Flying Formation - Around the Moon at 3,600 MPH

The act of two or more aircraft flying together in a disciplined, synchronized manner is one of the cornerstones of military aviation, as well as just about any organized air show. But as amazing as the U.S. Navy's elite Blue Angels or the U.S. Air Force's Thunderbirds are to behold, they remain essentially landlocked, anchored if you will, to our planet and its tenuous atmosphere. What if you could take the level of precision of these great aviators to, say, the moon? 

"Our job is to ensure our two GRAIL spacecraft are flying a very, very accurate trail formation in lunar orbit," said David Lehman, GRAIL project manager at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "We need to do this so our scientists can get the data they need." 

Essentially, trail formation means one aircraft (or spacecraft in this case), follows directly behind the other. Ebb and Flow, the twins of NASA's GRAIL (Gravity Recovery And Interior Laboratory) mission, are by no means the first to synch up altitude and "air" speed while zipping over the craters, mountains, hills and rills of Earth's natural satellite. That honor goes to the crew of Apollo 10, who in May 1969 performed a dress rehearsal for the first lunar landing. But as accurate as the astronauts aboard lunar module "Snoopy" and command module "Charlie Brown" were in their piloting, it is hard to imagine they could keep as exacting a position as Ebb and Flow. "It is an apples and oranges comparison," said Lehman. "Lunar formation in Apollo was about getting a crew to the lunar surface, returning to lunar orbit and docking, so they could get back safely to Earth. For GRAIL, the formation flying is about the science, and that is why we have to make our measurements so precisely." 

As the GRAIL twins fly over areas of greater and lesser gravity at 3,600 mph (5,800 kilometers per hour), surface features such as mountains and craters, and masses hidden beneath the lunar surface, can influence the distance between the two spacecraft ever so slightly.

How slight a distance change can be measured by the science instrument beaming invisible microwaves back and forth between Ebb and Flow? 

How about one-tenth of one micron? Another way to put it is that the GRAIL twins can detect a change in their position down to one half of a human hair (0.000004 inches, or 0.00001 centimeters). For those of you who are hematologists or vampires (we are not judging here), any change in separation between the two twins greater than one half of a red corpuscle will be duly noted aboard the spacecraft's memory chips for later downlinking to Earth. Working together, Ebb and Flow will make these measurements while flying over the entirety of the lunar surface. 

This begs the question, why would scientists care about a change of distance between two spacecraft as infinitesimal as half a red corpuscle a quarter million miles from Earth?

"Mighty oaks from little acorns grow – even in lunar orbit," said Maria Zuber, principal investigator of the GRAIL mission from the Massachusetts Institute of Technology, Cambridge. "From the data collected during these minute distance changes between spacecraft, we will be able to generate an incredibly high-resolution map of the moon's gravitational field. From that, we will be able to understand what goes on below the lunar surface in unprecedented detail, which will in turn increase our knowledge of how Earth and its rocky neighbors in the inner solar system developed into the diverse worlds we see today."

Getting the GRAIL twins into a hyper-accurate formation from a quarter million miles away gave the team quite a challenge. Launched together on Sept. 10, 2011, Ebb and Flow went their separate ways soon after entering space. Three-and-a-half months and 2.5 million miles (4 million kilometers) later, Ebb entered lunar orbit. Flow followed the next day (New Year's Day 2012). 

"Being in lunar orbit is one thing, being in the right lunar orbit for science can be something else entirely," said Joe Beerer, GRAIL's mission manager from JPL. "The twins initial orbit carried them as close to the lunar surface as 56 miles (90 kilometers) and as far out as 5,197 miles (8,363 kilometers), and each revolution took approximately 11.5 hours to complete. They had to go from that to a science orbit of 15 by 53 miles (24.5 by 86 kilometers) and took all of 114 minutes to complete."

To reduce and refine Ebb and Flow's orbits efficiently and precisely required the GRAIL team to plan and execute a series of trajectory modification burns for each spacecraft. And each maneuver had to be just right. 

"Because each one of these maneuvers was so important, we did a lot of planning and testing for each," said Beerer. "Over eight weeks, we did nine maneuvers with Ebb and 10 with Flow to establish the science formation. We would literally be watching our screens for a signal telling us about an Ebb rocket burn, then go into a meeting about the next burn for Flow. Our schedule was very full." 

Today, the calendar for GRAIL's flight team remains a busy one with the day-to-day operations of keeping NASA's lunar twins in synch. But as busy as the team gets, they still have time to peer skyward.

"Next time you look up and see the moon, you might want to take a second and think about our two little spacecraft flying formation, zooming from pole to pole at 3,600 mph," said Lehman. "They're up there, working together, flying together, getting the data our scientists need. As far as I'm concerned, they're putting on quite a show." 

NASA's Jet Propulsion Laboratory in Pasadena, Calif., manages the GRAIL mission for NASA's Science Mission Directorate, Washington. The Massachusetts Institute of Technology, Cambridge, is home to the mission's principal investigator, Maria Zuber. The GRAIL mission is part of the Discovery Program managed at NASA's Marshall Space Flight Center in Huntsville, Ala. Lockheed Martin Space Systems in Denver built the spacecraft. JPL is a division of the California Institute of Technology in Pasadena.

Synchronized NASA and ESA flights across Arctic Ocean - a success!

By Malcolm Davidson/ESA and Michael Studinger/NASA

Arctic sea-ice from the NASA P-3 (NASA/M. Studinger)

Monday April 2 has been much anticipated by the teams in Thule, Greenland (NASA) and Alert, Canada (ESA). While the objectives for the day were clear – jointly fly with all available planes beneath CryoSat’s early morning pass over the Arctic Ocean – the execution of such flights is and always will be a challenge. 

Flying joint multi-plane missions is a rather daunting task. Departure and rendezvous times and locations need to be calculated and maintained to ensure that the instruments on the different planes will see the same sea-ice floes below (these move after all), flight altitudes need to be established and maintained for safety reasons, instruments need to be warmed up and ready ‘in-time’, somewhat grumpy firefighters need to be coaxed out to the airstrip ahead of working hours to support an early departure and the list goes on.

With both teams committed to the flights, the first task early this morning was to check the weather forecast for the day. These proved to be good with temperatures of –29°C (–20°F) and generally clear skies; but not ideal! Some rather worrying cloud formations featured near the coast in satellite images.

NASA P-3 cockpit (NASA/M. Studinger)

Nevertheless, after a quick phone call between the NASA and ESA coordinators (at a time before most people have yet to reach for their mug of morning coffee) the decision was made: it's a go.

From then on it there was a flurry of activity on both sides, pilots warmed up their planes, instrument teams checked out their instruments, flight plans were programmed into the onboard computers and so on.

Twin Otter takes off

The NASA P-3 plane was the first to go out, leaving Thule a full hour before the two ESA planes located closer to the track. On the tarmac in Alert there was the first casualty of the day – despite heroic efforts the EM-bird ice-thickness instrument could not be coaxed into life. The die was cast – the second Twin-Otter plane would have to go it alone and meet up with the NASA P-3.

NASA’s sea-ice mission plan for April 2 (yellow). We teamed up with ESA at 10520 north of Alert. (NASA/M. Studinger)

Around 07:30 (local time) the CryoSat satellite – always on schedule – ripped above the Arctic Ocean taking about one minute to race along the 500-km (310 mile) transect that would later take several hours of plane time to cover.

At 08:00 both the ESA and NASA planes reached the edge of the Arctic Ocean almost simultaneously and headed across the sea ice flying exactly along the same line that CryoSat had just covered. The timing was so good that, for the first time, there was visual contact between the planes, a remarkable achievement!

The image below, which is a DMS mosaic from Eric Fraim shows one of the many leads we saw from the NASA P-3 today with a variety of different types of sea ice.

DMS mosaic of lead in the sea ice (NASA/DMS/E. Fraim)

The rest of the day turned out very well indeed. The clouds that had worried the teams in the morning only formed only a thin band near the coast. The rest of the line out on the ocean was clear and beautifully lit by the oblique Arctic Sun. All the onboard scientific instruments on both planes worked well so that by the end of the day it was clear that the day had been a success.

By joining forces both the ESA and NASA teams collected a highly valuable dataset that will benefit the scientific achievements of ESA’s CryoSat and NASA’s future ICESat-2 mission to better monitor sea ice from space.

Space Is My Mistress

Seeing as how April is National Poetry Month….

Space is My Mistress

Space is my Mistress,
and she beckons my return.
Since our departure I think of you
and yearn to fly across the heavens arm in arm.
I marvel at your figure,
defined by the edges of continents.
You gaze at me with turquoise eyes,
perhaps mistaken for ocean atolls.
You tease me to fall into your bosom,
sculptured by tectonic rifts,
only to move away as if playing some tantalizing game.
Time and time we turn together,
through day, and night, and day,
repeating encounters every 90 minutes with a freshness,
as if we have never seen our faces before.
We stroll outside together,
enveloped by naked cosmos,
filled with desire to be one.
So close,
you sense my every breath,
which masks your stare through visor haze.
We dance on the swirls of cloud tops,
while skirting the islands of blue.
You know my heart beats fast for you.
Oh, Space is my mistress,
and when our orbits coincide,
we will once again make streaks of aurora across the sky.

NASA GRAIL Returns First Student-Selected Moon Images

PASADENA, Calif. -- One of two NASA spacecraft orbiting the moon has beamed back the first student-requested pictures of the lunar surface from its onboard camera. Fourth grade students from the Emily Dickinson Elementary School in Bozeman, Mont., received the honor of making the first image selections by winning a nationwide competition to rename the two spacecraft.

The image was taken by the MoonKam, or Moon Knowledge Acquired by Middle school students. Previously named Gravity Recovery And Interior Laboratory (GRAIL) A and B, the twin spacecraft are now called Ebb and Flow. Both washing-machine-sized orbiters carry a small MoonKAM camera. Over 60 student–requested images were taken by the Ebb spacecraft from March 15-17 and downlinked to Earth March 20.

"MoonKAM is based on the premise that if your average picture is worth a thousand words, then a picture from lunar orbit may be worth a classroom full of engineering and science degrees," said Maria Zuber, GRAIL mission principal investigator from the Massachusetts Institute of Technology in Cambridge, Mass. "Through MoonKAM, we have an opportunity to reach out to the next generation of scientists and engineers. It is great to see things off to such a positive start."

GRAIL is NASA's first planetary mission to carry instruments fully dedicated to education and public outreach. Students will select target areas on the lunar surface and request images to study from the GRAIL MoonKAM Mission Operations Center in San Diego.

The MoonKAM program is led by Sally Ride, America's first woman in space, and her team at Sally Ride Science in collaboration with undergraduate students at the University of California in San Diego. More than 2,700 schools spanning 52 countries are using the MoonKAM cameras.

"What might seem like just a cool activity for these kids may very well have a profound impact on their futures," Ride said. "The students really are excited about MoonKAM, and that translates into an excitement about science and engineering."

Launched in September 2011, Ebb and Flow will answer longstanding questions about the moon and give scientists a better understanding of how Earth and other rocky planets in the solar system formed.

NASA's Jet Propulsion Laboratory in Pasadena, Calif., manages the GRAIL mission for NASA's Science Mission Directorate in Washington. The Massachusetts Institute of Technology, Cambridge, is home to the mission's principal investigator, Maria Zuber. GRAIL is part of the Discovery Program managed at NASA's Marshall Space Flight Center in Huntsville, Ala. Lockheed Martin Space Systems in Denver built the spacecraft. The California Institute of Technology in Pasadena manages JPL for NASA.

NASA GRACE Data Hit Big Apple on World Water Day

To highlight declines in the world's groundwater supplies, a new visualization of Earth's groundwater reserves, created in part with space data from the joint NASA/German Aerospace Center (DLR) Gravity Recovery and Climate Experiment (GRACE) mission, debuted on New York's Times Square on March 22, International World Water Day.

The 30-second animation, titled "Visualizing Seasonal and Long-term Changes in Groundwater Levels," will be on display several times each hour through April 22 on Times Square's massive Thomson Reuters and NASDAQ digital signboards. Viewers of the interactive animation are invited to use their mobile devices to submit their city and add a graph to the sign.

Netherlands designer Richard Vijgen developed the animation using GRACE data analyzed by professor Jay Famiglietti, director of the UC Center for Hydrologic Modeling at the University of California, Irvine; and from United States Geological Survey data supplied by Leonard Konikow. Vijgen was the winning entry in an international design visualization competition sponsored by the organization HeadsUP!, in collaboration with Visualizing.org. Founded by digital media artist Peggy Weil, HeadsUp! challenges designers to visualize critical global issues and create a shared sign for the public square.

Groundwater is a critical, but often overlooked, natural resource. According to a U.N. report, more than 1.5 billion people around the world depend on groundwater for their drinking water. It comes from the natural percolation of precipitation and other surface waters down through Earth's soil and rock, accumulating in cavities and layers of porous rock, gravel, sand or clay. Groundwater levels respond slowly to changes in weather and can take months or years to replenish once pumped for irrigation or other uses.

Famiglietti's analyses show that groundwater is being depleted at alarming rates in many of the world's major aquifers. "The GRACE data set is exciting, because it gives us the first global pictures of Earth's changing freshwater," he said.

The twin GRACE satellites, which celebrated their 10th year in orbit this week, measure minute changes in Earth's gravity field by measuring micron-scale variations in the separation between the two spacecraft, flying in formation 137 miles (220 kilometers) apart in low Earth orbit. These variations in gravitational pull are caused by local changes in Earth's mass. Masses of water, ice, air and solid Earth can be moved by weather patterns, seasonal change, climate change and even tectonic events such as large earthquakes. GRACE was developed by NASA's Jet Propulsion Laboratory, Pasadena, Calif.

The depletion of groundwater from large aquifers due to drought and human activities affects gravity enough to provide a signal that GRACE can measure, in concert with other remote sensing data. After accounting for other mass variations, such changes in gravity can be translated into an equivalent change in water. GRACE has been used to detect major depletion of groundwater in northern India, California's Central Valley and elsewhere around the globe.

Groundwater levels are monitored by local sensors as well as from space with GRACE, but the data are formatted for expert hydrologists, rather than concerned citizens. Underground and out of sight, the public lacks a clear indicator of changing groundwater levels. By using the GRACE satellite data, HeadsUP! offered designers the chance to visualize the water under the surface of Earth, as "seen" from space.

What's Next For NASA?

The end of the space shuttle program does not mean the end of NASA, or even of NASA sending humans into space. NASA has a robust program of exploration, technology development and scientific research that will last for years to come. Here is what's next for NASA:

Exploration
NASA is designing and building the capabilities to send humans to explore the solar system, working toward a goal of landing humans on Mars. We will build the Multi-Purpose Crew Vehicle, based on the design for the Orion capsule, with a capacity to take four astronauts on 21-day missions.

NASA is also moving forward with the development of the Space Launch System -- an advanced heavy-lift launch vehicle that will provide an entirely new national capability for human exploration beyond Earth's orbit. The SLS rocket will use a liquid hydrogen and liquid oxygen propulsion system, which will include shuttle engines for the core stage and the J-2X engine for the upper stage.

We are developing the technologies we will need for human exploration of the solar system, including solar electric propulsion, refueling depots in orbit, radiation protection and high-reliability life support systems.

International Space Station
The International Space Station is the centerpiece of our human spaceflight activities in low Earth orbit. The ISS is fully staffed with a crew of six, and American astronauts will continue to live and work there in space 24 hours a day, 365 days a year. Part of the U.S. portion of the station has been designated as a national laboratory, and NASA is committed to using this unique resource for scientific research.

The ISS is a test bed for exploration technologies such as autonomous refueling of spacecraft, advanced life support systems and human/robotic interfaces. Commercial companies are well on their way to providing cargo and crew flights to the ISS, allowing NASA to focus its attention on the next steps into our solar system.

Aeronautics
NASA is researching ways to design and build aircraft that are safer, more fuel-efficient, quieter, and environmentally responsible. We are also working to create traffic management systems that are safer, more efficient and more flexible. We are developing technologies that improve routing during flights and enable aircraft to climb to and descend from their cruising altitude without interruption.

We believe it is possible to build an aircraft that uses less fuel, gives off fewer emissions, and is quieter, and we are working on the technologies to create that aircraft. NASA is also part of the government team that is working to develop the Next Generation Air Transportation System, or NextGen, to be in place by the year 2025. We will continue to validate new, complex aircraft and air traffic control systems to ensure that they meet extremely high safety levels.

Science
NASA is conducting an unprecedented array of missions that will seek new knowledge and understanding of Earth, the solar system and the universe. NASA has observatories in Earth orbit and deep space, spacecraft visiting the moon and other planetary bodies, and robotic landers, rovers, and sample return missions. NASA's science vision encompasses questions as practical as hurricane formation, as enticing as the prospect of lunar resources, and as profound as the origin of the Universe.

5 NASA rockets to light up stretch of East Coast skies

A quintuple rocket launch promises to put on a spectacular, but brief, overnight light show of luminescent vapor trails in the skies above the U.S. East Coast tonight, weather permitting. The sky display may puzzle and amaze some unsuspecting observers, so before you make that phone call to your local news or police, here is why this is happening and when you may see it.

The bright phenomenon will be caused by NASA's Anomalous Transport Rocket Experiment (ATREX), which will launch five chemical-bearing suborbital rockets in about five minutes to test the flow of winds and electrical currents at high altitudes. The rockets will blast off from NASA's Wallops Flight Facility on Wallops Island, Va., on the Atlantic coast during a window that opens tonight at midnight EDT and closes at 1:30 a.m. EDT Thursday.

As part of the mission, the five rockets will each release a chemical tracer that should inscribe brilliant milky white trails in the nighttime sky and allow scientists and the general public to actually "see" high-altitude winds at the edge of space, according to a NASA description.

Midnight launch lights
If all goes well, NASA intends to photograph the trails from three different sites: Wallops Island, southern New Jersey and the outer banks of North Carolina. Should weather conditions be unfavorable, the firings will be delayed to another night, with alternate launch dates available between March 16 and April 3.

Three different types of sounding rockets will be used to create the five cloud trails: two Terrier Improved Malemutes, two Terrier Improved Orions and one Terrier Oriole. These small rockets are powerful enough to launch instruments off the planet on short flights, but not strong enough to reach orbit and circle the Earth.

Each rocket will eject a stream of the chemical trimethyl aluminum (TMA), which will be illuminated at high altitudes by the sun (which will be below the local horizon at ground level). Initially, the clouds are expected to glow in reddish hues, then quickly turn to white, They could persist in the sky for as long as 20 minutes before fading completely away.

The ATREX project is aimed at gathering information to better understand the processes responsible for the high-altitude jet stream winds located 60 to 65 miles (97 to 105 kilometers) above the surface of the Earth.

That works out to a potential viewing radius of up to 450 miles (725 km), suggesting that the resultant cloud trails might be glimpsed from perhaps as far north as southern Vermont and New Hampshire, as far south as the border of coastal North and South Carolina and as far west as central West Virginia.

NASA's Goddard, Glenn Centers Look to Lift Space Astronomy out of the Fog

A fogbank is the least useful location for a telescope, yet today's space observatories effectively operate inside one. That's because Venus, Earth and Mars orbit within a vast dust cloud produced by comets and occasional collisions among asteroids. After the sun, this so-called zodiacal cloud is the solar system's most luminous feature, and its light has interfered with infrared, optical and ultraviolet observations made by every astronomical space mission to date.

"To put it simply, it has never been night for space astronomers," said Matthew Greenhouse, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Md. Light from zodiacal dust can be a thousand times brighter than the sources astronomers actually target, limiting sensitivity in much the same way that bright moonlight hampers ground-based observatories. The dust and its unwanted illumination are greatest in the plane of Earth's orbit, the same plane in which every space telescope operates.

Placing future astronomy missions on more tilted orbits would let spacecraft spend significant amounts of time above and below the thickest dust and thereby reduce its impact on observations. So Greenhouse teamed with Scott Benson at NASA's Glenn Research Center in Cleveland, Ohio, to investigate how these "dark sky" or extra-zodiacal orbits might improve mission science and to develop a means of cost-effectively reaching them.

"Just by placing a space telescope on these inclined orbits, we can improve its sensitivity by a factor of two in the near-ultraviolet and by 13 times in the infrared," Greenhouse explained. "That's a breakthrough in science capability with absolutely no increase in the size of the telescope's mirror."

Greenhouse, Benson and the COllaborative Modeling and Parametric Assessment of Space Systems (COMPASS) study team at NASA Glenn designed a mission that utilizes new developments in solar arrays, electric propulsion and lower-cost expendable launch vehicles. Their proof-of-concept mission is the Extra-Zodiacal Explorer (EZE), a 1,500-pound EX-class observatory that could accommodate a telescope in the size range of the recently completed WISE mission — all within the cost and schedule constraints of NASA’s Explorer Program.

Launched on a SpaceX Falcon 9 rocket, EZE would use a powerful new solar-electric drive as an upper stage to direct the spacecraft on a gravity-assist maneuver past Earth or Mars. This flyby would redirect the mission into an orbit inclined by as much as 30 degrees to Earth's.

The result, the scientists say, will be the highest-performance observatory ever achieved in the decades-long history of NASA's Explorer program.

"We see EZE as a game-changer, the first step on a new path for NASA Explorers that will yield major science goals despite limited resources," said Benson, who previously managed the new electric propulsion technology project.

Solar storm shakes Earth magnetic field

WASHINGTON (AP) — A solar storm shook the Earth's magnetic field early Friday, but scientists said they had no reports of any problems with electrical systems.

After reports Thursday of the storm fizzling out, a surge of activity prompted space weather forecasters to issue alerts about changes in the magnetic field.

"We really haven't had any reports from power system operators yet," Rob Steenburgh, a space weather forecaster at the National Oceanic and Atmospheric Administration's Space Weather Prediction Center in Boulder, Colo., said early Friday. "But sometimes they don't come in until after the storm."

He said the storm reached a moderate level late Thursday, before going to a strong level early Friday. For most of Thursday, it was rated as minor.

Scientists say such storms don't pose a threat to people, just technology.

The space weather center's website says a storm rated as strong could force corrections to voltage systems and trigger false alarms on some protection devices, as well as increase drag on satellites and affect their orientation.

The forecasters weren't aware of any significant impact to electrical or technological systems, but said there was a two-hour blackout of high frequency radio communications — affecting mainly ham radio operations — stretching from eastern Africa to eastern Australia.

Steenburgh also said that there was another solar flare late Thursday, similar to the one a few days ago that set off the current storm.

"Right now we're still analyzing when it will arrive" and how strong it could be, he said.

The space weather center had reports of Northern Lights across Canada and dipping into the northern tier of U.S. states, Steenburgh said.

While some experts thought the threat from the solar storm passed by earlier Thursday, the space weather center maintained the storm's effects could continue through Friday morning.

The current storm, which started with a solar flare Tuesday evening, caused a stir Wednesday because forecasts were for a strong storm with the potential to knock electrical grids offline, mess with GPS and harm satellites. It even forced airlines to reroute a few flights on Thursday.

It was never seen as a threat to people, just technology, and teased skywatchers with the prospect of colorful Northern Lights dipping further south.

But when the storm finally arrived around 6 a.m. EST Thursday, after traveling at 2.7 million mph, it was more a magnetic breeze than a gale. The power stayed on. So did GPS and satellites. And the promise of auroras seemed to be more of a mirage.

Scientists initially figured the storm would be the worst since 2006, but now seems only as bad as ones a few months ago, said Joe Kunches, a scientist at the NOAA center. The strongest storm in recorded history was probably in 1859, he said.

"It's not a terribly strong event. It's a very interesting event," Kunches said.

Forecasters can predict the speed a solar storm travels and its strength, but the north-south orientation is the wild card. This time it was a northern orientation, which is "pretty benign," Kunches said. Southern would have caused the most damaging technological disruption and biggest auroras.

On Thursday, North American utilities didn't report any problems, said Kimberly Mielcarek, spokeswoman for the North American Electric Reliability Corporation, a consortium of electricity grid operators. Her office didn't respond to a phone call early Friday.

NASA Mars Orbiter Catches Twister in Action

An afternoon whirlwind on Mars lofts a twisting column of dust more than half a mile (800 meters) high in an image from the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter.

HiRISE captured the image on Feb. 16, 2012, while the orbiter passed over the Amazonis Planitia region of northern Mars. In the area observed, paths of many previous whirlwinds, or dust devils, are visible as streaks on the dusty surface.

The active dust devil displays a delicate arc produced by a westerly breeze partway up its height. The dust plume is about 30 yards or meters in diameter.

The image was taken during the time of Martian year when that planet is farthest from the sun. Just as on Earth, winds on Mars are powered by solar heating. Exposure to the sun's rays declines during this season, yet even now, dust devils act relentlessly to clean the surface of freshly deposited dust, a little at a time.

Dust devils occur on Earth as well as on Mars. They are spinning columns of air, made visible by the dust they pull off the ground. Unlike a tornado, a dust devil typically forms on a clear day when the ground is heated by the sun, warming the air just above the ground. As heated air near the surface rises quickly through a small pocket of cooler air above it, the air may begin to rotate, if conditions are just right.

The Mars Reconnaissance Orbiter has been examining Mars with six science instruments since 2006. Now in an extended mission, the orbiter continues to provide insights into the planet's ancient environments and how processes such as wind, meteorite impacts and seasonal frosts continue to affect the Martian surface today. This mission has returned more data about Mars than all other orbital and surface missions combined.

More than 21,700 images taken by HiRISE are available for viewing on the instrument team's website: http://hirise.lpl.arizona.edu . Each observation by this telescopic camera covers several square miles, or square kilometers, and can reveal features as small as a desk.