Every two years or so, Mars lines up nicely with the Earth. It only takes two minutes to communicate with rovers, you can see the polar ice caps in a small telescope, and it’s the best time to send spacecraft to the red planet.
Mars in Opposition (NASA)
Mars opposition 2020: get ready to observe the Red Planet (Sky at Night Magazine)
What is a ‘launch window’? (European Space Agency)
It’s time to start watching Mars (EarthSky)
The Phases of the Moon (Time and Date)
Holmann transfer orbit diagram (Planetary Society)
Basics of Space Flight (NASA)
Your Guide to Tianwen-1 (Planetary Society)
Mars 2020 Perseverance (NASA)
Twitter: PercyRover account
China moon lander (Planetary Society)
About Ground penetrating radar (GPR) (US Radar – commercial site, no sponsorship)
NASA Mars InSight (NASA)
Transcriptions provided by GMR Transcription Services
Fraser Cain: Astronomy Cast Episode 577. Mars in Opposition. 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. I’m Fraser Cain, publisher of Universe Today and with me, as always is Dr. Pamela Gay, a Senior Scientist for the Planetary Science Institute and the Director of Cosmo Quest. Pamela, welcome back from summer hiatus. I missed you.
Dr. Pamela Gay: Thank you. I missed you too. Although, I have to say it feels like we’re experiencing March 200 instead of September at this point.
Fraser Cain: Time has no meaning.
Dr. Pamela Gay: It doesn’t. It really has no meaning.
Fraser Cain: Yeah. Yeah, it’s a snake in a circle, eating its own tail, made of everything and nothing all at the same time. I don’t know whether I’m coming or going. The days just blur. And yet, time just takes forever. When do I get my vaccination? You know what I want to do. I was thinking about this, you know what I really want to do?
Dr. Pamela Gay: What?
Fraser Cain: I want to go places and see people. That’s what I really want to do.
Dr. Pamela Gay: Yeah, I – to have gone from having that amazing experience in January where we were together in Hawaii for the AAS meeting. And towards the end of that meeting, we were starting to talk about the news about this strange illness in China. And I remember the Thursday night talking with a couple of my friends at the conference about, “Okay, I just want to get home before the illness makes it to Hawaii.” And I had no idea that nine months later –
Fraser Cain: This would be our life. Still. Yeah. No, I had my suspicions. And now we do feel like we’re closing in now on the final stretch, that more and more vaccines are coming into the final stage of trials. And there’s going to be some kind of roll-out but I really hope that that herd immunity will start to get kicked in and we can start to see the end of this. Hopefully during this season, so we will –
Dr. Pamela Gay: And herd immunity from vaccines.
Fraser Cain: Yeah exactly.
Dr. Pamela Gay: Not –
Fraser Cain: Yeah not from everybody getting sick. So, we will, yeah.
Dr. Pamela Gay: We have to be specific.
Fraser Cain: I’m hoping we will see the end of it during this season and regular life will return.
Dr. Pamela Gay: This is season 14. Our show is a teenager and I feel that having a very cranky year is consistent with going through our teenageness as a broadcast.
Fraser Cain: Thank you for reminding me what season this is. All right, every two years or so Mars lines up nicely with the Earth. It takes only two minutes to communicate with the rovers. You can see the polar ice caps in a small telescope and it’s the best time to send your spacecraft to the Red Planet. And also, I guess Mars opposition, that’s when your horoscope, your Mars horoscope is really good? Is that how that works? I dunno.
Dr. Pamela Gay: I have no idea.
Fraser Cain: Maybe that’s Mars in retrograde. Or is that an unlucky time?
Dr. Pamela Gay: That can happen at the same time.
Fraser Cain: Mars in retrograde and in opposition? Yeah, I guess they can. That’s true. All right, so we’re going to talk about how Mars in opposition is a really, like the best time for Mars. That’s when Mars really takes over the night sky and shows us what it’s got. But what is Mars in opposition?
Dr. Pamela Gay: So, technically it is that moment in time when you have the Sun, the Earth, and Mars precisely lined up. So that at midnight on Earth, Mars is at its highest possible point in our terrestrial sky.
Fraser Cain: And if you were to look at it from space, what would they look – from above, if you were looking down on the solar system and you were looking at Earth, Mars, and the Sun. What would you see?
Dr. Pamela Gay: A line, they’re just nicely in a line. And there’s some years where because Mars’ orbit is a lot more elliptical than Earth’s orbit that we are noticeably closer. There’s some years that we’re noticeably farther apart. So, back in 2003, there’s a whole lot of hoopla because we were closer than we’d been in hundreds of years or would be for another hundred some odd years.
Fraser Cain: Fifty thousand, it was 50,000 years, was the closest it had been, 2003.
Dr. Pamela Gay: And, at these closest points we are more than 20 million miles closer than we are during opposition when Mars is at its farther points. So, there is a substantial difference but in the grand scheme of things Mars is still smaller than allows you to see it as a disc without really good binoculars or a telescope, so.
Fraser Cain: But just to give – I mean just to give people a sense of perspective, I mentioned this at the beginning of the show, it takes two light minutes to communicate with Mars, just over two light-minutes right now. Well, when Mars is in opposition and so you can – you send your beep boop commands to your rover and your rover goes beep boop and sends back its commands. And it’s just like you’re playing a video game with fairly reasonable times. But when Mars is –
Dr. Pamela Gay: That’s an old dial-up modem playing an internet game.
Fraser Cain: It gets worse, right? On average, the time to transmit to Mars is about 12 and a half minutes and at the very worst when Mars is on the opposite side of the sun, it’s more than 20 minutes. So, if you want to send some pieces of information to Mars you’ve got to wait 20 minutes for the message to get there and then 20 minutes to come back. So, the distances are really significant.
Dr. Pamela Gay: And what’s interesting is because it takes Mars 700 some odd days, Mars year is 687 days to be precise, to go all the way around the sound. What we’re looking at is every year the earth has to go all the way around the sun. And because Mars is chugging along we go all the way around the sun and now Mars is over there and we’re trying to catch up and we’re trying to catch up and we’re only able to catch up every two-plus years. And when we finally catch up, it’s this grand observing time but right before we finally catch up is the launch window to Mars. Which is a very important thing.
Fraser Cain: Yeah. Right so let’s talk about the observing and then we’ll talk about the launch window. So, if you’ve – just with the unaided eye, without a telescope, Mars is super obvious in the sky.
Dr. Pamela Gay: And it appears quite red and as we get closer and closer to it being in opposition and this year the opposition is going to be on October 13th. And as we get closer and closer to opposition it’s going to actually appear towards the end of this month, September, to be brighter –
Fraser Cain: Wow.
Dr. Pamela Gay: – than Jupiter. And at that opposition, it is going to not only be brighter than Jupiter, but it’s going to appear to be 22.6 arc seconds across. Which is still really tiny.
Fraser Cain: Too small to see with your eyeballs.
Dr. Pamela Gay: But this is starting to be the size of some of the craters we reasonably look at on the Moon. It’s 182nd the size of the Moon at this point. And the alignment in time is such that we have that Mars at opposition on October 6th and October 3rd when Mars is basically as bright as it’s going to get. Basically, as big as it’s going to get, a couple of days don’t make a huge difference. It’s going to be 1.1 degrees away from the full Moon. So, there’s going to be this fabulous moment where, in a completely reasonable camera shot, you’re going to be able to get the full Moon and Mars right together, and trying to get the exposure times correct to get both well isn’t going to be as hard as it usually is.
Fraser Cain: And then we’re going to get all those people saying how come I never noticed that bright red star beside the Moon before. When people don’t understand that the Moon moves, Mars moves. Mars is getting brighter and dimmer. That, that’s not a star. It is the Moon though, you got the Moon part right, but –
Dr. Pamela Gay: There’s a shocking number of people who don’t realize that the Moon isn’t in the sky every night.
Fraser Cain: Yeah, I know. And the Moon changes through its phases. Yet people, I guess just don’t look up. Normally when interesting things are happening and the full moon is out, the full moon rains on the parade with its light. But in this case, Mars will be bright enough that no problem. Full Moon, use your telescope, look at the Moon, look at Mars. They’ll both look great. And Saturn and Jupiter will also be up in the sky at the same time.
Dr. Pamela Gay: Yes. And we saw those worlds go through their opposition during the summer. So, this is really a great time to go out and observe planets. And given the observing conditions in most of the country, you can’t see many stars. It’s either cloudy –
Fraser Cain: Or moody.
Dr. Pamela Gay: – for fall. Or smokey because the west coast of North America’s on fire. But planets are going to be one of the few things capable of cutting through thin haze and thin smoke.
Fraser Cain: Yeah, the planets are so bright even in a city. If you’ve got any kind of telescope, now is your chance to see all of the best objects at their closest, brightest – like really, all the hits are going to be out in one night. Saturn, Jupiter, Mars at opposition, and the Moon. This is the time. So, let’s talk about the launch windows then and why it’s such a great time to send spacecraft to Mars.
Dr. Pamela Gay: Now, this really comes down to, we like fuel efficiency in our rockets. Fuel weighs a lot. And so, the easiest way to get to Mars is to use what’s called a Hohmann Transfer Orbit. And this is an orbit where it’s highly elliptical. And the shape of the orbit is such that the orbit’s closest point to the sun is at the Earth. And when you’re transferring to Mars, the furthest point from the Sun is at Mars. And you need to launch when the alignment of Earth, Mars is such that you get to Mars orbit the same time Mars gets to that point in its orbit. And you can do this for, ideally you want to be six weeks before opposition when the Earth is still lagging behind Mars waiting to catch up to Mars in the orbit.
And there’s a window, you change your velocity as needed, you change the shape of your orbit as needed. And that will get you to the right place, at the right time. So, right before opposition we always see this grand line-up of spacecraft trying to make the window. Trying to get themselves complete and launched and on their way to the world that is most likely to eat them instead of let them do science.
Fraser Cain: Right because if they don’t, how long do they have to wait?
Dr. Pamela Gay: They have to wait another two-plus years.
Fraser Cain: Right. So, if you miss your deadline, you’ve got to wait with your spacecraft, keep your team going for another two years.
Dr. Pamela Gay: Yeah, so we’re looking at the correct alignments occur roughly every 780 days. So, it’s a wait.
Fraser Cain: Yeah.
Dr. Pamela Gay: It’s a wait.
Fraser Cain: So, this batch, the 2020 Mars opposition batch, who went to the Red Planet?
Dr. Pamela Gay: So, we saw Hope launching from an Arab nation. This was the first time that that had occurred. We had Tianwen-1. And of course the Mars 2020 rover with its helicopter. And I’ve got to say, no mission has previously filled my inbox with the verve of the Mars 2020 system.
Fraser Cain: You’ve gotten used to spelling its pet name, Perseverance?
Dr. Pamela Gay: I’m in the camp of calling it Percy.
Fraser Cain: Percy. Oh.
Dr. Pamela Gay: Percy.
Fraser Cain: So, it’s Per – sever – ance. That’s how I do it. Per – sever – ance. But sure Percy, yeah fine, call it Percy. That’s, why not?
Dr. Pamela Gay: And if you’re not following the Mars Percy Twitter account, it is delightful and worthy –
Fraser Cain: Now is that the official one?
Dr. Pamela Gay: No.
Fraser Cain: Or one of those hilarious, like oh okay, like the sarcastic rover Twitter feed?
Dr. Pamela Gay: Yes. Yeah, it is truly delightful following the journey and they’re keeping up with the science fairly nicely, so.
Fraser Cain: So, what do we know about these missions? I mean, it’s great, right? Was it – is it the UAE? And –
Dr. Pamela Gay: Yes, the United Arab Emirates.
Fraser Cain: The China, the Tianwen-1, and the Perseverance from NASA. Three different – and there could have been a fourth, but somebody didn’t make their deadline.
Dr. Pamela Gay: Yeah that would be the Rosalind Franklin rover from the European Space Agency. They were working to land a heavy rover for the first time and getting the parachutes right is really hard. And they did everything they could to try and hit their deadline. But they decided they would be better off and their spacecraft would have a better chance of survival, if they just held back one more cycle and well, tried again in 2023.
Fraser Cain: We could see that one coming. They were having a lot of trouble with that parachute system. It’s a very similar parachute system to the one that Curiosity and Perseverance were using and they were pretty sure that they had it all figured out. And then they were just having more and more trouble just making the whole system work. And they do these really great high atmospheric tests where they will take the spacecraft up on a sub-orbital rocket. They’ll release it at the right, at sort of –
Dr. Pamela Gay: A model of the spacecraft.
Fraser Cain: Yes, yes. Sorry. Yes, a model. The parachute and a model of the spacecraft and then they will – it will try to enter the atmosphere at the same density that Mars atmosphere is when it will be doing entry. And then they have to make sure that the parachute will deploy all properly. And it couldn’t pull it together. And NASA at the last minute actually assisted them, sent some engineers to help them try to get it all together. Let them use, I think they let them use a test facility to try and speed up some of the iterations. And in the end, they just couldn’t get it to come together as quickly as they needed to, for safety’s sake. And better to take a two-year break.
Dr. Pamela Gay: And it’s one of these things that it’s a really hard call to make. I know that I remained heart-pounding about including that helicopter which was very much a last-minute decision in terms of the timeline to build a spacecraft. But the way that I’m trying to look at it is, Percy is built on the same frame as Curiosity. The same basic infrastructure with updated instrumentation. So, they weren’t designing from the ground up. They were designing from the frame up. And so that gave them a little bit of a buffer zone to add in a helicopter at the last moment.
Fraser Cain: So, let’s talk about the purpose. Let’s run through these missions then. So, what is the purpose of – and I’m going to call it Perseverance? What is the purpose of this mission?
Dr. Pamela Gay: It’s a sample collector. And it is out there literally starting to do essentially fossil hunting on Mars. They’re collecting samples. They’re starting to look for organic materials. And with Curiosity, they collect samples and then they poop them out because they only have so much space on board. And once they’ve completely processed a sample it’s out the door. With Perseverance, on the other hand, they are actually filing up canisters of samples in hopes that someday a second spacecraft will come. And they’re going to be able to take their canister and hand it off so that that canister can be brought back to earth. Now, this is a high-risk possibility.
Spacecraft work with what are called landing ellipses where we know fairly well where our spacecraft should end up on the surface of a world. But the landing ellipses are fairly large and rovers don’t move very fast. So, it becomes an issue of will we eventually be able to safely land a return vehicle close enough to Perseverance to collect the sample? And then bring the sample safely back to Earth. So, there’s the landing close enough. There’s the doing the handoff and the returning all the way back to earth are all high-risk but that is one of the ultimate goals. The helicopter is actually just to test a concept. It doesn’t have a lot of science planned for it. They basically want to see, does this concept work?
And it’s not a quadcopter people. It’s an actual bona fide helicopter with –
Fraser Cain: But it’s got two rotors, right?
Dr. Pamela Gay: – central. Yeah. Central rotor, balancing rotor.
Fraser Cain: Right. And it’s actually pretty big. It’s not a tiny little quad car. I think it’s, I feel like it’s several feet across. It is a large vehicle.
Dr. Pamela Gay: You have to have a really big propellor when the atmosphere is that thin. So, the body, the basically propellor-to-mass ratio is very different from what we have here on Earth, where we’re used to propellors that are roughly the same length as our helicopters. Here the propellor is substantially bigger than the body of the helicopter.
Fraser Cain: When does it – when will it get there?
Dr. Pamela Gay: With these missions, we’re generally looking at about a six-month travel time. In this case, we’re looking at Mars Perseverance will get there mid-February, February 18th. In fact, we’re going to have this whole flock of them all landing roughly the same time.
Fraser Cain: Or orbiting. Yeah or the UAE mission. Yeah, yeah.
Dr. Pamela Gay: Or orbiting, this is true. They aren’t all landing this time.
Fraser Cain: So, and I mean the thing I really love about Perseverance. I mean, you talked about the samples that it’s going to be retrieving. I mean NASA has been building this case for the search for life on Mars. They’ve been following the water and with spirit and opportunity, was there ever water on Mars? The answer is yes. Curiosity, was there water on Mars for long periods of time? The answer is yes. Perseverance is were there conditions that were good for life? The kinds of chemicals that you would want to have for life. Maybe even the by-products of life. This is the first mission that possibly will detect ancient life. The residue of ancient life on Mars.
And it will be the follow-up mission, the sample return that you talked about, that’s going to be the one that actually brings these samples home. And then the scientists get to crack them open and take a look at them. All right so we know what Perseverance is going to do and the helicopter. The helicopter is as you say, it’s just really it’s an experiment right? This isn’t – they’re not going to depend on a ton of science. What will the helicopter do?
Dr. Pamela Gay: It will flit about. There will be a handful of attempts to flit.
Fraser Cain: Flit.
Dr. Pamela Gay: It’s aiming to go tens to hundreds of meters. But this isn’t going to be a way that they greatly increase the distance that the rover is able to travel. This isn’t a way that they are going to scout ahead, although that would be cool and it wouldn’t surprise me if they decided to use it to scout ahead. As always with these tech checks, they don’t make a lot of promises ahead of time. But then they often figure out oh this thing actually does work far better than we thought it would.
Fraser Cain: Right, right. So, the expectation is that they are going to fly it a couple of times, they are going to crash it because that’s what happens when you have a toy helicopter. Right? You just crash it. It’s inevitable.
Dr. Pamela Gay: Yes.
Fraser Cain: Within –
Dr. Pamela Gay: I don’t know about you, but I’ve done that many times.
Fraser Cain: Many times, yeah are you kidding? That’s the first thing you do with a helicopter I mean is, you crash it. A drone.
Dr. Pamela Gay: Or get it in your hair, that’s another issue.
Fraser Cain: Or a tree, or whatever. So, there’s no trees on Mars. There’s no hair on Mars, so I like their chances of at least flying a couple of times. But it’s got a little solar panel on it. It’s got its own little battery, so once it takes off and gets to work, it’ll just as you say, be flitting around. Ideally staying close to Perseverance, but not necessarily.
Dr. Pamela Gay: There’s comms limitations but that’s about it. It’s really kind of cute and cool.
Fraser Cain: But I mean for how cute and cool as this is, a pack of lightweight, flying helicopters like this, for future missions or for even human explorers to fly around and provide some kind of external scouting, will be incredibly valuable. Because right now when you think about the rovers, they’re just on the ground, they’re looking around. They see what they can see from their perspective. They can’t see that rock that’s just over that hill. All they can see is what they can just see and what the satellite pictures will show them, so that’s great. All right, let’s talk about the UAE mission, Hope.
Dr. Pamela Gay: So, Hope is going to follow in the footsteps of the trace mission that NASA has. And it’s going to be working on studying the atmosphere of Mars, looking at atmospheric loss, and helping us understand what is the rate at which Mars loses an atmosphere. So that we can better model what may once have been and better explain why you can’t terraform Mars. People you cannot terraform Mars. Stop asking.
Fraser Cain: Oh, I just heard 1,000 hearts break. Yeah, what I also love about this mission is they launched on a Japanese rocket.
Dr. Pamela Gay: Yes. And out of nowhere.
Fraser Cain: Well, I mean, Japan.
Dr. Pamela Gay: So, I mean in terms of with Mars Perseverance, the amount of grand ceremony associated with this launch was truly a thing to behold. It was a spectator sport. With Hope, we knew when the launch window was. We knew there’d been some weather issues and their window opened and they launched. No fanfare, just got it done. I think we had a few hours’ notice that the countdown clock was go. So, the simplicity of it was deeply pleasing. It’s let’s just wait and see Mars eats things, don’t do the ceremony and the this and the that, until it works.
Fraser Cain: Yeah. Then as I’ve mentioned in the past, Mars eats spacecraft for breakfast. And then the last one is the Tianwen-1 which is the Chinese orbiter and rover. And this is going to be very similar to the Chang’e 4 mission that’s currently…
Dr. Pamela Gay: Yes.
Fraser Cain: Yeah.
Dr. Pamela Gay: It’s following in the footsteps of their exploration of the Moon where we’ve seen them putting in orbit communication satellites that are also imagers, which is a tradition we’ve long had. And then landing these rovers that use the orbiters to relay their communications back to Earth so that they don’t need to consume as much power with their transmitters. They’ve mastered that, being the first nation to explore the far side of the Moon. And now they’re taking their lessons learned and seeing how their luck fairs at the Red Planet.
Fraser Cain: Now, they’ve got a bunch of regular old rovery stuff that’s going on. It does look similar to the one that’s going to the Moon, but the piece of technology that’s on board, that’s very exciting, is the ground-penetrating radar.
Dr. Pamela Gay: And with ground-penetrating radar, we can start to answer questions about, is there frozen reservoirs of water underneath the surface? What is the density? We can use ground-penetrating radar here on Earth to figure out what are the sub-surface conditions of the tundra. Where is it soil? Where is it ice? It’s one of the ways we find old buildings buried in farmer’s fields. We’re not going to find that on Mars. But it is going to help us answer questions that InSight has really confused us with. Because InSight was supposed to have this mole that buried itself under the ground and it basically discovered that Mars ground just falls apart when you hammer on it.
With the ground-penetrating radar, we’re going to start to be able to see what is the density, the structure of the soil as a function of depth. And start to understand is this just layers of built-up sand mixed with ice? Is there bedrock? Where is it? Is there ice? Yeah, it’s super exciting.
Fraser Cain: Yeah. Yeah, the thing that we saw – I don’t know if people remember there was this study that came out from the Chinese Space Agency about six months ago maybe? Where they were talking about that the rover or the lander on the Moon was able to see down into the regolith and see how deep the regolith goes and how it turns into just larger and larger jumbles of rock until it turns into the bedrock. And it’s quite deep, so imagine being able to drive around and see how thick is the – how deep is the sand? Are there deposits of water? Are there even other interesting things – salty, briny solutions underneath? Do they change with the seasons?
So, with this mission, they are bringing a pretty exciting piece of technology to the surface of Mars. So, it’s a great addition to what’s happening on Mars.
Dr. Pamela Gay: And I know this is probably never going to happen but it would be amazing if they just happened to find gorgeous lava tubes that are beautifully empty, right next to all sorts of underground cool deposits that we can eventually imagine going and exploring. And the likelihood of something like that happening is zero but that doesn’t make it actually zero.
Fraser Cain: But to see one that’s pristine, not with the whole – not with the roof cracked open. Yeah, yeah that would be amazing.
Dr. Pamela Gay: Right. Exactly.
Fraser Cain: Good, so I think everyone I hope you’ve got your preview for the Mars opposition. With your eyeballs, you’re going to see Mars brighter and brighter and brighter. And then you’re going to remind all your friends that, that bright star beside the Moon isn’t a star. It’s the planet Mars, in opposition. And then you will watch over the next six months after that, the coverage. And we get to go through the whole seven minutes of terror again as Perseverance follows the fiery trail that Curiosity left entering the atmosphere of Mars.
Dr. Pamela Gay: So, the dates to remember are October 3rd, we’re going to have the Moon and Mars 1.1 degrees apart. And on October 6th, if you want to drag people out and have a reason to look up, well that’s when Mars is at opposition and will be straight overhead at midnight, latitude dependent
Fraser Cain: And then February 18th will be the landing for Perseverance. I’m sure we’ll bring it to you live. We did the last one, I’m sure we’ll do this one as well. Yeah. Right on.
Dr. Pamela Gay: Excellent. And we will bring it to you as we can.
Fraser Cain: Well, Pamela, I’m looking forward to watching Mars opposition 2020 with you and the rest of our fans over the next six months. So, everybody enjoy and we’ll see you next week. Do you have some names for us?
Dr. Pamela Gay: I do. Thank you for the reminder. And thank you all for staying with us through the summer. You are the reason we’re able to do everything that we do. So, to our Patreon’s at patreon.com/astronomycast. Thank you to Harold Brandonhogin. Thank you to Daniel Loosli. Thank you to Omar delRiveria. Thank you to Marco Irasi. Thank you to Brian Kelby. Thank you to William Lauer. Thank you to John. Thank you to Dustin Araf. Thank you to Mark Steven Rasnick. Thank you to Michelle Cullen. Thank you to Jeremy Kerwin. Thank you to Bruno Letz. Thank you to Jay Alex Alexanderson. Thank you to Tim Garrish. Thank you to Ander Hamsworth. Thank you to Arzo Latshaul. Thank you to Mark Grundy. And thank you to Iran Sagif. Thank you all. You keep this show going.
Fraser Cain: And we’ll see you all next week.
Dr. Pamela Gay: Bye, bye everyone.
Fraser Cain: Bye.
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