We were witness to a once in a million year event. A close approach of Comet Siding Spring to the Planet Mars. And fortunately, humanity had a fleet of spacecraft orbiting the Red Planet, ready to capture this monumental event in real time. What did we see? What will we learn?
- Siding Spring Observatory
- Is a Comet on a Collision Course with Mars? (Early article after the comet’s discovery) — Universe Today
- HiRISE images
- Mars Rover Curiosity Images
- MAVEN information
- Comet Siding Spring (C/2013 A1) Real Time Data
- Hubble Composite Image Shows How Close Comet Siding Spring Was to Mars — Universe Today
- MAVEN Ultraviolet Image of Comet Siding Spring’s Hydrogen Coma — JPL
- Curiosity Rover Snaps Photos of Comet Siding Spring, Giant Sunspot and Mars-shine
- EPOXI Misson
- A Compendium of Universe Today articles on Comet Siding Spring
- European Planetary Science Conference 2014
Transcription services provided by: GMR Transcription
Announcer: This episode of Astronomy Cast is brought to you by Swinburne Astronomy Online, the world’s longest-running online astronomy degree program. Visit astronomy.swin.edu.au for more information.
Fraser: Astronomy Cast Episode 354: Comet Siding Spring Vs. Mars. 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 and the Director of Cosmoquest. Hey Pamela, how are you doing?
Pamela: I am doing well. I am in fact doing far better than my internet connection is. So if any of you hear any weird context to our voices it’s because we have lag today.
Fraser: Right and so if I ask a question and then there is this long – well you know what? Preston will fix it. So if there’s this big long pause after I ask a question and then Preston will fix it and the audio listeners will have no idea that this is a terrible, herky jerky video while we were trying to record this episode of Astronomy Cast. But this is what we get, this is karma coming back. When you travel around the world you get to have awesome adventures in Australia, you get to see kangaroos, and you come back and the internet isn’t going to play nice.
Pamela: Well it’s not just the internet isn’t going to play nice it’s that my home computer died a bitter and brutal death upon hearing that my husband is getting a new computer. Like literally he said, ‘Hey, I’m getting a new computer’ and at that moment as I typed in my password to get rid of my screensaver it died. And tomorrow the hard drive gets replaced at the genius bar. So I’m on my office.
Fraser: See I was sure that this was a good chance for you to just completely throw out that computer and get a new one. Hard drive is dead, I need one of these brand new retina iMax the 5K display. But I guess you weren’t able to make that kind of agreement with the pocketbook?
Pamela: Well, NASA kind of like cancelled the program that I’ve been relying on for the majority of my funding for six years. So knowing that the possibility of getting new funding from NASA on that particular grant call is zero has made me realize all of everything needs to go into making sure that the rest of my stuff at Cosmoquest who don’t necessarily have husbands getting brand new computers are okay. Donate please.
Fraser: Right, austerity measures are in place.
Pamela: Yeah. Yeah.
Fraser: All right, so let’s get crackin’.
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Fraser: So we were witness to a once in a million year event, so we have been told. A close approach of Comet Siding Springs at the planet Mars and fortunately, humanity had a fleet of spacecraft orbiting the red planet. Now that’s a one to the million year event. Ready to capture this monumental event in real time, what will we see? What will we learn?
So before we go into this, you were in Australia – actually part of what you were doing and one of the big reasons why you were there was you were helping with iTelescope’s –
Pamela: Dedication of a new 27 inch telescope.
Fraser: 27 inches.
Pamela: Right, so I just spent two weeks – unfortunately, I got home before the flyby of Comet Siding Spring. I was down in Australia for two weeks and talk, talk, talk, talk, but a lot of the activities that I did were around the Siding Spring Observatory open house weekend, which is called Star Fest. iTelescope took advantage of Star Fest to dedicate a new 27 inch telescope that is named after three women astronomers; Joselyn Bell Burnell, Anna Jumppanen and Dorrit Hoffleit. They had myself and Amanda Bower, who is a senior fellow down in Australia – they had the two of us do the dedication of the new telescope.
Fraser: That’s fantastic. They must have been pretty psyched about that Siding Spring close encounter with Mars.
Pamela: It was really – the thing that everyone was talking about – first of all it was a discovery made by a really amazing astronomer who’s also just a nice guy. So it was discovered by Robert McNaught using the Uppsala Southern Schmidt Telescope, which is a nice half meter telescope with an amazingly large and beautiful field of view. And because of their tradition it’s not Comet McNaught, we’ve had those –
Fraser: We’ve already had those.
Pamela: He is, as I said, an amazing astronomer but since he was using one of the national facilities it was named after the observatory itself and got the Siding Spring Observatory designation. It was discovered back in January of 2013. It’s one of those telescopes that it does great work. It’s when the scientist who does great work and is a great guy and then it was a comet that a lot of people in the mountain had gotten to get time in on following. Peter Lake, who is one of the engineers and educators at iTelescope, actually took a number of the images that went into calculating the orbit of this particular comet.
And getting at the orbit of this comet was one of those things that had a lot of us on the edge of our chairs for quite some time.
Fraser: So it’s important to distinguish between this comet and for example, comet 67 Churyumov, which is the term that Emily Lakdawalla has given it and so we’re all just going to go with it. If it’s good enough for Emily Lakdawalla from the Planetary Society, it’s good for us. But yeah, just to distinguish between Siding Spring and 67P; they are two different kinds of comets. What kind of comet is Siding Spring?
Pamela: It is a comet that is probably on its first round through the solar system that is coming in from the Oort cloud. So when it was discovered last January, well two Januarys ago back in 2013, it was out at a distance that had it been ideally placed in solarium would have been nice and neat in between Jupiter and Saturn. It was out a little bit beyond seven astronomical units away from the sun when it was discovered and it’s on its way in from the Oort cloud and it will take it order of a million years before it comes back into the inner solar system.
So this isn’t a once in a lifetime, it’s a once in this geological epic kind of comet and it not only came in but then decided it was going to give Mars an unprecedented view that actually allowed some of the spacecraft at Mars to get the highest resolution images we’ve ever had of an Oort cloud comet.
Fraser: And I think that’s the really important distinguishing feature here which is that Rosetta and – there has been a mission to Haley’s Comet and there’s been the Stardust mission.
Fraser: Yeah, so we’ve had close encounters with comets before but the problem with these Oort cloud comets is they come out of nowhere, they buzz past the sun, and then they head back out into the outer reaches of the solar system and so you just can’t task a spacecraft to catch up with them or do a flyby in time. But nature just did the next best thing.
Pamela: Right and while it was a small comet, it was probably somewhere between 500-700 meters in diameter, it got so close to Mars that even the Mars rovers down on the surface of the planet were doing imagery of it. It got within about 86,000 miles of the surface, 130,000ish kilometers, and that – well being further away than some of the moons in the grand scheme of things if we’re comparing that distance to the distance of an Earth geosynchronous satellite it would have been closer.
Fraser: And we happen to have the most powerful telescope operating around another world, which is the Mars reconnaissance orbiter. It has the high-rise instrument which is a really powerful telescope used for observing Mars but it was able to observe Siding Spring as well.
Fraser: No problem.
Pamela: And so this is where these really high-rise images are coming in. They took exposures of varying lengths so that they could get a good look at the coma, the fuzzy cloud of gas and dust that’s reflecting sunlight around the nucleus. They took shorter exposures so that they were able to try and get a good view of that nucleus. And so these are the highest resolution images that we’ve gotten so far.
The other neat thing was we just stuck a couple of new spacecraft into orbit around Mars and one of those new Spacecraft was the Maven Mission, which is designed specifically to study atmospheres and has things like particle detectors onboard. This comet just happens to have left a few particles in the atmosphere of Mars.
Fraser: Yeah. Yeah, absolutely. I mean when the comet was first discovered there was concern that it was actually going to hit Mars.
Pamela: Yes, this is where the sitting on the edge of the seat part comes in.
Pamela: It was a couple of months while the air and the orbital determination was sufficient that while the orbit looked like it wouldn’t coincide with the surface of Mars the air circle still overlapped with the surface of Mars. And the concern was if you have this brand spanking new, shiny atmospheric-detecting spacecraft orbiting the planet just as you hit the planet with something, that we at the time thought was maybe a couple kilometers across, you really have to worry about what all is going to get thrown up into space.
You’re looking at a crater that’s tens of kilometers across for that one to two kilometer impactor. It turned out it was much smaller so that wouldn’t have been an issue, but it still would have done damage and as it is it put enough extra debris and more importantly, enough extra heat into the upper atmosphere of Mars that it significantly increased the drag on the spacecraft. So they’re going to have to put more effort into maintaining orbits and it may have actually shortened the useful lifetime of the spacecraft. We’re still figuring that out.
Fraser: Right. And so if it had actually hit Mars, from what I was reading, it would have pretty much shut down human exploration of Mars for decades, that it would have kicked up so much dust into the atmosphere it would have made the environment completely obscure like where none of the orbiting spacecraft could see the ground, the Mars rovers on the ground – nothing else could land. Like we would be blocked from Mars for decades.
Pamela: And that was probably more dire than reality simply because you’re looking at this two-fold problem of Mars doesn’t have sufficient gravity to pull things out of the atmosphere very quickly. But at the same time it doesn’t have an extremely thick atmosphere so you end up with situations where you’ll end up with storms on the surface of Mars that obscure most of the surface when they get going.
Fraser: Yeah, we’ve seen this.
Pamela: But then winter comes and you freeze the atmosphere out of the atmosphere. And so these massive hemispheric changes in where the poles are as you freeze the southern atmosphere out and grow the southern pole, melt that and then freeze it back down at the north pole – it becomes hard to figure out just how long would that dust have been in the atmosphere. But yes, what you’re saying was most dire of predictions and there was talk of even potentially putting the Maven spacecraft into a different kind of orbit to get to Mars just in case they needed to hold it back if that impact was going to occur and figure out new orbits and things like that.
Storing a spacecraft on Earth and delaying launch is a great way to get your mission cancelled, to ruin your spacecraft. Earth is the least safe place to store a spaceship.
Pamela: But, once it was in orbit there was at least room to maneuver.
Fraser: Right. But this maneuvering was still important because you know if you read a bunch of the articles that were coming out just before the pass they were talking about how the spacecraft were taking cover as the –
Pamela: Yes. I just have this mental image of like all the spacecraft slowly poking their solar rays around the limb of the planet as they –
Fraser: Cowering behind Mars, yeah.
Pamela: Yes. So they did take care to put the spacecraft in orbits that would allow them to be maximally behind Mars during that closest approach. Now Maven has admittedly only a several hour orbit. The same is true of the fabulously functional Indian spacecraft, but they did what they could to get them behind during that critical time as the comet passed by at a relative 56 kilometers per second.
Fraser: Let’s talk a bit about like what the various spacecraft would be capable of seeing. From the ground we had Curiosity, we had Opportunity and they were able to see it from the ground.
Fraser: So what would they see?
Pamela: Well it’s awesome because those images are online so we can go in and we can look at Mars reconnaissance orbiters, high-rise camera images. We can look at Mars Exploration Rover has this great image of it in the constellation of SETI. I haven’t so far, but this doesn’t mean they’re not out there, found images from Curiosity, but Maven is already making atmospheric measurements and looking at yes, this is a spacecraft that dumped temperature into the atmosphere. And the way you do that is the particles as they go through the atmosphere and burn up their kinetic energy, their motion energy, and their chemical energy and getting shed as heat energy into the atmosphere and so there may have been as much as 40 Kelvin added to the upper atmosphere.
Fraser: Now here on Earth like when we have meteor showers that’s because we’re going through the tail of a comet.
Fraser: And so Mars has gone through the tail of the comet. Will the rovers get some meteor showers?
Pamela: So they did see a meteor shower or they would have had they had sufficient resolution to make out a meteor shower? But the neat thing about the way comet geometry works is that tail is always pointed away from the sun. The tail does not stream out behind the comet because of the motion of the comet. It’s actually pushed outwards from the sun by the solar wind. The comet’s tail itself didn’t really have a close encounter with Mars; it was more the particles from the coma. And one of the images that really got my attention is someone combined an Earth-based image and an image of Mars that showed the orbital size of Phobos and Deimos and at closest approach there was 135,000 kilometers between the center of the comet and the center of Mars, and Mars is only about 6,700 kilometers across whereas the visible coma of the comet was 20,000 kilometers across.
Fraser: So it was bigger visually than Mars.
Pamela: Yes. So that cloud of sunlight reflecting dust and debris was more than three times the diameter of Mars.
Fraser: Yeah, and then of course you’ve got – the Hubble took some pictures. As you said, Maven is probably one of the most interesting instruments there because Maven isn’t a telescope. It doesn’t even have a camera, but it is designed to look at atmosphere, to look at atmospheric particles and dust, and what a perfect target for it to watch.
Pamela: And it’s probably going to take quite some time to figure out everything that happened because there is going to be a long-term decay in effects to the atmosphere and they’re there to see them. So they’re going to be able to see how long does it take Mars’ atmosphere to return to the state that it had prior to the comet. And this is one of the really neat things with the timing of Maven is it did get there just in time to get a solid baseline of what does Mars’ atmosphere normally look like? And now it’s going to have, for however many days, weeks, months, or even years that it takes for the atmosphere to depoof. And it’s probably going to be order of weeks to months.
It’s going to be there to see all of those changes and actually measure changes in the chemical properties of the atmosphere that in part reflect just different molecules being around you to changes in temperature and also what the comet left behind.
Fraser: Yeah. I mean one of the interesting things about this is that Maven wouldn’t have been ready to take observations. They were going to go through their whole shakedown period, they would have done all of their testing each instrument and done all of their baselines, as you said. But because there was this once in a million year opportunity to get these shots they had to get Maven to return a bunch of data about Mars immediately when it arrived to be able to get this baseline. And so now they’re going through the proper implementation to bring everything online now and getting all of the calibration over the next few months.
So they took advantage of an amazing opportunity but to push the spacecraft into science a lot earlier than they normally would have done.
Pamela: Right. It is one of these kind of amazing times when all in all this wasn’t a particularly distinguished comet, it wasn’t even the brightest comet in the sky that night. There are actually a number of different comets currently visible; there’s 2012 K1 PanSTARRS at a 7.5 magnitude, there’s 2013 V5 Oukaimeden. It’s a Japanese named one that I’m sure I just destroyed the name of that’s at magnitude 7.7. Comet Siding Springs is only at magnitude 10, so it’s significantly fainter but it almost hit a planet and there are a whole lot of us in camp go boom.
I was really hoping for an impact so that we could really see the physics.
Fraser: You’re a monster.
Pamela: I am. I truly am. But we haven’t figured out how to solve the radiation problems for human beings going to Mars yet so I’m good with making it a little difficult to go there for a little while because physics.
Pamela: I mean think of everything we could have learned with these rovers on the surface, with all of these spacecraft in orbit. We would have got see what is the damage caused by a small comet and that gives us insight into what we need to be looking for. We’re pretty good and pretty thorough at finding the multi-kilometer stuff out there. We know that we’re missing a lot of the hundreds of meter stuff out there.
Fraser: Yeah, absolutely. It was a funny sort of watching – like I was quite tuned in as the event was happening. There was a bunch of hangouts. The folks at the European Space Agency and I know Slew and iTelescope did live coverage of the comet. I think everybody was expecting or hoping for this kind of – the telescopes and the various space missions to come online and start streaming their views and it was a bit of a letdown as all of that data – nothing came out. There was some great shots from amateur astronomers on earth and then it took a couple of days for the actual pictures to start percolating out and becoming available.
I could see this sort of sentiment out there on the internet. People were like, ‘Well, that’s it? That’s all? We didn’t get to see much.’ But yet I’m sure the scientists were just out of their heads excited with this opportunity to see these first time close-up images of an Oort cloud comet, a long-period comet.
Pamela: But what I was really enjoying was watching the people who are the scientists on the various teams tweeting things along the lines of, ‘Oh my God. Can’t tell you’ and the sheer excitement of what they were seeing that they’re not allowed to share and I’m sorry Preston I just totally blew my mic levels on that. The people were so excited to share and the problem is you can’t just release a raw image because the public doesn’t know how to deal with a lot of the weird features that you get with CCDs and occasionally decide things like lens flare is a UFO.
Pamela: So there’s a whole lot coming.
Fraser: But there’s good folks like Emily Lakdawalla at the Planetary Society who is watching the raw feeds coming from the spacecraft and is able to clean these things up and do the job and actually we do it all the time too at Universe Today. Jason Major and Bob Cane, we’ve got a bunch of people now on our team who are watching these raw feeds and as soon as a picture comes out – like we were literally refresh, refresh, refresh and in fact Bob Cane was one of the first people to see in an Opportunity’s view.
So no, I think they can release the stuff in the raw. I think they did.
Fraser: I mean they released the stuff out pretty quick.
Pamela: They did for a lot of the spacecraft but I don’t think they did it for all of the spacecraft. We actually have a question coming in from Twitter. Rashawn Bacari is asking could Curiosity rover actually use the chem cam on the comet?
It could try but the problem is it just wasn’t bright enough to do spectroscopy with an instrument like that. A lot of times what you really need is a whole lot of bright light and I think chem cam may actually have them heating things up in an oven. I have to admit that’s not one of the instruments.
Fraser: They have a laser.
Fraser: Curiosity has a laser that it zaps things with. So what’s going to happen next? I mean the comet has passed Mars, it’s passed out of the field of view of all of these robots, it’s going to go around the sun and then it’s going to leave us.
Pamela: It’s going to spend the next year slowly getting fainter and fainter and fainter until we no longer care because it’s not bright enough for the telescopes most of us have access to. But then it’s going to happily return its way to the Oort cloud unless it decides to collide with something along the way, and statistically that’s not going to happen.
Fraser: And then we’ll see it in a million years.
Pamela: Not us but –
Fraser: Us in our third robot bodies, absolutely.
Pamela: It’s fascinating to imagine though a million years from now – ignoring climate change, destroying society. But if you imagine that we figure out how to continue surviving on the surface of our planet will they still have knowledge of our early observations today that they can use to try and understand it in that extraordinarily distant tomorrow? And how much will they make fun of us?
Pamela: I mean we use Galileo’s sketches occasionally to go back and try to figure things out. Yeah, you’ve got to wonder. Yeah, I’ve got to wonder.
Fraser: I mean you can just imagine some kind of future press release coming out where they update the orbit of the comet Siding Spring by .1 degree thanks to their second observations. It’s three weeks off schedule.
I guess sort of where this goes and one of the Holy Grails of planetary astronomy is to send a mission to a long-period comet. We’ve talked about long-period comets in the past. What would it take to actually get something that on purpose got close to a comet and maybe even orbited it and went along for the ride?
Pamela: Well you don’t really orbit comets, you sort of zigzag along beside them because they just don’t have enough gravity. You pseudo orbit them basically. But in order to do that pseudo orbiting, zigzagging orbiting the sun alongside that icy body you’d really need to have a spacecraft not too different from Rosetta out there in a parking orbit with a whole lot of maneuvering fuel onboard ready when you get that year and a half notice as it comes in from Jupiter to be sent to intercept it as it gets close to the sun. It’s kind of expensive to have spacecraft in parking orbits, but there’s always the hope and it’s not a futile hope that we’ll have a spacecraft like Epoxy that got used for one purpose and when it’s done and it’s still fully functional gets repurposed to go and visit something that happens to have a serendipitous orbit.
Fraser: Yeah and I think you’re exactly right it would be something that’s maybe orbiting out in the Jupiter range which can do a slingshot around Jupiter when a comet trajectory is known and the math works. And this thing would be all fuel and it would be able to increase its speed tremendously to be able to get into a proper orbit.
Fraser: Because these things are moving fast and they’re completely unpredictable. We don’t know where they’re coming from. So that would be amazing. Okay cool, well thanks a lot Pamela.
Pamela: It was my pleasure.
Fraser: Welcome back.
Pamela: Thank you.
Fraser: Thanks for listening to Astronomy Cast, a non-profit resource provided by Astrosphere New Media Association, Fraser Cain, and Dr. Pamela Gay. You can find show notes and transcripts for every episode at astronomycast.com. You can email us at firstname.lastname@example.org. Tweet us @AstronomyCast, like us on Facebook or circle us on Google+.
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