Astronomy

How long does it take Dawn to orbit Ceres?

How long does it take Dawn to orbit Ceres?


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I haven't been able to find the orbit time of Dawn around Ceres. Do you know how long it takes?


As of March 6, 2015, Dawn has entered orbit around Ceres. But it's really so far only "captured by Ceres' gravitational pull". Then, it was still 61,000 km from Ceres.

It's slowly spiraling down into an orbit that JPL's Dawn Journal calls "RC3", which will be 13,500 km above Ceres. This orbit will last 15 days per revolution.

It will take about 15 days to complete a single orbital revolution at this altitude.

The first news link above indicates that Dawn will reach RC3 on April 23, 2015.

This picture from the Dawn Journal gives us a picture of Dawn's path: it's not completing any revolutions around Ceres yet; it's still approaching the RC3 orbit as of this writing (March 10, 2015).

So as of now, March 10, 2015, there is no orbital period yet. But when RC3 is achieved, it will be a slow orbit -- 15 days.

There are other orbital altitudes planned past RC3.

  • "second orbital phase, survey orbit" - Altitude 4,400 km, Orbital period 3 days, 3 hours
  • "high altitude mapping orbit" - Altitude 1,470 km, Orbital period 19 hours
  • "low altitude mapping orbit" - Altitude 375 km, Orbital period 5.5 hours

According to Dawn's schedule, the "survey orbit" will only last 22 days before it spirals in to the "high altitude mapping orbit" in August 2015, although it's unclear exactly when the "survey orbit" will take place. The "low altitude mapping orbit" will be in November 2015. In between orbits, when spiraling down to the next scheduled orbit, Dawn's orbital period will slowly decrease. At the last orbit, Dawn will be left in this orbit after its batteries and hydrazine fuel are exhausted.


Update (Oct 23, 2015)

Excerpt from latest news update from the Dawn mission (Sept 30, 2015):

Dawn is currently orbiting Ceres at an altitude of 915 miles (1,470 kilometers), and the spacecraft will image the entire surface of the dwarf planet up to six times in this phase of the mission. Each imaging cycle takes 11 days.

Starting in October and continuing into December, Dawn will descend to its lowest and final orbit, an altitude of 230 miles (375 kilometers). The spacecraft will continue imaging Ceres and taking other data at higher resolutions than ever before at this last orbit. It will remain operational at least through mid-2016.


We Did It! Dawn Arrives at Dwarf Planet Ceres

Since its discovery in 1801, Ceres has been known as a planet, then as an asteroid, and later as a dwarf planet. Now, after a journey of 3.1 billion miles (4.9 billion kilometers) and 7.5 years, Dawn calls it “home.”

Earth’s robotic emissary arrived at about 4:39 a.m. PST today. It will remain in residence at the alien world for the rest of its operational life, and long, long after.

Before we delve into this unprecedented milestone in the exploration of space, let’s recall that even before reaching orbit, Dawn started taking pictures of its new home. Last month we presented the updated schedule for photography. Each activity to acquire images (as well as visible spectra and infrared spectra) has executed smoothly and provided us with exciting and tantalizing new perspectives.

While there are countless questions about Ceres, the most popular now seems to be what the bright spots are. It is impossible not to be mesmerized by what appear to be glowing beacons, shining out across the cosmic seas from the uncharted lands ahead. But the answer hasn’t changed: we don’t know. There are many intriguing speculations, but we need more data, and Dawn will take photos and myriad other measurements as it spirals closer and closer during the year. For now, we simply know too little.

For example, some people ask if those spots might be lights from an alien city. That’s ridiculous! At this early stage, how could Dawn determine what kinds of groupings Cereans live in? Do they even have cities? For all we know, they may live only in rural communities, or perhaps they only have large states.

What we already know is that in more than 57 years of space exploration, Dawn is now the only spacecraft ever to orbit two extraterrestrial destinations. A true interplanetary spaceship, Dawn left Earth in Sep. 2007 and traveled on its own independent course through the solar system. It flew past Mars in Feb. 2009, robbing the red planet of some of its own orbital energy around the sun. In July 2011, the ship entered orbit around the giant protoplanet Vesta, the second most massive object in the main asteroid belt between Mars and Jupiter. (By the way, Dawn’s arrival at Vesta was exactly one Vestan year ago earlier this week.) It conducted a spectacular exploration of that fascinating world, showing it to be more closely related to the terrestrial planets (including Earth, home to many of our readers) than to the typical objects people think of as asteroids. After 14 months of intensive operations at Vesta, Dawn climbed out of orbit in Sep. 2012, resuming its interplanetary voyage. Today it arrived at its final destination, Ceres, the largest object between the sun and Pluto that had not previously been visited by a spacecraft. (Fortunately, New Horizons is soon to fly by Pluto. We are in for a great year!)

What was the scene like at JPL for Dawn’s historic achievement? It’s easy to imagine the typical setting in mission control. The tension is overwhelming. Will it succeed or will it fail? Anxious people watch their screens, monitoring telemetry carefully, frustrated that there is nothing more they can do now. Nervously biting their nails, they are thinking of each crucial step, any one of which might doom the mission to failure. At the same time, the spacecraft is executing a bone-rattling, whiplash-inducing burn of its main engine to drop into orbit. When the good news finally arrives that orbit is achieved, the room erupts! People jump up and down, punch the air, shout, tweet, cry, hug and feel the tremendous relief of overcoming a huge risk. You can imagine all that, but that’s not what happened.

If you had been in Dawn mission control, the scene would have been different. You would mostly be in the dark. (For your future reference, the light switches are to the left of the door.) The computer displays would be off, and most of the illumination would be from the digital clock and the string of decorative blue lights that indicate the ion engine is scheduled to be thrusting. You also would be alone (at least until JPL Security arrived to escort you away, because you were not cleared to enter the room, and, for that matter, how did you get past the electronic locks?). Meanwhile, most of the members of the flight team were at home and asleep! (Your correspondent was too, rare though that is. When Dawn entered orbit around Vesta, he was dancing. Ceres’ arrival happened to be at a time less conducive to consciousness.)

Why was such a significant event treated with somnolence? It is because Dawn has a unique way of entering orbit, which is connected with the nature of the journey itself. We have discussed some aspects of getting into orbit before (with this update to the nature of the approach trajectory). Let’s review some of it here.

It may be surprising that prior to Dawn, no spacecraft had even attempted to orbit two distant targets. Who wouldn’t want to study two alien worlds in detail, rather than, as previous missions, either fly by one or more for brief encounters or orbit only one? A mission like Dawn’s is an obvious kind to undertake. It happens in science fiction often: go somewhere, do whatever you need to do there (e.g., beat someone up or make out with someone) and then boldly go somewhere else. However, science fact is not always as easy as science fiction. Such missions are far, far beyond the capability of conventional propulsion.

Deep Space 1 (DS1) blazed a new trail with its successful testing of ion propulsion, which provides 10 times the efficiency of standard propulsion, showing on an operational interplanetary mission that the advanced technology really does work as expected. (This writer was fortunate enough to work on DS1, and he even documented the mission in a series of increasingly wordy blogs. But he first heard of ion propulsion from the succinct Mr. Spock and subsequently followed its use by the less logical Darth Vader.)

Dawn’s ambitious expedition would be truly impossible without ion propulsion. (For a comparison of chemical and ion propulsion for entering orbit around Mars, an easier destination to reach than either Vesta or Ceres, visit this earlier log.) So far, our advanced spacecraft has changed its own velocity by 23,800 mph (38,400 kilometers per hour) since separating from its rocket, far in excess of what any other mission has achieved propulsively. (The previous record was held by DS1.)

Dawn is exceptionally frugal in its use of xenon propellant. In this phase of the mission, the engine expends only a quarter of a pound (120 grams) per day, or the equivalent of about 2.5 fluid ounces (75 milliliters) per day. So although the thrust is very efficient, it is also very gentle. If you hold a single sheet of paper in your hand, it will push on your hand harder than the ion engine pushes on the spacecraft at maximum thrust. At today’s throttle level, it would take the distant explorer almost 11 days to accelerate from zero to 60 mph (97 kilometers per hour). That may not evoke the concept of a drag racer. But in the zero-gravity, frictionless conditions of spaceflight, the effect of this whisper-like thrust can build up. Instead of thrusting for 11 days, if we thrust for a month, or a year, or as Dawn already has, for more than five years, we can achieve fantastically high velocity. Ion propulsion delivers acceleration with patience.

Most spacecraft coast most of the time, following their repetitive orbits like planets do. They may use the main engine for a few minutes or perhaps an hour or two throughout the entire mission. With ion propulsion, in contrast, the spacecraft may spend most of its time in powered flight. Dawn has flown for 69% of its time in space emitting a cool blue-green glow from one of its ion engines. (With three ion engines, Dawn outdoes the Star Wars TIE (twin ion engine) fighters.)

The robotic probe uses its gentle thrust to gradually reshape its path through space rather than simply following the natural course that a planet would. After it escaped from Vesta’s gravitational clutches, it slowly spiraled outward from the sun, climbing the solar system hill, making its heliocentric orbit more and more and more like Ceres’. By the time it was in the vicinity of the dwarf planet today, both were traveling around the sun at more than 38,600 mph (62,100 kilometers per hour). Their trajectories were nearly identical, however, so the difference in their speeds was only 100 mph (160 kilometers per hour), or less than 0.3 percent of the total. Flying like a crackerjack spaceship pilot, Dawn elegantly used the light touch of its ion engine to be at a position and velocity that it could ease gracefully into orbit. At a distance of 37,700 miles (60,600 kilometers), Ceres reached out and tenderly took the newcomer from Earth into its permanent gravitational embrace.

If you had been in space watching the event, you would have been cold, hungry and hypoxic. But it would not have looked much different from the 1,885 days of ion thrust that had preceded it. The spacecraft was perched atop its blue-green pillar of xenon ions, patiently changing its course, as it does for so much of quiet cruise. But now, at one moment it was flying too fast for Ceres’ gravity to hang on to it, and the next moment it had slowed just enough that it was in orbit. Had it stopped thrusting at that point, it would have continued looping around the dwarf planet. But it did not stop. Instead, it is working now to reshape its orbit around Ceres. As we saw in November, its orbital acrobatics first will take it up to an altitude of 47,000 miles (75,000 kilometers) on March 19 before it swoops down to 8,400 miles (13,500 kilometers) on April 23 to begin its intensive observations in the orbit designated RC3.

In fact, Dawn’s arrival today really is simply a consequence of the route it is taking to reach that lower orbit next month. Navigators did not aim for arriving today. Rather, they plotted a course that began at Vesta and goes to RC3 (with a new design along the way), and it happens that the conditions for capture into orbit occurred this morning. As promised last month, we present here a different view of the skillful maneuvering by this veteran space traveler.

If Dawn had stopped thrusting before Ceres could exert its gravitational control, it wouldn’t have flown very far away. The spacecraft had already made their paths around the sun very similar, and the ion propulsion system provides such exceptional flexibility to the mission that controllers could have guided it into orbit some other time. This was not a one-time, all-or-nothing event.

So the flight team was not tense. They had no need to observe it or make a spectacle out of it. Mission control remained quiet. The drama is not in whether the mission will succeed or fail, in whether a single glitch could cause a catastrophic loss, in whether even a tiny mistake could spell doom. Rather, the drama is in the opportunity to unveil the wonderful secrets of a fascinating relict from the dawn of the solar system more than 4.5 billion years ago, a celestial orb that has beckoned for more than two centuries, the first dwarf planet discovered.

Dawn usually flies with its radio transmitter turned off (devoting its electricity instead to the power-hungry ion engine), and so it entered orbit silently. As it happened, a routine telecommunications session was scheduled about an hour after attaining orbit, at 5:36 a.m. PST. (It’s only coincidence it was that soon. At Vesta, it was more than 25 hours between arrival and the next radio contact.) For primary communications, Dawn pauses thrusting to point its main antenna to Earth, but other times, as in this case, it is programmed to use one of its auxiliary antennas to transmit a weaker signal without stopping its engine, whispering just enough for engineers to verify that it remains healthy.

The Deep Space Network’s exquisitely sensitive 230-foot (70-meter) diameter antenna in Goldstone, Calif., picked up the faint signal from across the solar system on schedule and relayed it to Dawn mission control. One person was in the room (and yes, he was cleared to enter). He works with the antenna operator to ensure the communications session goes smoothly, and he is always ready to contact others on the flight team if any anomalies arise. In this case, none did, and it was a quiet morning as usual. The mission director checked in with him shortly after the data started to trickle in, and they had a friendly, casual conversation that included discussing some of the telemetry that indicated the spacecraft was still performing its routine ion thrusting. The determination that Dawn was in orbit was that simple. Confirming that it was following its flight plan was all that was needed to know it had entered orbit. This beautifully choreographed celestial dance is now a pas de deux.

As casual and tranquil as all that sounds, and as logical and systematic as the whole process is, the reality is that the mission director was excited. There was no visible hoopla, no audible fanfare, but the experience was powerful fuel for the passionate fires that burn within.

As soundlessly as a spacecraft gliding through the void, the realization emerges …

It is in orbit around a distant world!!

Yes, it’s clear from the technical details, but it is more intensely reflected in the silent pounding of a heart that has spent a lifetime yearning to know the cosmos. Years and years of hard work devoted to this grand undertaking, constant hopes and dreams and fears of all possible futures, uncounted challenges (some initially appearing insurmountable) and a seeming infinitude of decisions along the way from early concepts through a real interplanetary spacecraft flying on an ion beam beyond the sun.

And then, a short, relaxed chat over a few bits of routine data that report the same conditions as usual on the distant robot. But today they mean something different.

Everyone on the team will experience the news that comes in a congratulatory email in their own way, in the silence and privacy of their own thoughts. But it means the same to everyone.

And it’s not only the flight team. Humankind!! With our relentless curiosity, our insatiable hunger for knowledge, our noble spirit of adventure, we all share in the experience of reaching out from our humble home to the stars.

It was a good way to begin the day. It was Dawn at Ceres.

Let’s bring into perspective the cosmic landscape on which this remarkable adventure is now taking place. Imagine Earth reduced to the size of a soccer ball. On this scale, the International Space Station would orbit at an altitude of a bit more than one-quarter of an inch (seven millimeters). The moon would be a billiard ball almost 21 feet (6.4 meters) away. The sun, the conductor of the solar system orchestra, would be 79 feet (24 meters) across at a distance of 1.6 miles (2.6 kilometers). But even more remote, Dawn would be 5.3 miles (8.6 kilometers) away. (Just a few months ago, when the spacecraft was on the opposite side of the sun from Earth, it would have been more than six miles, or almost 10 kilometers, from the soccer ball.) Tremendously far now from its erstwhile home, it would be only a little over a yard (a meter) from its new residence. (By the end of this year, Dawn will be slightly closer to it than the space station is to Earth, a quarter of an inch, or six millimeters.) That distant world, Ceres, the largest object between Mars and Jupiter, would be five-eighths of an inch (1.6 centimeters) across, about the size of a grape. Of course a grape has a higher water content than Ceres, but we can be sure that exploring this intriguing world of rock and ice will be much sweeter!

As part of getting to know its new neighborhood, Dawn has been hunting for moons of Ceres. Telescopic studies had not revealed any, but if there were a moon smaller than about half a mile (one kilometer), it probably would not have been discovered. The spacecraft’s unique vantage point provides an opportunity to look for any that might have escaped detection. Many pictures have been taken specifically for this purpose, and scientists scrutinize them and all of the other photographs for any indication of moons. While the search will continue, so far, no picture has shown evidence of companions orbiting Ceres.

And yet we know that as of today, Ceres most certainly does have one. Its name is Dawn!

Dawn is 37,800 miles (60,800 kilometers) from Ceres, or 16 percent of the average distance between Earth and the moon. It is also 3.33 AU (310 million miles, or 498 million kilometers) from Earth, or 1,230 times as far as the moon and 3.36 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take 55 minutes to make the round trip.


Mission

Dawn is not engineered to land on any asteroid.

There is some debate on the exact size of Pallas. My student and I used HST to examine Pallas and we got a smaller diameter than yours, much closer to that of Vesta and possibly smaller than it. But we do not ignore Pallas because of its size. It is impossible to reach with a mission in the same class as Dawn because it takes too much thrust to reach Pallas.

Pallas is highly inclined to the ecliptic plane. A lot of energy is needed to climb out of the ecliptic plane especially as far out of the plane as Pallas is. I DID try to design a mission to reach Pallas and it was impossible with the Dawn spacecraft even if we went nowhere else than Pallas.

We are going to Vesta first because it is closer to the Sun than Ceres and we pass it on the way to Ceres. This possibility also depends on Vesta and Ceres being both in the right part of the sky (nearly aligned with the Sun). This in turn happens every 17 years so we are very fortunate to be able to do this dual asteroid mission right now.

Answer provided by Chris Russell, Dawn mission Principal Investigator

Unlikely, because there is greater return by spending more of our resources on Vesta and Ceres.

The reason that Dawn has a longer trip time than might be required by conventional means is that Dawn uses an ion propulsion system which precludes achieving a Hohmann transfer orbit. Hohmann transfer orbits are the most propellant-efficient means of moving between two circular coplanar orbits. Hohmann transfers are certainly not the fastest route between orbits however, they are used frequently because most missions are tightly constrained in mass, so propellant is a very precious resource.

To accomplish a Hohmann transfer, two propulsive maneuvers are required. The first one breaks the spacecraft out of the initial orbit and puts it in an orbit that intersects the desired final orbit. The spacecraft is then in the Hohmann transfer orbit, which is an ellipse tangent to both circular orbits. After the spacecraft has coasted to the point that connects the transfer orbit to the desired final orbit, it fires its engine a second time, now to circularize its orbit, thus matching the target orbit.

Dawn's ion propulsion system is far more efficient than a chemical propulsion system would be, but it produces much less thrust. In other words, it takes significantly less xenon propellant for Dawn to change its velocity by a given amount than it would if it used chemical propellants, but it also takes longer. Ultimately ion propulsion can allow a spacecraft to achieve a higher speed than one with chemical propulsion could. (Ion propulsion provides what I always like to call acceleration with patience.)

Dawn cannot provide a sufficiently large acceleration to follow a Hohmann transfer orbit -- the thrust is simply too gentle. As a result, after receiving its initial boost out of Earth orbit from the Delta rocket, it spirals away from the Sun until it reaches Vesta's orbit. It thrusts most of the way to Vesta, very gradually adding energy to its orbit around the Sun, rather than beginning with a huge burn and coasting to Vesta. This gentle reshaping of the orbit, in contrast to the more abrupt changes typical of chemical propulsion, is a characteristic of ion propulsion and other so-called low-thrust propulsion systems, such as solar sails. As low-thrust propulsion is just beginning to be used for reaching destinations, some of our standard conceptions for how spacecraft move around the solar system may need to be revised.

An example might help illustrate the difference between using chemical and ion propulsion. The engine on a conventional interplanetary spacecraft may burn roughly 300 kilograms of propellants in around 20 minutes of operation, achieving a velocity change of perhaps 1000 meters/second. At its maximum thrust, Dawn's ion engine can expend only about 0.25 kg of xenon per day, changing the spacecraft's velocity by 10 m/s. To achieve that 1000 m/s thus would require only 25 kg of xenon -- a tremendous savings given the high cost of launching spacecraft from Earth -- but it would take 100 days. As the spacecraft recedes from the Sun, its solar arrays produce less power, so it operates at a lower throttle level, using still less propellant and taking still longer to achieve these velocity changes.

Dawn will carry enough propellant to change its speed by more than 10 kilometers/s (or about 6 miles per second) over the course of the mission, far more than any spacecraft's propulsion system has ever accomplished, but it will require an accumulated thrust time of more than 6 years. Although it will take Dawn longer to go from Earth to Vesta and from Vesta to Ceres with ion propulsion than it would with chemical propulsion, the longer trip time is well worth it. Dawn will use a significantly less expensive rocket than it would if it had to carry the much more massive propellants required for a conventional chemical propulsion system. In fact, Dawn simply would be unaffordable without ion propulsion. Now, however, your tax dollars and mine can be used to accomplish a broad and exciting program of solar system exploration, including the acquisition of a wonderfully rich set of science data at Vesta and Ceres.

Answer provided by Marc Rayman, Dawn Chief Engineer, JPL

There is a wide range of geometries that can make planetary gravity assists effective, and while approaching from outside the orbit of the planet may appear unusual, Dawn is not unique in doing so. The specifics of the gravity assist include not only the relative speed between the probe and the planet but also the direction each one is moving at the time of the encounter.

In our case, the principal benefit of the gravity assist is to change the plane of Dawn's orbit around the Sun. Based on your choice of words, you seem to have some understanding already of the key principles, so you probably already know that most planets orbit the Sun close to the plane of Earth's orbit, also known as the ecliptic. You may also know that changing the plane of an orbit can be propulsively very expensive. Vesta and Ceres orbit farther from the ecliptic than most planets do.

If we had launched in 2006, the ion propulsion system could have achieved the plane change by itself. The mission is a little more difficult with a 2007 launch, because there is less time to complete the required ion thrusting before the relative alignment of Vesta and Ceres makes the trip between them inconveniently long. Therefore, we take advantage of the gravity of Mars to reduce the time Dawn needs to thrust, allowing it to reach Vesta at about the same time, even after launching a year later. The principal effect of the encounter is to change the plane of Dawn's orbit by about 5ᄁX, with most of the plane change being in inclination. That is equivalent to about 2.3 km/s, but it does not change Dawn's orbital energy. The gravity assist also provides about 1.1 km/s to raise the energy of Dawn's orbit around the Sun. The combined effect is to impart a delta-v of about 2.6 km/s.

Answer provided by Marc Rayman, Dawn Chief Engineer, JPL

Not as far as we can tell. If there is any damage, it would be very minor and well below the threshold that we can measure.

More precisely, Dawn flies IN the asteroid belt, so it has a very similar speed to the material around it. So, the material is a little less dangerous that you might assume. But, most importantly, the small meteoroids are far between and the chance of hitting one if you are the size of Dawn is small (but not totally negligible). We, therefore, are concerned and will avoid any region where we think there might be higher than usual danger.

For more information about "flying through the asteroid belt," check out Dawn Chief Engineer, Marc Rayman's November 27, 2009 Dawn Journal.

Answer provided by Chris Russell, Principal Investigator for the Dawn mission and Marc Rayman, Dawn Chief Engineer, JPL

A spacecraft that would be close enough to Ceres to have a good view of it will have to be in orbit around it. Ceres and Vesta are quite unlike most asteroids. They are massive bodies with significant gravity. Hayabusa was able to orbit the Sun near Itokawa because that asteroid's gravity is so weak that it did not pull the craft into orbit. That is not the case with Ceres and Vesta. Were Dawn to remain in orbit around the Sun and not be captured by Ceres' gravity, it would have to stay more than about 200,000 km from the dwarf planet.

Being in orbit is not an obstacle to using the rotation to reveal the surface. The tentative design for the first science orbit at Ceres is at an altitude of about 5,900 kilometers. It will take Dawn about 112 hours to complete one such orbit, but Ceres rotates in about 9 hours. Therefore, it is almost as if Dawn hovers it progresses only a short distance in its orbit as Ceres rotates beneath it. The spacecraft will be in a near-polar orbit, so with the combination of the rotation of its target and its own orbital motion from pole to pole, Dawn will be able to see the entire illuminated surface easily. (For the analogous orbit at Vesta and further details about observations from there, you might want to take a look at Dawn Chief Engineer, Marc Rayman's Dawn Journal from May 27, 2010.)

"Having Dawn travel besides Ceres" means having Dawn match Ceres' orbit around the Sun. To get into orbit around Ceres, Dawn will do that, thanks to its use of ion propulsion. Marc explains how we use ion propulsion to orbit another body in the April 28, 2010 Dawn Journal.

Answer provided by Marc Rayman, Dawn Chief Engineer, JPL


Dawn spacecraft dropping to record low altitude at Ceres

NASA’s Dawn spacecraft is in the process of dropping into an elliptical orbit that will carry it within 50 kilometres (30 miles) of the surface of the dwarf planet Ceres. Image: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

NASA’s Dawn spacecraft is in the process of spiralling down into its final, lowest-ever orbit around the dwarf planet Ceres, aiming for an elliptical trajectory that will carry it to within 50 kilometres (30 miles) of the surface at its low point – 10 times lower than its ever been before.

Starting in early June, Dawn will begin collecting gamma ray and neutron spectra to better understand the composition of the topmost rock and soil layers while taking high-resolution photographs of the cratered terrain below.

“The team is eagerly awaiting the detailed composition and high-resolution imaging from the new, up-close examination,” said Carol Raymond, Dawn principal investigator at NASA’s Jet Propulsion Laboratory. “These new high-resolution data allow us to test theories formulated from the previous data sets and discover new features of this fascinating dwarf planet.”

Launched in 2007, the Dawn entered orbit around Ceres in March 2015 after wrapping up similar studies at the dwarf planet Vesta. The spacecraft had not fired its ion thrusters since last June, orbiting Ceres once every 30 days, but it’s now using engine No. 2 to slowly lower its orbit.

Lowering Dawn into its new orbit is a complex process requiring engineers to synchronise the trajectory with the rotation of Ceres. Image: NASA/JPL-Caltech

The descent began on 16 April. When the manoeuvre is complete, “Dawn will swoop down to an incredibly low 22 miles (35 kilometres) above the exotic terrain of ice, rock and salt,” Marc Rayman, the mission director, writes in his blog. “The last time it was that close to a solar system body was when it rode a rocket from Cape Canaveral over the Atlantic Ocean more than a decade ago.”

The final orbit will have a high point of 4,000 kilometres (2,500 miles) and a period of 27 hours and 13 minutes.

The goal is to synchronise Dawn’s orbit with the nine-hour four-minute rotation of Ceres to ensure the spacecraft will repeatedly fly over a specific point on the surface – Occator Crater, where highly reflective salt deposits are visible – during the low point of each orbit.

“The flight team will synchronise the orbit so that each time Dawn swoops down to low altitude, it does so at just the right time so that Ceres’ rotation will place the Occator geological unit under the probe’s flight path,” Rayman writes.

But it will not be easy, and it will not last.

The spinning reaction wheels that once helped Dawn control its orientation no longer work, forcing the spacecraft to rely on small thrusters instead. Those thrusters have a small but noticeable impact on the trajectory, as do areas of Ceres that have slightly higher or lower densities, resulting in slight changes in the total gravitational pull experienced by the spacecraft.

JPL flight planners studied more than 45,000 possible trajectories before choosing the one now being implemented.

Occator Crater on Ceres. Image: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

“The low point of Dawn’s orbit will gradually shift southward on each successive revolution,” Rayman writes. “That means we will have only a limited number of opportunities to fly over Occator before the low point is too far south. Given the complexity of the operations, the planned measurements are not at all assured.”

Even if Dawn achieves and maintains the desired orbit, taking sharp, focused pictures will pose yet another challenge. The spacecraft will be racing across Ceres, from south to north, at 1,690 kph (1,050 mph) at the low point of the ellipse. Occator crater is 92 kilometres across (57 miles) and from Dawn’s perspective it will be moving to the right at more than 310 kph (190 mph).

Dawn’s camera will image an area 3.4 kilometres (2.1 miles) across.

“Even if the probe arrived at Occator’s latitude a mere 20 seconds off schedule, a spot on the ground that was expected to be in the center of the camera would have moved entirely out of view and so would not even be glimpsed,” Rayman explained. “If Dawn were four minutes too early or too late, the ground beneath the spacecraft would shift west or east by 13 miles (21 kilometres), and the terrain that’s photographed could be entirely different from what was expected.”


NASA’s Dawn Spacecraft Finally Arrives at Dwarf Planet Ceres

After a seven-year cruise, and a one-year successful mission at the giant asteroid 4 Vesta, NASA’s Dawn space probe today successfully entered the orbit of its second and final target, the dwarf planet Ceres.

Dawn will use its ion propulsion system to change orbits at Ceres, allowing it to observe the dwarf planet from different vantage points. Image credit: NASA / JPL.

Located in the main asteroid belt between Mars and Jupiter, Ceres is the largest unexplored world of the inner Solar System.

It was discovered on January 1, 1801 by the Italian astronomer and monk Giuseppe Piazzi.

For the last century, it was known as the largest asteroid in the Solar System. But in 2006, the International Astronomical Union reclassified it as a dwarf planet because of its large size – Ceres is roughly 950 km in diameter.

Planetary scientists believe Ceres contains rock in its interior with a thick mantle of ice that, if melted, would amount to more fresh water than is present on our planet.

The materials making up Ceres likely date from the first few million years of the Solar System’s existence and accumulated before the planets formed.

NASA’s Dawn robotic spacecraft has become the first mission to achieve orbit around Ceres.

The spacecraft was about 61,000 km from the dwarf planet when it was captured by the planet’s gravity at about 7:39 a.m. EST (4:39 a.m. PST, 12:39 p.m. GMT).

Mission controllers received a signal from Dawn at 8:36 a.m. EST (5:36 a.m. PST, 1:36 p.m. GMT) that the probe was healthy and thrusting with its ion engine, the indicator Dawn had entered orbit as planned.

“We feel exhilarated. We have much to do over the next year and a half, but we are now on station with ample reserves, and a robust plan to obtain our science objectives,” said Dr Chris Russell of the University of California, Los Angeles, principal investigator of the Dawn mission.

In addition to being the first spacecraft to visit a dwarf planet, Dawn also has the distinction of being the first mission to orbit two different worlds in deep space.

The spacecraft has already delivered more than 30,000 images and many insights about 4 Vesta, the second most massive body in the asteroid belt. Dawn orbited Vesta, which has an average diameter of 525 km, from 2011 to 2012.

The most recent images received from the spacecraft, taken on March 1, show Ceres as a crescent, mostly in shadow because the spacecraft’s trajectory put it on a side of Ceres that faces away from the Sun until mid-April.

When Dawn emerges from Ceres’ dark side, it will deliver ever-sharper images as it spirals to lower orbits around the planet.


Dawn on Ceres: Nasa probe to enter dwarf planet's orbit

Nasa scientists are making final preparations for a spacecraft to begin the first orbits around a dwarf planet in the planetary rubble on the far side of Mars.

Almost eight years after blasting off from Cape Canaveral in Florida, and travelling 3bn miles (4.8bn km), the $450m (£290m) Dawn probe is due to arrive at Ceres, the largest object in the main asteroid belt that separates Mars from Jupiter, on Friday 6 March.

A technical glitch that knocked out thrusters on the ship in September means that Dawn has already overshot Ceres and must now swing back towards the 590-mile-wide ball of minerals and ice to enter the right orbit. On Sunday, it was 30,000 miles away from Ceres.

If all goes to plan, the spacecraft will circle the dwarf planet for months, mapping its surface and measuring changes in its gravitational field, from which scientists can glean crucial insights about the body’s interior.

Early observations of Ceres already have astronomers enthralled. The dwarf planet is thought to have a rocky core encased in more than 62 miles of subterranean ice. If Dawn confirms this, it will mean the body holds more fresh water than the whole of the Earth’s surface.

On its approach to Ceres, Dawn’s camera revealed a bright patch on the otherwise dark and dull, carbon-rich terrain. But in higher resolution pictures released last week, the patch was found to be two spots: one very bright, the other dimmer.

What the spots are is unclear. They may be ice patches, shiny silicates on the surface, or reflective impact material left after a hit-and-run collision by another space rock. Ceres is not thought to be geologically active, but if its innards are still stirring, the bright spots may be eruptions from ice volcanoes.

The Dawn probe was flung into space in September 2007 to learn about the formation of the planets at the birth of the solar system 4.6bn years ago. The boulders drifting in the asteroid belt are the primordial material from which all planets are made. Some, like Ceres, became large by asteroid standards, but ultimately they are failed planets. Their growth was disrupted by the intense gravitational pull of Jupiter, which scattered the asteroids like billiard balls.

Dwarf planet Ceres and the giant asteroid Vesta in comparison to Mars, Mercury, and Earth’s moon. Photograph: Nasa/JPL-Caltech/UCLA

When Dawn arrives in orbit around Ceres, at a distance of more than 249m miles from the sun, it will become the first spacecraft to have circled two different bodies in deep space. Four years into its journey, in 2011, Dawn caught up with Vesta, the brightest asteroid in the solar system and the only one visible to the naked eye.

Dawn’s 14-month survey of Vesta, a rock roughly half the size of Ceres, revealed it to be similar to the inner planets of the solar system: Mercury, Venus, Earth and Mars. Like Earth, Vesta has an iron core, surrounded by a mantle and crust. The surface is scarred with giant canyons and craters punch deep into its surface. One pit is 311 miles across and has at its centre a mountain that rises up more than twice as high as Mount Everest.

Ceres is a different beast. The first asteroid to be discovered, it was spotted by accident on new year’s day in 1801 by the Italian monk Giuseppe Piazzi of the Palermo observatory. Unlike Vesta, the makeup of Ceres is far more like the icy bodies in the outer solar system. About one-quarter of its mass is water, and some may be liquid under the surface.

The International Astronomical Union designated Ceres a “dwarf planet” in 2006, along with Pluto, which found itself demoted from full planetary status. Dwarf planets must orbit the sun and be massive enough to be shaped by their gravity, but, unlike proper planets, have not cleared a path through the solar system.

“We think that the building blocks of Earth were the siblings of Ceres and Vesta,” said Christopher Russell, the lead scientist on the Dawn mission at the University of California, Los Angeles. “Those like Vesta came to Earth and delivered the iron core, and other materials, while others, like Ceres, brought water.”

Last year, Michael Küppers, a planetary scientist at the European Space Astronomy Centre in Villanueva de la Cañada, Spain, reported observations for the Herschel space telescope, which found jets of water vapour coming from Ceres. Every second, the dwarf planet loses 6kg in steam.

Küppers hopes that Dawn will shed light on the source of the steam plumes. One possibility is that part of the crust was knocked off Ceres in a cosmic impact, exposing hard ice beneath, which vaporises in sunlight. But the interior of Ceres may still be active, and driving out gas from inside.

Andreas Nathues, the lead scientist on Dawn’s framing camera at the Max Planck Institute for Solar System Research in Göttingen, Germany, said the mission targeted Vesta and Ceres because they were so unlike each other. “Why is Ceres a body that contains water, and Vesta not? Why are they so different? Understanding that will help us understand how the planets formed,” he said.

Two views of Ceres are seen in images acquired by Nasa’s Dawn spacecraft from a distance of about 52,000 miles on 12 February. Photograph: NASA/Reuters

The Dawn probe is powered by an ion thruster that forces xenon plasma out of the spacecraft at 77,670mph and can run continuously for years, accelerating the craft over time.

In September, the thruster failed when a highly energetic particle slammed into its electronics, forcing the probe into safe mode for four days. The loss of power means that, while Dawn will arrive at Ceres on time, it will take weeks to correct its orientation and point its cameras at the surface.

“We’ll be pointing in the wrong direction when we get there,” said Russell. “We have a period coming up where we won’t be taking much data, but we will get the next set of good pictures at the end of April.”

Some of those images could resolve the mystery of the bright spots on the surface of Ceres. Russell suspects that as the images from Dawn get sharper, the spots could become smaller and shinier, until they reflect nearly all the sunlight falling on them. “In a few months, the reflectivity may get to 100%, and that could mean water ice,” he said.

When the mission is over later this year, the Dawn probe will remain in orbit around Ceres at a safe enough distance to ensure it does not crash into the surface. Since Ceres has no atmosphere, there is no drag to bring Dawn spiralling down to the dwarf planet’s surface. “We are about to arrive. And when we do, we are at Ceres to stay,” said Russell.


No Ceres Pictures Yet?

I've been watching for new pictures of Ceres and have yet to see any.

The NASA site keeps showing the same images and it's been in orbit for a few days now I kinda figured we'd see something even on the first day or so. am I missing something here?

I want Ceres pictures and I want them NOW!

#2 coolrocketdude

Yes, Dawn is in "orbit" around Ceres. Dawn uses its ion propulsions system and this is somewhat different than the rather large engine firings and capture techniques used by say, a Mars orbiter. In the Dawn orbit capture at Ceres, the spacecraft slipped behind Ceres (the dark side) in a rather large loop that went out many tens of thousands of miles. Over the next few weeks the orbit will be adjusted to where it will be a polar circular orbit 8400 miles in altitude. This will take several weeks (about April 23rd). So for the meantime, Dawn is on the dark side of Ceres and hence no pictures. After a inital recon at that orbit NASA intents to lower the orbit in steps to where Dawn will be about 230 miles high by the end of the year.

#3 csrlice12

I tend to not look at things that look back. at least they look like eyes.

#4 Feidb

I'm anxious to see what that bright spot is in that one crater, up close. So far, nothing yet. Ceres is the one with the bright spot, right?

#5 coolrocketdude

29,000 miles away - and have something like 4 km resolution. I'm sure there will be some new (and better!) images by the end of next month.

#6 Dartguy

Yes, Dawn is in "orbit" around Ceres. Dawn uses its ion propulsions system and this is somewhat different than the rather large engine firings and capture techniques used by say, a Mars orbiter. In the Dawn orbit capture at Ceres, the spacecraft slipped behind Ceres (the dark side) in a rather large loop that went out many tens of thousands of miles. Over the next few weeks the orbit will be adjusted to where it will be a polar circular orbit 8400 miles in altitude. This will take several weeks (about April 23rd). So for the meantime, Dawn is on the dark side of Ceres and hence no pictures. After a inital recon at that orbit NASA intents to lower the orbit in steps to where Dawn will be about 230 miles high by the end of the year.

Yes, the Dawn Probe has only 90 mN of thrust, which is less than the small model rocket motors. It does burns for weeks instead of seconds. When it finally does get into a low orbit, it will be there for a LONG time. Probably longer than any of us will live. We should get quite a lot of good data from Ceres.


Where is the Ice on Ceres? New NASA Dawn Findings

At first glance, Ceres, the largest body in the main asteroid belt, may not look icy.

At first glance, Ceres, the largest body in the main asteroid belt, may not look icy. Images from NASA's Dawn spacecraft have revealed a dark, heavily cratered world whose brightest area is made of highly reflective salts -- not ice. But newly published studies from Dawn scientists show two distinct lines of evidence for ice at or near the surface of the dwarf planet. Researchers are presenting these findings at the 2016 American Geophysical Union meeting in San Francisco.

"These studies support the idea that ice separated from rock early in Ceres' history, forming an ice-rich crustal layer, and that ice has remained near the surface over the history of the solar system," said Carol Raymond, deputy principal investigator of the Dawn mission, based at NASA's Jet Propulsion Laboratory, Pasadena, California.

Water ice on other planetary bodies is important because it is an essential ingredient for life as we know it. "By finding bodies that were water-rich in the distant past, we can discover clues as to where life may have existed in the early solar system," Raymond said.

Ice is everywhere on Ceres

Ceres' uppermost surface is rich in hydrogen, with higher concentrations at mid-to-high latitudes -- consistent with broad expanses of water ice, according to a new study in the journal Science.

"On Ceres, ice is not just localized to a few craters. It's everywhere, and nearer to the surface with higher latitudes," said Thomas Prettyman, principal investigator of Dawn's gamma ray and neutron detector (GRaND), based at the Planetary Science Institute, Tucson, Arizona.

Researchers used the GRaND instrument to determine the concentrations of hydrogen, iron and potassium in the uppermost yard (or meter) of Ceres. GRaND measures the number and energy of gamma rays and neutrons emanating from Ceres. Neutrons are produced as galactic cosmic rays interact with Ceres' surface. Some neutrons get absorbed into the surface, while others escape. Since hydrogen slows down neutrons, it is associated with fewer neutrons escaping. On Ceres, hydrogen is likely to be in the form of frozen water (which is made of two hydrogen atoms and one oxygen atom).

Rather than a solid ice layer, there is likely to be a porous mixture of rocky materials in which ice fills the pores, researchers found. The GRaND data show that the mixture is about 10 percent ice by weight.

"These results confirm predictions made nearly three decades ago that ice can survive for billions of years just beneath the surface of Ceres," Prettyman said. "The evidence strengthens the case for the presence of near-surface water ice on other main belt asteroids."

Clues to Ceres' inner life

Concentrations of iron, hydrogen, potassium and carbon provide further evidence that the top layer of material covering Ceres was altered by liquid water in Ceres' interior. Scientists theorize that the decay of radioactive elements within Ceres produced heat that drove this alteration process, separating Ceres into a rocky interior and icy outer shell. Separation of ice and rock would lead to differences in the chemical composition of Ceres' surface and interior.

Because meteorites called carbonaceous chondrites were also altered by water, scientists are interested in comparing them to Ceres. These meteorites probably come from bodies that were smaller than Ceres, but had limited fluid flow, so they may provide clues to Ceres' interior history. The Science study shows that Ceres has more hydrogen and less iron than these meteorites, perhaps because denser particles sunk while brine-rich materials rose to the surface. Alternatively, Ceres or its components may have formed in a different region of the solar system than the meteorites.

Ice in permanent shadow

A second study, led by Thomas Platz of the Max Planck Institute for Solar System Research, Gottingen, Germany, and published in the journal Nature Astronomy, focused on craters that are persistently in shadow in Ceres' northern hemisphere. Scientists closely examined hundreds of cold, dark craters called "cold traps" -- at less than minus 260 degrees Fahrenheit (110 Kelvin), they are so chilly that very little of the ice turns into vapor in the course of a billion years. Researchers found deposits of bright material in 10 of these craters. In one crater that is partially sunlit, Dawn's infrared mapping spectrometer confirmed the presence of ice.


This movie of images from NASA's Dawn spacecraft shows a crater on Ceres that is partly in shadow all the time. Such craters are called "cold traps." Dawn has shown that water ice could potentially be preserved in such place for very long amounts of time. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
› Full image and caption

This suggests that water ice can be stored in cold, dark craters on Ceres. Ice in cold traps has previously been spotted on Mercury and, in a few cases, on the moon. All of these bodies have small tilts with respect to their axes of rotation, so their poles are extremely cold and peppered with persistently shadowed craters. Scientists believe impacting bodies may have delivered ice to Mercury and the moon. The origins of Ceres' ice in cold traps are more mysterious, however.

"We are interested in how this ice got there and how it managed to last so long," said co-author Norbert Schorghofer of the University of Hawaii. "It could have come from Ceres' ice-rich crust, or it could have been delivered from space."

Regardless of its origin, water molecules on Ceres have the ability to hop around from warmer regions to the poles. A tenuous water atmosphere has been suggested by previous research, including the Herschel Space Observatory's observations of water vapor at Ceres in 2012-13. Water molecules that leave the surface would fall back onto Ceres, and could land in cold traps. With every hop there is a chance the molecule is lost to space, but a fraction of them ends up in the cold traps, where they accumulate.

'Bright spots' get names

Ceres' brightest area, in the northern-hemisphere crater Occator, does not shine because of ice, but rather because of highly reflective salts. A new video produced by the German Aerospace Center (DLR) in Berlin simulates the experience of flying around this crater and exploring its topography. Occator's central bright region, which includes a dome with fractures, has recently been named Cerealia Facula. The crater's cluster of less reflective spots to the east of center is called Vinalia Faculae.

"The unique interior of Occator may have formed in a combination of processes that we are currently investigating," said Ralf Jaumann, planetary scientist and Dawn co-investigator at DLR. "The impact that created the crater could have triggered the upwelling of liquid from inside Ceres, which left behind the salts."

Dawn began its extended mission phase in July, and is currently flying in an elliptical orbit more than 4,500 miles (7,200 kilometers) from Ceres. During the primary mission, Dawn orbited and accomplished all of its original objectives at Ceres and protoplanet Vesta, which the spacecraft visited from July 2011 to September 2012.

Dawn's mission is managed by JPL for NASA's Science Mission Directorate in Washington. Dawn is a project of the directorate's Discovery Program, managed by NASA's Marshall Space Flight Center in Huntsville, Alabama. UCLA is responsible for overall Dawn mission science. Orbital ATK Inc., in Dulles, Virginia, designed and built the spacecraft. The German Aerospace Center, Max Planck Institute for Solar System Research, Italian Space Agency and Italian National Astrophysical Institute are international partners on the mission team. For a complete list of mission participants, visit:


Distance from Earth:

The distance between the Asteroid Belt and Earth varies considerably depending on where we measure to. Based on its average distance from the Sun, the distance between Earth and the edge of the Belt that is closest to it can be said to be between 1.2 to 2.2 AUs, or 179.5 and 329 million km (111.5 and 204.43 million mi).

The asteroids of the inner Solar System and Jupiter: The donut-shaped asteroid belt is located between the orbits of Jupiter and Mars. Credit: Wikipedia Commons

However, at any given time, part of the Asteroid Belt will be on the opposite side of the Sun, relative to Earth. From this vantage point, the distance between Earth and the Asteroid Blt ranges from 3.2 and 4.2 AU – 478.7 to 628.3 million km (297.45 to 390.4 million mi). To put that in perspective, the distance between Earth and the Asteroid Belt ranges between being slightly more than the distance between the Earth and the Sun (1 AU), to being the same as the distance between Earth and Jupiter (4.2 AU) when they are at their closest.

But of course, for reasons of fuel economy and time, asteroid miners and exploration missions are not about to take the long way! As such, we can safely assume that the distance between Earth and the Asteroid Belt when they are at their closest is the only measurement worth considering.


Dawn dead in Ceres orbit, ran out of fuel Oct 2018

3970 km and 279 mph earlier today. A strange detour. But it certainly gives high-resolution pictures if they choose to take some this orbit.

They really could fix that black hole at the poles in the MYSTIC simulator ).

At least they finally hired Kip Thorne.
Can you imagine the sim-view of them orbiting my log, or worse yet, a basketball:

"You bet your asteroid, kid"

Rahman says the plan is for Dawn to be in survey orbit, and conclude thrusting, on 3 June, in just a couple of days.
Today's brief "status report" was informative:
==quote==
June 1, 2015 - Dawn Closing in on Second Mapping Orbit

Dawn spent the weekend maneuvering with its ion propulsion system and is now almost in its targeted mapping orbit. Last night it completed its final ascent in this complicated trajectory. Today it is descending from . (4,900 kilometers) to . (4,600 kilometers). It is scheduled to conclude thrusting on June 3 at an altitude of . (4,400 kilometers).
==endquote==
http://dawn.jpl.nasa.gov/mission/status.html

According to simview during the weekend it briefly switched around from braking to thrusting ahead, which I guess would have been to circularize the elliptical orbit it got into when descending from the earlier altitude 13500 km orbit.

What is the spell-checker thinking of? Noodle soup? I tried to type the Dawn mission director's name Marc Rayman and it corrected it to Rahman. I swear the whole thing was unintentional. Or was I thinking of spectroscopy?, or bee-less Brahmans?

Anyway there are indications that Om's correspondence with Marc Rayman has contributed to a beneficial effect. The almost daily status reports have become very informative as to things of interest to us here: orbit mechanics, orientation to sun, photo resolution, altitude, speed, thrusting schedule, the degree of reliability of simview. We are getting more of the prate stoop these days.

What is the spell-checker thinking of? Noodle soup? I tried to type the Dawn mission director's name Marc Rayman and it corrected it to Rahman. I swear the whole thing was unintentional. Or was I thinking of spectroscopy?, or bee-less Brahmans?

Anyway there are indications that Om's correspondence with Marc Rayman has contributed to a beneficial effect. The almost daily status reports have become very informative as to things of interest to us here: orbit mechanics, orientation to sun, photo resolution, altitude, speed, thrusting schedule, the degree of reliability of simview. We are getting more of the prate stoop these days.

Prate stoops and Dr. Top Ramen. Ha! I bet he'd like that.
Was that supposed to be "Pirate scoop"?

hmmm. I've never heard of "prate" before.

prate: babbling (hmmm. )
stoop: to do something reprehensible (hmmmm. )

ps. My last correspondence from him was from May 20th. I'd imagine he's a bit busy these days.
pps. Sorry I've been a bit silent lately. I've been out of town 7 of the last 11 days. And the pests(let's go out and get drunk!) of summer are swarming.

Phew!
I was afraid you and Dr. Rayman were corresponding behind my back.

I do look back at some of my comments, and think "That was reprehensible babble. It's obvious I didn't even bother engaging my brain".

ps. On a hopefully not true side note, I had an argument with someone at JPL a couple of weeks ago. I'm assuming it wasn't Dr. Rayman:

So that wasn’t you I was arguing with on Facebook?
Someone asked

To which I responded, and appear to have started an argument:

I guess, technically, we are both correct.​

pps. Followers
Facebook: 19k
Twitter: 84k

As is usually the case, 95% of the comments on Facebook, are prate stoop(not a spoonerism, by my favorite new phrase).
I wouldn't even bother checking it out, as most of the posts mirror the Twitter site.

Om, Canberra 45 is standing by to talk with Dawn! It is 2AM in the morning there (9AM pacific 2 June).

Maybe a prate stoop means a kind of humorous indirection where one arranges to stumble on the straight story seemingly by accident. A kind of serendipitous pratefall which lands on the essential fact.

Hey! Simview is using a beautiful new globe map of Ceres instead of the old Lumpy guess-ball

The 19:30 UTC simview even has the famous double bright spot showing. The new Ceres ball in simview is made of real photos taken by Dawn, with some latitude and longitude lines projected on it.

"Yumyum" is so far the only one I've memorized.

The bright splash crater is in the quad named Hobnil.

I’m not sure just how many of these there are, or how memorable their names will turn out to be. But as the Dawn mission’s principal investigator Chris Russell pointed out, there is one Mayan deity named Yum (Yum Kaax, god of agriculture and the jungle), who should readily be remembered. One can only hope the mission scientists find a suitably delicious feature on Ceres to give that name.

Om, thanks for posting the grid of Ceres named regions. Some pretty strange names. Every culture from every part of the world seems to have had a grain deity or fertility spirit. Happy Hobnil to you! Don't forget to celebrate YumYum day next Tuesday!

I'm trying to make sense of the current simview. It looks like Dawn has thrust turned off, and I see Canberra is assigned to Dawn but no signal.
It looks like as of 3Jun 15:50 UTC the altitude is right 4400 km and the speed is very nearly right 254 mph

and simview shows Dawn apparently approaching the S pole terminator which I guess it should cross early on 4 Jun UTC or like 6PM this evening pacific time (just a rough guess)

.
ps. On a hopefully not true side note, I had an argument with someone at JPL a couple of weeks ago. I'm assuming it wasn't Dr. Rayman:

Peter Fries ‏@Peter_Fries Jun 2
@NASA_Dawn @b0yle Does Dawn have the capability to send back 'natural color' images?

NASA's Dawn Mission ‏@NASA_Dawn Jun 2
@Peter_Fries @b0yle yes, I can take data with which to make color images, but the team has not yet released any yet

Have I totally lost my mind?

Sorry for my slow replies. Dawn keeps me busy, which comes as no surprise to you. We arrived in survey orbit this morning, and that will be tweeted and put on our mission status page.

You’re right that that was not I on Facebook. I mentioned about giving the information for tweeting. For Facebook, if they send a question back to me, I answer it, but most of the time they don’t. So I’m quite unaware of what gets posted there.

As usual, the topic is a little more complicated than it appears from what you quoted below. For the approach phase images, we used two different camera integration times (what most people call exposure times). One value was chosen to ensure Ceres was correctly exposed and the other was chosen to bring out the background stars. The images alternate, so we interpolate to get Ceres' location relative to stars. We did it the same way at Vesta. In at least one of the Ceres OpNavs, it just so happened that some stars showed up in the images exposed for Ceres. I don’t know what the Dawn person (who is not technical) had in mind with the comment about adding stars. We’ve never done that.

As for what Ceres would look like, you’re quite right that Ceres is significantly brighter than the background stars. That’s why we had two exposure values. I wrote in my March 31 Dawn Journal that Ceres’ mean albedo is about 0.09 and the Moon’s is about 0.12. So you’re also correct that the Moon’s is 1/3 higher. If it matters, remember that Ceres is farther from the sun. The Planetary Society reposts my Dawn Journals (as do some other sites), and sometimes (but not often), I respond to comments there. I did address this aspect of it in responding to a comment by Solon. That is, the intensity of the sunlight is around 12% at Ceres what it is at Earth or the Moon, so it would look darker to your eye. You’re also right that Ceres’ variation in albedo seems much lower, but, of course, there are those famous bright spots and others that are not so famous.

I hope I'm not getting his staff in trouble.

On a trivial side note, I was curious at what distance Ceres would fully fill Dawn's framing cameras.
So I did some maths, and determined that it was around 3400 km.
It's a bit problematic, as Marcus pointed out that polar and equatorial diameters are a bit different: 891 & 963 km, respectively.


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