Kuiper Belt objects—they make sense. When we look at the orbits of Uranus and Neptune–they make sense. When we look at the orbits of even all of their moons–they make sense. So, whatever it is, if it is fundamental physics, is only working on this radial axis from the sun, and it’s not affecting things orbiting the sun. And that just seems crazy.

Fraser: So, things moving away from the sun experience this thing… whatever it is. And it could be, you know…

Pamela: Just the way we built the suckers causes them to behave differently… that could be it.

Fraser: Right. And this is one of those things… it’s so great because it’s so simple. It could be either… oh, yeah, we have a slight modification to our math… oh, we wrote down the numbers wrong, or we don’t understand gravity… you know…. It’s quite a wide range of possibilities, so… anyway… so that’s it–mystery! We don’t know… stay tuned! So, mystery number two–the strange axes of Uranus and Venus. So, Venus is flipped completely upside down, so…

Pamela: 177.3 degrees off of normal.

Fraser: Right, so imagine you take the earth spinning… you flip it upside down but still keep it spinning in the same direction… from your perspective looking at the planet now… it’s going the wrong direction. Venus rotates backwards to all the other planets in the solar system. Uranus has just been rolled only onto its side, so, you know, sometimes it’s pointing its south pole at the sun, and other times it’s pointing its north pole at the sun, and… you know… is spinning on its side.

Pamela: It’s tilted 97.7 degrees. So neither of them are quite dead on… but, wow they’re close.

Fraser: So what is up with that?

Pamela: Well, we don’t quite know.

Fraser: Right, the earth has an axial tilt of 23.5 degrees… Mars is kinda similar… Mercury is kinda similar… Jupiter, Saturn, they’re all close to that.

Pamela: So, we have two different mainstream theories. The first is that in both cases… take a planet, whack a planet with another planet, and it flips over. With Uranus, that starts to get a little bit troubling because you need to get things really big to hit it, and we just don’t know if there was anything that big hanging out doing the colliding back then.

Fraser: But couldn’t just time do the trick for you? You hit it with something… I don’t know… Mars-sized, and then you just give it 4.5 billion years to roll over?

Pamela: No, because these things tend to either keep rolling once set into motion–it’s “things in motion stay in motion” that’s a problem–or, once you whack it, it just stays put. That’s the way it normally works out is you just whack something into a new stability. Rotating objects are very consistent in keeping their axes pointing in one direction–this is how gyroscopes work on space stations, on spacecraft. Without this characteristic of spinning objects, we wouldn’t be able to move spacecraft around. Planets are just spinning tops, they’re their own form of gyroscopes so they’re spin-stabilized is one way to think of it.

Fraser: Right, and here on Earth we have the precession, right… where we have a bit of a wobble, but that wobble stays within that very specific range, and so you still have the wobbling of the top but it’s not like it wobbles over to one point and then just stays there… it’s always kind of moving back and forth and back and forth.

Pamela: And so here… it could be that we played “Whack-a-World” but the other option is…. well, maybe this is just tidal effects, maybe this is resonances. One of the things about the formation of the solar system that people are playing with is it’s hard to explain how to explain how Uranus and Neptune could have formed where they are located today. But, what is easier to imagine, is that all of the gassy planets, all of the two ice giants and the two giant gases–Jupiter and Saturn, Uranus and Neptune–what if they all formed closer to the sun but Saturn and Jupiter hit a resonance where their resonance caused all sorts of crazy things to happen. There are several different ways of modeling this that start out with all four planets basically tumbling in a gas-giant ball and then moving apart and you basically end up flinging Uranus and Neptune out to the outer solar system. Other cases they start out as four distinct orbits but Saturn ends up on a more and more elliptical orbit over time due to a resonance with Jupiter until it finally settles into an almost circular much larger orbit and in the process also flings Uranus and Neptune out to the outer solar system.

Fraser: So it’s almost like you need one process to start the movement and then a second process to stop it. You need the start, and then you need the brakes… to kick on the brakes again to make it stop.

Pamela: And this is where ending the resonance is essentially putting the brakes on.

Fraser: Right, right. Because, I mean, we have examples of asteroids that are tumbling in two directions… they’re rotating and they’re also tumbling because… and they’ll never stop because nothing’s ever stopping them from doing the tumbling part.

Pamela: Right. And with Venus it’s thought that maybe some sort of a chaotic process where it was getting gravitationally beat up by the planet Earth in some ways was what got it into its situation. If you look at how long its day is… it’s a resonance with how often Venus and Earth and the Sun all line up into a nice straight line. So it’s possible that this is just the pull of gravity over time gradually tilting and tilting and flipping through all the different resonances in the solar system. Venus just happened to be the one that was susceptible to being put on its head.

Fraser: So why are Uranus and Venus… they’re axial tilts off the plane of the ecliptic? It’s a mystery. Alright, mystery number three… what is underneath the ice on Europa?

Pamela: Hopefully water.

Fraser: Hopefully water… right, so once again, we’ve got the situation where Jupiter has its four Jovian moons: Io, Europa, Ganymede, Callisto, and the tidal flexing from the gravity of Jupiter is kinda squishing these moons and then… keeping them softer than they ought to be. With Io, it’s full-blown volcanism with huge… magma and lava coming out, with Europa it’s not quite as devastating, but you can see… astronomers are pretty certain that there’s a shell of ice and underneath that is a great big liquid water ocean… maybe?

Pamela: Maybe. And this is what we’re hoping. What we do know is that when you look at images of Europa, it’s one of the most beautiful moons in the solar system, I think, it in many ways looks like some sort of a blown-glass ball covered in cracks in the glaze. It highlights in blues and in oranges in many of the different Galileo images. This strange little icy world is actually the reason that we plunged Galileo into the Jovian atmosphere. This moon, through cracks in its surface, is constantly resurfacing. What this means is craters that form on Europa don’t get to stay there. They instead get filled in. Basically, a geophysical Zamboni is constantly clearing the ice of Europa.

Fraser: I was going to use the Zamboni reference! That’s exactly what it is, right? Every now and then the ice gets all smoothed over again.

Pamela: Right, and the easiest way to explain this is the Zamboni method…. you just spray the sucker with liquid and the liquid refreezes and you’re back to a nice smooth surface.

Fraser: And where’s the spray coming from?

Pamela: And that’s the question… we don’t see it directly, but more likely we simply have this slow coming-up, this slow puddling… more like what you see if you go to Yellowstone and visit the bubbling mud pots than if you go and visit the geyser of Old Faithful. So somehow liquid is coming up to the surface, and if liquid is coming up to the surface, that means there is liquid below the surface.

Fraser: Right.

Pamela: And the models… some of them say the ice is a kilometer deep, some of them say it’s tens of kilometers deep… but no matter how deep it is, there’s probably an active rocky core underneath that’s doing the heating.

Fraser: Io… what’s happening to Io is happening to the core of Europa… it’s being flexed and heated, and putting out heat, but it’s not turning into great big plumes of lava… it’s just keeping this ocean warm.

Pamela: And the amazing thing to think about–and there are a few papers related to this–is it could be that you have mid-European ocean volcanoes and basically lava plumes just like you find in the deep trenches here on the planet Earth. And it’s those deep ocean plumes that are so rich with life that never sees any sunlight, so we know that this form of volcanism under water is capable of supporting life. This makes people wonder, very honestly, could there be life supported under the ice on Europa?

Fraser: Yeah, people don’t realize you could destroy the sun and there would still be life on Earth.

Pamela: Until it cooled off…

Fraser: Until it cooled off, but for billions of years you would have the geothermal heat heating the oceans, keeping life going… no problem. So, who knows what’s under there… Now, is there going to be any way that we’re going to know? I know there were ideas to send a probe that could melt down through the ice and try to make its way down to the ocean.

Pamela: Like so many problems, this is one that comes strictly down to money. There are robots being designed and tested right now that, if you drop them into an underground lake, are capable of going down and on their own exploring and mapping what exists down beneath the surface of the planet Earth. Then they come back and they radio their results. So what we need is to develop a robot that takes this one step further and digs a hole for itself through the ice and drops itself into what is hopefully not too far down… liquid water, and then digs itself back up to the surface and beams its results back.

Fraser: Or, leaves a tether behind, right… some kind of communication tether… it leaves that up on the surface, melts its way or bores its way down through the ice, gets down to the ocean, leaves that as a way to communicate and then travels down into the ocean to see what’s below. It’s a monumental engineering challenge to make that work.

Pamela: And beyond just the budget difficulties, anything that’s swimming around underneath the ocean of Europa… or underneath the ice of Europa, rather… won’t be able to use solar panels. To continue exploring the outer solar system, and to explore places where literally the sun doesn’t shine, we need to use radioactive fuel cells, we need to use radioisotopes. Right now, here in the United States, we have a shortage of these. We’re simply not developing the fuels that are needed to power spacecraft. A lot of international treaties govern what nuclear isotopes you develop and you process and you refine and all those other different things. And under treaty, it’s unclear if we can create fuel cells we need for our space program.

Fraser: So, who knows… this is one of those situations where I’ll bet you someone’s going to come up with a clever way to analyze the ice on the surface and detect evidence of life’s outputs… right? Micropoop in the ice on Europa… so we’ll stay tuned on that one…
Ok, so next… mystery number four… what is creating the methane on Mars?

Pamela: Yeah, we don’t know that one either…

Fraser: No, I know… but this is huge!

Pamela: This is one of those amazing discoveries!

Fraser: Yeah, so once again, to set the scene… the European Space Agency’s Mars Express spacecraft discovered the faintest whiff of methane in the atmosphere of Mars. This is really shocking and surprising because methane is destroyed by sunlight in a very short period of time so there has to be some source replenishing the methane. What’s creating it?

Pamela: And during the northern summer, they were actually finding as much as 30 parts per billion of methane in the Martian atmosphere, and methane is something that gets actively destroyed by the sun. Sunlight… ultraviolet light hits methane… methane stops being methane, it’s happy to do that. So this is something that’s being actively produced, and we only know of two sources of methane.

Fraser: Source number one?

Pamela: …is lava, geophysical activity, something indicative of the planet being alive geophysically.

Fraser: And that would be very exciting to discover… we could see Olympus Mons erupt again…

Pamela: I’m not quite sure we could go that far… but it does mean that there is some sort of process going on that–well, it’s always cool when rocks are alive–but the other process is… well, life produces methane. Meet a cow–you’ve met a methane-producer. Small biological entities, bacteria, single-celled organisms in all their different forms, there’s many different ways to produce methane and so if Mars is as geophysically dead as we’ve been teaching for, well, as long as I’ve been alive, that means that there’s methanogens or some other form of methane-producing life in Mars.

Fraser: And, I mean, if they can find that, the ramifications of that are gigantic. That means that there’s life on Earth and there’s life on Mars. And if there’s life on two planets, then life could be all over the place in the universe. And you would, in theory, eventually be able to find the source and be able to study it and see if the two are connected. Did life begin on Earth and separately on Mars, or are they somehow interconnected? Do they share a common ancestor? The ramifications of this are mind-boggling. Now there are plans to get to the bottom of this mystery.

Pamela: Yes, and everything from the upcoming Mars Science Laboratory to most of the plans for the future for Mars all include going and digging in the surface and looking for signs of life. One of the most exciting ideas that I haven’t seen any missions attached to yet, is going and… there’s several different places that we’ve seen along the volcanoes on Mars skylights into deep dark caves that are likely completely protected from radiation. If we can go and explore in those caves… those caves may represent our best bet for places capable of supporting human colonies and supporting life that exists in the dark.

Fraser: And there’s also been some orbital missions proposed that will map out the methane concentrations with more accuracy and try and even find out exactly where it’s coming from.

Pamela: And everyone just wants to go dig… because who doesn’t like digging in the dirt?

Fraser: Oh, for sure… but I mean this discovery… this could change everything.

Pamela: Yes.

Fraser: So if there’s one mystery that we’ve really got to get to the bottom of… it is this one. But, let’s move on… so, mystery number five–where did Titan’s atmosphere come from? Titan is Saturn’s largest moon… second largest moon in the solar system… and it has an atmosphere that is thick… like as thick as Earth’s… and rich in hydrocarbons which scientists think is a very similar environment that we had here on Earth early on. How on Earth… ha, ha! How on Titan could you get an atmosphere like that so far out in the solar system orbiting Saturn? It should just be a block of ice, right? A ball of ice…

Pamela: Right, right… and this is where Titan gets to be a really interesting planet to look at.. it’s not even a planet, it’s a moon… it gets to be a really interesting object to look at from a geophysics perspective because it doesn’t just have a thick atmosphere, but it has a “insert the expletive of your choice” thick atmosphere. This is atmosphere that is 1.5 atmospheric pressure–or atmospheric bars, rather. That’s thicker than the atmosphere on the planet Earth.

Fraser: You could take off your spacesuit and not freeze-dry… you would merely freeze!

Pamela: And the thing about having an atmosphere this thick is… I love this… it’s a low-gravity world. It’s a tiny, tiny moon–compared to the size of the planet Earth–and so with this low gravity, if you attached a pair of Icarus’ wings to your arms, you could actually fly around in this really thick atmosphere. Now, the majority of the atmosphere is nitrogen–it’s 98.4% nitrogen. But, along with that nitrogen, there’s another 1.6% composed of methane and other organics, and like I just said about Mars, methane is destroyed by the sun. So, somehow there’s something about Titan that’s causing it to constantly generate methane that’s getting replenished in its atmosphere. People have looked to see… well, maybe it just captured the methane and it still hasn’t had enough time to all be destroyed from the solar nebula. No, that model doesn’t work. Well, maybe it just comes from getting clobbered by comets. No, that doesn’t work either… the composition ratios are all wrong. Somehow, something inside Titan is generating this, and one of the really awesome things about the combination of Titan being really cold, really tiny, and having this carbon-atom rich environment, is it can have geophysical processes that carve rivers, that carve canals, that in many ways look just like the processes that we have with water here on Earth. So, for Titan, the methane in the atmosphere is like the water in the Earth’s atmosphere. It can rain, it can form rivers on the surface, it can freeze, and so you can have an entire environmental cycle built out of methane… but we don’t know where it’s coming from.

Fraser: Right. So, methane is too short-lived to have been left over from the solar nebula, so some thing is either protecting or replenishing it on Titan.

Pamela: Exactly.

Fraser: Crazy. Alright, well I think we’re actually out of time. We’ve gotten through five, and we’ve got more. So this is going to at least be a two-part series, so stay tuned for next week. Thanks Pamela!

Pamela: Sounds good Fraser.

This transcript is not an exact match to the audio file. It has been edited for clarity.

Ep. 159: Planet X

Astronomy Cast — Tue, 03 Nov 2009 23:00:10 +0000

Artist's illustration of the dwarf planet Eris. Image credit: NASA

Astronomers have been searching for the mysterious Planet X for hundreds of years. It was the search for a theoretical planet beyond Uranus that turned up Neptune, and then again for Pluto. And even now there are some astronomers who think there’s a more distant planet out there. Oh, and there are a bunch of pseudoscience cranks trying to freak people out about the end of the world. Don’t worry, we’ll make time for them too, but first let’s start with some real science.

Ep. 159: Planet X

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