21 Oct

In Appreciation: Dr. Gerhard Neukum

by Dawn EPO
Dr. Gerhard Neukum

Professor of Planetary
Sciences, Freie Universität Berlin. Credit: ESA

We are remembering Gerhard Neukum today: a mentor, a friend, and a superlative colleague.

Professor Gerhard Neukum was a planetary scientist with a particular fascination for craters and the story they tell about the age and composition of a solar system body—and the solar system itself. A co-investigator on the Dawn science team, he advised with characteristic perception and tenacity.


Gerhard Neukum was an international expert on cratering. Double crater on giant asteroid Vesta.
Credit: NASA/ JPL-Caltech/ UCLA/ MPS/ DLR/ IDA

Neukum’s career as a distinguished planetary scientist began in the 1970s, when he conducted research for NASA’s Apollo program as a physics student at the University of Heidelberg. Eventually he became the director of the German Aerospace Center Institute of Planetary Research before moving to the Free University of Berlin. Throughout his long and successful career he made major contributions to international space missions that visited the moon, Mars, Jupiter, Saturn, and the main asteroid belt. Neukum will always be remembered for his uncompromising determination to explore the solar system. Without his charismatic leadership, planetary science would not be where it is today.

Neukum had very high standards. He loved scientific discussions and admitted it freely when he was wrong. Amazingly this did not happen very often! Gerhard was a person you could call late at night to discuss a science issue—especially when it came to crater counting results, a particular passion.

Gerhard Neukum Image: David Ausserhofer

Gerhard Neukum Credit: David Ausserhofer

He was a great scientist who taught us about the will power to accomplish goals. Those who worked with him always appreciated his direct and energetic way of approaching and solving problems. Some did not always agree with Neukum’s outspoken way of arguing for new space missions, or the scientific details of crater counting throughout the solar system. However, everyone respected him for his intellectual capabilities and his love of exchanging fair arguments in scientific discourse.

Neukum was also the inventor of the High Resolution Stereo Camera (HRSC). With nine sensors that scan an object from a different perspective and combine the images, it pushed the boundaries of solar system imaging. A version of his camera was aboard the unsuccessful Russian Mars ’96 probe, which did not make it beyond Earth orbit. Gerhard remained undeterred. “On the plane back to Moscow,” Gerhard recalled, “I thought to myself, ‘This can’t be the end.’”1 In 2003, his camera was on board the European Space Agency’s Mars Express. Since then, scientists and citizens alike have enjoyed these sharp and stunning images.

Mars' Gale Crater

Gerhard Neukum developed the High Resolution Stereo Camera, which flew on the Mars Express mission. Here is an image of Mars’ Gale Crater. It is color-coded based on a digital terrain model derived from stereo image data.
Credit: ESA/DLR/FU Berlin (G. Neukum)

Besides being a great mentor, scientist and a person who touched the lives and careers of a large number of people, he was a friend to so many of us. We all recall numerous conversations about his kids, grandchildren and his garden projects. His family was certainly dear to his heart and we all appreciated that he let us be part of this part of his life. He will be missed dearly.

The Dawn team sends its sincere condolences to the family of Professor Neukum, and shares some special memories, below.

Gerhard was an inspiring and energetic leader not only for Mars Express but also for missions like Galileo, Dawn, Cassini and all the attempts we made to go back to the moon. Gerhard was a great planetary scientist on many space projects and a long term friend for many of us.
     Ralf Jaumann
     German Aerospace Center

Gerhard has been an unparalleled leader in planetary science and his accomplishments and personality will be long remembered with great fondness. The Dawn team is particularly indebted to his tireless efforts and enthusiasm. It has been a unique honor to know and work with him.
     Carle M. Pieters
    Brown University

Day/Night boundary on giant asteroid Vesta

Day/night boundary on giant asteroid Vesta.
Credit: NASA/ JPL-Caltech/ UCLA/ MPS/ DLR/ IDA

I met Gerhard during the Galileo lunar flybys as a student of Ron Greeley, and I am appreciative of all of the support that Gerhard gave to me as a graduate student (learning how to do crater counting for age dating), a postdoc and faculty researcher, and finally as Co-PI on HRSC, and as a participating scientist on Dawn. Gerhard’s tenacious search for understanding the ages of planetary objects has been an ongoing inspiration. All of us at Arizona State University who knew him will miss him.
     David A. Williams
     Arizona State University

I first met Gerhard as Herr Professor Doktor Neukum, when I was a graduate student at Brown. Gerhard gave me my first instruction in crater age dating statistics as part of my thesis work on Ganymede, and he continued to be a great mentor and colleague throughout my career. I count myself fortunate to finally be able to work closely with him again, however briefly, on the Dawn at Vesta team.

He was a great inspiration and mentor and I will miss him a lot! I don’t know how many students and scientists he touched with his enthusiasm and determination to explore the solar system. He certainly took a lot of heat for saying things that were correct but that nobody besides him dared to say in public. He was a man who would not bend! I always appreciated his direct way of approaching problems.
     Harald Hiesinger
     University of Munster

A few months ago I met Gerhard Neukum at “his” Institut für Planetenphysik in Berlin. He was Gerhard Neukum as we all know him: active, determined and not talking about compromises. Gerhard Neukum has been one of the outstanding planetary scientists in Germany during the last 30 years.
     H. Uwe Keller
     Braunschweig University of Technology

Everybody knows that he has been a great scientist, but I will forever remember him for the help and friendship he gave me.
     Maria Teresa Capria
     Italy’s National Institute for Astrophysics


For more information about Gerhard Neukum:
1. European Space Agency | A Man with a Plan: An Interview with Gerhard Neukum: 10.12.2003
2. Planetary Society | Planetary Radio podcast: 4.25.2005
3. Time Magazine | Aerospace Inspiration: Gerhard Neukum: 4.20.2007

Special thanks to Dr. Harold Hiesinger and Dr. Ralf Jaumman for their contributions to this post.


27 Sep
Marc Rayman
Marc Rayman
Chief Engineer/ Mission Director, JPL

Dawn Journal | September 27

by Marc Rayman

Dear Dawnniversaries,

On the seventh anniversary of embarking upon its extraordinary extraterrestrial expedition, the Dawn spacecraft is far from the planet where its journey began. While Earth has completed its repetitive loops around the sun seven times, its ambassador to the cosmos has had a much more varied itinerary. On most of its anniversaries, including this one, it reshapes its orbit around the sun, aiming for some of the last uncharted worlds in the inner solar system. (It also zipped past the oft-visited Mars, robbing the red planet of some of its orbital energy to help fling the spacecraft on to the more distant main asteroid belt.) It spent its fourth anniversary exploring the giant protoplanet Vesta, the second most massive object in the asteroid belt, revealing a fascinating, complex, alien place more akin to Earth and the other terrestrial planets than to typical asteroids. This anniversary is the last it will spend sailing on the celestial seas. By its eighth, it will be at its new, permanent home, dwarf planet Ceres.

The mysterious world of rock and ice is the first dwarf planet discovered (129 years before Pluto) and the largest body between the sun and Pluto that a spacecraft has not yet visited. Dawn will take up residence there so it can conduct a detailed investigation, recording pictures and other data not only for scientists but for everyone who has ever gazed up at the night sky in wonder, everyone who is curious about the nature of the universe, everyone who feels the burning passion for adventure and the insatiable hunger for knowledge and everyone who longs to know the cosmos.

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31 Aug
Marc Rayman
Marc Rayman
Chief Engineer/ Mission Director, JPL

Dawn Journal | August 31

by Marc Rayman

Dear Omnipodawnt Readers,

Dawn draws ever closer to the mysterious Ceres, the largest body between the sun and Pluto not yet visited by a probe from Earth. The spacecraft is continuing to climb outward from the sun atop a blue-green beam of xenon ions from its uniquely efficient ion propulsion system. The constant, gentle thrust is reshaping its solar orbit so that by March 2015, it will arrive at the first dwarf planet ever discovered. Once in orbit, it will undertake an ambitious exploration of the exotic world of ice and rock that has been glimpsed only from afar for more than two centuries.

An important characteristic of this interplanetary expedition is that Dawn can linger at its destinations, conducting extensive observations. Since December, we have presented overviews of all the phases of the mission at Ceres save one. (In addition, questions posted by readers each month, occasionally combined with an answer, have helped elucidate some of the interesting features of the mission.) We have described how Dawn will approach its gargantuan new home (with an equatorial diameter of more than 600 miles, or 975 kilometers) and slip into orbit with the elegance of a celestial dancer. The spacecraft will unveil the previously unseen sights with its suite of sophisticated sensors from progressively lower altitude orbits, starting at 8,400 miles (13,500 kilometers), then from survey orbit at 2,730 miles (4,400 kilometers), and then from the misleadingly named high altitude mapping orbit (HAMO) only 910 miles (1,470 kilometers) away. To travel from one orbit to another, it will use its extraordinary ion propulsion system to spiral lower and lower and lower. This month, we look at the final phase of the long mission, as Dawn dives down to the low altitude mapping orbit (LAMO) at 230 miles (375 kilometers). We will also consider what future awaits our intrepid adventurer after it has accomplished the daring plans at Ceres.


Dawn’s spiral transfer from HAMO to LAMO. The trajectory turns from blue to red as time progresses during the two months. Red dashed sections are where ion thrusting is stopped so the spacecraft can point its main antenna to Earth. Credit: NASA/JPL

It will take the patient and tireless robot two months to descend from HAMO to LAMO, winding in tighter and tighter loops as it goes. By the time it has completed the 160 revolutions needed to reach LAMO, Dawn will be circling Ceres every 5.5 hours. (Ceres rotates on its own axis in 9.1 hours.) The spacecraft will be so close that Ceres will appear as large as a soccer ball seen from less than seven inches (17 centimeters) away. In contrast, Earth will be so remote that the dwarf planet would look to terrestrial observers no larger than a soccer ball from as far as 170 miles (270 kilometers). Dawn will have a uniquely fabulous view.

As in the higher orbits, Dawn will scrutinize Ceres with all of its scientific instruments, returning pictures and other information to eager Earthlings. The camera and visible and infrared mapping spectrometer (VIR) will reveal greater detail than ever on the appearance and the mineralogical composition of the strange landscape. Indeed, the photos will be four times sharper than those from HAMO (and well over 800 times better than the best we have now from Hubble Space Telescope). But just as in LAMO at Vesta, the priority will be on three other sets of measurements which probe even beneath the surface.

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31 Jul
Marc Rayman
Marc Rayman
Chief Engineer/ Mission Director, JPL

Dawn Journal | July 31

by Marc Rayman

Dear Studawnts and Teachers,

Patient and persistent, silent and alone, Dawn is continuing its extraordinary extraterrestrial expedition. Flying through the main asteroid belt between Mars and Jupiter, the spacecraft is using its advanced ion propulsion system to travel from Vesta, the giant protoplanet it unveiled in 2011 and 2012, to Ceres, the dwarf planet it will reach in about eight months.

Most of these logs since December have presented previews of the ambitious plan for entering orbit and operating at Ceres to discover the secrets this alien world has held since the dawn of the solar system. We will continue with the previews next month. But now with Dawn three quarters of the way from Vesta to Ceres, let’s check in on the progress of the mission, both on the spacecraft and in mission control at JPL.

The mission is going extremely well. Thank you for asking.

For readers who want more details, read on…

The spacecraft, in what is sometimes misleadingly called quiet cruise, has spent more than 97 percent of the time this year following the carefully designed ion thrust flight plan needed to reshape its solar orbit, gradually making it more and more like Ceres’ orbit around the sun. This is the key to how the ship can so elegantly enter into orbit around the massive body even with the delicate thrust, never greater than the weight of a single sheet of paper.

The probe is equipped with three ion engines, although it only uses one at a time. (The locations of the engines were revealed shortly after launch when the spacecraft was too far from Earth for the information to be exploited for tawdry sensationalism.) Despite the disciplined and rigorous nature of operating a spaceship in the main asteroid belt, the team enjoys adding a lighthearted touch to their work, so they refer to the engines by the zany names #1, #2, and #3.

Dawn & TIE Fighter comparison

Artist’s comparison of Dawn spacecraft and Star Wars TIE Fighter.
Credit: NASA/JPL

Darth Vader and his Empire cohorts in “Star Wars” flew TIE (Twin Ion Engine) Fighters in their battles against Luke Skywalker and others in the Rebel Alliance. Outfitted with three ion engines, Dawn does the TIE Fighters one better. We should acknowledge, however, that the design of the TIE Fighters did appear to provide greater agility, perhaps at the expense of fuel efficiency. Your correspondent would concur that when you are trying to destroy your enemy while dodging blasts from his laser cannons, economy of propellant consumption probably shouldn’t be your highest priority.

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30 Jun
Marc Rayman
Marc Rayman
Chief Engineer/ Mission Director, JPL

Dawn Journal | June 30

by Marc Rayman

Dear Mastodawns,

Deep in the main asteroid belt, between Mars and Jupiter, far from Earth, far from the sun, far now even from the giant protoplanet Vesta that it orbited for 14 months, Dawn flies with its sights set on dwarf planet Ceres. Using the uniquely efficient, whisper-like thrust of its remarkable ion propulsion system, the interplanetary adventurer is making good progress toward its rendezvous with the uncharted, alien world in about nine months.

Dawn’s ambitious mission of exploration will require it to carry out a complex plan at Ceres. In December, we had a preview of the “approach phase,” and in January, we saw how the high velocity beam of xenon ions will let the ship slip smoothly into Ceres’s gravitational embrace. We followed that with a description in February of the first of four orbital phases (with the delightfully irreverent name RC3), in which the probe will scrutinize the exotic landscape from an altitude of 8,400 miles (13,500 kilometers). We saw in April how the spacecraft will take advantage of the extraordinary maneuverability of ion propulsion to spiral from one observation orbit to another, each one lower than the one before, and each one affording a more detailed view of the exotic world of rock and ice. The second orbit, at an altitude of about 2,730 miles (4,400 kilometers), known to insiders (like you, faithful reader) as “survey orbit,” was the topic of our preview in May. This month, we will have an overview of the plan for the third and penultimate orbital phase, the “high altitude mapping orbit” (HAMO).

(The origins of the names of the phases are based on ancient ideas, and the reasons are, or should be, lost in the mists of time. Readers should avoid trying to infer anything at all meaningful in the designations. After some careful consideration, your correspondent chose to use the same names the Dawn team uses rather than create more helpful descriptors for the purposes of these logs. What is important is not what the different orbits are called but rather what amazing new discoveries each one enables.)

It will take Dawn almost six weeks to descend to HAMO, where it will be 910 miles (1,470 kilometers) high, or three times closer to the mysterious surface than in survey orbit. As we have seen before, a lower orbit, whether around Ceres, Earth, the sun, or the Milky Way galaxy, means greater orbital velocity to balance the stronger gravitational grip. In HAMO, the spacecraft will complete each loop around Ceres in 19 hours, only one quarter of the time it will take in survey orbit.

Sprial to Hamo

Dawn’s spiral descent from survey orbit to the high altitude mapping orbit. The trajectory progresses from blue to red over the course of the six weeks. The red dashed segments are where the spacecraft is not thrusting with its ion propulsion system (as explained in April). Credit: NASA/JPL

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31 May
Marc Rayman
Marc Rayman
Chief Engineer/ Mission Director, JPL

Dawn Journal | May 31

by Marc Rayman

Dear Dawnosaurs,

Silently streaking through the main asteroid belt, emitting a blue-green beam of xenon ions, Dawn continues its ambitious interplanetary expedition. On behalf of creatures on distant Earth who seek not only knowledge and insight but also bold adventure, the spacecraft is heading toward its appointment with Ceres. In about 10 months, it will enter orbit around the ancient survivor from the dawn of the solar system, providing humankind with its first detailed view of a dwarf planet.

This month we continue with the preview of how Dawn will explore Ceres. In December we focused on the “approach phase,” and in January we described how the craft spirals gracefully into orbit with its extraordinary ion propulsion system. The plans for the first observational orbit (with a marvelously evocative name for a first examination of an uncharted world: RC3 — is that cool, or what?), at an altitude of 8,400 miles (13,500 kilometers), were presented in FebruaryLast month, we followed Dawn on its spiral descent from each orbital altitude to the next, with progressively lower orbits providing better views than the ones before. Now we can look ahead to the second orbital phase, survey orbit.


This figure shows Dawn’s second observational orbit, “survey orbit,” at the same scale as the size of Ceres. At an altitude of 2,730 miles (4,400 kilometers), the spacecraft will make seven revolutions in about three weeks. Credit: NASA/JPL

In survey orbit, Dawn will make seven revolutions at an altitude of about 2,730 miles (4,400 kilometers). At that distance, each orbit will take three days and three hours. Mission planners chose an orbit period close to what they used for survey orbit at Vesta, allowing them to take advantage of many of the patterns in the complex choreography they had already developed. Dawn performed it so beautifully that it provides an excellent basis for the Ceres encore. Of course, there are some adjustments, mostly in the interest of husbanding precious hydrazine propellant in the wake of the loss of two of the spacecraft’s four reaction wheels. (Although such a loss could have dire consequences for some missions, the resourceful Dawn team has devised a plan that can achieve all of the original objectives regardless of the condition of the reaction wheels.)

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29 May

Greetings From Berlin–Grüße aus Berlin!

by Chris Russell

The Dawn Team Converges at the German Aerospace Agency

The Dawn spacecraft moved back in solar system time when it cruised into the main asteroid belt, first orbiting protoplanet Vesta in 2011-12, and now on its way to dwarf planet Ceres, due in March 2015. When the Dawn team met in Berlin this month, it offered an opportunity for the mission to do a bit of its own time travel.

Dawn Team at the German Aerospace Agency, Berlin, 2014

fig 1: Dawn Team at the German Aerospace Agency, Berlin, 2014

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23 May

Vesta 360

by David O'Brien

The Dawn mission is currently en route to dwarf planet Ceres, its second destination. It spent a productive fourteen months orbiting its first destination, giant asteroid Vesta, in 2011-12, gathering splendid sets of data. The spacecraft may have moved on, but the science team continues to explore that data, enriching our understanding of Vesta’s formation and history.

Getting the “Big Picture”

Vesta: Clementine color ratios

Clementine color ratios

Vesta is a large protoplanet with remarkably variable topography—mountains, troughs, boulders, craters, cliffs, and more. The wealth of high-resolution imaging data from the Dawn mission has given us an amazing view of its surface. However, looking through individual frames or image mosaics can make it difficult to see its surface features in a global context and get the “big picture” of Vesta. On the other hand, the images taken early on as the mission approached the protoplanet show the whole of Vesta, but with low surface resolution. To better visualize Vesta at high resolution, I used the open-source program POV-Ray[1], combining images and topography data to create striking 3-D graphics.

The program let me take a shape model of Vesta, created from Dawn’s framing camera data by Bob Gaskell at the Planetary Science Institute, and wrap an image around it. For the image, I used a global mosaic[2] developed by our framing camera team partners at the German Aerospace Center (DLR) from high altitude mapping orbit clear-filter images. This mosaic has a resolution of 60 meters (about 200 feet) per pixel. I then used POV-Ray to make ‘snapshots’ of this model of Vesta as it rotated, varying the latitude from +45 to -45 degrees. Those individual frames were combined into the movie shown below.

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  1. [1] Persistence of Vision Raytracer
  2. [2] The global mosaics used here can be downloaded from this page at the Dawn Public Data website, although they are very large files. For labeled maps of smaller regions of the surface, see the Vesta Atlas.


2 May
Marc Rayman
Marc Rayman
Chief Engineer/ Mission Director, JPL

The Hundredth Journal

by Marc Rayman
Colleague Keri Bean's festive (and delicious) cake

Colleague Keri Bean’s festive (and delicious) cake with some of the greetings used in the Dawn Journals.

I have been captivated by space since I was four years old, and my enthusiasm has grown stronger and stronger ever since. With a lifelong passion for the exploration and utilization of space, covering the science, the engineering and the pure thrill of a cosmic adventure, working on a mission to explore some of the last uncharted worlds in the inner solar system has been a dream come true for me. My work is indescribably exciting.

And although it literally is indescribable, I can’t help but try! As one facet of that effort, I started writing the Dawn Journal eight years ago. Now that I have written 100, I was invited to write a short blog to celebrate. (In other words, I’ve been asked to blog about blogging.)

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30 Apr
Marc Rayman
Marc Rayman
Chief Engineer/ Mission Director, JPL

Dawn Journal | April 30

by Marc Rayman

Dear Compedawnt Readers,

Less than a year from its rendezvous with dwarf planet Ceres, Dawn is continuing to make excellent progress on its ambitious interplanetary adventure. The only vessel from Earth ever to take up residence in the main asteroid belt between Mars and Jupiter, the spacecraft grows more distant from Earth and from the sun as it gradually closes in on Ceres. Dawn devotes the majority of its time to thrusting with its remarkable ion propulsion system, reshaping its heliocentric path so that by the time it nears Ceres, the explorer and the alien world will be in essentially the same orbit around the sun.

Dawn thrusting in orbit

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

In December, we saw what Dawn will do during the “approach phase” to Ceres early in 2015, and in January, we reviewed the unique and graceful method of spiraling into orbit. We described in February the first orbit (with the incredibly cool name RC3) from which intensive scientific observations will be conducted, at an altitude of 8,400 miles (13,500 kilometers). But Dawn will take advantage of the extraordinary capability of ion propulsion to fly to three other orbital locations from which it will further scrutinize the mysterious world.

Let’s recall how the spacecraft will travel from one orbit to another. While some of these plans may sound like just neat ideas, they are much more than that; they have been proven with outstanding success. Dawn maneuvered extensively during its 14 months in orbit around Vesta. (One of the many discussions of that was in November 2011.) The seasoned space traveler and its veteran crew on distant Earth are looking forward to applying their expertise at Ceres.

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