Hubble Space Telescope. Image credit: NASA

Hubble Space Telescope. Image credit: NASA

The atmosphere keeps us alive and breathing, but it really sucks for astronomy. Fortunately, humanity has built and launched space telescopes that get above the pesky atmosphere, where the skies are really clear. Let’s take a look at the past, current and future of orbital observation.

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Female Speaker 1: This episode of Astronomy Cast is brought to you by Swinburne Astronomy Online, the world’s longest running online astronomy degree program. Visit for more information.
Fraser Cain: Astronomy Cast episode 386, Orbiting Observers. Welcome to Astronomy Cast, your weekly fact-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 Gay: I’m doing well. How are you doing, Fraser?
Fraser Cain: Good. And by the time you are listening to this, Pamela and I will be together in person in Ohio, in Columbus, Ohio, participating in a series of science outreach with a bunch of our friends.
Fraser Cain: As one does. So, hopefully –
Pamela Gay: With an astronaut.
Fraser Cain: I know. Right? So, look forward to a bunch of stuff we’re gonna try and do live on location for you guys when we get a chance to hang out together and do some shows and answer some questions. That’ll be coming up in the feed.
Pamela Gay: And we will put all of the live stream links out on the Cosmoquest Astronomy Cast and our personal Twitters. Fraser is @fcain. I am @starstryder with a ‘y.’
Fraser Cain: Also, I’ve seen The Martian. It was really good. You should also see it, in case you needed that permission. I give you permission. It’s fantastic. Thank you. All right. Let’s move on to this episode.
Female Speaker 1: This episode of Astronomy Cast is brought to you by 8th Light, Inc. 8th Light is an agile software development company. They craft beautiful applications that are durable and reliable. 8th Light provides disciplined software leadership on demand and shares its expertise to make your project better. For more information, visit them online at Just remember, that’s www.the digit 8 T-H Drop them a note. 8th Light: Software is their craft.
Fraser Cain: The atmosphere keeps us alive and breathing but it really sucks for astronomy. Fortunately, humanity has built and launched space telescopes that get above the pesky atmosphere where the skies are really clear. Let’s take a look at the past, current, and future of orbital observation, aka probes. All right, Pamela. You picked this topic. Where are you going? What is this about? These orbital observers of which you speak.
Pamela Gay: We’re currently in mission selection season, and anyone who tuned into the weekly space hangout last week saw that we were talking about the down selects that just happened that narrowed the field of possible missions down to two potential Venus spacecraft; one potentially going to a Trojan asteroid; a whole bunch of different, interesting, fairly inner solar system ideas. This got me thinking. We haven’t really done a good roundup of all that stuff that’s out in the Solar System currently sending us back a whole lot of data.
Fraser Cain: I think, also, in addition to the roundup, which spacecraft are where and what spacecraft weren’t where, and which spacecraft are going to be where, but what are the things that they need to really think about when they’re planning these kinds of missions. What are the parameters? Because, in fact, a big one came up with this selection process, the sort of lack of plutonium for powering these probes into the outer Solar System. That’s one of the reasons why everything that’s potentially gonna be targeted is gonna be for the inner Solar System. There’s a lot of requirements that we should also talk a bit about. But where do you wanna start?
Pamela Gay: Probably a good place to start is what’s out there right now. What’s in our sky tonight, I guess. By sky I mean it might be on the other side of the Sun, but it’s out there somewhere.
I think the oldest mission still out there sending us back a ton of data is Cassini, right now. Cassini’s out there. It was launched in 1998. I didn’t even have a master’s degree when this mission took off. It’s really scary that that’s how I apparently age date things, but it is. Cassini took its gravity assist to get on its way all the way out to Saturn and it’s in a continuing mission, but it’s in its final continuation. They are going to quite purposefully suicide it into the atmosphere of Saturn in a few more years. But hey! We’ve gotten a good chunk of Saturn’s orbit observed up close and personal.
Fraser Cain: And Cassini was like the last of one of the great observing orbiting missions, with Galileo. I’m trying to think of any other missions that were orbiting. We had the Voyager series head off into deep space, and I guess we’re still communicating with them. But Cassini was really this flagship sensor suite with a ton of amazing scientific instruments, cameras, etc. Not a lot else out there that’s as sophisticated as Cassini is.
Pamela Gay: Part of that is it built on that already tried-and-true technology that was originally developed for the Voyager 1 and Voyager 2 missions. We have this defined platform, known technology just upgraded to the modern era and set off and explore. It’s always easier when you don’t have to recreate the wheel.
Fraser Cain: Which sort of leads down a bit of a theory that I have, which is that I wish more of the spacecraft could use that reusable platform, that they use an orbiter-style platform but then they put just different science instruments and send it to a different target. As opposed to necessarily reinventing the wheel with each mission.
Pamela Gay: We do see a little bit of that. It’s not as much recreating the wheel as you might think right off the bat. A good pair of examples is there’s Mars Express, which is still out there, still happily doing its thing at Mars, and then you have its sister spacecraft which is no longer doing its thing at Venus, which was Venus Express. Between those two spacecraft, you have very similar names and you also have very similar spacecraft. Venus Express only recently retired; it retired back in January. One of the reasons that I think we have to give tribute to and we push Mars spacecraft as long as possible because they also get used as communication satellites.
So, we have 2001 Mars Space Odyssey, or just Odyssey, but in tribute of those classic books. It’s still out there orbiting, taking not the best data, but taking data on Mars, but it’s a relay satellite also. It’s getting us data back from Curiosity and Opportunity, and had Beagle survived when it got carried there by Mars Express, it didn’t survive, but it would also be relaying its data back.
Fraser Cain: And Mars Odyssey gave us some of the best evidence for the large amounts of water underneath the surface of Mars. We really learned about these vast ice deposits on Mars. Although now, of course, we’ve seen, in fact, liquid water, potentially, flowing on the surface of Mars.
Pamela Gay: Flowing’s a strong word. Seeping –
Fraser Cain: Seeping.
Pamela Gay: – across. I’ll give you seeping.
Fraser Cain: Sure. Oozing out of the sides of some craters.
Pamela Gay: But that’s the next episode. We’re gonna talk about that next time.
Fraser Cain: Yup. Yeah. Spoiler alert! Right. So, you’ve clearly shifted to Mars. Skipped the asteroid belt, as if –
Pamela Gay: Well, I was going in chronological order and you did…
Fraser Cain: Okay. Sure. Let’s do it.
Pamela Gay: We had Mars Odyssey, got there in 2001. Mars Express launched 2003, arriving late that year. Opportunity rover was another 2003, this time arriving in 2004 in January. There was this great beginning of this century, let’s just send all the things to Mars. Followed by – Rosetta got launched in 2004, but it just got there, so, we can talk about it later. But Mars Reconnaissance Orbiter, which has the sister spacecraft Lunar Reconnaissance Orbiter – Mars Reconnaissance Orbiter, it was launched in 2005. It’s still up there; it’s still doing its thing.
What you see with this Mars, Mars, Mars, Mars is that era when we were planning to get astronauts there when the budgets were a little higher and the goals and missions that we were mandated by Congress were a little loftier and a little more funded. So, as the funding has been scaled back we’ve had to scale back our dreams a little bit. We don’t see launches nearly as frequently and we don’t bombard single worlds with quite so many robots anymore.
Fraser Cain: It also reflects the thinking at the time, a decade ago, was that the place to look for life in the Solar System was Mars, and that all of the other places were potentially not as likely for life. But now, with the discovery of the sort of full oceans under ice on Europa, on, potentially, Enceladus, maybe even Callisto, and the fact that some of this liquid water actually gets up to the surface of these worlds, there’s more and more emphasis being placed on potentially sending orbiter missions to these places. We’ll talk a bit about that in the future.
Pamela Gay: We had this great era of Mars and then launching things all over the rest of the Solar System with the 2004 launch of Rosetta, which has finally arrived several months ago at 67p Churyumov-Gerasimenko or Chury-Gery is pronounceable. And then New Horizons took off in 2006. So, there was this whole let’s just go all the places. 2007, we launched Dawn which went to Vesta and then Ceres.
Now, we’re in the era of seeing other nations start to fill in the science that we’re not still building space probes for. That’s a kind of interesting change to get to watch.
Fraser Cain: Yeah. There’s Chinese missions, Indian missions.
Pamela Gay: We saw, in 2007, America launched the Artemis mission and then after that it all became other countries. You had Chang’e 2 which was the Chinese mission that went to the Moon. This is the mission that has the most awesome orbital work I have seen in the inner Solar System. It arrived in the Moon in October 2010, and then from there it went to a Lagrange point. Then it went to an asteroid, 4179 Toutatis. Then it decided hey, I’m gonna go get myself in heliocentric orbit instead. Now it’s out there in heliocentric orbit.
Fraser Cain: That’s it, though.
Pamela Gay: Yeah, but that’s still kind of awesome for one little spacecraft.
Fraser Cain: Absolutely. Is that sort of the full sweep of spacecraft that are currently orbiting or buzzing around objects right now?
Pamela Gay: There’s a few more but we tend to forget about them because they don’t produce cool pictures and they’re not their nations’ first big ones. I’m gonna destroy the pronunciation of this. You may know how to pronounce it better. Mangalan, Mangalyaan, the Indian probe that is at Mars and has sent back some pretty cool images.
Fraser Cain: We just call it MOM.
Pamela Gay: That works. Okay!
Fraser Cain: Yeah. The Mars Orbiter Mission? But yeah. Yeah.
Pamela Gay: It’s there showing that India does have interplanetary capacity. It’s not the highest resolution mission out there, but it is really a testbed for what this new exploring nation is capable of. Chang’e 1 and 2 have been followed up by Chang’e 3 which was a lander on the Moon. Then Chang’e 5 is also now hanging out at the Moon. China is now following our lead and covering other worlds in robots, as one does.
Fraser Cain: There’s a few spacecraft that are orbiting the Sun. There’s the STEREO spacecraft which are orbiting ahead and behind Earth in its orbit. And there’s a bunch of stuff that’s in, I guess, various Lagrange points. We’ll skip the stuff that’s actually orbiting Earth because there’s 1300 of those. We’ll talk about other stuff. And then we lost Messenger, which is too bad, and we lost Venus Express.
Pamela Gay: And one of the things that don’t get talked about nearly enough is we’re slowly but surely losing our suite of Earth-imaging satellites in polar orbits that are needed for weather. We have some. We just don’t have as many as weather forecasters might like. If you find that your weather forecasts aren’t as good as they might have been a few years ago, it’s not that our understanding of the weather isn’t as good, although that is a part of it. Our planet is undergoing radical change and it’s hard to keep the models up to date.
Fraser Cain: As we’re Venus-forming Earth.
Pamela Gay: Yeah. Exactly. Venusian-forming? Is that maybe how you put it? But we also don’t have the full suite of satellites.
Fraser Cain: We’ve talked a bit about what’s out there right now. But I think what people are going to be very interested in is what’s coming? I think the new selection of missions is a great time to talk about some of the kinds of spacecraft that are coming out. We talk about them, and let’s also talk about the Europa mission which is pretty well and truly selected at this point.
Pamela Gay: I have to admit, this is where, for me, spacecraft for me are dead until they have first light. Or at least unborn, I guess is a good way to put it. I had a spacecraft I needed for my dissertation fail to function and since then I’ve been a little overly cautious, you might say, in following them up.
Fraser Cain: It’s like the terrestrial planet finder.
Pamela Gay: Yeah. Yeah. All of these things we get our hopes and aspirations pinned upon and then it doesn’t happen.
Fraser Cain: Do they even exist for you when they’ve been launched? Or not –
Pamela Gay: They do. Once they’ve been launched, once they’re on their way. So, Juno, totally alive to me. I believe in Juno. But the Europa probe, part of me’s like, “Congress can still kill it.” We do have to be cautious and careful.
Fraser Cain: All right. Fine. Let’s talk a bit about what is sort of the overall philosophy that’s driving planetary exploration, especially the orbiters and probes into the future? There was a selection process that just happened. What are some of the priorities that the scientists are dealing with?
Pamela Gay: We have a two-fold issue that we’re dealing with. One is the mandates that we have coming down from Congress and the President. And that includes the fact that plutonium keeps not getting created. That’s kind of a Congressional decision. And then the other is we set priorities using the decadal surveys. It’s starting to be time to start thinking about doing a new decadal survey, but we are still going on the priorities of the last one. Some of our priorities are to start to understand those icy worlds in the outer Solar System. This is where we start looking at how do we get to Europa? This is where we have successfully looked to push the Juno mission forward.
Then we also start looking at – from Congress and the President we have this vision of Moon/asteroid/Mars as places of exploration, potential commercial venues. So, you see in the mission selections let’s keep looking at ways to keep exploring asteroids. We have the OSIRIS-REx mission with its sample return to Bennu coming up in the coming years. That mission is well under construction.
Fraser Cain: But that doesn’t count, right? Spacecraft under construction can get cancelled, too.
Pamela Gay: It’s true. That one’s more real to me because I do get funded as part of OSIRIS-REx, so, disclosure, I guess. When you have money from it, it makes it a little bit more real than when you’re simply hoping on it.
But there’s also always that question of where don’t we have any modern data? And Venus is definitely one of those places where we don’t have modern data. The Magellan probes back at – well, the Magellan probe back in the ‘90s, side radar, great job getting us maps of its mysterious surface. But technology is better. Maybe now we can figure out how to get something that lives a little bit longer on the surface. Maybe we can get a little bit deeper down into the clouds using balloons or other technologies. This is where we’re starting to figure out how do we get back to Venus, and we’ll get a little bit more data on this planet we’re not hopefully going to actually turn our planet into. But let’s face it. Understanding its greenhouse will certainly help us understood our own world.
Fraser Cain: Yeah. When you see the pictures that came back from the Venera probes when they landed those on the surface of Venus, and they lasted for – the longest was just under an hour and then they all died. It would be great to have something that could last a little longer; maybe stay up in the cloud tops; use ground-penetrating radar. That would all be terrific. Let’s do that.
What is the – I don’t know. What is the big scientific emphasis right now, though? Are you saying it’s looking for places that we haven’t seen yet? Or is there a sort of a theme to what – are people looking for liquid water? Looking for evidence of extra-planetary life? What are scientists really looking for?
Pamela Gay: There’s the follow-the-water, which I think is actually happening in all of the different space agencies. With NASA, we definitely have the journey to Mars hash tag going out, and it’s not just a hash tag. It’s actually kind of an ideal. Let’s go there. Get the rovers following the story of the water.
Curiosity is out there doing one set of experiments. The Mars 2020 rover is going to land in as different an area as possible. So, Curiosity is in Gale crater where it can explore a very old part of Mars that potentially had water in the past. With Mars 2020, they’re looking to select a site that is undergoing constant erosion, revealing the surface over – and basically, it’s just like when you go fossil hunting. You wanna go somewhere where the cliff is crumbling down. Well, we’re gonna go look to see where the sand dunes are blowing the ground away, revealing potential organics, potential – may we say fossils from the past, allowing us to understand what the past on Mars was like.
Fraser Cain: Based on all of the evidence that’s come out recently, the nucleus of images that Rosetta has taken of 67p, the new images of Ceres, the new images from Pluto from New Horizons, where would you like more orbiters sent?
Pamela Gay: I have to admit the more orbiters is something that on the inner Solar System I’m pretty good with the suite of orbiters we have. Venus, it needs something up above to linger longer because its surface is kind of death. But for the inner Solar System where we don’t need the radioactive isotopes, I want to go figure out what the heck that white stuff on Ceres is. And, like many others, I’m deeply concerned that we won’t get a definitive answer from an orbiter. We need to go land, take a sample, and –
Fraser Cain: Taste test.
Pamela Gay: Yeah. Robotic equivalent of lick the rock. Is it salt? Is it ice? We don’t know. Can we find out with that spacecraft? We don’t yet know. I wanna know what is that weird mountain on Ceres? I think it’s time for us to take the idea of fillet, execute it with harpoons that don’t have to live in deep space for quite so long, and go stab ourselves into the surface of more worlds and see what’s there to be sampled. So, I wanna see more and more let’s go stab rocks.
Fraser Cain: There are some pretty intriguing – some of the concepts that were recently chosen. One was to send a spacecraft to a metal asteroid, which would be pretty fascinating. That’s a kind of world that we’ve never really explored, although I wonder what it would be like to stab your harpoons into the metal.
Pamela Gay: Yeah. I think there you’re gonna look – can we magnet ourselves to..? I don’t know.
Fraser Cain: Yeah. That would probably – That’s a good idea. You talked about Ceres. Are there some mysteries – I would love to see – I would like to see that Europa mission orbiting Europa.
Pamela Gay: That starts get to the we need the more plutonium. We still know almost nothing about Neptune and Uranus. We need to have orbiters on these worlds. Not on, but around these worlds.
As we enter the era of commercial space, it’s gonna be awesome to watch companies like Planetary Resources start to solve the problems of how do you move asteroids. How do you land on little itty bitty tiny things? Can we actually burrow through them the way we’d like and the way science fiction authors have been talking for generations? Those things are gonna start to happen in the next couple of decades. We’ll hopefully be around to report on them.
Fraser Cain: What’s a place that we – you talked a bit about Venus, for sure, that we don’t have a lot of information about Venus. What are some other places that we just don’t know really anything about that we really should get a spacecraft there? I’ve heard Emily Lakdawalla call for a probe to Uranus, mostly because she likes to say probe to Uranus, but I think she does feel like there’s some pretty good science there, to be exploring some of the ice giants.
Pamela Gay: I think we definitely need to go to Uranus or Neptune. I think there’s also a lot of good cases for going Neptune so that we can also study its moon, Triton and get this comparison between Pluto and Triton. But it gets so hard to narrow things down right now because the question is what is it that you want to learn? Are you looking to try and pioneer manned space exploration? If that’s what you’re looking to do, asteroids and Mars and the Moon is where it’s at. We need to figure out how to dig. We need to figure out how to safely get in and out of those caves on the Moon and Mars. If it’s pure science, if it’s the search for life, we need to be going out to Titan and Europa and Enceladus and all of these worlds where we see different chemical reactions not entirely alien to the idea of life.
Fraser Cain: I think there’s a lot of questions that a lot of regular people might not think are super interesting, but to scientists they’re really core. What did the early formation – how did the Solar System form? What did it look like in its earliest times? How did things change over time? What are some of the processes, the geologic processes that are happening on these worlds? They have nothing to do with life. They’re really just fundamentally understanding how our Solar System came to be and how it’s been changing over time. A lot of the kinds of instruments on these spacecraft are designed to answer those kinds of questions.
Pamela Gay: And it’s really kind of amazing to think how far we’ve come. When we were in, I think, about fourth grade in ’84, you may have been a grade or two ahead of that, when Halley’s Comet first came through. That was when we first tried sending spacecraft to a comet and they got nowhere near Halley compared to what Rosetta’s doing today. In our lifetime, we’ve seen advancement after advancement, and it’s today that we’re now looking to the how do we start harvesting this ice? How do we start taking advantage of these asteroids as things we can move by our own manpower or robot power?
Fraser Cain: What do you think about the sort of ongoing advancement, both of miniaturization of the actual technology that’s used in these satellites and also the decreased launch costs that we’re potentially seeing through places like SpaceX and some of the other launch providers? What impact is that gonna, maybe, have on our ability to sense the Solar System?
Pamela Gay: The big missions, unfortunately, you can only miniaturize things so much because you are limited by the well, my lens needs to be this big, or my reflecting area needs to be this big. That’s kind of defined by the rules of optics. But in terms of a lot of basic probes, we’re going to first be able to get a better idea of our own planet from college students launching CanSats. We’re then going to slowly but surely be able to send, instead of just one big old spacecraft to Mars that we cram all the instruments on, imagine sending something and instead of dropping a rover, drops ten very well-tested CanSats that we know will succeed. Suddenly, we have a lot more students, a lot more early-career researchers that are pioneering new ideas that maybe you can’t quite get to via the current funding requirements.
Fraser Cain: Right. That’s sort of the letting a thousand flowers bloom. It’s this idea of getting a lot of ideas out there to test out, and then take the ones that really work best and use those across the Solar System. That almost does feel a bit like it’s log-jammed, with just Congress having to approve this mission or that mission, and things take a long time. As you said, they take decades for these missions to come from idea to actual implementation. If we could shorten that that would be great.
Pamela Gay: And if it takes us 30 years to testbed the technology for a major Mars mission but five years to pioneer that CanSat we’ll be able to take advantage of almost modern technology for the first time ever. For those of us who kind of lament the sad state of memory on so many of these spacecraft, we want all the data, all of it. So, send so many more terabytes. Send so much more powerful antennas. Just get everything back, not in years, but maybe in days? Wouldn’t that be awesome?
Fraser Cain: Absolutely. That, I think, is gonna be the big revolution, getting the smaller, less expensive, more specific satellites to a lot of places. I think, hopefully, if people can figure that out, we’re gonna get a lot of really interesting data. Although it’s probably just gonna be a million more questions that then require new spacecraft to try and even answer those questions. I mean, just these white spots on Ceres alone is, as you said, that’s a mission. That’s a question.
Pamela Gay: It drives me crazy.
Fraser Cain: I know. How could a spacecraft have gone to Ceres, found something so unusual and not been able to provide enough of an answer that people could know what’s going on there?
Pamela Gay: And satellites beget information that begets the need for new satellites. It really is space probes all the way down.
Fraser Cain: That’s exactly what it is. That’s a good place to stop.
Pamela Gay: It is. And onward and upward into the future, I guess.
Fraser Cain: Awesome. All right. Thanks, Pamela.
Pamela Gay: Thank you.
Male Speaker 2: 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 You can email us at, tweet us @AstronomyCast, like us on Facebook, or circle us on Google+. We record our show live on Google+ every Monday at 12 p.m. Pacific, 3 p.m. Eastern, or 2000 Greenwich Mean Time. If you miss the live event, you can always catch up over at
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