By Julie Cooper

Each month in “Slice of History” we feature a historical photo from the JPL Archives. See more historical photos and explore the JPL Archives at https://beacon.jpl.nasa.gov/.

Viking Stereo Viewer — Photograph Number 324-1954

This interactive computer-based stereo viewing system was used to analyze Mars topography images generated by the cameras on NASA’s Viking 1 Mars lander. Two 17-inch video monitors faced a scanning stereoscope mounted between them on a table. Left and right lander camera image data were sent to the left and right monitors. Panning controls on the stereoscope helped align one image with the other to create a stereo image, 640 by 512 pixels in size. A mouse was used for finely controlled rotation of the monitors. An article about the system described a prototype mouse, used before this photo was taken in 1976. “The track ball is a baseball-sized sphere protruding from the top of a retaining box and capable of being rotated freely and indefinitely about its center …”

The resulting images could be displayed on additional monitors and were used to create contour maps and other images that aided lander surface operations. The system was developed by Stanford University and NASA’s Jet Propulsion Laboratory in Pasadena, Calif.

This post was written for “Historical Photo of the Month,” a blog by Julie Cooper of JPL’s Library and Archives Group.

By Doug Ellison

Follow the excitement as NASA prepares to land, Curiosity, its most technically advanced rover ever on Mars. JPL Visualization Producer Doug Ellison shares live, behind-the-scenes action from the mission control room at NASA’s Jet Propulsion Laboratory in Pasadena, Calif..

TOUCHDOWN

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.”

Thanks for the ride

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.

Nominal!

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.

Spin

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.

Three Degrees

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.

By Rob Manning

In the wee morning hours of Nov. 26, 2011, scientists and engineers gathered in the mission control room at NASA’s Jet Propulsion Laboratory to help launch the next Mars rover, Curiosity. The mission’s chief engineer, Rob Manning, shares the developing story from the control room as tensions and excitement for a mission eight years in the making reached all new heights.

NASA’s Mars Science Laboratory spacecraft, sealed inside its payload fairing atop the United Launch Alliance Atlas V rocket, launched on Nov. 26 from Kennedy Space Center in Florida.

5:45 a.m. PST (L-01:17:00)
I drove in this morning at 4:30 a.m. As usual, I was greeted by the cheery guards at the gate along with a small family of local deer, who keep sentry over a small patch of greenery at NASA’s Jet Propulsion Laboratory.

I quickly march into JPL’s mission control area to find the first shift quietly following the prelaunch procedure in sync with the Assembly, Test and Launch Operations (ATLO) procedure. They had been on station since 1:30 a.m. I tried that procedure at last week’s launch rehearsal and found the hour a bit unpleasant. Today, I am working on the Anomaly Response Team (ART) for post-launch anomalies. This means that if all goes well, I will have little to do but cheer when NASA’s Mars Science Laboratory rover launches. I have my own console where I can monitor both the spacecraft and listen to the voice nets (there are 10 of them!).

There are about 30 people here. Usually there are not as many, but today we have two people for every subsystem: power, thermal, propulsion, systems, fault protection, attitude control and management. I can hear the JPL ATLO test conductor, Art Thompson, at NASA’s Kennedy Space Center in Florida double check that the right sequence files have been sent. One in particular has commands that tell the rover when to automatically transition into “eclipse” mode. This software mode puts the entire vehicle into the configuration needed for the period prior to separation from the Centaur. In particular this mode turns on the descent stage and cruise stage tank heaters. This timer should be set about 15 minutes after launch, which is planned for 7:02 am PST today. It is an absolute time so they have to send a new time every time we have a new launch attempt. The voice net that is the most interesting is the launch vehicle’s fueling operations. I have not heard that one before. They are more than 50 percent of the way through fueling!

It is fun to see the crowd here. No dress code, but some have come in ties, others with pink mohawks. Nice combo. Professionals all. The peanuts have already made the rounds.

6:15 a.m. (L-00:47:00)
Brian Portock, today’s flight director at JPL, just finished the launch poll of the room to see if everyone is go for transition to launch mode. This is a command to the rover that will put everything on the rover into a mode that is used for the first 15 minutes of flight. In particular, the heaters are all put into a launch and cruise configuration. We expect that the cruise stage heaters will be on more than off due to the air conditioning needed to keep the spacecraft cool (hot generators, you know).

6:29 a.m. (L-00:33:00)
Arm pyros! Once these relays are closed, they will be that way for the next 8.5 months.

6:32 a.m. (L-00:30:00)
The data rate is lowered to launch nominal to 200 bits per second. This will allow the rover’s data to flow to both the ground (via wires to the power van at the foot of the launch pad that provides power to the rover before launch) and to the launch vehicle where it will be available throughout launch (very cool). The JPL management showed up. Charles Elachi is behind me. My old friend and JPL Chief Engineer Brian Muirhead is here with his family.

6:40 a.m. (L-00:22:00)
The flight director is doing the launch poll for the team here at JPL: “All stations at JPL report go.” ATLO is going through its poll at lightening speed. All stations go. This is going fast! The weather guys report of scattered skies at 5,000 feet looks good. I am getting excited.

6:47 a.m. (L-00:15:00)
We lost the flow of data from MSL via the Atlas Space Flight Operations Center (ASOC) land lines, but they switch it to the radio path from the launch vehicle, and it starts flowing again.

7:00 a.m. (L-00:02:00)
All Quiet. Peanuts going around the room again … everyone is excited!

7:01 a.m. (L-00:01:20)
Everything is armed …

7:01 a.m. (L-00:00:30)
GO ATLAS! GO CENTAUR!

7:03 a.m. (L+00:01:00)
GO, GO, GO!

7:06 a.m. (L+00:04:00)
Fairing falls off! Wind on MSL

7:07 a.m. (L+00:05:00)
Rob Zimmerman, our power systems engineer, reports power on solar arrays! 3.3 x 2 = 6. 7 amps! The spacecraft is still power-negative for a while which means that the battery is still discharging. We need more sunlight - very soon.

7:11 a.m. (L+00:09:00)
Getting intermittent data from the rover via the Centaur. So far, no computer reboots!

7:12 a.m. (L+00:10:00)
The ATLO test conductor reports that they are done building and launching MSL (hey, it took ‘em long enough! ). We all cheer and smile. They are supporting the cruise team now.

7:14 a.m. (L+00:12:00)
We’ve reached the end of the first burn (MECO1). All is well. Eighteen minutes to second burn. Battery is charging at 4.3 amps for each battery — very good.

7:17 a.m. (L+00:15:00)
The eclipse-mode transition should be done; don’t know yet. Got it. The tank heaters should be on now; They are. Batteries are still charging at 95 percent state of charge (SOC).

7:35 a.m. (L+00:33:00)
Waiting for telemetry from over Africa …

7:36 a.m. (L+00:34:00)
It’s five minutes to MECO2, pushing out of Earth orbit. Heavy rover! KEEP PUSHING! Mars awaits.

7:39 a.m. (L+00:37:00)
The spacecraft is nearly out of Earth orbit, six minutes until separation from Centaur upper stage. Everyone is relaxed, but there’s not a lot of data from the rover. It still says it is in launch mode — missed the data that said eclipse.

7:42 a.m. (L+00:40:00)
MECO2. next is turn to separation attitude and spin up. Separation! We get a beautiful view of MSL spinning away from us — in the right attitude and the right direction! (› See Video)

Video: The Mars Science Laboratory spacecraft separates from the upper stage of its Atlas V launch vehicle and heads on its way to Mars.
› See video

7:53 a.m. (L+00:51:00)
We have lock from NASA’s Deed Space Network in Canberra, Australia!

8:07 a.m. (L+01:05:00)
Data-slowing coming … All looks good, batteries at 98 percent. The rover is now in cruise mode. The heaters are on and cycling as designed. The spacecraft is spinning at 2.5 rotations per minute with only 1 degree of nutation (or swaying) — that is not a lot. The Atlas and Centaur did a fantastic job! The generator is working.

8:26 a.m. (L+01:24:00)
Now let’s try the uplink (sweep). Sweep is working! We have strong signals both ways. We are getting two-way Doppler - navigation says that the frequency is just a few hertz off so we had a very nominal injection to solar orbit. We can command!

Everyone is relaxed and trying to see if there is anything that looks wrong, but so far, nothing. Everything is fine. This is weird. Our bird is on its way - it’s where it belongs. We are happy to be in a completely new mode. No more last-minute fixes (to anything but the software). We have a lot to do, but at least our bird is on its way.

By John Callas

Below are remarks made by Mars Exploration Rover Project Manager John Callas at the NASA Jet Propulsion Laboratory’s Spirit Celebration on July 19, 2011.

Artist’s concept of NASA’s Mars Exploration Rover. Image credit: NASA/JPL-Caltech

“We are here today to celebrate this great triumph of exploration, the incredible mission of this Mars rover. As bittersweet as the conclusion of Spirit’s time on Mars is for each of us, our job was to get to this day. To wear these rovers out, to leave behind no unutilized capability on the surface of Mars. For Spirit, we have done that.

What is truly remarkable is how much durability and capability Spirit had. These rovers were designed for only 90 days on the surface and one kilometer of driving distance. On her last day, Spirit had operated for 2210 Martian days, drove over 7730 meters and returned over 124 thousand images.

But it is not how long this rover lasted or how far she had driven, but how much exploration and scientific discovery she has accomplished. Spirit escaped the volcanic plains of Gusev Crater, mountaineer-ed up the Columbia Hills, survived three cold, dark Martian winters and two rover-killing dust storms, and surmounted debilitating hardware malfunctions. But out of this adversity, she made the most striking scientific discoveries that have forever changed our understanding of the Red Planet.

With the rovers originally designed only for a limited stay in the relatively comfortable environment of the Martian summer, the many years of extended operation meant these vehicles operate most of their time in the extreme environments of frigid temperatures and dark skies, well outside of their original design limits. The longevity and productivity of these rovers under such severe environmental conditions speak to the talent and dedication of the people, who designed, built, tested and operated these vehicles.

Spirit’s discoveries have changed our understanding of the Red Planet. We know now that Mars was not always a cold, dry and barren planet. That at one time liquid water flowed on it surface, sustained by a thicker atmosphere and warmer temperatures. At least, kilometer-scale lakes persisted in places. And that there were even sources of energy, hydrothermal systems, that could have supported life in this earlier habitable world.

We can’t do the impossible, make these machines operate forever. But, we have come as close to that as humans can. Spirit’s very accomplished exploration of Mars has rewritten the textbooks about the planet. Further, this rover has changed our understanding of ourselves and of our place in the Universe and approached questions of, are we alone and what is the future of this world?

But, beyond all the exploration and scientific discovery, Spirit has also given us a great intangible. Mars is no longer this distant, alien world. It is now our neighborhood. We go to work on Mars everyday.

But, let’s also remember that Spirit’s great accomplishments did not come at the expense of some vanquished foe or by outscoring some opponent. Spirit did this, we did this - to explore, to discover, to learn - for the benefit of all humankind. In that respect, these rovers represent the highest aspiration of our species.

Well done little rover. Sleep in peace. And, congratulations to you all. Thank you very much.”

By Jane Houston Jones

Are you eager to see the annual Perseids meteor shower tonight? You’ll have to wait until near midnight to see it, so why not pass the time by viewing Venus, Saturn and Mars right from your doorstep? Step outside for the planetary warm-up act just as soon as the sun sets. (Viewing times will be best over the next week. By August 20, the planets set lower on the horizon and are harder to see.)

All you have to do is look towards the west for bright Venus to appear. Now hold your clenched fist up to the sky, covering Venus. To the right of Venus, about half of a clenched fist away, is a second planet: That’s Saturn! And to the upper left of Venus is another planet: Mars!

That’s not all you’ll be able to see. Look below Venus for the slender crescent moon. If you don’t see the moon, look again on the night of Friday, August 13 — it will be a larger crescent to the left of Venus.

Though the three planets appear together in our line of sight, they are really far apart from each other. Mars is about 300 million kilometers (about 185 million miles) from Earth, while Venus is 112 million kilometers (about 70 million miles) away. Saturn? It’s 1,535 million kilometers (about 954 million miles) from Earth. And finally, the moon is only 363 thousand kilometers (about 225 thousand miles) away. It’s fun to compare the size of the moon and Mars, especially if you received that annual email incorrectly stating that Mars will be as big as the moon this month.

Jane Houston Jones

Updated Aug. 26, 2010

If you’re like me, you may have received an e-mail this summer telling you to go outside on August 27 and look up in the sky. The e-mail, most likely forwarded to you by a friend or relative, promises that Mars will look as big as the moon on that date and that no one will ever see this view again. Hmmm, it looks like the same e-mail I received last summer and the summer before that, too. In fact this same e-mail has been circulating since 2003, but with a few important omissions from the original announcement.

I’m Jane Jones, an amateur astronomer and outreach specialist for the Cassini mission at Saturn, and I’m here to set the record straight on when and how you can actually see Mars this month.

1. How did the “Mars in August” e-mail get started in the first place?

In 2003, when Mars neared opposition — its closest approach to Earth in its 22-month orbit around the sun — it was less than 56 million kilometers (less than 35 million miles) away. This was the closest it had been in over 50,000 years. The e-mail that circulated back then said that Mars, when viewed through a telescope magnified 75 times, would look as large as the moon does with the unaided eye. Even back in 2003, to the unaided eye, Mars looked like a reddish star in the sky to our eyes, and through a backyard telescope it looked like a small disc with some dark markings and maybe a hint of its polar ice cap. Without magnification, it never looked as large as the moon, even back in 2003!

2. Can the moon and Mars ever look the same size?

No. The moon is one-quarter the size of Earth and is relatively close — only about 384,000 kilometers (about 239, 000 miles) away. On the other hand, Mars is one-half the size of Earth and it orbits the sun 1-1/2 times farther out than Earth’s orbit. The closest it ever gets to Earth is at opposition every 26 months. The last Mars opposition was in January and the next one is in March 2011.

At opposition, Mars will be 101 million kilometers (63 million miles) from Earth, almost twice as far as in 2003. So from that distance, Mars could never look the same as our moon.

3. Is Mars visible in August 2010?

Mars and Saturn made a dramatic trio with brighter Venus this month. Skywatchers enjoyed seeing the three planets closely gathered on the 12th and 13th with the slender crescent moon nearby. On the 27th, you’ll see Venus shining brightly in the west. If you look above Venus, you may find faint Mars. Saturn is barely visible above the horizon, getting ready for its solar conjunction next month.

4. Can I see Mars and the moon at the same time this month?

Both the moon and Mars were next to one another on the 12th and 13th, but now you can see both planets a few hours apart. Look for Mars in the west at sunset, and watch the moon rise in the east a few hours later. On August 26th and 27th you can see the nearly full moon rising in the east at about 10 p.m. The bright planet below the moon on the 26th is Jupiter! On the 27th, the moon is to the left of the planet.

5. Will the “Mars in August” e-mail return next year?

Most certainly! But next year, you’ll be armed with facts, and perhaps you will have looked at the red planet for yourself and will know what to expect. And you will know exactly where to put that email. In the trash!

by Sue Smrekar
Deputy Project Scientist - Mars Reconnaissance Orbiter

A theme of Mars exploration is “Follow the Water,” since understanding the history of water on our planetary neighbor will help us understand if there were environments favorable for life to occur and how climate has changed over time. This is because all life on Earth requires water and we assume the same applies elsewhere in the universe. The Mars Reconnaissance Orbiter has made numerous discoveries that have provided new insights into past wet environments on Mars, water vapor in the planet’s current atmosphere and ice in the subsurface. However, so far, liquid water remains elusive.

The Shallow Radar, or “SHARAD” instrument is the only one on the Mars orbiter that was designed with a goal of discovering liquid water below Mars’ surface. This ground-penetrating radar instrument, which was supplied by the Italian Space Agency, transmits a radar signal at approximately 20 megahertz, and receives any radar waves that bounce off the surface or subsurface layers. The radar instrument has sufficient strength to see layers to a depth of about one kilometer (a little more than one-half mile), and even deeper in the polar caps. Layers in the subsurface reflect the radar wave if there is sufficient contrast in their dielectric properties (their bulk electrical properties), as for example between dry sand and ice-filled sand. Water is a much better conductor than other geologic materials, and thus should be readily detected if present.

This image from NASA’s Mars Reconnaissance Orbiter shows gully channels in a crater in the southern highlands of Mars.The gullies emanating from the rocky cliffs near the crater’s rim (upper left) show meandering and braided patterns typical of water-carved channels. Image credit: NASA/JPL/University of Arizona

Of all the features believed to be formed by water on Mars, we have found only two gullies known to have recent flows – within the last 5-10 years. Gullies are narrow channels that emanate from cliff walls, starting well below the local ground surface. Dr. Michael Malin used the Mars Orbital Camera on Mars Global Surveyor to repeatedly image these features because of their fresh, unweathered appearance. These efforts led to the discovery of the two relatively new gullies.

To date, the Shallow Radar instrument’s observations of dozens of regions containing gullies show no evidence of liquid water. Since slopes of the cliffs where the two new gullies occur are extremely steep, some scientists put forth an alternate hypothesis in which dry debris tumbling downhill could have formed the latest channels. Yet many of the features observed at these and other gullies strongly suggest that liquid water had at least some role in carving the channels. These channels may have formed when a past climate change caused subsurface ice to melt. Or perhaps liquid water was trapped in a past aquifer. But for now, liquid water, if it exists today on Mars, remains out of reach of the Mars Reconnaissance Orbiter.