This blog entry from John Grotzinger, the project scientist for NASA's Curiosity Mars rover, was originally prepared for use by the Planetary Society and explains the importance of some of the rover's findings.
It was fun for me to catch up with Emily Lakdawalla of the Planetary Society at the American Geophysical Union meeting, and to discuss our new Curiosity mission results. They focus on the discovery of an ancient habitable environment; we are now transitioning to the focused search for organic carbon. What's great about Emily's blog is that with her strong science background she is able to take complex mission results and translate these into something that can reach a broader and more diverse audience. I'll try to do the same here.
Since we first reported our results on March 12, 2013, from drilling in Yellowknife Bay it has been my experience that lots of people ask questions about how the Curiosity mission, and future missions, will forge ahead to begin with looking for evidence of past life on Mars. There is nothing simple or straightforward about looking for life, so I was pleased to have the chance to address some of the questions and challenges that we find ourselves most frequently discussing with friends and colleagues. The Planetary Society's blog is an ideal place to take the time to delve into this.
I also need to state at the outset that what you'll read below is my opinion, as Curiosity science team member and Earth geobiologist, and not necessarily as its Project Scientist. And I have only worked on Mars science for a decade. However, I can say that many other members of the Curiosity team share this opinion, generated from their own experiences similar to mine, and it was easy for us to adopt these ideas to apply to our future mission. To a large extent, this opinion is shaped by our experience of having spent decades trying to explore the early record of life on Earth. As veterans of the Mars Exploration Rover and Curiosity missions, we have learned that while Mars has significant differences from Earth, it also has some surprising similarities that could be important in the search for evidence of ancient Martian life - a "paleobiosphere," if you will. The bottom line is that even for Earth, a planet that teems with life, the search for ancient life is always difficult and often frustrating. It takes a while to succeed. I'll try to explain why later on.
So here goes....
The Dec. 9, 2013, publication of the Curiosity team's six papers in Science provides the basis for understanding a potentially habitable environment on ancient Mars. The search for habitable environments motivated building the rover, and to that end the Curiosity mission has accomplished its principal objective. This naturally leads to the questions of what's next, and how we go about exploring for organic carbon?
To better understand where we're coming from, it helps to break down these questions and analyze them separately. With future advocacy of missions to Mars so uncertain, and with difficult-to-grasp mission objectives located between "the search for water" (everyone got that) and "the search for life" (everyone wants NASA to get on with it), the "search for habitability" and the "search for carbon" are important intermediate steps. By focusing on them scientists can identify specific materials to study with more sophisticated future missions and instruments, or to select for sample return, or to be the target of life detection experiments.
Note: You can get access to all six of these Science papers here or here. The latter site also has the papers we published back in September. Science has a policy that allows us to post a "referrer link" to our home websites. This redirects the query to AAAS, where the paper can be downloaded without cost.
Let's start with "habitability." We reported the discovery of an ancient lake, and one that formed clay minerals. The presence of clays represents more benign environmental conditions than the acid sulfates found by Spirit and Opportunity. However, clays are not the only thing needed to demonstrate habitability. The bar is high: In brief, a mission needs to demonstrate the presence of water, key elements regarded as the building blocks of life (including carbon), and a source of energy. And you need to find them all together, and at the same instant in geologic time. In turn, each one of these must be characterized further to qualify an environment as having been habitable. Finally, it's never black and white; understanding habitability is part of a broad continuum of environmental assessment, which is why orbiters and earlier rovers and landers are important assets in this process as well.
It is also important to define what group of organisms is being imagined to have inhabited the environments - their requirements will vary. Single-celled microorganisms are a great place to start based on our understanding of the early evolution of life on Earth, which was dominated by microbes for at least the first two billion years of the planet's history. More specifically, the Curiosity team has been focusing on the conditions of habitability relevant to "chemolithotrophs," a group of microbes that feeds on chemical energy available in rocks.
The water of a habitable environment should be relatively fresh, or at least not contain so much salt that the relative abundance of water is so low (what chemists call "water activity") that the osmotic pressure on cells would cause them to collapse. My favorite analog here is honey. Yes, it's an aqueous environment but no, it's not habitable: The sugar content is so high that microbes can't live in it. This is why honey doesn't spoil when not refrigerated. Salt serves the same role as sugar; too much salt inhibits life. Acidity is also important, although microbes have been shown to tolerate an extraordinary range of pH, including the very lowest values encountered in natural environments on Earth. However, more moderate pH favors a greater diversity of microorganisms, and thus more options to explore for emerging life forms. Finally, the water needs to last a long time on the surface; the longer, the better. A flow of water emerging on the surface of Mars from an underground source and boiling off in the presence of Mars' modern low atmospheric pressure is not a good scenario for life. A stable source, such as a very ancient lake, with associated streams, and water flowing through the ground beneath it, is much better. We envision for the lake/stream/groundwater system that Curiosity discovered at Yellowknife Bay that the water could have existed for millions of years potentially. But even shorter periods are viable - the qualitative point here is that the rocks at Yellowknife Bay record more than a one-time event.
Key building blocks of life.
A conventional list of key elements for life will include "CHNOPS" - carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur. Previous orbiter and landed missions have provided ample evidence for H, O, and S via observations of sulfate and clay minerals, and P was measured by earlier rovers and landers. Curiosity has done the same. The tricky stuff is N and C and, along with P, they must all be "bioavailable," which means to say they cannot be bound tightly within mineral structures that water and microbial chemical processes could not unlock. Ideally, we are looking for concentrated nitrogen- and phosphorous-bearing sedimentary rocks that would prove these elements were actually dissolved in the past water at some point, and therefore could have been available to enable microorganism metabolism. But in the interim Curiosity has been able to measure N as a volatile compound via pyrolysis (heating up rock powder in the SAM instrument), and P is observed in APXS data. We feel confident that N was available in the ancient environment, however we must infer that P was as well. Two of the Science papers, Grotzinger et al. and Ming et al., discuss this further.
Carbon is the elephant in the room. We'll discuss organic carbon further below, but here it's important to make one very important point: Organic carbon in rocks is not a hard-line requirement for habitability, since chemoautotrophs can make the organics they need to build cellular structures from metabolizing carbon dioxide (CO2). These organisms take up inorganic carbon as CO2 dissolved in water to build cellular structures. Organic carbon could serve as fuel if it was first oxidized to CO2, or could be used directly for biomass, or could be part of waste products. As applied to Mars it is therefore attractive to appeal directly to CO2, presumed to have been abundant in its early atmosphere. Curiosity does indeed see substantial carbon generated from the ancient lake deposits we drilled. The CO2 that was measured is consistent with some small amount of mineral carbon present in those lake mudstones. These minerals would represent CO2 in the ancient aqueous environment. Furthermore, it is possible that Martian organic sources have been mixed with inorganic sources of carbon in the mudstone; however, any organic contributions from the mudstone would be mixed with Earth-derived sources during analysis (see Ming et al. paper).
All organisms also require fuel to live and reproduce. Here it is essential to know which kind of microorganism we're talking about, since there are myriad ways for them to harvest energy from the environment. Chemolithotrophs derive energy from chemical reactions, for example by oxidizing reduced chemical species like hydrogen sulfide or ferrous iron. That's why Curiosity's discovery of pyrite, pyrrhotite, and magnetite are so important (see Vaniman et al. and Ming et al. papers). They are all more chemically reduced than their counterparts discovered during earlier missions to Mars (for example, sulfate and hematite). Chemolithotrophic microbes, if they had been present on Mars at the time of this ancient environment, would have been able to tap the energy in these reduced chemicals (such as hydrogen sulfide, or reduced iron) to fuel their metabolism. If you are interested in more detail regarding these kinds of microbial processes I can strongly recommend Nealson and Conrad (2000) for a very readable summary of the subject.
The next section describes where I think we're headed in the future. We'll continue to explore for aqueous, habitable environments at Mt. Sharp, and along the way to Mt. Sharp. And if we discover any, they will serve as the starting point for seeing if any organic carbon is preserved and, if so, how it became preserved.
Now there's a ten-dollar word. Taphonomy is the term paleontologists use to describe how organisms become fossilized. It deals with the processes of preservation. Investigations of organic compounds fit neatly in that category. We do not have to presume that organic compounds are of biologic origin. In fact, in studies of the Earth's early record of life, we must also presume that any organic materials we find may be of inorganic origin - they may have nothing to do with biology. Scientific research will aim to demonstrate as conclusively as possible that the materials of interest were biogenic in origin. For Earth rocks that are billions of years old, it's rare to find a truly compelling claim of ancient biogenic carbon. Here's why.
On a planet that teems with life, one would presume these discoveries would be ordinary. But they aren't, and that's why fossils of almost any type, including organic compounds (so-called "chemofossils"), are so cool - it's because they are rare. That's also why taphonomy emerged as an important field of study. We need to understand how biologic materials become recorded in Earth's rock record. It's important in understanding modes of organism decomposition, to interpret ancient environmental conditions, and in reconstructing ancient ecosystems. But there also is one other reason that is particularly relevant for early Earth, and even more so for Mars: If you want to find something significant, you have to know where to look.
To explore for organics on Mars, three things have to go right. First, you need to have an enrichment of organics in the primary environment where organic molecules accumulate, which is large enough so that your instrument could detect them. Second, the organics have to survive the degrading effects associated with the conversion of sediment to rock. Third, they must survive further degradation caused by exposure of rock to cosmic radiation at Mars' surface. Even if organics were once present in Martian sediment, conversion to rock and exposure to cosmic radiation may degrade the organics to the point where they can't be detected.
Organics degrade in two main ways. The first is that during the conversion of sediment to rock, organics may be chemically altered. This generally happens when layers of sediment are deposited one on top of the other, burying earlier-deposited layers. As this happens, the buried sediment is exposed to fluids that drive lithification - the process that converts sediment to rock. Sediments get turned into rocks when water circulates through their pores, precipitating minerals along the linings of the pores. After a while the sediment will no longer feel squishy and it becomes rigid - lithified.
During the process of lithification, a large amount of water may circulate through the rock. It can amount to hundreds, if not thousands, of times the volume of the pore space within the rock. With so much water passing through, often carrying other chemicals with it, any organics that come into contact with the water may be broken down. Chemically, this occurs because organics are reduced substances and many chemicals dissolved in water are oxidizing. Those two chemical states don't sit well together, and this tends to drive chemical reactions. Simply put, organics could be broken down to the point where the originally organic carbon is converted into inorganic carbon dioxide, a gas that can easily escape the lithifying sediment. Water on Mars may be a good thing for habitability but it can, paradoxically, negatively affect the preservation of organics.
Now, if any organics manage to escape this first step in degradation, then they are still subject to further degradation when the rock is exhumed and exposed to the surface of Mars. There it will be bombarded by cosmic radiation. I won't go into the details here, but that is also bad news for organics because the radiation tends to break apart organic molecules through a process called ionization. The upper few meters of a rock unit is the most susceptible; below that the radiation effect rapidly dies away. Given enough time the organics could be significantly degraded.
The Hassler et al. paper just published in Science reports that the surface radiation dose measured by Curiosity could, in 650 million years, reduce the concentration of small organic molecules, such as amino acids, by a factor of 1000, all other factors being equal. That's a big effect - and that's why we were so excited as a team when we figured out how to measure the cosmogenic exposure age of rocks we drilled (see Emily's blog and the Farley et al. paper). This gives us a dependable way to preferentially explore for those rocks that have been exposed for the shortest period of time. Furthermore, it is unlikely that organics would be completely eliminated due to radiation effects and the proof of this is that a certain class of meteorites - the carbonaceous chondrites - have been exposed to radiation in space for billions of years and yet still retain complex organics. This provides hope that at least some types of organics should be preserved on Mars.
Being able to account for the radiation history of rocks that Curiosity might drill is a very big step forward for us in the search for organic molecules. It is a big step forward in learning how to explore for past life on Mars (if it ever existed there). Now we have the right tools to guide the search for rocks that might make the best targets for drilling. Coupled with our other instruments that measure the chemistry and mineralogy of the rocks, to help select those that might have seen the least alteration of organics during burial, we have a pretty good sense of what we need to do next. That's because we have been through this before on Earth.
Over the years Emily has written many blogs dedicated to the discovery of interesting minerals on Mars. There are many reasons for this, but I'll suggest one more that may grow in importance in years to come.
Believe it or not, the story starts with none other than Charles Darwin. In pondering the seemingly instantaneous appearance of fossils representing complex and highly differentiated organisms in Cambrian-age rocks (about 500 million years ago), Darwin recognized this as a major challenge to his view of evolution. He explained the sudden appearance of fossils in the record by postulating that Cambrian organisms with no known antecedents could be explained by "record failure" - for some unknown reason, older rocks simply didn't record the emergence and evolution of life's beginning. Conditions weren't suitable to preserve organisms as fossils.
Most of that story goes on in the direction of evolutionary biology, and we'll skip that, rather focusing instead on learning more about taphonomy. What is important for Mars was the discovery of minerals that could preserve evidence of early microorganisms on Earth. (For a good read on Precambrian paleobiology, try Andy Knoll's "Life on a Young Planet: The First Three Billion Years of Evolution on Earth.")
We now know that pre-Cambrian time represents about 4 billion years of Earth's history, compared to the 540 million years represented by Cambrian and younger rocks that Darwin had studied. (See Emily's blog on the Geologic time scale.) We also know now that the oldest fossil microbes on Earth are about 3.5 billion years old, and that in between there is a compelling, but very sparse record of the fossil organisms that Darwin had anticipated. However, what's even more remarkable is that it took 100 years to prove this. And this was with hundreds, maybe thousands, of geologists scouring the far corners of the Earth looking for evidence.
The big breakthrough came in 1954 with the discovery of the "Gunflint microbiota" along the shores of Lake Superior in southern Canada. A University of Wisconsin economic geologist, Stanley Tyler, discovered microscopic threads of what we now understand to be fossil bacteria in a kind of rock called "chert". Chert is a microcrystalline material formed of the mineral quartz, or silicon dioxide, which precipitates very early in waters that contain microbial colonies. It forms so early that it turns the sediment almost instantly into rock, and any microbes become entombed in a mineral so stable it resists all subsequent exposure to water, and the oxidizing chemicals dissolved in water, for billions of years.
As it turned out, this was the Rosetta stone that helped decipher the code to the field of pre-Cambrian paleontology. It took almost 10 years for the discovery to be fully appreciated (the initial report in Science was viewed with much skepticism), but once it was confirmed, in the mid-1960s, the field exploded. Once geologists and paleontologists knew what to search for, they were off to the races. Since that initial discovery, other magic minerals have been found that preserve ancient microbes, sometimes with spectacular fidelity. But chert is still the mineral of choice, and I never pass by it in the field without collecting some.
We don't know yet what magic minerals exist on Mars that could have trapped and preserved organics. Clays and sulfates hold promise, and that's why we're so interested in them. Silica, perhaps similar to terrestrial chert, has been observed from orbit at a few places on Mars, and in Spirit rover data from Gusev crater. The great thing about Gale crater as a landing site is that we have so many choices in this trial-and-error game of locating a mineral that can preserve organic carbon.
The figure below provides some sense of the impact of this discovery. It is modified from a similar figure published in a very nice summary by Bill Schopf, a Professor of Paleontology at UCLA. Bill also was a very early participant in this race for discovery and has made a number of very significant contributions to the field.
In studying Mars, the importance of this lesson in the search for life preserved in the ancient rock record of Earth cannot be overstated. Curiosity's discovery of a very Earth-like ancient habitable environment underscores this point. With only one or two rovers every decade, we need to have a search paradigm: something to guide our exploration, something to explain our inevitable failures. If life ever evolved on Mars, we need to have a strategy to find it. That strategy begins with the search for organics, and regardless of their origin - abiotic or biotic, indigenous to Mars or not - they are important tracers for something more significant. Curiosity cannot see microfossils, but it can detect organic compounds. And just as with microfossils on Earth, we first have to learn where organics on Mars might be preserved. So that's what we're going to try and do.
Dear Fellow Martians,
While the Curiosity rover is busy exploring the Martian surface, I am going to school as a sophomore at Shawnee Mission East High School in Prairie Village, Kan. I am very involved in my school's environmental club, and this year we started a composting program in our cafeteria.
I've also taken on a role in my local Sierra Club chapter's energy efficiency campaign. I think caring for our planet goes hand-in-hand with science and exploration. It is something that is very important to me.
In February, I rode a bus to Washington, D.C., with 40 other people to attend the Forward On Climate Change rally. The bus ride was a little over 24 hours, but it didn't feel that long at all. I had so much fun meeting and talking with people who had similar passions and motivations to those that I have. The rally and its immense energy opened my eyes to the things I could accomplish in my own community.
In May, I visited my grandparents in Beijing, China. Saying goodbye is always hard, because I absolutely love seeing them, talking to them, and being with them.
This week, I started my internship at JPL, one of my favorite places in the entire world. I am sure this will be the first of many letters that I will write to you. I can't wait to tell you more about my experiences in Pasadena as my summer continues.
With love, Clara
Aug. 5, 2012: Curiosity lands in Gale Crater. I watch from Earth, crying and shouting on the edge of my seat.
Sept. 27, 2012: Curiosity finds evidence of an ancient streambed. I play my third tennis match of the season, and share the rover's exciting discovery with my parents when I get home from school.
March 12, 2013: A rock sample analysis shows ancient Mars could have supported microbial life. I write about it in my chemistry assignment.
June 10, 2013: This is the first day of my internship at JPL, a day I have been dreaming about since I was a little girl. I don't know how I got to be so lucky.
Monday, August 6, 2012 1:13:26 AM
Welcome to Gale Crater. "Adam...you're a genius!" I shout to Adam Steltzner. He pauses. Stops. Turns around. "I'm not a genius -- I just work with a team of them."
Sunday, August 5, 2012 10:04:10 PM
The EDL Phase Lead, Adam Steltzner, has just thanked the cruise team for their 350-million-mile ride. "Curiosity is in fantastic shape, she's here because you guys got her here. See you on Mars."
Go Curiosity. And break out the peanuts.
Mars really has us now.
Sunday, August 5, 2012 10:03:56 PM
Ten thousand and sixty three. Sixty four. Sixty five. As quick as you can count it, our speed towards Mars is accelerating.
Mars is about half the diameter of Earth, but only about 10 percent as heavy as Earth. Even so -- on its surface, gravity is about 38 percent that of Earth. In the next 28 minutes, we will gain another 3,000 miles per hour until Curiosity, heatshield ready, slams into the top of the Martian atmosphere.
40 billion to 1
Sunday, August 5, 2012 9:15:28 PM
A quiet approach to Mars as we watch a tiny plot of a graph. The X-band frequency that Curiosity is currently transmitting is a frequency of more than 8 Gigahertz -- 8 billion cycles per second. As it rotates, that tiny little graph shows that frequency moving up and down, by about 0.2 Hz. One part in 40 billion. That little bounce up and down is the rotation of the spacecraft, two revolutions per minute. We have that accuracy because we're bouncing a radio signal from the ground, up to spacecraft and back again. But that signal, after a final poll, will be going away.
Systems Go. Power Go. Thermal Go. Propulsion Go. Nav Go. Uplink Go. Avionics Go. Flight. Software Go. Fault Protection Go. Chief Engineer Go. EDL FLight System Go. Data Management Go. GDS Go. Telecom Go. ACS Go. EDL Activity Lead Go. ACE Go.
"You are clear to bring down the uplink." So in just over 13 minutes time, Curiosity will no longer have that amazing signal to bounce back - and our little squiggly 1-in-40-billion line will be gone. We will just hear the spacecraft's own transmitter from more than 150 million miles.
Curiosity is truly on her own.
A Final Check
Sunday, August 5, 2012 8:44:21 PM
This full poll of the flight team is a lengthy and exhaustive tour of the rover, the cruise stage and all the systems. My favorite call is from the chief engineer:
"We are green across the board"
That's the word from Rob Manning -- a veteran of four successful Mars landings. When Rob says things are green, you know you're in good shape. If you were hoping to spend some time exploring the martian moon Deimos on your way to Gale Crater -- please alight the rover now, we just crossed its orbit. Now there are 16,000 miles to go.
Calm before the Storm
Sunday, August 5, 2012 8:32:58 PM
Things got a little quiet in the control room. People heading out for some food before we get down to the business of landing on Mars. It takes huge team to watch over a spacecraft as complex, and activites and intricate as a Mars landing. As they get back to their consoles, they do a comm check to make sure they can all hear each other. Systems. Power. Thermal. Prop. Nav. Uplink. Flight Software. Fault Protection. EO Team Chief. GDS. Telecom. EDL Comm. ACS ... the calls, and acronyms, go on and on. Now they are all back on console, the whole team is about to do a full system poll.
Can you hear me?
Sunday, August 5, 2012 7:59:37 PM
Between now and landing, Curiosity will use a total of eight antennas. The Deep Space Network is now listening to a medium-gain antenna transmitting on X-Band on the cruise stage. During entry, two low gain antennas on the back of the spacecraft continue that signal of "tones." There are also low-gain antennas on the descent stage and the rover. However, Earth will have set at this time.
Meanwhile, a UHF antenna on the backshell, followed by another on the descent stage and finally one on the rover, will continue to transmit telemetry during landing. This data will be received by Mars Odyssey and Mars Reconnaissance Orbiter. Odyssey will relay it straight to Earth so we can track landing. Mars Reconnaissance Orbiter records everything it hears and sends it back a few hours later. Mars Express will also record just the pitch of this signal as a final backup.
The ground stations at the Canberra, Australia Deep Space Communications Complex will follow us the whole way -- direct from the rover 'til Earth sets behind it -- and from Odyssey and Mars Reconnaissance Orbiter as well. All the way to the ground, a complex system of systems will be trying to keep that tenuous link between Earth and Mars alive.
Sunday, August 5, 2012 5:58:00 PM
"Nominal" sounds like a very boring word, but in the world of spaceflight, nominal is engineer for "awesome." Thanks to the Deep Space Network, we know just how nominal everything is. Deep Space Station 43, a 70-meter-diameter antenna in Tidbindilla, Austraila is currently receiving a steady stream of data at 2,000 bits per second that informs the engineers how all their subsystems are doing. Attitude control, thermal performance, power systems, avionics, propulsion, communication, the list is long. The flight team (meet them all here: www.gigapan.com/gigapans/110926) just took a poll, and all subsystems are nominal. The MEDLI instrument is now powered up, and healthy. It's talking to the flight computer, and the power system can see it drawing just 300 milliamps. It will record first-of-its-kind data on temperature, pressure and other readings through Curiosity's heatshield during entry. This data will help us understand how the heatshield behaves and can help us make them better for the future. As MEDLI lives on the inside of the heatshield, it is thrown overboard when the heatshield is separated about six miles above the surface. Its data will be safely stored on the rover to be downlinked after landing.
Sunday, August 5, 2012 1:15:54 PM
When you're a spacecraft it's important to know which way you're facing. If you know which way you're facing, you know which way Earth is, so you can talk to home; which way the sun is, so you can get power on a solar array; and if you're Curiosity, you know which way Mars is. There are two ways spacecraft typically orient themselves. One is called "three-axis stabilized," which means the spacecraft uses thrusters and reaction wheels to keep itself pointed the right way. You may have heard about trouble with reaction wheels on the Mars Odyssey orbiter recently (it carries a spare just in case, and we're now using it). Curiosity (as well as its older sisters Spirit and Opportunity, and Juno right now on its way to Jupiter) just spin their way through deep space. They point in one direction and spin, like a top. That spin stops the spacecraft wandering off and pointing somewhere else. Curiosity, all the way till after we wave goodbye to its cruise stage about 17 minutes before landing, spins at 2 rpm. During its 253-day cruise, Curiosity will have spun more than 720,000 times. It's enough to give a rover a headache.
Sunday, August 5, 2012 1:05:01 PM
I've arrived "on lab" (JPL-speak for "at the office") to check up on our computer running Eyes on the Solar System (http://eyes.nasa.gov) that will be fed to NASA Television tonight. Looking up in the control room -- I see we've just crossed 80,000 miles to go. Less than four- times the distance from Earth to our geostationary communication satellites. Mars is about 4,200 miles in diameter - so with a little high school trig, we can calculate that Mars would appear 3 degrees across to Curiosity. That's six times larger than the size of the full moon from Earth. This time yesterday, Curiosity was only 170 mph slower than it is now. In the next 10 hours as it falls to Mars it gains another 5,000. As an astronaut onboard Apollo 13 said to mission control on their way home, "The world's getting awful big in the window."
The Runners Up
Friday, August 3, 2012 11:15:00 AM
Adam Steltzner (MSL EDL phase lead) is a great speaker and real highlight of today's NASA Social event. A fantastic question from the audience asked what ideas for landing Curiosity were rejected.
The runner-up: airbags. There isn't a fabric that we know of strong enough to handle the impact loads that a 899-kg rover would create. Good enough for the 180-kg of Spirit and Opportunity, but it just can't get scaled up to something as big as Curiosity.
Third place: Put the rover on top of the rockets. The problem there is that the rover is so heavy, and the propellant tanks so large, that you would have a very tall vehicle prone to toppling over on touchdown.
It may look a little crazy -- but the skycrane actually makes a lot of sense.
Speed Up, Slow Down
Thursday, August 2, 2012 5:12:47 PM
The art of flying between the planets is a balancing act of gravity, velocity, trajectory and timing. These variables come to a thrilling climax on Sunday evening as Curiosity reaches the Red Planet.
Launched into a trajectory around the sun in November 2011, Curiosity is currently in a solar orbit that just reaches the orbit of Mars. That trajectory means that, from the perspective of the sun, by noon Pacific time on August 1 Curiosity was travelling at 47,500 miles per hour. Yet Mars is travelling at more than 53,000 mph -- some 5,500 mph faster than Curiosity. Left alone, Curiosity would soon begin a slow cruise back towards the orbit of Earth, while Mars would carry on along its own, faster trajectory.
But breathtaking accuracy by the navigation team guiding Curiosity means that Mars will be at the right place Sunday to pick up Curiosity. The planet's gravity will speed up the spacecraft by 13,000 mph (as viewed from the sun) until their speeds match and Curiosity is safely on the surface. On the freeway of interplanetary navigation, Curiosity is the bug, and Mars is the windshield. To get ready for a martian year of exploration, you've got to take a big hit.
Welcome to the Landing Blog
Thursday, August 2, 2012 5:12:16 PM
Welcome to the Curiosity landing blog. I'm Doug Ellison, a visualization producer here at JPL. Our group is responsible for many of the graphics you will see that show how Curiosity has made its way to Mars, and what it will do when it gets there.
The landing animation was a nine-month-long project of obsessing over details of every piece of the spacecraft and its adventure. We've launched a special version of Eyes on the Solar System at http://eyes.nasa.gov that lets you ride with Curiosity all the way to the surface. We've become so familiar with the spacecraft and what it does that we even surprise the mission team themselves sometimes!
On landing night, I'll be in our mission control (the "Dark Room") keeping you up to date with some of the goings-on as Curiosity approaches Mars. Until then I'll post a few little factoids about Curiosity, its trip to Mars, and its epic landing at Gale Crater.
The Mars Exploration Rovers, Spirit and Opportunity, have been exploring the geology of Mars for nearly five years - well beyond their expected lifetime of three to six months. In that time they have made amazing discoveries, most importantly finding proof that Mars was once a much wetter planet that may have been capable of supporting life. Spirit has been exploring a region around a small mountain range that seems to have once had hot water or steam, the very kind of place life might have originated on Earth. Opportunity has been investigating craters in the plains that provide views deep underground and show evidence of flowing water in the ancient past.
I am a roboticist at JPL, and just one member of the large team of people who work together to enable Spirit and Opportunity to explore. My work focuses on getting robots to do things intelligently, both by developing software for robot autonomy and by operating our two spacecraft on the surface of Mars. Spirit and Opportunity have become like old friends to the operations team. Every day we are anxious to hear the latest news and see the snapshots taken from the new places they are visiting. Working with the rovers never gets routine as each new location brings new circumstances and new problems to solve.
The challenges of operating Spirit and Opportunity have continued to grow and change as they age, and we have had to develop new ways of driving and operating the robotic arm as capabilities decrease. We are discovering how to operate these rovers in ways for which they were never designed. The discovery process requires a lot of imagination and a lot of practice, both on Earth with our engineering rover and on Mars. It’s this kind of completely new and unanticipated problem that is the most fun for engineers like myself to solve.
Both rovers are now starting to show their old age of 4¾ years (that’s at least 300 in rover-years!), and some parts do not function quite as well as they used to. Spirit has to drive more slowly and constantly monitor her progress to make sure she is staying on the right path to compensate for a broken right front wheel that tends to dig into the soil. Opportunity has limited reach with her instrument arm due to a failed shoulder joint, and has to approach science targets in a very precise way. Despite these limitations, both rovers are now about to embark on difficult journeys which will require them to set new milestones and we will need to learn new ways of driving yet again.
After surviving a very difficult winter, Spirit is soon going to be heading south toward some interesting geological features: a hill called von Braun and a depression called Goddard. Scientists hope investigating these unique features will provide insights into the Martian past. They are looking for additional evidence of hot springs or steam vents that have been hinted at by other observations in this region. Based on comparisons to similar locations on Earth (like deep sea vents), this could be an ideal place for life. Reaching these exciting features requires a long drive through sandy terrain in a very short period of time before next winter arrives. This will mean pushing Spirit to new levels of performance.
Opportunity is finishing up her observations of the 800-meter Victoria crater and then will begin a 12-kilometer, two-year odyssey toward a huge crater (about 22 kilometers across) to the southeast. As this means more than doubling the total distance Opportunity has driven in her lifetime, we are excited to be developing new methods to make record distance drives safely. This will require relying on the rover’s onboard autonomy to keep her safe more than ever before as we drive each day well past what we can see.
Spirit and Opportunity’s story of continued exploration - boldly striking out after one new goal after another, far beyond their design lifetimes - is a genuinely inspiring one. It’s as if Magellan circumnavigated the Earth, then paused and said, ‘You know, that’s not good enough. Let’s go to the moon, too.’
Mars Science Laboratory is a mission to create and send to Mars the largest, most capable and most exciting rover that has been sent to another planet to date. It will be a remote robotic scientist that will help us investigate our most Earth-like neighbor in the solar system. It is literally a mobile laboratory -- the size of a car, with a wide array of science instruments that will help us determine whether Mars has the capability to support life, both in the past and in the present.
Most of my work at JPL has been in the area of research robotics, small projects with very focused goals, such as the Urban Robot project, the Spiderbot, and many others. These robots were created using a small team of engineers who each covered a wide area of responsibility such as mechanical, electrical, and different areas of computer science for perception and navigation.
At times, to get one of these robots working right we would “hack” together a solution, and get it implemented in a very short amount of time! By throwing our energy and ideas into each project, we could push the cutting edge of different technologies and robotic capability that could then be used by future projects and researchers.
In contrast I’m now working on the motor control system of the Mars Science Laboratory mission, which as opposed to research is a “flight project” (it’s going to fly!). This is quite a different experience than the research area - the mission is kind of like taking the goal or purpose of the robot, breaking it down into a million pieces, and putting every piece under a microscope to make sure everything will work absolutely perfectly. Instead of 10 or fewer engineers each working on the different subsystems of the robot, we have hundreds of engineers and scientists who are planning, designing, developing, manufacturing, testing and in general creating a very complicated remote-sensing system.
Sending a robot of any kind to another planet is a completely different story than running any such thing on Earth. For one thing, the robot must operate within very extreme temperatures and handle harsh exposure to the sun’s rays. Future robots may have to deal with steep or challenging terrain, or even a lack of a solid surface such as on Titan, Saturn’s largest moon. And throughout all this, the robot has to work perfectly and stay in communication with Earth. There is no control-alt-delete button to handle software crashes, and no technician around who can run out to push the big red reset button. In other words, if you’re going to run a robot on another planet, it has to land unharmed, work the first time, and run correctly every time you command it to do something, so that you’re guaranteed to get back the vital science data you’re after.
Who ever thought that being in the desert in the middle of summer would be so much fun?!
I'm working on a mission called the Mars Science Laboratory, the next rover that NASA is going to send to Mars. Its mission is to help us find out whether or not Mars might have offered a favorable environment for life at one point in time (read more about the mission).
I'm part of the group designing the mission's entry, descent, and landing phase, also known as the "7 minutes of terror." This is a really exciting part of the mission because we're trying to slow the spacecraft down from over 12,500 mph (about 5 times as fast as a speeding bullet) to a screeching halt in about 7 minutes! To do this, so many things have to go right in such a small amount of time. Once the spacecraft enters the Martian atmosphere, and because it's going so fast, the spacecraft gets hotter than the surface of the sun. Then we deploy a parachute supersonically (faster than the speed of sound), fire retro-rockets at a very precise altitude, and gently lower the rover to the surface of Mars on a bridle. No one ever said rocket science was easy!
Since so many things need to happen perfectly, we test things here on Earth before we launch the spacecraft to Mars. One of my responsibilities includes field testing the radar, which will tell the spacecraft how far off the ground it is and how fast it is going during its descent. If the radar doesn’t work properly, the spacecraft could fire its rockets at the wrong time and crash on the surface of Mars. That would be a very, very bad day.
To make sure the radar will work on Mars, a group of us went out to the desert two weeks ago to test it out. The weeks leading up to the test were pretty frantic, with numerous hurdles along the way as we were trying to get the system working in the lab. After we got it working, we took it out to the desert where we attached our radar to a cable, which was attached to a pulley, and all of this in turn was suspended between two towers about 400 feet tall. The other end of the cable was attached to a truck. When the truck drove forward, the radar was lowered at about the speed that it will be descending on Mars just prior to landing.
The testing was so successful that we finished a day early, and were able to leave the really hot desert. We ended up with great data that will help us improve our radar so that it will work flawlessly on Mars. The success of this test made the hard work and desert heat all worth it. But when it was all said and done, we were all pretty glad to go back home, rest and then come back to work to start the cycle over for our next two sets of radar tests–on a helicopter and an F-18 jet!