Curiosity, NASA's third generation Mars Rover, successfully landed on the Red Planet after a 350-million mile journey through the depths of space.  Using a novel landing mechanism known as the 'Sky Crane,' the rover touched down on the surface of Mar's Gale Crater on  August 6, 2012.  NASA scientists now have another oppurtunity to further explore Earth's mysterious cosmic neighbor–and potentially determine if it ever hosted life.  This week in Science we ask Cornell experts about Curioisity and its historic landing.

What is the goal of Curiosity? How will it accomplish its mission? 

As I understand it, Curiosity's scientific goal is to try to better understand the habitability of Mars, both currently and long in the past.  We have reason to believe that Mars was once wetter than it is now, and perhaps warmer as well (from visible flowing-water sculpted channel seen from orbit, and more recently from the geology discovered by the rovers Spirit and Opportunity), and this begs the question whether it once had life in addition to water.  Curiosity has been sent to a region of Mars where there is a large layer of sedimentary rocks that are exposed and relatively easy to drive up (presumably moving forward in the geologic/historic record) and thus investigate the environmental history of Mars over the last few billion (with a B!) years.  We believe Mars was wetter something like 3 billion years ago, so the best chance of there being life on Mars was long ago.  Nevertheless, recent research into life in extreme environments on Earth has taught us that life can be tenacious.  Perhaps there is still some form of life on Mars.  Curiosity is mainly equipped to investigate the past environments, but it also can look for methane today, which could be indicative of current life on Mars.  Curiosity's main goal isn't to detect current life (which may be a long-shot), but obviously if something exciting shows up, we'll all be keenly interested.

-Prof. Don Banfield, astronomy

Why, again, did we send a rover to Mars?

Because there's so much more to learn about Mars!  We've only been to a handful of places there, and it's a whole planet, with diverse geology, and once upon a time, diverse environments.  Mars has the same dry-land area as Earth.  Each landing site tells us a different part of the story.

Curiosity is the most recent step in a long-term campaign of increasingly detailed science and exploration investigations.  Back in 1997, the Sojourner rover, which was part of the Mars Pathfinder mission, proved that we can operate mobile robots on Mars.  Sojourner was primarily a technology demonstration, so its part in the mission was actually focused on engineering rather than science.

Spirit and Opportunity, the 2003 Mars Exploration Rovers, were designed to be robotic field geologists.  Their mission is to look for evidence of ancient water on Mars, and characterize the environments in which that water existed.  They both found evidence of past watery environments, and Opportunity is still going!

When geologists go out to a field site, they walk around the site, examining rocks and soil and where those are in relation to each other, characterizing the types of rocks and soils that they see, and looking at the local and regional context of the site.  They collect samples, which they then bring back to a lab for detailed analysis.  Spirit and Opportunity have explored their fields sites thoroughly, and we've used data from their instruments and cameras to examine the local context and composition of the rocks and soils at their sites.  We examine the regional context with data from orbital spacecraft.

Curiosity is the next step -- the lab that can do detailed analyses.  The rover is essentially a high-tech lab on wheels, which is why it's called the Mars Science Laboratory.  It's got an amazing suite of instruments -- it can do mass spectroscopy and X-ray diffraction; it even has a rock-zapping laser that lets it examine the composition of rocks that are meters away!  It also has a weather station, and detectors that will tell us about the radiation environment on Mars today.  On Earth, our magnetic field protects us from a lot of high-energy particles that permeate space, and various constituents of our atmosphere protect us from the more harmful electromagnetic radiation from the Sun (e.g., ozone in our stratosphere absorbs a lot of UV, so most of the UV that hits Earth doesn't make it down to the surface).  Mars has a very thin atmosphere and no global magnetic field, so more radiation gets to the surface.  If we ever want to send people to Mars (and have them survive), we need to learn about the radiation environment.

This is a great time for me to describe what Mars scientists mean when we talk about "water".  We consider "liquid water" to be any aqueous fluid, i.e., any fluid that has H2O in it.  An aqueous fluid that's way more acidic than battery acid would count as water, as would a brine so salty that it couldn't freeze, or a fluid with a pH of 14 (or above!) that could easily turn you into soap.  So we're not talking tap water, or even something that would be okay for you touch.  Also, the "ancient" watery environments we study existed about 3 billion years ago.  To put that in perspective, most of the earliest multicellular life forms you've heard of began about 600 million years ago.

-Shoshanna Cole, grad

Why was the Gale Crater chosen as the location for Curiosity landing?

Gale crater was chosen because it is a very old, very deep crater with a giant mountain of layered rocks in the middle named Mt. Sharp. Geologists love layers because they capture the changing environments where they formed, so with the right tools and expertise, we can read the layers of rock like pages in a Martian history book.

As expected, Gale is spectacular! It looks a lot like the Mojave desert: we're on a nice flat plain but in the distance the crater rim rises like a mountain range. And of course, the mountain of layered rocks in the center of the crater is beautiful and tantalizing. It looks a lot like the buttes and mesas famous in the American southwest, in places like Sedona, AZ.

-Ryan Anderson, grad 

The main attraction is the 5km-high "mound" in the middle of the crater, which is called Mount Sharp.  It's made up of layers that were deposited over many millions of years of Martian history; it's analogous to the layering you can see in the Grand Canyon, but about three times as thick! Because layers are deposited on top of each other (younger layers sit atop older layers), as Curiosity ascends the mound, it will in a sense travel through Martian history, observing the environmental changes that took place here billions of years ago.  We know from orbital data that the mound records some major climatic changes, and data from Curiosity will show us the specifics.

Scientists literally spent years deciding on Curiosity's landing site. We've got some amazing cameras and detectors in orbit around Mars, which actually made it harder to pick the site because there were so many great candidates.

-Shoshanna Cole, grad

What were the steps involved in Curiosity’s landing? 

When Curiosity flew from Earth to Mars, it was safely inside a capsule that had a similar shape to those used in the Apollo program.  The capsule's heat shield took the brunt of the heating that occurred when the spacecraft entered the Martian atmosphere.  After a few minutes, a huge supersonic parachute was deployed, which slowed the capsule down.  These parts of entry and descent were similar to what Spirit, Opportunity, Pathfinder, and the Viking and Phoenix landers used.  The next part was novel: the rover dropped its heat shield, activated its radar, let go of the parachute, and turned on its descent stage's retro-rockets!  The rover was attached to the underside of the descent stage by the Sky Crane, which is a giant winch.  Once the descent stage was essentially hovering close to the ground, the Sky Crane lowered the rover the last few dozen meters. When the rover detected that its wheels were on the ground, it cut the lines to the Sky Crane, and the descent stage flew off and crashed a safe distance away from the rover.

Curiosity is way too big to land with airbags like Spirit, Opportunity and Pathfinder did.  Spirit and Opportunity were pushing the maximum mass that airbags could support.  They have a mass of 185kg each, and Curiosity has a mass of 900kg!  In order to land the rover safely on Mars, the JPL engineers came up with a complicated landing system including the Sky Crane.  Another big advantage to this system is that we can aim it much better than we can aim a rover that uses airbags.  We knew that Curiosity would land somewhere within a region about the size of the Town of Groton.

-Shoshanna Cole, grad

The sky crane sounds incredibly complex, and when I first heard its full description I thought that that can't work.  In fact I was quite skeptical until it actually came down 2 weeks ago!  The airbags used for the previous 3 rovers couldn't handle as large a rover as curiosity (its about 5X the mass of the MER rovers from 8 years ago).  They also didn't want to simply lower Curiosity down on retrorockets, as when they neared the ground, they could kick up so much debris that they could damage the rover, and then you'd also need to shed the extra weight of the retrorockets and they might get in the way.  So the sky crane was invented.

The first big difference for Curiosity was that it used guided entry.  That is, rather than preprogram the "attitude" (the specific orientation of the spacecraft) as it entered, the attitude was actively adjusted, based on the rover's best estimate of where it was in the atmosphere, to allow it to come as close as possible to the target landing site.  You can think of this like a frisbee that can modify it's pitch in flight to best land in your friend's hand.  Previous landers at Mars were more like normal Frisbees we throw, that is you better throw it right to get close to the target.  Curiosity was like a frisbee that adjusted it's pitch and yaw to best fly to the target.  This allowed Curiosity to come within about 1 mile of its planned target (after traveling 350 million miles!).  This is akin to sinking a free throw from the opposite side of the earth.

Once guided entry was complete, the spacecraft had decelerated from 13000 mph to about 1000 mph.  Still quite fast.  Curiosity then used a supersonic parachute to decelerate some more, down to about 200 mph.  But because Mars' atmosphere is so thin, the parachute wasn't going to slow it down much more than that.  So the parachute was cut off, and retrorockets slowed it down to only a few mph, and brought it to within about 60 feet of the surface (as judged by an on-board radar, that figured out not only the height of the spacecraft, but also its sideways motion (from winds) and canceled that out too).  Finally, at this 60 feet altitude, it started lowering the rover down on a 20' tether and very slowly descended until that touched down.  Once the rover felt weight on its wheels and the tether go slack, it cut the tether, and was ready for exploring!  But before it could do that, the hovering retrorocket sky crane had to safely move away from the rover (to not fall back on it). Fortunately, this ALL worked as planned.  Quite amazing.

-Prof. Don Banfield, astronomy

What type of equipment and instruments does Curiosity have to help it complete its mission? 

Curiosity has a wealth of cameras, some to just help it drive safely, others to survey the area, and still more to scientifically probe the rocks it finds.  The science cameras use carefully chosen filters to study the precise color of the rocks to help understand what minerals they are.  There is also a camera that is set up to act like a hand-lens that geologists typically carry in the field to better study the mineral samples they find.  It also has two other instruments to help it understand the mineralogy of the minerals by looking at the results when the rocks are irradiated with Alpha particles or X-rays.  Probably the coolest instrument is one with a laser to vaporize rocks from a distance, and then analyze the spectrum of the plasma that is produced.  Again, this one helps identify the make-up of the rocks, but in this case from 10 meters away, so investigation of a particular location can proceed much faster and more efficiently.  Finally, once a very interesting sample is identified, it can be brushed or the surface ground off of it and samples obtained from it (even drilled into to get samples a few cm deep).  These samples are then put in a sample analysis suite which is a mass spectrometer/gas chromatograph coupled with a tunable laser spectrometer. This instrument is mainly focused on understanding the organics contained in mineral samples, but can also sample the atmosphere of Mars.

There are also instruments to understand the weather on Mars.  Curiosity has landed in a crater and will be climbing up a mountain, so the local "micro-climatology" of the area may prove to be interesting as it moves.  The weather station measures wind, temperature, pressure, humidity, as well as the UV flux (to understand how that might present a problem to life near the surface of Mars).  There's also an instrument that estimates the water in the soil under the rover, and finally one to understand the radiation environment at the surface of Mars (again to understand how hospitable it might be to life (astronauts or martians) at the surface of Mars.

-Prof. Don Banfield, astronomy

What types of cameras are being used on Curiosity?

By my count, Curiosity is boasting eighteen visible-light cameras scattered throughout the rover. The cameras generally fall into two categories: engineering and science, although both types will be used for scientific discovery on the Martian surface. It is important to remember, however, that cameras only constitute a small part of Mars Science Laboratory's (MSL) considerable scientific capabilities. The rover also includes an x-ray diffraction instrument, x-ray spectrometer, mass spectrometer, neutron detector, cosmic-ray detector and meteorological station. MSL is the largest and most complex spacecraft ever sent to the surface of another planet.

The engineering cameras consist of eight Hazard Avoidance Cameras (Hazcams) and four Navigation Camers (Navcams). Hazcams and Navcams are used to plan traverse paths, avoid navigational hazards while driving, and provide context information for targeting other instruments. These cameras are optically identical to the Hazcams and Navcams found on the Mars Exploration Rovers Spirit and Opportunity. The Hazcams are mounted to the front and back of the rover in four stereo pairs. Similar to the way your eyes perceive depth, left-right images from each stereo pair are combined to generate three-dimensional views of the Martian surface. Hazcams utilize fish-eye lenses with 120 degree fields of view that can generate terrain models of the area directly in-front/behind the rover to an accuracy of better than +/- 5 mm (+/- 0.2"). These terrain models are used to plan movements of MSL's robotic arm and fill in the rover's "blind spots", which are places where the mast-mounted cameras can't see because they are obstructed by the rover deck. While the rover is driving, the Hazcams periodically take pictures to determine the location of hazards (typically defined as objects bigger than the size of a rover wheel), and avoid them autonomously. Similar to the Hazcams, the Navcams also come in stereo pairs. Two sets of Nacams are mounted on MSL's Remote Sensing Mask (RSM), which sits about 1.9 m (6'3") above the surface. This is ~0.4 m (1'4") higher than the mounting height of their cousins on MER. These cameras, each of which have 45 degree fields of view, are used to generate terrain models which are essential to both deciding the path Curiosity will take while driving and determining how to point science instruments such as ChemCam and Mastcam. Both the Hazcams and Navcams were built at the Jet Propulsion Laboratory (JPL) in Pasadena, CA. For MER, a team of Cornell researchers and students, under the supervision of Professors Jim Bell and Steve Squyres, calibrated Spirit and Opportunity's Hazcams and Navcams during the summer of 2003. These same calibration procedures (and targets) were used to prepare MSL's engineering cameras for flight.

Unlike the Hazcams and Navcams, which are grayscale cameras, the six science cameras on MSL provide full color images. These cameras are part of the Mast Camera (Mastcam), Mars Hand Lens Imager (MAHLI), Mars Decent Imager (MARDI), and Chemistry & Cameras (ChemCam) instruments. The Mascam is two-instrument suite of high-resolution cameras mounted on the RSM. One camera provides a 15 degree field of view while the other, which can resolve a 10 cm object (3") at distance of 1 km (0.6 miles), has a 5.1 degree field of view. The imaging sensors on these cameras are comparable in performance to a mid-range commerical digital SLR camera. Both Mastcam cameras can also operate as full HD movie cameras, a feature that Co-Investigator James Cameron plans to utilize to film the Martian surface. MAHLI is located on the end of MSL's robotic arm and acts as MSL's microscope. MAHLI can generate close-up views with a pixel scale as high as 13.9 micro-meters (0.00055") and includes a set of LEDs to allow for nighttime imaging. When MAHLI is viewing targets up-close (working distances around 25 mm or 1") , there is limited range over which the surface is in focus. In order to generate an in-focus image of an irregular surface, the robotic arm and camera work together to acquire a series of images at slightly different ranges. The images are then combined to generate a single in-focus image as well as a micro-topography map of the target surface. MARDI is a 70x55 degree field of view camera mounted to the bottom of the rover chassis. MARDI was used to obtain images at ~5 frames per second during the rover's touchdown on Mars and is responsible for the iconic photo of the heat shield just after it separated from the spacecraft. Mastcam, MAHLI, and MARDI were all built by Malin Space Science Systems in San Diego, CA. The final camera-bearing science instrument on MSL is ChemCam, a two-instrument package consisting of a Remote Micro-Imager (RMI) and the first Laser Induced Breakdown Spectrometer (LIBS) to be sent to another planet. The LIBS instrument shoots high-energy laser pulses at a rock and then views the resulting plasma emission lines to determine its chemistry. The RMI is a color camera with a 1 degree field of view that provides geologic context for each of the ChemCam targets. ChemCam fired its laser for the first time last Saturday (August 18th) when it analyzed a fist-size rock called "Coronation". ChemCam was developed and built at Los Alamos National Laboratory in New Mexico.

-Prof. Alex Hayes, astronomy

How will the data from Curiosity be analyzed?  Will Curiosity be able to send back samples from Mars? 

Data arrive in many forms: images, spectra returned from laser probing, and compositional data from materials picked up, as well as from scattered neutrons, among other methods of investigation.  The analysis primarily consists of determining what is present (the compositional data) and the context, such as geologic structures indicating the manner of deposition.  No samples are returned by Curiosity.  That would be a vastly more difficult and expensive enterprise, one that is well into the future.

-Prof. Peter Thomas, astronomy

Every day Curiosity beams its data back to Earth, where it is received by the "Deep Space Network" which is a worldwide network of radio telescopes used to listen for signals from NASA missions. The data gets sent to NASA's Jet Propulsion Laboratory in Pasadena, California, and from there it is distributed to the science team. Each instrument on the rover has its own team who are experts in that particular type of data, and so they interpret the data and share their results with the broader science team.

The raw images from the mission are also publicly released right away

at the mission website:http://mars.jpl.nasa.gov/msl/multimedia/raw/

-Ryan Anderson, grad

Why were the first images coming back from the rover low-resolution?

The first images that were beamed back by Curiosity were thumbnails, low-resolution previews analogous to the icons you see when you look at a folder full of images on your home PC. Thumbnails take up significantly less data volume and can be transmitted between Mars and Earth much more quickly than full-resolution images.If you were watching the news coverage of the landing, you may have noticed that higher resolution versions of the same images followed soon after the thumbnails were released. During rover operations, thumbnails are a great way for scientists and engineers to know whether or not a particular imaging sequence completed successfully. With so many high resolution cameras and other data-intensive instrumentation, data volume is a valuable commodity on the spacecraft. Data products are temporarily stored on-board the rover and downlinked to earth based on assigned priorities. Thumbnails are a great way to verify that a lower-priority image, which may not be downlinked for a while, was taken successfully. 

-Prof. Alex Hayes, astronomy

How is Curiosity powered? What is its fuel source? 

Curiosity has a "radioisotope thermoelectric generator" (RTG) on its back that provides the power it needs.  This is a can containing plutonium (about 4 kg), that radioactively decays.  In the process of that decay, it produces heat.  The plutonium is surrounded by thermocouples that can generate electrical power from the thermal gradient that is produced by the internal heat source, and the relatively cold environment of Mars.    Apparently Curiosity's RTG producers only about 100W, i.e., that of a strong light bulb.  All of the rover's activities: driving, grinding and drilling rocks, running lasers and cameras, radio-ing data back to Earth and just staying warm through the very cold Martian nights is all done off of this tiny 100W.

-Prof. Don Banfield, astronomy

What are the differences between this rover and previous rovers? 

Every aspect of Curiosity is bigger and more complex than Spirit and Opportunity. Curiosity is five times heavier and almost twice as tall - it’s the size of a small car (the previous rovers were more golf-cart sized). The scientific instruments are far more sophisticated. With this rover we’ll be able to determine the mineralogy and chemical makeup of rocks and soils much more precisely, and take pictures with a much higher resolution. We can perform new types of investigations, such as searching for organic materials, measuring radiation, and monitoring winds. While Spirit and Opportunity relied on solar energy, Curiosity has a nuclear power source, so it can operate at night and keep driving after she gets caked in dust. The landing mechanism is also brand new; too big for the previous airbag system, Curiosity was lowered to the Martian surface with a “sky crane”.

And that’s just the hardware. Operating this rover is a bigger and more complex task as well. We have 400+ science team members working on the mission here at JPL, and that doesn’t include the engineers. Instead of a single Principal Investigator (PI) for the mission (Steve Squyres’ role for Spirit and Opportunity), the highest-level decisions are made by a “Project Science Group,” a committee which includes PI’s of each of the 10 rover instruments and other scientists.

-Melissa Rice, grad

What constitutes evidence of life on Mars? 

First, you must define whether you are looking for existing--"extant" life--or evidence of past life on a now-dead planetary surface. Mars' surface is so inhospitable to even the chemical building blocks of life--organic molecules--that if life exists today it must be deep beneath the surface. How can we tell if such life exists by making surface measurements?  One way is to look for gases in the air that might be produced by life beneath the surface, gases that are not chemically stable under the strong ultraviolet light from the Sun. The best candidate is methane, and some measurements of the Martian atmosphere suggest tiny amounts of it are present thereby implying an active production of methane somewhere. But is it life producing the methane, or simple chemical processes in the interior? To determine this requires measuring how much of each stable isotope, carbon-12 and carbon-13, are present in a sample of the methane gas. Given the tiny amounts in the Martian air, this will be very difficult to do.   For extinct life, the Martian surface is so oxidizing that any chemical traces of such life are destroyed quickly. The only hope would be to find fossil imprints of once living organisms in sediments, something we don't expect to see. But we could be surprised. 

Curiosity isn't designed to search for life. Its instrument payload is designed for a different purpose: to determine how long Mars had an environment suitable for life. Earlier missions, including the rovers Spirit and Opportunity, found evidence that in the very distant past Mars had liquid water on or near its surface. How long was the water there, and by what processes was it lost? Answering these questions by exploring the many layers of rock present on the slopes of Mount Sharp in Gale Crater--Curiosity's destination--will tell us a lot about whether we expect life to have gained a toehold on ancient Mars. Understanding the ancient Martian environment is not easy--it requires an array of sophisticated instruments which Curiosity is carrying.  In addition to this goal, Curiosity will sniff the atmosphere to see if methane really is present, though it won't be able to measure the isotopic ratio. The rover also will sample soil to search for organic molecules--the building blocks of life. And, finally, one of the many cameras on Curiosity can look at tiny grains in the sediments. It is highly unlikely that any fossils will be there to see, but of course scientists will be looking!

Curiosity will find new things--this is guaranteed, because its cameras and geochemical instruments are more sophisticated than on past missions. And I suspect the results will be groundbreaking in understanding the history of Mars. But we should not set the bar so high--that every mission must produce an Earth-shattering result. Scientific research doesn't work that way. We're too immersed in the Hollywood version of science--a compressed and distilled version of reality in which every biology experiment creates a global plague or a superhero/supervillain, and every expedition to another planet finds an alien species that was either our Mother or wants to eat us (or both).  In real life, discoveries proceed more slowly, with far more blind alleys and dead ends than eurekas and Nobel Prizes. That's science, but it is from that process that our lives, and our worldview, have changed dramatically over the past century. There are more surprises to come from Mars and other places in our solar system... if we continue to send our robotic proxies.  

-Prof. Jonathan Lunine, astronomy

What is the significance of the Curiosity Mars Rover Landing to human exploration? 

I am a historian, so first I will make historical points. Let's remember--as NASA reminds us on its web site--that most attempts to land on Mars have failed. Let's also remember that during what might seem a comparable feat--the moon landing in 1969--problems arose at the last minute and Neil Armstrong had to take over manual control of the Eagle lander to avoid disaster. No such human fallback was available for Curiosity. Everything had to work perfectly, and it did.

That engineers were able to pull off such an extraordinary feat as successfully landing such a large instrument on Mars bodes well for the future of human exploration of space.

-Mary Beth Norton, history