NASA’s Dawn spacecraft has become the first mission to achieve orbit around a dwarf planet. The spacecraft was approximately 38,000 miles (61,000 kilometers) from Ceres when it was captured by the dwarf planet’s gravity at about 4:39 a.m. PST (7:39 a.m. EST) Friday.
Mission controllers at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California received a signal from the spacecraft at 5:36 a.m. PST (8:36 a.m. EST) that Dawn was healthy and thrusting with its ion engine, the indicator Dawn had entered orbit as planned.
Ceres is seen from NASA’s Dawn spacecraft on March 1, just a few days before the mission achieved orbit around the previously unexplored dwarf planet. The image was taken at a distance of about 30,000 miles (about 48,000 kilometers).
Image Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
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 extraterrestrial targets. From 2011 to 2012, the spacecraft explored the giant asteroid Vesta, delivering new insights and thousands of images from that distant world. Ceres and Vesta are the two most massive residents of our solar system’s main asteroid belt between Mars and Jupiter.
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.
Using its ion propulsion system, Dawn will entered orbit around Ceres on March 6. As scientists receive better and better views of the dwarf planet over the next 16 months, they hope to gain a deeper understanding of its origin and evolution by studying its surface. The intriguing bright spots and other interesting features of this captivating world will come into sharper focus.
This image was taken by NASA’s Dawn spacecraft of dwarf planet Ceres on Feb. 19 from a distance of nearly 29,000 miles (46,000 kilometers). It shows that the brightest spot on Ceres has a dimmer companion, which apparently lies in the same basin. Image Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDAM
“The brightest spot continues to be too small to resolve with our camera, but despite its size it is brighter than anything else on Ceres. This is truly unexpected and still a mystery to us,” said Andreas Nathues, lead investigator for the framing camera team at the Max Planck Institute for Solar System Research, Gottingen, Germany.
Dawn visited the giant asteroid Vesta from 2011 to 2012, delivering more than 30,000 images of the body along with many other measurements, and providing insights about its composition and geological history. Vesta has an average diameter of 326 miles (525 kilometers), while Ceres has an average diameter of 590 miles (950 kilometers). Vesta and Ceres are the two most massive bodies in the asteroid belt, located between Mars and Jupiter.
Ceres Mission Plan
Dawn will make its first full characterization of Ceres later in April, at an altitude of about 8,400 miles (13,500 kilometers) above the icy surface. Then, it will spiral down to an altitude of about 2,750 miles (4,430 kilometers), and obtain more science data in its survey science orbit. This phase will last for 22 days, and is designed to obtain a global view of Ceres with Dawn’s framing camera, and global maps with the visible and infrared mapping spectrometer (VIR).
Dawn will then continue to spiral its way down to an altitude of about 920 miles (1,480 kilometers), and in August 2015 will begin a two-month phase known as the high-altitude mapping orbit. During this phase, the spacecraft will continue to acquire near-global maps with the VIR and framing camera at higher resolution than in the survey phase. The spacecraft will also image in “stereo” to resolve the surface in 3-D.
Then, after spiraling down for two months, Dawn will begin its closest orbit around Ceres in late November, at a distance of about 233 miles (375 kilometers). The dance at low-altitude mapping orbit will be a long waltz — three months — and is specifically designed to acquire data with Dawn’s gamma ray and neutron detector (GRaND) and gravity investigation. GRaND will reveal the signatures of the elements on and near the surface. The gravity experiment will measure the tug of the dwarf planet, as monitored by changes in the high-precision radio link to NASA’s Deep Space Network on Earth.
At this low-altitude mapping orbit, Dawn will begin using a method of pointing control that engineers have dubbed “hybrid” mode because it utilizes a combination of reaction wheels and thrusters to point the spacecraft. Up until this final mission phase, Dawn will have used just the small thruster jets, which use a fuel called hydrazine, to control its orientation and pointing. While it is possible to explore Ceres completely using only these jets, mission managers want to conserve precious fuel. At this lowest orbit, using two of the reaction wheels to help with pointing will provide the biggest hydrazine savings. So Dawn will be spinning up two of the gyroscope-like devices to aid the thrusters.
Why Vesta and Ceres?
Caught up in a cosmic tug of war between the Sun and Jupiter, two of the largest inhabitants of the main asteroid belt, Vesta and Ceres, survived the collisional environment of the region and have remained intact since their formations. Furthermore, evidence shows that each has distinct characteristics; therefore, each must have followed a different evolutionary path. Vesta appears to be dry, evolved, and differentiated with surface features ranging from basaltic lava flows to a deep crater near its southern pole. Ceres, in contrast, has a dusty, clay-like surface and evidence of water, which has led scientists to suspect the presence of a thick water-ice mantle. Vesta’s physical characteristics reflect those of the inner planets, whereas Ceres’ are more like the icy moons of the outer planets. By studying these contrasts and comparing these two minor planets, scientists will develop an understanding of the transition from the rocky inner regions to the icy outer regions of the Solar System.
New Views of Old Worlds
The Dawn mission marks the first time a spacecraft will orbit a body in the main asteroid belt and the first time a spacecraft will orbit two targets, enabling a detailed and intensive study of both. Dawn thus uses the same suite of instruments to gather comparative data on Vesta and Ceres. Aboard the spacecraft, the science payload consists of two cameras, a visible and infrared mapping spectrometer to reveal the surface minerals, and a gamma ray and neutron spectrometer to determine the elements that make up the outer parts of the asteroids. The spacecraft also will be used to measure the gravity field, thereby revealing details of these asteroids’ interiors. With the data from these systems, scientists will study surface features and the complex and varied landscapes, gaining valuable new insights into the internal structure of these ancient worlds. What role did size have in determining how planets evolved throughout the Solar System? How did water affect the process of planetary formation? Data gathered during the Dawn mission will help scientists uncover the answers to these and other questions.
SOURCE – NASA JPL
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