The Star Witness News. The Star Witness News Dawn Spacecraft Will Go Asteroid Hopping

Transcription

1 Name The Star Witness News Your assignment is to read the issues of the Star Witness News. After reading your issues, answer the questions on the worksheet. All answers must be complete sentences. The Star Witness News Dawn Spacecraft Will Go Asteroid Hopping 1. What are asteroids? Why do you think there are so many of them? 2. Identify at least two things that make the Dawn mission unique. a. b. 3. How is Hubble supporting the Dawn mission? 4. Why do astronomers want to study asteroids?

2 5. Compare and contrast Vesta and Ceres. The Star Witness News Hubble Witnesses Fireworks From a Comet Mission 1. What was the purpose of the Deep Impact mission? 2. Describe the makeup of a comet. 3. Why were the Hubble Space Telescope and other space telescopes involved in the Deep Impact mission?

3 4. If you could ask a Deep Impact scientist several questions about the mission, what would they be? 5. If you were an astronomer, what question(s) about the solar system would you want to investigate? The Star Witness News Comet Holmes Dazzles Sky Watchers 1. Why is Comet Holmes different from many other short-period comets? 2. Why is Comet Holmes causing a stir?

4 3. List the four parts of a comet. a. b. c. d. 4. Explain the dramatic brightening of Comet Holmes. 5. Describe Hubble s role in studying the comet.

5 National Aeronautics and Space Administration THESTAR WITNESS A P U B L I C A T I O N O F N A S A S A M A Z I N G S P A C E E D U C A T I O N P R O G R A M Special Feature Dawn Spacecraft Will Go Asteroid-Hopping By NASA s Amazing Space reporters Sept AT least 100,000 rocky objects called asteroids reside between Mars and Jupiter. Scientists believe that asteroids are the leftover building blocks of our solar system planets. These space rocks orbit the Sun in a large, circular region called the asteroid belt. Locked inside these small bodies are clues to how our planets formed 4.5 billion years ago. Now, for the first time, a NASA spacecraft is speeding toward the asteroid belt to tour two of its most massive members. The Dawn spacecraft: This artist s illustration shows Dawn leaving Earth. IMAGE: NASA, UCLA Astronomers had dreamed since the 1940s about launching a visible-light telescope into space. Ground-based telescopes are hampered by our Earth s atmosphere, which blurs the light from stars and makes them appear to twinkle. The unmanned spacecraft, called Dawn, is on a four-year journey to the asteroids Vesta and Ceres. Dawn was launched on a rocket on September 27. This asteroid-hopping mission marks the first time a satellite will orbit two objects. The Dawn spacecraft will first visit Vesta in After orbiting Vesta for nine months, Dawn then will travel to Ceres, arriving in The Texas-sized Ceres is one of three dwarf planets in the solar system. The International Astronomical Union (IAU), a professional society for astronomers, created the dwarf-planet category in The three dwarf planets have many characteristics of planets. For example, they are round and orbit the Sun. Unlike planets, however, they have not cleared away all the rocks in their orbit. The Dawn mission will be the first to get a closeup view of a dwarf planet. Why travel to Vesta and Ceres? Scientists think the asteroids were budding planets that stopped growing because of Jupiter s powerful gravity. Continued, page

6 Continued from page 1 These objects have lost even more mass over billions of years through collisions with other asteroids. Vesta and ceres are unique because they have not had many close encounters with other space rocks. The only evidence of a major collision is a large crater in Vesta s southern hemisphere. The impact broke off chunks of rock, producing more than 50 smaller asteroids which astronomers have nicknamed vestoids. Dawn s destination: The asteroid belt INNER SOLAR SYSTEM, plus Jupiter (Orbits enlarged) Mars Earth The asteroid belt Dawn s launch: September 2007 ASTEROID BELT observations: 2011: Dawn reaches Vesta 2015: Dawn reaches Ceres Although the two asteroids orbit together in the same region, they have very different physical makeups. Astronomers, therefore, think the pair must have formed differently. Vesta is shaped like a mushroom and appears to be dry. Its varied landscape ranges from lava flows to the deep crater near its southern pole. ceres, by contrast, is round and has a thin, dusty outer crust. Water may even be locked beneath the crust. ceres also contains 30 to 40 percent of the asteroid belt s mass. OUTER SOLAR SYSTEM Jupiter Saturn Uranus Neptune Kuiper Belt Pluto Space Telescope Science Institute, Graphics Dept. Vesta s physical characteristics are like those of the inner rocky planets, like earth, whereas ceres resembles the icy moons of the outer planets. By exploring these two asteroids, the Dawn mission will help scientists understand the early stages of planet development. Scientists hope, for example, to gain insight into why the inner region of our solar system is composed of rocky planets and the outer, icy region is made up of gas giant planets. The spacecraft s mission The spacecraft s many science instruments will study the asteroids surface features, their varied landscapes, and perhaps even their Continued, page 3 The asteroid belt lies between the orbits of Mars and Jupiter, straddling the inner and outer solar system. The inner solar system orbits (enlarged, at top) are, in order from the Sun: Mercury, Venus, Earth, and Mars. Jupiter is part of the outer solar system. The outer solar system orbits are, in order: Jupiter, Saturn, Uranus, Neptune, and Pluto. The Kuiper Belt, a realm of icy, rocky objects that often become comets, begins near the orbit of Neptune and continues beyond Pluto. Relative sizes of dwarf planets Earth Mars Earth s Moon Dwarf planets NASA, ESA; image of Eris is an artist s conception by Adolf Schaller Diagram compares objects in order of size. The diagram does not display the order of their orbits. Eris and Pluto are Kuiper Belt objects and Ceres is an asteroid. Eris Pluto Ceres 2

7 Continued from page internal structure. By examining these ancient worlds, scientists hope to answer questions such as What role did size have in determining how planets evolved throughout the solar system? and How did water affect the process of planetary formation? Dawn is powered by a unique solarelectric engine that uses the Sun s rays to make electricity, which keeps the spacecraft speeding through space. This engine has never been used in scientific exploration. Hubble s supporting role The Hubble Space Telescope is playing a supporting role in the Dawn mission by snapping several images of Vesta in May 2007 and ceres in 2003 and Although Hubble has taken photos of Vesta before, these new images are the best views of the asteroid s Southern Hemisphere. The photos clearly show the large impact basin created from a collision billions of years ago. The huge crater is 285 miles (456 kilometers) across, which is nearly equal to Vesta s 330-mile (530- kilometer) diameter. Vesta is about as wide as Arizona. If earth had a crater of similar size, it would fill the Pacific ocean basin. The Hubble images of ceres revealed bright and dark regions on the asteroid s surface, which may be craters that were created from collisions. The asteroid s surface may also be made up of different types of material. These sharp Hubble images of ceres and Vesta are helping astronomers prepare for Dawn s visit to the asteroid belt. The snapshots offer two unique stories from our solar system s past. Who knows what surprises await us when Dawn takes a close-up look at ceres and Vesta. Asteroid Ceres Asteroid Vesta Thin, dusty crust Ceres layers (Artist s conception) Rocky core HST image, above, left: NASA, ESA, J. Parker (Southwest Research Inst.), and L. McFadden (Univ. of Md.); Computer model, above, right: P. Thomas (Cornell Univ.), B. Zellner (Georgia Southern Univ.), NASA Above: Vesta is shaped like a mushroom and appears to be dry. Its varied landscape ranges from lava flows to a deep crater near its southern pole, which resulted from a major collision. Vesta s physical characteristics are like those of the inner rocky planets, like Earth. Hubble s image of Vesta is at left, in box above. The lower surface of the computer model of Vesta, at right, above, shows evidence of the collision. Water ice Top (HST image): NASA, ESA, J. Parker (Southwest Research Inst.), and L. McFadden (Univ. of Md.); Bottom: Ann Feild, STScI Graphics Dept. Left: Ceres is round and has a thin, dusty outer crust. Water may even be locked beneath the crust. Ceres physical characteristics are like those of the icy moons of the outer planets. The artist s conception, at lower left, shows the layers of Ceres. Hubble s image is at top, far left. 3

8 National Aeronautics and Space Administration THESTAR WITNESS A P U B L I C A T I O N O F N A S A S A M A Z I N G S P A C E E D U C A T I O N P R O G R A M Special Feature Hubble Witnesses Fireworks From Comet Collision By NASA s Amazing Space reporters July 2005 On JULY FOURTH, 2005, not all the fireworks were on Earth. NASA s Deep Impact spacecraft helped create some spectacular celestial fireworks by crashing into comet 9P/Tempel 1, a potato-shaped object about 3 miles (5 kilometers) wide and 7 miles (11 kilometers) long. NASA s Hubble Space Telescope had a front-row seat for the big event, providing the best visible-light view from Earth of the collision (see photos, page 2). The telescope watched as an 820-pound probe, called an impactor, punched through the comet s crusty surface. The impactor hurtled into the comet s core at 23,000 miles per hour, releasing lots of energy. The impactor, made up mostly of copper, formed a crater big enough to swallow a large stadium. By breaking through the outer baked crust, the collision unleashed ancient Continued, page Deep Impact s view: The moment of collision IMAGE: NASA/JPL-Caltech/UMD The Deep Impact spacecraft s view of its impactor hitting the comet: This close-up image was taken by Deep Impact s flyby spacecraft 67 seconds after its impactor smashed into comet 9P/Tempel 1 s nucleus. The flyby craft was 300 miles away from the collision when it snapped this picture.

9 Continued from page material that had been trapped inside the comet since its birth billions of years ago. It will take astronomers a long time, however, to analyze all the information collected about the comet and share the results. The mission Scientists launched the Deep Impact spacecraft six months ago on its oneway trip to the comet. The spacecraft was as large as a mid-size sport utility vehicle and had two parts: a flyby spacecraft and the impactor (see photos, page 3). Both parts were fitted with instruments designed to record the event. The flyby spacecraft launched the impactor and then moved out of Tempel 1 s path to avoid being hit by the comet. As the impactor traveled to its planned meeting with the comet, its camera snapped images of the nucleus. Tempel 1 s nucleus is only the fourth ever seen. A comet is surrounded by dust, which makes its nucleus difficult to view. The flyby spacecraft s camera spotted the nucleus because it was very close to the comet, about 300 miles away. The instruments onboard the flyby craft took detailed images of the impact and recorded other data needed to identify the ejected material. A key to the past Why were astronomers daring enough to take on a comet? They want to study the material locked beneath a comet s icy surface. For billions of years, comets have been baked by sunlight as they pass through the inner solar system. Their warmed surfaces develop a black, carbon-rich crust. The baked crust seals material inside the comet. By cracking through the surface crust, astronomers can learn Hubble s view of the collision Three minutes before impact After impact more about a comet s makeup and structure. Looking inside a comet also may help explain how our solar system formed about 4.5 billion years ago. Comets are an important link to our early These images, taken by the Hubble Space Telescope from 80 million miles away, show comet 9P/Tempel 1 before and after the Deep Impact probe slammed into it. Astronomers used these pictures to determine how much material was released from the impact. 12 minutes after impact Innermost coma of dust appears 10 times brighter than the cloud in the pre-impact photo. 1 hour, 4 minutes after impact An expanding fan of dust speeds from the comet. The fan of debris is moving at 450 miles (720 km) per hour, or about the speed of a jet airplane. 1 hour, 28 minutes after impact 4 hours, 41 minutes after impact 19 hours, 7 minutes after impact The dust cloud is 2,000 miles (3,200 km) across. It is beginning to spread out into space, becoming less visible. PHOTO SERIES: NASA, ESA, P. Feldman (JHU), H. Weaver (JHU APL) solar system. These celestial snowballs are the remains of material created in the coldest outer regions of our solar system. They may still contain the original building blocks of the Sun and the planets. Continued, page

10 Continued from page What are the parts of a comet? The heart of a comet is its nucleus, an object made up of chunks of ice and rock that is surrounded by a cloud of gas and dust, called a coma (see illustration, page 4). The icy comet releases the gas and dust when it is warmed by sunlight. The solar wind pushes the coma away from the comet, forming one or more tails of gas and dust. The gas and dust surrounding a comet prevent scientists from learning more about the makeup of the nucleus. Astronomers are eager to learn whether comets exhaust their supply of gas and ice over time or keep some of it in their interiors. By breaking through Tempel 1 s surface, scientists may find an answer to this question. They also may discover how Tempel 1 s interior is different from its surface. Tempel s tale Amateur astronomer Ernst Wilhelm Leberecht Tempel of Marseilles, France, discovered comet 9P/Tempel 1 in 1867 while using a telescope to search for comets. It is named Tempel 1 because it was the first comet spotted by Tempel. The 9P part of the name means that Tempel 1 was the ninth periodic comet discovered by sky watchers. Periodic comets have stable orbits and can be regularly observed from Earth. Tempel 1 has completed more than 100 orbits around our star. The frequent trips have helped it develop a crusty layer of carbon-rich material. Little else, however, is known about the comet. Astronomers are eager to learn whether Tempel 1, which has depleted much of its outer layers of gas and ice, has kept some gas and ice in its interior. The encounter with the Deep Impact probe did not change Tempel 1 s course. So, the comet will continue to orbit the Sun every 5.5 years. A visible impact Besides the Hubble telescope, an array of other space-based observatories Continued, page The Deep Impact spacecraft Deep Impact, shown in a cleanroom at right, was as large as a mid-size sport utility vehicle. The spacecraft was made up of two parts: a flyby spacecraft and an 820-pound impactor. Both the spacecraft and the impactor had cameras to take pictures of the comet and the impact. The spacecraft released the impactor about a day before the scheduled meeting with comet Tempel 1. The impactor, traveling at 23,000 miles an hour, collided into the comet early July 4, The collision created a large crater on Tempel 1 and unleashed material that had been trapped inside the comet for billions of years. Flyby spacecraft Impactor Impactor (enlarged below) Impactor s copper dome helped make a crater Flyby spacecraft IMAGES: Ball Aerospace & Technologies Corp.

11 Continued from page viewed this once-in-a-lifetime event, including the ultraviolet Galaxy Evolution Explorer, the infrared Spitzer Space Telescope, and the Chandra X-ray Observatory. Many ground-based observatories also witnessed the smashup. The views obtained by all of the observatories provided a treasure trove of information about the comet. The cameras aboard the Deep Impact flyby craft, for example, provided a closeup view of the comet, from about 300 miles away (see photo, page 1). From its distance of 80 million miles away, Hubble captured a wider view of the encounter, before, during, and after the impact (see photos, page 2). Hubble s view measured changes in the comet s brightness. By analyzing those changes, astronomers determined how much material was released from the impact. This information will help astronomers learn about Tempel 1 s makeup. Anatomy of a comet Comet Hale-Bopp (image, below left) is used as an example of a typical comet. Image below, right, is an artist s conception of a comet s nucleus. A typical comet Gas ion tail Direction of solar wind IMAGE: Alessandro Dimai Dust tail Nucleus Close-up of a comet s nucleus Tail Tail Nucleus Artist s conception (STScI Graphics Dept.) Coma SEE MORE Hubble images and read more Star Witness news stories at Amazing Space, NASA s award-winning educational Web site for K-12 students and teachers. amazing-space.stsci.edu

12 National Aeronautics and Space Administration THESTAR WITNESS A PUBLICATION OF NASA S AMAZING SPACE EDUCATION PROGRAM Special Feature Returning Comet Holmes Dazzles Sky Watchers By NASA s Amazing Space reporters Nov Alittle-known comet is causing quite a stir during its visit to the inner solar system. The dim comet, called Comet Holmes, brightened unexpectedly over just a few hours in mid-october 2007, catching astronomers by surprise. The comet s sudden burst of light was almost as if someone had turned on a light switch. Comet Holmes is now visible in the night sky to the unaided eye. The comet, discovered in 1892, resembles a fuzzy tennis ball cruising in the constellation Perseus. A comet is a ball of rock and ice, often referred to as a dirty snowball. It orbits the Sun and sometimes exhibits a coma, a cloud of gas and dust that forms around the comet s nucleus (see illustration, page 4). Comet Holmes on Oct. 29, 2007 IMAGE: NASA, UCLA Astronomers do not know why the comet has brightened so dramatically. One possible answer is that a crack the size of the Grand Canyon opened up, exposing chunks of ice beneath the comet s surface. Sunlight heated the ice, causing pieces to break off and form a large cloud of gas and dust around the comet. This cloud helps make the comet appear brighter. The Hubble Space Telescope snapped an image of the comet s bright core (see page 3). Although the nucleus is too small to Continued, page 2 NORTHEAST Photo illustration courtesy Laurent Laveder Locating Comet Holmes: Find the sideways W of Cassiopeia, then look below to find Comet Holmes.

13 Continued from page 1 see, the central portion of the image reveals the dust near the nucleus. Scientists hope to use this and other Hubble images to determine how big the nucleus is and how much of it was blasted away during the recent outburst. Many comets lose ice particles when they travel close to the Sun. Comet Holmes, however, appears to have ejected its material when it was moving away from the Sun. The frozen wanderer made its closest approach to the Sun last spring, and even then, it did not travel that close to our star. Locating Comet Holmes Nov. 16 Nov. 9 Nov. 2 Nov. 23 Nov. 30 Dec. 7 Dec. 14 Dec. 21 Comet Holmes path across the constellation Perseus from Nov. 2 to Dec. 21, The comet will become dimmer as time passes, so only some of the comet s path is shown. Wee Com (yell Frid to F 2007 (Dia com whe eno how com min it wi to s Comet Holmes is called a short-period comet. These comets orbit mainly in the inner solar system and travel around the Sun in less than 200 years. Comet Holmes swings by the Sun every seven years. It is a member of the Jupiter family of comets, which orbits between Jupiter and the Sun. Asteroids also follow a similar orbit. Although this dramatic flare-up is surprising, it is not the first time Comet Holmes has had an explosive outburst. The comet had a flare-up in November 1892, when British amateur astronomer Edwin Holmes discovered it. Stargazers continued watching the comet s return visits. They lost the icy object, however, after the 1906 visit. For decades, Comet Holmes was out of the limelight. Then, in 1964, astronomers found it again with the help of computer predictions by astronomer Brian Marsden. Amateur and professional astronomers have been monitoring Comet Holmes every seven years during its return. Since its discovery, Comet Holmes has made 16 trips around the Sun. The comet will remain bright for at least a few more weeks. C O M E T HOLMES (Early Nov position, approximate) CASSIOPEIA NORTHEAST Image generated by Lucy Albert, STScI, using Starry Night software PERSEUS Space Telescope Science Institute, Graphics Dept. How to find Comet Holmes After it gets dark (about 8 p.m. to 9 p.m.), go outside and face north. You may need a compass to help you. Make a quarter turn to your right. You will be facing northeast. Look for a grouping of stars that traces a sideways W (that points to the left) high in the sky. This is the constellation Cassiopeia. Now look to the right and slightly below Cassiopeia. You will see a triangle of stars. Comet Holmes is the star on the lower left corner of that triangle. The comet is located in the constellation Perseus. Comet Holmes stands out because it is not just a pinpoint of light like a star. It is a fuzz ball. 2

14 Comet Holmes gallery Comet Holmes as seen through a backyard telescope Coma Nucleus This close-up view of Comet Holmes shows an unusually large coma of gas and dust around the bright nucleus [the white dot in the center]. Amateur astronomer Philip Good of Denver, Colo., snapped this image Oct. 29, 2007 with his backyard telescope. A similar view can be seen with a pair of binoculars. Image courtesy Philip Good Comet Holmes as seen through a ground-based telescope and the Hubble Space Telescope Nucleus of Comet Holmes Coma Tail Image courtesy Alan Dyer HST image: NASA Ground-based image (above): This image was taken Nov. 1 by an amateur astronomer with a ground-based telescope. It reveals an unusually large coma of gas and dust [the white and blue-green rings]. The photo also reveals a faint tail flowing from the comet s right side. Hubble image (above): Taken Nov. 4, this image shows the heart of the comet. Although the nucleus is too small to see, the central portion of the image reveals the dust near the nucleus. Scientists hope to use this and other Hubble images to determine how big the nucleus is and how much of it was blasted away during the recent outburst. 3

15 Anatomy of a comet Comet Hale-Bopp (image, below left) is used as an example of a typical comet. Image below, right, is an artist s conception of a comet s nucleus. A typical comet Dust tail Close-up of a comet s nucleus Tail Coma Gas ion tail Nucleus Tail Direction of solar wind Nucleus IMAGE: Alessandro Dimai Artist s conception (STScI Graphics Dept.) SEE MORE Hubble images and read more Star Witness news stories at Amazing Space, NASA s award-winning educational Web site for K-12 students and teachers. amazing-space.stsci.edu