MESSENGER Webcast: MESSENGER Science and Technology
Question and Answer with Dr. Ralph McNutt

Cheryle Mako: Today, we are fortunate to have, live in our studios, Dr. Ralph McNutt, MESSENGER's Project Scientist. Thank you for joining us today, Dr. McNutt, we're so glad to have you with us.

Dr. Ralph McNutt: Well thanks, Cheryle, I'm glad to be here.

Mako: I should note that Dr. McNutt is the chief scientist in the Space Department at Johns Hopkins University Applied Physics Laboratory. And he's also part of the Cassini team and was a science team member for two Voyager investigations.

This is an incredible mission. We're eager to know more about the MESSENGER spacecraft and the science and technology it took to get it to the launch pad. Dr. McNutt, tell us what your role is in the MESSENGER mission? Your biography says you are the principle investigator's right hand man. Sounds like a challenging but exciting role!

Dr. McNutt: Well, it's certainly exciting. Basically, I work as the interface between principal investigator Dr. Sean Solomon and the rest of the project to make sure that all the science flows into what's being done on the engineering side. So, I end up talking to the mission systems engineer, the lead engineers, the program managers, the payload manager, talk back to Sean and make sure everything comes together and also make sure that everyone's talking who needs to be.

Mako: We've received loads of questions about the MESSENGER mission from many parts of the world from our NASA Direct! question board. Dr. McNutt is here to help us answer them. Our first question comes from Wade from Adelaide. He writes:

Do you expect any major surprises or unknowns to be unearthed during the investigation of Mercury by MESSENGER?

Dr. McNutt: Well of course, one of the things that always happens with an exploratory mission is that you're looking for unknowns as well as the things that you're planning to look for. The Mariner 10 mission, which previously went to Mercury, only saw about 45 percent of the surface. And so, one of the big surprises, of course, is going to be seeing what the rest of the planet actually looks like.

The other thing is that since the Mariner 10 mission, of course, is we know that there are these polar deposits and we're going to be taking a close-up look at those and hopefully get some ideas about the composition from MESSENGER.

So, there could be some real surprises there, and then of course there are all the things that we may find about that we just don't even know how to pose the questions yet.

Mako: Excellent. The next question is from Junichi Maki (and please forgive any mispronunciations) from Niihama-city. What is the most significant difference between the previous Mariner 10 mission and the upcoming sophisticated MESSENGER?

Dr. McNutt: Well of course, operationally we're going to be going into orbit; the Mariner 10 just had the flybys. But on top of that, we've also gotten much more sophisticated instrumentation, which has been allowed because of changes in technology. In particular, we have various spectrometers which will allow us to do elemental and mineral composition. So we're going to be able to find out what the crust of Mercury is really made out of and what kind of rocks are there. And this is going to be a real advance for Mercury, something that Mariner 10 just couldn't tell us.

Mako: Excellent. The next one is from Art from Los Altos . What imaging and spectrographic instruments will be aboard the spacecraft, and what data do you hope to gather, and what are you expecting to learn from this information?

Dr. McNutt: Well, this sort of feeds into the previous question. We've got several spectrometers that are on board. With the wide-angle camera that we're carrying, we have 12 filter-reel positions, and some of those are going to be looking at various absorption bands and minerals to try to figure out exactly what those minerals are and where they are. We have an infrared spectrometer on board which will also be looking at mineralogy. We have an ultraviolet spectrometer that will help with that and also be looking at atmospheric emissions to try to connect up with what we see in the very tenuous atmosphere and what's actually on the surface.

And then perhaps most interesting, we have a suite of instruments. We have an X-ray spectrometer, a gamma ray spectrometer and a neutron spectrometer. And what we're going to be doing with those is we'll actually be able to look at the elements that are in the top part of Mercury's crust, and really figure out what elements are there and how they came together in the early part of the Solar System to form the planet.

Mako: Wow. Next is from Pawan from Sharjah.Will MESSENGER be able to find out the contents in Mercury's core? What type of materials and terrain are the scientists expecting to be found on the surface of Mercury?

Dr. McNutt: Well, you know, it's interesting. We know, of course, from Mariner 10, the mass and the volume of Mercury. If you look at those numbers, the planet's got to be about two-thirds iron. Iron is very common in the Solar System. It's in the solar wind, it's in the Earth, it's in the other planets. But Mercury weighs too much for its size.

One of the questions is whether the core of Mercury is liquid and to what extent that it is. We think that there is at least some liquidity there because of the magnetic field that was seen with Mariner 10. That suggests that there's some sulfur added in to perhaps keep part of the core liquid, and by finding out how large the core actually is, we'll be able to put some limits on what the sulfur content is.

As far as the terrain is concerned, there are three major terrains that you see at Mercury. We saw them on Mariner 10. There's these very heavily cratered highlands, which is from the original period of bombardment from the formation of the Solar System (kind of as the planets were coming together). There are the so-called inter-crater plains, which are perhaps somewhat younger in terms of the terrain, and then finally there are these smooth plains on Mercury, which might have some relation to the same processes which formed the maria on the Moon and may be related to lava flow, sort of at the end of the bombardment era.

So again, looking at the composition and by trying to get an idea of how much volume the liquid core has, that Mercury will be able to put all these pieces together and hopefully learn a little about the planet.

Mako: Our next question is from Matthew from Big Lake . Why it is hot on one side of Mercury and cold on the other side of the planet?

Dr. McNutt: Well, it happens, it's because of the Sun, of course, but more than just that. It's because it takes Mercury about 88 days to go around the Sun once, that's one Mercury year. But Mercury spins only about on its axis once every 59 days, so by not spinning very fast, it can actually heat up on the sunlit side and cool down a lot on the cold side. As a matter of fact, the temperature extremes are such that it actually gets up to about 130 degrees Centigrade, and that's getting up around 800 degrees Fahrenheit. That's getting pretty warm, but it's the Sun that's doing it.

Mako: Next up is Robert from Tucson Ariz.There is a trace of an atmosphere on Mercury. What would that be composed of?

Dr. McNutt: Well, we know it's composed of several things. The scientists like to call it an exosphere, because there's not too much there. Actually, the Moon has an exosphere too, which a lot of people don't realize. There's not a lot there. We know from Mariner 10 there's oxygen, helium and hydrogen, and there's actually been some really groundbreaking telescopic work from the ground here on Earth. We know that there are sodium atoms that come off of Mercury and we know that there are calcium atoms that come off of Mercury, and those seem to be related to what the solar wind is doing at any one time.

So there's this real interplay with interplanetary conditions and what's going on at the surface and how does this exosphere come into all that. And so, by being in orbit for a full Earth year around Mercury, we're hoping to try to disentangle some of these things and also look for atmospheric species like the noble gas argon, which exists, of course, in the Earth's atmosphere. One would think that it would be at Mercury, but it wasn't seen with Mariner 10, so we're going to be looking for it.

Mako: Again from Robert from Tucson, Arizona. What is the Caloris Basin and why is this area of Mercury unique in our solar system? Would this be a primary point of interest to MESSENGER?

Dr. McNutt: Well, it will be. Caloris is actually a very interesting object. The Caloris Basin is like Mare Orientale on the Moon. It's a relatively young impact basin, and young here means that it's only about 3.9 billion years old, rather than 4.5 billion years old. But we only saw part of the basin with Mariner 10, we didn't actually see the center of it. It's about 1300 kilometers, about 800 miles across. This is about half the radius of the planet.

What we think happened is that there was a big chunk of something that ran into Mercury, probably late in the formation stages of the planet, which formed the basin. And what's very intriguing is that from the Mariner 10 pictures, if you look at the exact opposite side from where the center of Caloris should be, you see all this really rough and jagged terrain, so it's almost like a shock wave went shooting through the entire planet, maybe blew some of the material off on the other side of the impact. So Caloris is certainly very much a target of interest because again, it's looking at similarities and differences of some of these things on the Moon and looking at sort of this endgame of when the planets were formed.

Mako: Now from Renato from South Paulo.How close will be the Mercury flybys? What level of resolution can we expect of the pictures taken during these flybys?

Dr. McNutt: Well, during the Mercury flybys -- and we need the flybys in order to help slow down the spacecraft, of course, to finally get into orbit -- we're going to be getting down to about 200 kilometers. That's about 120 miles of the surface, although at the closest approach we're actually going to be on the dark side. So we're going to be taking the pictures while we're somewhat further out, but we'll get down to resolutions of something on the order of maybe about 60 meters or so, so that's about 180 feet.

So that's some of the smallest things we'll be able to see, and that’s in black in white. In color, we'll be able to do maybe on the order of 400 to 800 meters, and we'll actually be able to get the entire hemisphere that we're looking at during the flybys. We get one hemisphere on two of the flybys and then the other hemisphere on one of the other flybys. So we'll actually have a pretty good map of Mercury even before we go into orbit and that'll help us to be planning the orbital campaign.

Mako: Great. From Bob from Belvidere: Will MESSENGER be able to take pictures in color?

Dr. McNutt: That's right. We will be able to. Again, it's with this wide-angle imager. And basically, what you do is you take pictures in black and white through various filters and then in the processing on the ground, you put those black and white pictures back together and you can extract color from them. So we will be providing color pictures of Mercury.

Mako: Can't wait. Juan from Spain: What researching will you do during the Venus flybys?

Dr. McNutt: Well of course, Venus isn't the primary part of the mission, but on the other hand, we do have to go by Venus in order to help slow down, and so we will be exercising the instruments. In a way, the Venus flybys act as a good dress rehearsal for the Mercury flybys. So we'll be turning on, for example, the particle instruments and the magnetic instruments; we know that there's an interaction at Venus with the solo wind and we'll look at that.

We'll be looking at the cloud decks with the cameras. They're pretty bland in most of the wavelengths we're looking at, but we'll actually be using those to help with some of the calibration. So we will be exercising the payload during the Venus flybys.

Mako: Great. From Ashutosh from Mumbai: During this long journey of 7 years, are you going to do any science to study the space between Sun and Earth?

Dr. McNutt: Oh, yes we will. It's going to be limited by the amount of downlink that we have, but the plan is certainly to have some of the particle instruments turned on, as well as the magnetometer, and a lot of this has to do with really calibrating the instruments, so we need the data anyway before we get to Mercury.

It turns out that the last time that a spacecraft actually got so close to the Sun to make these kinds of interplanetary missions was the joint German-U.S. HELIOS mission, which were two spacecraft back in the 1970s.

So, it's going to be interesting to be able to actually make these measurements in the inner part of the Solar System. We've now got a lot of other sophisticated instruments in Earth orbit and other parts of the Solar System to make the comparisons and figure out better what the global structure of interplanetary space and the magnetic field actually looks like.

Mako: Okay, our last question that we have is from Hardik from Ahmedabad. What is the reason to send a probe to Mercury, where life is not possible? Don't you think that it will be good to spend more on Mars rather than spending on Mercury or other such planets?

Dr. McNutt: Actually, this is a very good philosophical question to ask and I've been thinking about the answer to this one. And you know, really, if you think about what we've been able to do with planetary exploration, when you're actually getting close to a planet, you're able to actually make the detailed measurements that you need to really let you know what's going on there. And in the Solar System we found that different planets are so diverse, even among the terrestrial planets -- Mercury, Venus, Earth and Mars -- that you need to have a close-up look at all of them to kind of put the pieces together.

If you think about it, it's a little bit like the tale of the blind men and the elephant, where each of the blind men is feeling a different part of the elephant and describes the elephant as something different. But without being able to have the whole picture, you can't really see the whole thing. So even if it turns out that we find life on Mars eventually, it may be that if we don't have the other pieces of the picture from places like Mercury, about how the terrestrial planets formed and evolved, then we might end up drawing the wrong conclusions about how it got there.

So, there's an importance to having a balanced strategy and you do have limited resources, but this whole idea of kind of going out and getting this sort of veil of the unknown pushed back to where you can see what's going on globally in the Solar System is one of the things that we're about in the scientific business.

Mako: Great. That concludes our question and answer session today. Thank you, Dr. McNutt, for being with us today on NASA Direct!

Dr. McNutt: Well, thank you for having me, Cheryle. It's been a pleasure.