Even before Hughes Aircraft Company was selected as the contractor that would design and build the Surveyor landers, JPL began conducting tests of materials that would help to cushion the impact of a moon landing. It was to be a soft landing, in contrast to the Ranger crash landings, but there would still be a drop of about 13 feet, where the Surveyor vernier engines would cut off and the lander would free fall to the surface of the moon.
The lander had a tripod structure, with hydraulic shock absorbers in the landing legs. JPL also planned to use three blocks on the underside of the lander, one near each leg, that would absorb some of the impact. Various materials, sizes, and configurations were tested, including aluminum tubes and sheets, some formed into a hexagonal honeycomb pattern. The JPL Photolab took dozens of photos for the Engineering Research Section (354) which are identified simply as “crushable materials” and they show several series of tests completed in 1960-1962. The results were reported in JPL’s bimonthly Space Programs Summaries and other technical reports.
For more information about the history of JPL, contact the JPL Archives for assistance. [Archival and other sources: Surveyor Mission Reports; various Space Programs Summaries; RS36-5, vol. 2; Section 354 photo indexes, JPL telephone books and organization charts.]
At 8 p.m. after a long day of work in the Houston humidity, Derek Rutavic, manager of the NASA Gulfstream-III that will head back to Greenland this fall, and I were in the back of the plane singing One Direction’s "Drag Me Down" over the high frequency radio system. It was stifling hot, getting dark and we were tired and hungry.
But Oceans Melting Greenland (OMG) Principal Investigator Josh Willis and Project Manager Steve Dinardo, too busy to take off their sweaty fire retardant flight suits, were troubleshooting electronics at two racks of computers, and they’d asked Rutavic to get on the headset to find out if the headset noise was interfering with the high radio frequency data signal the ocean science probes were sending back to the plane. Rutavic sat on an empty science probe container, while I lounged on one of the sofas singing along in awe of the amount of hard work this team was putting in.
We’d been up early, flown multiple test flights, worked through lunch. And all of this after days and days of maintenance, and weather delays, and more hard work after more hard work. Earlier in the day, NASA T-38 supersonic jet pilot Bill Rieke flew mind-bogglingly close to the G-III to photograph the science probe deployment and determine if the technique of launching the probes through a hole in the bottom of the plane would succeed. And yes, it did. But that success merely signaled the OMG team to continue working.
And I understood exactly why this team kept going, kept moving, kept pushing on into the evening, regardless of being tired and hot and hungry. I knew exactly why they decided to keep working on the challenge. They chose to push through because they’d found something to care about, and that's always more important than our difficulties and problems. When we focus on what we really care about, we get busy doing something, even in the face of trouble. And that’s how science works.
Lessons from a sea slug
I first learned to care about the natural world around me during my junior year in college. I was in an oceanography course and we were studying sea slugs. (Yes, sea slugs.) A sea slug changed my life. Before then, I’d been, like many people, disengaged and uninterested in science. In third grade, someone came to our classroom and told us we could be the first female astronaut, and I remember thinking, “No, I couldn’t, not me.”
And now? Even though I have a job at NASA, I still feel like I don’t belong in the world of science. I feel more comfortable around athletes and artists than I do with a bunch of Ph.D.s. Maybe it’s some poorly defined stereotype that I’ve somehow bought into or some preconceived notion of how someone who does science is supposed to behave.
But those sea slugs taught me that I cared more about the natural world than I cared about the struggle of not fitting in or the challenge of the work. They appeared so delicate, small and defenseless, and I identified with that. They helped me feel connected. Noticing them forced me to wonder what else I’d start to notice if I slowed down enough to pay attention. And that connection to the natural world helped me stay committed to science, even when it was hard, even when there were problems, even when I felt like running away.
Sure, scientific experimentation, just like much of real life, includes problems, troubles, obstacles and difficulties almost every day. And while it’s true that someone, somewhere has to troubleshoot something every step of the way, we can also be excited about the effort. The OMG team understands that problems and hard work are not the exception, they are the norm. They are part of accomplishment. And it’s totally possible to thrive on these difficulties and challenges.
Look, we could be setting the world on fire right now, not by burning fossil fuels, but by our burning desire to understand our environment. Because the whole point of this experimental mission is to find out how quickly the warmer waters around Greenland are melting the second-largest ice sheet on the planet. It’s major; it’s dire; it’s intense. It’s one of the most important issues of our time.
And sitting there in the back of that plane made me think about how we, as individuals and as a society, have to find something in this world to care about. We have to find something in this world that is more important than our challenges and problems.
And you? I hope you decide to find something to care about. I hope you find something that’s important enough that you’re willing to push through your struggles, your fears and your problems to just do the work.
Find out more about Oceans Melting Greenland.
View and download OMG animations and graphics.
We know more about the moon and other planets than we do some places on our home planet. Remote parts of the world ocean remain uncharted, especially in the polar regions, especially under areas that are seasonally covered with ice and especially near jagged coastlines that are difficult to access by boat. Yet, as global warming forces glaciers in places like Greenland to melt into the ocean, causing increased sea level rise, understanding these remote places has become more and more important.
This past spring, Oceans Melting Greenland (OMG) Principal Investigator Josh Willis led a team of NASA scientists to begin gathering detailed information about the interface between Greenland’s glaciers and the warming ocean waters that surround them. The next step in accessing this extremely remote region involves dropping a series of Airborne Expendable Conductivity Temperature Depth, or AXCTD, probes that will measure ocean temperature and salinity around Greenland, from the sea surface to the sea floor. With this information, they hope to find out how quickly this warmer ocean water is eating away at the ice.
Since no one has ever dropped AXCTDs through a tube at the bottom of a modified Gulfstream-III, the OMG team headed to Ellington Field Airport near NASA’s Johnson Space Center in Houston, Texas, for a test drop into the Gulf of Mexico. I went along for the ride.
The money shot
Temperature and salinity
3, 2, 1 ... drop!
AXCTD sails down
The flight path
Details, details, details
Find out more about Oceans Melting Greenland.
View and download OMG animations and graphics.
Thank you for your comments.
Surveyor mission planning began in 1960. The mission included seven spacecraft that would soft land on the Moon, using three vernier engines and a retrorocket. The spacecraft would collect data and images of the surface, in order to ensure a safe landing for Apollo astronauts a few years later. Hughes Aircraft Company was selected to design and build the landers and the project was managed by JPL, which also provided tracking and communications. Surveyor I was launched on May 31, 1966, landed on the Moon June 2, and sent back more than 11,000 photos of the lunar surface. The entire image set from Surveyors 1-7 has recently been digitized, and will soon be added to NASA’s Planetary Data System.
This image was created by Hughes artist Carlos Lopez. It was used in a Surveyor poster, which was a common practice in the days before computer aided drawing. This poster was recently received by the JPL Archives, as part of a collection of Surveyor documentation.
For more information about the history of JPL, contact the JPL Archives for assistance. [Archival and other sources: Surveyor Mission Reports, Ranger and Surveyor Fact Sheet, and the NASA Historical Data Book.]
Dear Glutdawnous Readers,
The distant dwarf planet that Dawn is circling is full of mystery and yet growing ever more familiar. Ceres, which only last year was hardly more than a fuzzy blob against the stars, is now a richly detailed world, and our portrait grows more elaborate every day. Having greatly surpassed all of its original objectives, the reliable explorer is gathering still more data from its unique vantage point. Everyone who hungers for new knowledge about the cosmos or for bold adventures far from Earth can share in the sumptuous feast Dawn has been serving.
One of the major objectives of the mission was to photograph 80 percent of Ceres' vast landscape with a resolution of 660 feet (200 meters) per pixel. That would provide 150 times the clarity of the powerful Hubble Space Telescope. Dawn has now photographed 99.8 percent with a resolution of 120 feet (35 meters) per pixel.
This example of Dawn's extraordinary productivity may appear to be the limit of what it could achieve. After all, the spaceship is orbiting at an altitude of only 240 miles (385 kilometers), closer to the ground than the International Space Station is to Earth, and it will never go lower for more pictures. But it is already doing more.
Since April 11, instead of photographing the scenery directly beneath it, Dawn has been aiming its camera to the left and forward as it orbits and Ceres rotates. By May 25, it will have mapped most of the globe from that angle. Then it will start all over once more, looking instead to the right and forward from May 27 through July 10. The different perspectives on the terrain make stereo views, which scientists can combine to bring out the full three dimensionality of the alien world. Dawn already accomplished this in its third mapping orbit from four times its current altitude, but now that it is seeing the sights from so much lower, the new topographical map will be even more accurate.
Dawn is also earning extra credit on its assignment to measure the energy of gamma rays and neutrons. We have discussed before how the gamma ray and neutron detector (GRaND) can reveal the atomic composition down to about a yard (meter) underground, and last month we saw initial findings about the distribution of hydrogen. However, Ceres' nuclear glow is very faint. Scientists already have three times as much GRaND data from this low altitude as they had required, and both spectrometers in the instrument will continue to collect data. In effect, Dawn is achieving a longer exposure, making its nuclear picture of Ceres brighter and sharper.
In December we explained how using the radio signal to track the probe's movements allows scientists to chart the gravity field and thereby learn about the interior of Ceres, revealing regions of higher and lower density. Once again, Dawn performed even better than expected and achieved the mission's planned accuracy in the third mapping orbit. Because the strength of the dwarf planet's gravitational tug depends on the distance, even finer measurements of how it varies from location to location are possible in this final orbit. Thanks to the continued smooth operation of the mission, scientists now have a gravitational map fully twice as accurate as they had anticipated. With additional measurements, they may be able to squeeze out a little more detail, perhaps improving it by another 20 percent before reaching the method's limit.
Dawn has dramatically overachieved in acquiring spectra at both visible and infrared wavelengths. We have previously delved into how these measurements reveal the minerals on the ground and what some of the interesting discoveries are. Having already acquired more than seven times as many visible spectra and 21 times as many infrared spectra as originally called for, the spacecraft is adding to its riches with additional measurements. We saw in January that VIR has such a narrow view that it will never see all of Ceres from this close, so it is programmed to observe features that have caught scientists' interest based on the broad coverage from higher altitudes.
Dawn's remarkable success at Ceres was not a foregone conclusion. Of course, the flight team has confronted the familiar challenges people encounter every day in the normal routine of piloting an ion-propelled spaceship on a multibillion-mile (multibillion-kilometer) interplanetary journey to orbit and explore two uncharted worlds. But the mission was further complicated by the loss of two of the spacecraft's four reaction wheels, as we have recounted before. (In full disclosure, the devices aren’t actually lost. We know precisely where they are. But given that one stopped functioning in 2010 and the other in 2012, they might as well be elsewhere in the universe; they don’t do Dawn any good.) Without three of these units to control its orientation in space, the robot has relied on its limited supply of hydrazine, which was not intended to serve this function. But the mission's careful stewardship of the precious propellant has continued to exceed even the optimistic predictions, allowing Dawn good prospects for carrying on its fruitful work. In an upcoming Dawn Journal, we will discuss how the last of the dwindling supply of hydrazine may be used for further discoveries.
In the meantime, Dawn is continuing its intensive campaign to reveal the dwarf planet's secrets, and as it does so, it is passing several milestones. The adventurer has now been held in Ceres' tender but firm gravitational embrace longer than it was in orbit around Vesta. (Dawn is the only spacecraft ever to orbit two extraterrestrial destinations, and its mission would have been impossible without ion propulsion.) The spacecraft provided us with about 31,000 pictures of Vesta, and it has now acquired the same number of Ceres.
For an interplanetary traveler, terrestrial days have little meaning. They are merely a memory of how long a faraway planet takes to turn on its axis. Dawn left that planet long ago, and as one of Earth's ambassadors to the cosmos, it is an inhabitant of deep space. But for those who keep track of its progress yet are still tied to Earth, on May 3 the journey will be pi thousand days long. (And for our nerdier friends and selves, it will be shortly after 6:47 p.m. PDT.)
By any measure, Dawn has already accomplished an extraordinary mission, and there is more to look forward to as its ambitious expedition continues.
Dawn is 240 miles (385 kilometers) from Ceres. It is also 3.73 AU (346 million miles, or 558 million kilometers) from Earth, or 1,455 times as far as the moon and 3.70 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take one hour and two minutes to make the round trip.
From 1967 through the early 1970s, a number of studies were conducted at JPL with the goal of reducing the size of computer memory and developing miniature storage media for spacecraft computers.
These early tests used Curie-point writing to communicate the bits (ones and zeroes) of computer data. In various tests, a hot wire stylus, an electron beam, or a ruby laser were used to heat tiny dots (around one micrometer in size) on thin ferromagnetic manganese bismuthide (MnBi) film. The material was heated to just above its Curie temperature (the point at which the material is demagnetized) then cooled within a magnetic field, controlling the direction of the magnetization for each dot. The recorded bits of information were observed with polarized light using the Faraday effect. The recorded information could be completely erased by saturating the film in an applied magnetic field, then the recording process could be repeated.
The newest Historical Photo of the Month http://beacon.jpl.nasa.gov/historical-photo-of-the-month shows Dr. George Lewicki and Dr. Dimiter Tchernev who worked on this task. It received NASA funding of $175,000 per year (about $1.2 million in 2016 dollars). The studies were documented in a series of published papers, articles in JPL Space Programs Summaries, and a press release. It was reported that one square inch of magnetic film could hold as much data as computer memory that (in 1967) took up ten cubic feet of space.
For more detailed information about the history of JPL, contact the Library and Archives Reference Desk at (818) 354-4200 or firstname.lastname@example.org. If you have questions about the Historical Photo of the Month, please contact archivist Julie Cooper at Julie.A.Cooper@jpl.nasa.gov.
Cimate change news is intense. Ice caps are melting, the fire season lasts all year long; we have epic storms plus record-breaking floods, droughts and cyclones.
And this year will probably be the Hottest. Year. Ever.
When I interact with the public, I’m bombarded with questions such as “Are we all going to die?” and “How soon will humans go extinct?”
Happy Earth Day, everyone (wipes brow, rolls eyes).
Yet, when I wake up in the morning I'm excited to come to work. I'm energized. I’m amped, really amped. As in, kicking-butt-and-taking-names amped. Why? Because global warming is the greatest challenge of our lives, and challenge is what drives us. Challenge provides us with opportunity, challenge forces us to grow, challenge opens the way for amazing achievement. Challenge is exciting. Without challenge, without struggle, without discomfort, no one would ever advance.
So, when someone gets in my face and is super negative, I try to stay powerful, strong and confident. I tell myself that pressure is okay and I'm going to keep moving no matter what. Because I care about this planet so much that I choose to make a difference.
Yes, carbon dioxide levels are high and increasing rapidly. Yes, future generations will have some extraordinarily difficult challenges to deal with. But denial, avoidance and helplessness aren’t solutions. Can you imagine if we NASA peeps just sat there saying “Oh no, that’s too hard” when faced with huge obstacles? Are you kidding me? Come on! You think it’s easy to build science instruments on satellites and launch them into space? You think it’s easy to measure glaciers melting around the edges of Greenland, or the condition of coral reefs in the Pacific, or plankton blooms across the North Atlantic, or conduct eight field research campaigns in one year?
When the going gets tough—and it does, almost every day—we don’t just stop. We keep working. We know that no successful person got As on every test and that failure and struggle are part of accomplishment. We know that grit and determination will get you everywhere!
In this blog, I write about ocean pollution, sea level rise, climate change and decreasing biodiversity not to scare you, but to empower you, so we can make a difference—you and I, together. Someone reading this blog entry might be the creator of a new breakthrough technology, and then there will be a whole new reality.
So, when you think about the challenge of climate change this Earth Day, consider the possibility of welcoming that challenge. Our shared story could be a story about not giving up, about looking forward to growth, about saying, “Game on.”
Find out more about NASA earth expeditions here.
Join NASA for a #24Seven celebration of Earth Day.
Thank you for caring enough to make a difference and for being powerful in the world.
In between 1982 and 1997, JPL had no active missions on the surface of Mars. July 1986 was the 10th anniversary of the Viking mission, and an artist was hired to help show the possibilities of future Mars exploration. This artist’s rendering depicts a fleet of landers with astronauts aboard. The one on its side enabled cargo bay doors to open so a vehicle could be driven out onto the surface of the planet and other cargo unloaded.
Hey, readers: Our team reads your comments. We share them at our meetings. Sometimes they make us laugh, or sigh, or even scratch our heads.
We see that you see us. Yay for connecting!
And this is how I know you’ve noticed NASA’s latest airborne campaign, where NASA scientists fly a bunch of NASA instruments on a NASA airplane to study more details about Earth. Cool, right?
Lately, we’ve been flying around the edge of Greenland collecting radar data about how much its glaciers are melting into the sea. And the most common comment we get goes something like “Wheee! Let’s go. Take me with you.” When I told a friend about the possibility of joining the team in the field, she exclaimed, “All expenses paid?”
HAHAHA … no. As if a NASA expedition to Greenland is like a resort vacation instead of a giant heaping pile of hard work.
“When I looked down at the rivers of ice running into the ocean, it was shocking to think about the effects of rising sea levels as far away as California or Antarctica,” said Principle Investigator Josh Willis, two days after returning from his first trip to observe this pristine part of our planet as it melts into the sea and goes bye-bye. “Yet, I had a blast.” Because even though we all probably have many complex emotions about climate change, ice mass loss and sea level rise, we can still simultaneously feel super duper stoked about the chance to fly over the glaciers of Greenland in a freaking NASA plane. “The mountains, the ice, the water and the ice in the water are incredibly striking even though it’s lonely to see it disappearing at the hands of human activity,” he told me.
Yes, emotions are weird, and yes, there’s an awkward contrast or odd juxtaposition between feeling both thrill and grief at the same time.
But that’s life, I guess.
So just in case you’re still envisioning a champagne-swilling, caviar-scoffing, gangsta, hip-hop music video scene, here are a few things that might surprise you about the kind of major effort it takes to get on board NASA’s G-III plane and join the Oceans Melting Greenland field campaign:
Kick booty in a fire-resistant flight suit
So, you think you’d kick some booty in one of these flight suits? Oh, yeah. Totally. Well, so do we. Would you kill to have one? But the real reason the pilots think they’re so fab is because they’re fire-resistant. They. Resist. Fire! With racks and racks of science equipment wired with electrical cables, the crew has to be extra careful about fire on the plane. So wearing one of these flight suits is required.
A load of gas and no mistakes
A trip to Greenland sounds all romantic ‘n’ stuff, but operating a science instrument aboard a flying science lab on a six-hour flight every day is hard work. Just check out these flight paths. According to Project Manager Steve Dinardo, “You get a full load of gas and no mistakes.” Notice the flight path zigzags across the complicated coastline of the entire island. That’s because global warming of Earth’s atmosphere is melting the top of the ice sheet. But, aha! The ocean water around Greenland is even warmer than the air. That warm water is busy melting the glaciers from around their edges, hence the name, Oceans Melting Greenland, which will find out exactly how much of this melting is going on.
Instruments, instruments and more instruments. And did I mention some serious training?
The NASA modified G-III aircraft is … modified. (Did you notice the word “modified”?) What modified means is the plane has holes in it so experimental science instruments can stick out. And more scientific instruments are attached in, under and onto the plane in all sorts of configurations. To get to fly on this baby, you’d better have some training. Yep, some serious training: Safety training, first aid training, survival training. You get the idea.
Keep warm, in style
I can work the runway like a glamazon in this red coat, but it’s rated for survival in 50 degrees below zero. I said survival. In case of emergency. Does this sound like your all-inclusive vacation package now? With a survival coat? And there’s a survival vest too, with a beacon attached, and food rations, a pocketknife tool set, fishing gear, first aid supplies, a radio and a laser pointer for playing with cats—oops, I mean for signaling emergency and attracting rescue. The thing weighs about 20 pounds. Everyone on the plane has one of these puppies, and you’d better believe they know how to use it. If there’s a problem, the team would have to survive three to five days out in the wilderness until they're rescued. I don’t mean to scare you, but at NASA, when we say we care about safety, we’re not messing around.
“It’s not a triumph of human achievement that we’re melting the ice sheet,” said Willis. “When you see how huge these glaciers are and this huge chunk of this ice sheet disappearing into the ocean, it’s almost incomprehensible even when you see it from 40,000 feet.”
Find out more about Oceans Melting Greenland here.
View and download an OMG poster/infographic here.
Thank you for your comments.
Oceans Melting Greenland is part of NASA Earth Expeditions, a six-month field research campaign to study regions of critical change around the world.
Dear Resplendawnt Readers,
One year after taking up its new residence in the solar system, Dawn is continuing to witness extraordinary sights on dwarf planet Ceres. The indefatigable explorer is carrying out its intensive campaign of exploration from a tight orbit, circling its gravitational master at an altitude of only 240 miles (385 kilometers).
Even as we marvel at intriguing pictures and other discoveries, scientists are still in the early stages of putting together the pieces of the big puzzle of how (and where) Ceres formed, what its subsequent history has been, what geological processes are still occurring on this alien world and what all that reveals about the solar system.
For many readers who have not visited Ceres on their own, Occator Crater is the most mysterious and captivating feature. (To resolve the mystery of how to pronounce it, listen to the animation below.) As Dawn peered ahead at its destination in the beginning of 2015, the interplanetary traveler observed what appeared to be a bright spot, a shining beacon guiding the way for a ship sailing on the celestial seas. With its mesmerizing glow, the uncharted world beckoned, and Dawn answered the cosmic invitation by venturing in for a closer look, entering into Ceres' gravitational embrace. The latest pictures are one thousand times sharper than those early views. What was not so long ago a single bright spot has now come into focus as a complex distribution of reflective material in a 57-mile (92-kilometer) crater.
Scientists are still working on refining their understanding of this striking region. As we described in December, it seems that following the powerful impact that excavated Occator Crater, underground briny water reached the surface. The detailed photographs show many fractures cutting across the bright areas, and perhaps they provided a conduit. Water, whether as liquid or ice, would not last long there in the cold vacuum, eventually subliming. When the water molecules disperse, either escaping from Ceres into space or falling back to settle elsewhere, the dissolved salts are left behind. This reflective residue covers the ground, making the spellbinding and beautiful display Dawn now reveals.
While the crater is estimated to be a geological youngster at 80 million years old, that is an extremely long time for the material to remain so reflective. Exposed for so long to cosmic radiation and pelting from the rain of debris from space, it should have darkened. Scientists don't know (yet) what physical process are responsible, but perhaps it was replenished long after the crater itself formed, with more water, carrying dissolved salts, finding its way to the surface. As their analyses of the photos and spectra continue, scientists will gain a clearer picture and be able to answer this and other questions.
These latest Occator pictures did not come easily. Orbiting so close to Ceres, the adventurer’s camera captures only a small scene at a time, and it is challenging to cover the entirety of the expansive terrain. (Perhaps it comes as a surprise to those who have not read at least a few of the 123 Dawn Journals that precede this one that operating a spacecraft closer to a faraway dwarf planet than the International Space Station is to Earth is not as easy as, say, thinking about it.) But the patience and persistence in photographing the exotic landscapes have paid off handsomely.
We now have high resolution pictures of essentially all of Ceres save the small area around the south pole cloaked in the deep dark of a long winter night. Seasons last longer on Ceres than on Earth, and Dawn may not operate there long enough for the sun to rise at the south pole. By the beginning of southern hemisphere spring in November 2016, Dawn's mission to explore the first dwarf planet discovered may have come to its end.
In addition to photographing Ceres, Dawn conducts many other scientific observations, as we described in December and January. Among the probe's objectives at Ceres is to provide information for scientists to understand how much water is there, where it is, what form it is in and what role it plays in the geology.
We saw that extensive measurements of the faint nuclear radiation can help identify the atomic constituents. While the analysis of the data is complicated, and much more needs to be done, a picture is beginning to emerge from Dawn's neutron spectrometer (part of the gamma ray and neutron detector, GRaND). These subatomic particles are emitted from the nuclei of atoms buried within about a yard (meter) of the surface. Some manage to penetrate the material above them and fly into space, and the helpful ones then meet their fate upon hitting GRaND in orbit above. (Most others, however, will continue to fly through interplanetary space, decaying into a trio of other subatomic particles in less than an hour.) Before it escapes from the ground, a neutron's energy (and, equivalently, its speed) is strongly affected by any encounters with the nuclei of hydrogen atoms (although other atomic interactions can change the energy too). Therefore, the neutron energies can indicate to scientists the abundance of hydrogen. Among the most common forms in which hydrogen is found is water (composed of two hydrogen atoms and one oxygen atom), which can occur as ice or tied up in hydrated minerals.
GRaND shows Ceres is rich in hydrogen. Moreover, it detects more neutrons in an important energy range near the equator than near the poles, likely indicating there is more hydrogen, and hence more (frozen) water, in the ground at the high latitudes. Although Ceres is farther from the sun than Earth, and you would not consider it balmy there, it still receives some warmth. Just as at Earth, the sun's heating is less effective closer to the poles than at low latitudes, so this distribution of ice in the ground may reflect the temperature differences. Where it is warmer, ice close to the surface would have sublimed more quickly, thus depleting the inventory compared to the cooler ground far to the north or south.
Dawn spends most of its time measuring neutrons (and gamma rays), so it is providing a great deal of new data. And as scientists conduct additional analyses, they will learn more about the ice and other materials beneath the surface.
Another spectrometer is providing more tantalizing clues about the composition of Ceres, which is seen to vary widely. As the dwarf planet is not simply a huge rock but is a geologically active world, it is no surprise that it is not homogeneous. We discussed in December that the infrared mapping spectrometer had shown that minerals known as phyllosilicates are common on Ceres. Further studies of the data show evidence for the presence of two types: ammoniated phyllosilicates (described in December) and magnesium phyllosilicates. Scientists also find evidence of compounds known as carbonates, minerals that contain carbon and oxygen. There is also a dark substance in the mix that has not been identified yet.
And in one place (so far) on Ceres, this spectrometer has directly observed water, not below the surface but on the ground. The infrared signature shows up in a small crater named Oxo. (For the pronunciation, listen to the animation below.) As with the neutron spectra, it is too soon to know whether the water is in the form of ice or is chemically bound up in minerals.
At six miles (10 kilometers) in diameter, Oxo is small in comparison to the largest craters on Ceres, which are more than 25 times wider. (While geologists consider it a small crater, you might not agree if it formed in your backyard. Also note that when we showed Oxo Crater before, the diameter was slightly different. The crater's size has not changed since then, but as we receive sharper pictures, our measurements of feature sizes do change.) Dawn's first orbital destination, the fascinating protoplanet Vesta, is smaller than Ceres and yet has two craters far broader than the largest on Ceres. Based on studies of craters observed throughout the solar system, scientists have established methods of calculating the number and sizes of craters that could be formed on planetary surfaces. Those techniques show that Ceres is deficient in large craters. That is, more should have formed than appear in Dawn's pictures. Many other bodies (including Vesta and the moon) seem to preserve their craters for much longer, so this may be a clue about internal geological processes on Ceres that gradually erase the large craters.
Scientists are still in the initial stages of digesting and absorbing the tremendous wealth of data Dawn has been sending to Earth. The benefit of lingering in orbit (enabled by the remarkable ion propulsion system), rather than being limited to a brief glimpse during a fast flyby, is that the explorer can undertake much more thorough studies, and Dawn is continuing to make new measurements.
As recently as one year ago, controllers (and this writer) had great concern about the spacecraft's longevity given the loss of two reaction wheels, which are used for controlling the ship's orientation. And in 2014, when the flight team worked out the intricate instructions Dawn would follow in this fourth and final mapping orbit, they planned for three months of operation. That was deemed to be more than enough, because Dawn only needed half that time to accomplish the necessary measurements. Experienced spacecraft controllers recognize that there are myriad ways beautiful plans could go awry, so they planned for more time in order to ensure that the objectives would be met even if anomalies occurred. They also were keenly aware that the mission could very well conclude after three months of low altitude operations, with Dawn using up the last of its hydrazine. But their efforts since then to conserve hydrazine proved very effective. In addition, the two remaining wheels have been operating well since they were powered on in December, further reducing the consumption of the precious propellant.
As it turned out, operations have been virtually flawless in this orbit, and the first three months yielded a tremendous bounty, even including some new measurements that had not been part of the original plans. And because the entire mission at Ceres has gone so well, Dawn has not expended as much hydrazine as anticipated.
Dawn is now performing measurements that were not envisioned long in advance but rather developed only in the past two months, when it was apparent that the expedition could continue. And since March 19, Dawn has been following a new strategy to use even less hydrazine. Instead of pointing its sensors straight down at the scenery passing beneath it as the spacecraft orbits and Ceres rotates, the probe looks a little to the left. The angle is only five degrees (equal to the angle the minute hand of a clock moves in only 50 seconds, or less than the interval between adjacent minute tick marks), but that is enough to decrease the use of hydrazine and thus extend the spacecraft's lifetime. (We won't delve into the reason here. But for fellow nerds, it has to do with the alignment of the axes of the operable reaction wheels with the plane in which Dawn rotates to keep its instruments pointed at Ceres and its solar arrays pointed at the sun. The hydrazine saving depends on the wheels' ability to store angular momentum and applies only in hybrid control, not in pure hydrazine control. Have fun figuring out the details. We did!)
The angle is small enough now that the pictures will not look substantially different, but they will provide data that will help determine the topography. (Measurements of gravity and the neutron, gamma ray and infrared spectra are insensitive to this angle.) Dawn took pictures at a variety of angles during the third mapping orbit at Ceres (and in two of the mapping orbits at Vesta, HAMO1 and HAMO2) in order to get stereo views for topography. That worked exceedingly well, and photos from this lower altitude will allow an even finer determination of the three dimensional character of the landscape in selected regions. Beginning on April 11, Dawn will look at a new angle to gain still another perspective. That will actually increase the rate of hydrazine expenditure, but the savings now help make that more affordable. Besides, this is a mission of exploration and discovery, not a mission of hydrazine conservation. We save hydrazine when we can in order to spend it when we need it. Dawn's charge is to use the hydrazine to accomplish important scientific objectives and to pursue bold, exciting goals that lift our spirits and fuel our passion for knowledge and adventure. And that is exactly what it is has done and what it will continue to do.
Dawn is 240 miles (385 kilometers) from Ceres. It is also 3.90 AU (362 million miles, or 583 million kilometers) from Earth, or 1,505 times as far as the moon and 3.90 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take one hour and five minutes to make the round trip.