Journey to the Dawn of the solar system Spacecraft set to begin odyssey for up-close examination of two asteroids Richard Monda is an astronomer living in the Capital Region.
In our solar system, hundreds of thousands of small rocky objects race around the sun between the orbits of Mars and Jupiter. Today, these minor worlds occupy a band 150 million to 400 million miles from our star. But 4.5 billion years ago, such minor league objects were spread throughout our newly forming solar system. Over hundreds of millions of years, collisions among these bodies, along with their mutual gravity, bonded masses together to build the four inner planets and form the cores of the four outer worlds. During September, NASA will launch an unmanned probe to this region of the solar system known as the asteroid belt. In a sense, it is a time-travel mission, because the asteroids are believed to be made of the original material remaining from the time the planets formed. The current-day “leftovers” in the asteroid belt, however, were unable to coalesce into another planet because of the dominance of nearby Jupiter’s gravity. Scientists hope that these minor “planets” are still in an unprocessed, pristine condition, unchanged over billions of years and that a spacecraft will allow them a close-up glance at the building blocks of the early system. Dawn is the name of this mission to the asteroid belt; it is subtitled by NASA as a “journey to the beginning of our solar system.” The Dawn spacecraft will visit two of the largest asteroids and become the first space machine to orbit one object for an extended length of time then break orbit and fly away to another object for a lengthy visit. NASA currently states liftoff for the Dawn mission as “no later than Sept. 26.” The mission had been scheduled for an early July departure, but Dawn mission managers along with other NASA administrators decided to move its take-off to September. This decision was based on the limited number of opportunities for Dawn to launch in July; in addition, its launch would have set back preparations being made to launch the Mars Phoenix Lander at that time. Phoenix was launched Aug. 4. Once Dawn leaves Earth, the first leg of its flight path will be to swing by Mars in 2009, where it will use the gravity of the planet to slingshot toward the asteroid belt. Dawn will then arrive at its fi rst destination, the asteroid Vesta, in late 2011, where it will orbit for seven months. After its investigation there, it will leave Vesta and start on a three-year flight to Ceres, the only asteroid that has been classifi ed as a dwarf planet. Dawn will reach Ceres in 2015 and orbit this dwarf planet for five months, ending its mission there. INSTRUMENTATION On board the Dawn spacecraft are two identical cameras built to obtain detailed images of the surface of Vesta and Ceres. The cameras are mounted in different locations on Dawn and each has its own optics and electronics for redundancy. The cameras will also be used track background stars that are used to navigate this space vehicle. Another instrument aboard Dawn can detect gamma rays (a high-energy form of light) and neutrons (particles usually found in the cores of atoms) that are emitted or reflected from the surface of Vesta and Ceres. Studies of gamma rays and neutrons from an object can reveal information about its composition to a depth of roughly 1 meter (about 3 feet). Such a device was used on the Mars Odyssey Orbiter to gather evidence of frozen water below the surface of the north polar region on Mars — the destination of the Mars Phoenix Lander. Dawn also carries an instrument that will analyze the visible light and infrared energy (heat) reflected from Vesta and Ceres. This piece of equipment, called a spectrometer, can determine which minerals are on the surface of the two celestial objects. Further, scientists can tell how the force of gravity varies around Vesta and Ceres by carefully measuring changes in the radio transmissions from the spacecraft as it orbits the two worlds. Those observations can reveal clues about their internal density and, therefore, their interior structure. SEPTEMBER SKY Vesta will be easy to find this week for someone using a small telescope. The asteroid is found slightly above Jupiter, which is found in the southwestern evening sky. A good tactic to see Vesta is to aim a telescope, equipped with an eyepiece that shows a wide field of view, at Jupiter. Even with a telescope, Vesta look like an extra moon of Jupiter — a dot of light next to the large planet. If you watch the asteroid during the coming week, you will have no trouble noticing that Vesta moves from the upper right of Jupiter to its upper left (west to east). However, your view could be different depending on the type of telescope you use. A moon event will take place early this Tuesday. Given clear skies during predawn hours that day, we will be able to see part of a lunar eclipse.The moon will be in the southwest and become partially eclipsed at 4:51 a.m.; this is when Earth’s shadow begins to fall on the lunar surface. Then the total lunar eclipse will start at 5:52 a.m., the moment when the moon is completely within Earth’s shadow; however, the moon will set at 6:18 a.m. while the total eclipse is still in progress. Mars rises before midnight over the east-northeastern horizon and is visible throughout the entire night. Look for the last quarter moon above Mars, high in the eastern sky before sunrise during morning hours of Sept. 4. Also visible in the east before sunrise are Venus and Saturn. Venus is presently rising after 5 a.m. and Saturn rises about a half-hour later. Watch for a thin crescent moon above Venus on Sept. 8. Later in the month, fall will officially begin when the autumnal equinox occurs at 5:51 a.m. on Sept. 23. The full Harvest Moon happens on Sept. 26. This is an illustration of the solar system from NASA’s Solar Exploration Web Site.
Body Period of planethood Solar System Region Present status Notes Sun Antiquity to 1600s Centre Star Planet under the geocentric model. Moon Antiquity to 1600s Earth's orbit Satellite Planet under the geocentric model. Ceres 1801-1864 Asteroid belt Dwarf planet Asteroid until at least 2006.[18] Pallas 1802-1864 Asteroid belt Asteroid Juno 1804-1864 Asteroid belt Asteroid Vesta 1807-1864 Asteroid belt Asteroid Pluto 1930-2006 Kuiper belt Dwarf planet Officially accepted by IAU for this period.
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