Solar Wind
Solar wind is a constant flow of charged particles from the Sun into space. It moves away from the Sun at a speed of 200 to 400 miles per second and flows across the solar system reaching just past Pluto. The region of outer space exposed to the solar wind is called the heliosphere. Helios was the mythical Greek god of the Sun. His Roman counterpart was named Sol.
Astronomers see visible proof of the solar wind when they look at comets. Comet tails are blown outward by the solar wind and always point away from the sun. The solar wind also contributes to the magnificent auroras seen on Earth. An aurora is a magnetic phenomenon that causes colorful streaks of bright light to appear in the upper atmosphere near Earth's two polar regions. Aurora is a
TABLE 6.4
Observatories in space
| Acronym | Name | Primary mission sponsors | NASA science program | Launch date | Location in space | Mission |
| CHIPS | Cosmic Hot Interstellar Plasma Spectrometer | NASA, University of California at Berkeley | Explorer (UNEX) | 1/12/2003 | Earth orbit | Collects spectrometry data to help scientists analyze million-degree gases. A spectrometer is an instrument used for measuring light wavelengths. |
| FUSE | Far Ultraviolet Spectroscopic | NASA, John Hopkins | Explorer (MIDEX) | 6/24/1999 | Earth orbit | An orbiting space telescope that detects far ultraviolet light (the shortest wavelengths Explorer University of radiation in the ultraviolet spectrum) |
| GALEX | Galaxy Evolution Explorer Institute of Technology | NASA, California | Explorer (SMEX) | 4/28/2003 | Earth orbit | An orbiting space telescope that detects ultraviolet light |
| HETE-2 | High Energy Transient Explorer | Massachusetts Institute of Technology | Explorer (Mission of Opportunity) | 10/9/2000 | Earth orbit | A small scientific satellite designed to detect and localize gamma-ray bursts |
| INTEGRAL | International Gamma-Ray Astrophysics Laboratory | ESA (Mission of Opportunity) | Explorer | 10/17/2002 | Earth orbit | An orbiting space telescope that detects gamma rays |
| RXTE | Rossi X-ray Timing Explorer Institute of Technology | NASA, Massachusetts | Explorer | 12/30/1995 | Earth orbit | Investigates x-ray emissions and measures x-ray variability over time. Named after the late astronomer Bruno Rossi. |
| SWAS | Submillimeter Wave Astronomy Astrophysics | NASA, Harvard-Smithsonian | Explorer (SMEX) | 12/5/1998 | Earth orbit | An orbiting space telescope that scans interstellar clouds to detect the photons emitted Satellite Center for by water, molecular oxygen, isotopic carbon monoxide, and atomic carbon |
| WMAP | Wilkinson Microwave Anisotropy Probe | NASA, Princeton University | Explorer | 6/30/2001 | L2 orbit | An orbiting space telescope that measures the temperature of cosmic background radiation. Named after the late physicist David Wilkinson |
| XMM-Newton | X-Ray Multi Mirror Newton | ESA | NASA supports participation by U.S. astronomers | 12/10/1999 | Earth orbit | An orbiting space telescope that detects x-rays. Named after scientist Isaac Newton |
| SOURCE: Created by the author, 2004 | ||||||
Latin word meaning dawn. It was also the name of the mythical Roman goddess of dawn.
The aurora centered on Earth's northern hemisphere is called aurora borealis or the northern lights. The southern lights are known as aurora australis. Usually auroras are only visible to people in the northern and southern regions of the Earth. For example, people in Canada, Alaska, and northern states are far more likely to see auroras than people in the southern United States.
The solar wind constantly pushes and shapes Earth's magnetosphere. This is the region of space around the Earth dominated by the planet's magnetic field. (See Figure 6.8.) The magnetosphere helps protect Earth from dangerous electromagnetic radiation moving through space. The outer boundary of Earth's magnetosphere is called the bow shock.
The speed, composition, density, and magnetic field strength of the solar wind are not constant but vary depending on conditions on the Sun. A "gust" in the solar wind can energize Earth's magnetosphere, producing beautiful auroras, but wreaking havoc on sensitive electronics.
Sunspots
Sunspots look like dark blemishes on the surface of the Sun. They are actually areas of plasma that are slightly cooler than their surroundings due to magnetic activity. Sunspots can be enormous in size, even bigger than planet Earth. Sunspots can appear, change size, and disappear. Each typically lasts from a few hours to a few months. Most sunspots are visible only through telescopes.
Sunspots were first identified in western literature by the Greek philosopher and scientist Theophrastus (c. 372–287 B.C.). However, some historians believe that Chinese astronomers knew about sunspots centuries before this. After the invention of the telescope in the 1600s many scientists reported seeing dark spots when they looked toward the Sun. Galileo argued that these spots
FIGURE 6.8
The Earth and the magnetosphere
were clouds moving across the Sun's surface. However, most astronomers of the time believed they were seeing a small unnamed planet moving near the Sun.
During the late 1800s European astronomers searched for this mysterious planet thought to orbit between Mercury and the Sun. It was called Vulcan. In 1826 an amateur German astronomer named Heinrich Schwabe was looking for the planet Vulcan. He began keeping detailed records of the number of sunspots he observed every day. After nearly two decades of doing this he noticed a cyclical pattern to the data. By the early 1900s scientists knew that the number of sunspots peaks approximately every eleven years and then drops off dramatically. (See Figure 6.9.) This is called the solar cycle. The period of peak sunspot activity is called the solar maximum.
In 1952 the International Council of Scientific Unions proposed that scientists around the world cooperate in conducting extensive earth science investigations between July 1957 and December 1958. This was the next expected solar maximum. Scientists hoped to collect large amounts of data on the relationship between sunspots and solar activity and the resulting effects on Earth's magnetic fields. This research remained a priority throughout the space age.
The SOHO satellite observed a sunspot group in September 2000, near the first peak of the latest solar cycle. A second, lower, peak occurred in late 2001. (See Figure 6.10.) The photos at the bottom of Figure 6.10 show how solar activity increased between 1997 and 2001 as the sunspot numbers increased.
FIGURE 6.9
The sunspot cycle
FIGURE 6.10
A double-peak of maximum activity in the solar cycle
Solar Flares
Solar flares are sudden energy releases that burst out from the Sun near sunspots. They are most common during the solar maximums. Solar flares emit electromagnetic radiation, and can include energy particles and bulk plasma. They can last from minutes to hours.
Solar flares that erupt in Earth's direction can shower the planet with energetic particles within thirty minutes. Solar flares are associated with auroras and magnetic storms on Earth and can cause radio interference if large amounts of x-ray radiation are released.
FIGURE 6.11
Geomagnetic storm effects
Scientists classify solar flares by the intensity of their x-ray radiation and its effects on Earth. These classifications are:
- C Class—Small flares with few consequences to Earth systems.
- M Class—Medium-sized flares resulting in brief radio blackouts in Earth's polar regions. May cause some minor radiation storms.
- X Class—Large flares that can cause worldwide radio blackouts and long-lasting radiation storms on Earth.
Auroras typically appear on Earth about two days after a solar flare occurs. On July 14, 2001, a powerful solar flare occurred that resulted in the northern lights appearing as far south as Florida. In November 2003 the largest solar flare ever recorded burst out from the Sun. Luckily it was pointed away from Earth and did not cause any major problems.
Solar Prominences
Solar prominences are giant clouds of dense plasma suspended in the Sun's corona (outermost atmosphere). They are usually calm, but occasionally erupt and snake out from the sun along magnetic field lines. Prominences can break away from the Sun and hurtle through space carrying large amounts of solar material.
Coronal Mass Ejections
Coronal mass ejections (CMEs) occur when billions of tons of particles are slung away from the sun by broken magnetic field lines. CMEs move away from the Sun into space at a tremendous speed (millions of miles per hour). These ejections happen frequently and are most common during the solar maximum, when they can occur several times a day. CMEs are known informally as solar storms.
When a CME blasts toward Earth the planet's magnetosphere is hit within two to four days by a cloud of electrically charged particles. This cloud distorts the entire magnetosphere as shown in Figure 6.11. The resulting disturbance is called a geomagnetic storm. These storms can harm satellites and disrupt telecommunications and electric power generation around the world.
Space Weather
The term space weather was created by scientists to refer to the overall effects of solar activities on the space around Earth (or geospace). Space weather encompasses all the solar phenomena (solar wind, sunspots, flares, prominences, and coronal mass ejections) and the resulting conditions in Earth's magnetosphere and upper atmosphere.
The National Oceanic and Atmospheric Administration (NOAA) monitors space weather and issues warnings about geomagnetic storms and solar radiation storms (increases in the number of energy particles in geospace). The NOAA's Space Environment Center (SEC) is located in Boulder, Colorado. It serves as the national and worldwide warning center for space weather disturbances. The Space Weather Operations branch is jointly operated by NOAA and the U.S. Air Force.
TABLE 6.5
National Oceanic and Atmospheric Administration space weather scales
| Category | Effect | |||
| Scale | Descriptor | Duration of event will influence severity of effects | Physical measure | Average frequency (1 cycle 11 years) |
| Geomagnetic storms | Kp values* determined every 3 hours | Number of storm events when Kp level was met; (number of storm days) | ||
| G5 | Extreme | Power systems: widespread voltage control problems and protective system problems can occur, some grid systems may experience complete collapse or blackouts. Transformers may experience damage. | Kp = 9 | 4 per cycle (4 days per cycle) |
| Spacecraft operations: may experience extensive surface charging, problems with orientation, uplink/downlink and tracking satellites. | ||||
| Other systems: pipeline currents can reach hundreds of amps, HF (high frequency) radio propagation may be impossible in many areas for one to two days, satellite navigation may be degraded for days, low-frequency radio navigation can be out for hours, and aurora has been seen as low as Florida and southern Texas (typically 40° geomagnetic lat.)**. | ||||
| G4 | Severe | Power systems: possible widespread voltage control problems and some protective systems will mistakenly trip out key assets from the grid. | Kp = 8, including a 9- | 100 per cycle (60 days per cycle) |
| Spacecraft operations: may experience surface charging and tracking problems, corrections may be needed for orientation problems. | ||||
| Other systems: induced pipeline currents affect preventitive measures, HF radio propagation sporadic, satellite navigation degraded for hours, low-frequency radio navigation disrupted, and aurora has been seen as low as Alabama and northern California (typically 45° geomagnetic lat.)**. | ||||
| G3 | Strong | Power systems: voltage corrections may be required, false alarms triggered on some protection devices. | Kp = 7 | 200 per cycle (130 days per cycle) |
| Spacecraft operation: surface charging may occur on satellite components, drag may increase on low-Earth-orbit satellites, and corrections may be needed for orientation problems. | ||||
| Other systems: intermittent satellite navigation and low-frequency radio navigation problems may occur, HF radio may be intermittent, and aurora has been seen as low as Illinois and Oregon (typically 50° geomagnetic lat.)**. | ||||
| G2 | Moderate | Power systems: high-latitude power systems may experience voltage alarms, long-duration storms may cause transformer damage. | Kp = 6 | 600 per cycle (360 days per cycle) |
| Spacecraft operations: corrective actions to orientation may be required by ground control; possible changes in drag affect orbit predictions. | ||||
| Other systems: HF radio propagation can fade at higher latitudes, and aurora has been seen as low as New York and Idaho (typically 55° geomagnetic lat.)**. | ||||
| G1 | Minor | Power systems: weak power grid fluctuations can occur. | Kp = 5 | 1700 per cycle (900 days per cycle) |
| Spacecraft operations: minor impact on satellite operations possible. | ||||
| Other systems: migratory animals are affected at this and higher levels; aurora is commonly visible at high latitudes (northern Michigan and Maine)**. | ||||
| *Based on this measure, but other physical measures are also considered. | ||||
| **For specific locations around the globe, use geomagnetic laltitude to determine likely sightings (see www.sec.noaa.gov/Aurora) | ||||
| Solar radiation storms | Flux level of ≥ 10 MeV particles (ions)* | Number of events when flux level was met** | ||
| S5 | Extreme | Biological: unavoidable high radiation hazard to astronauts on EVA (extra-vehicular activity); high radiation exposure to passengers and crew in commercial jets at high latitudes (approximately 100 chest x-rays) is possible. | 105 | Fewer than 1 per cycle |
| Satellite operations: satellites may be rendered useless, memory impacts can cause loss of control, may cause serious noise in image data, star-trackers may be unable to locate sources; permanent damage to solar panels possible. | ||||
| Other systems: complete blackout of HF (high frequency) communications possible through the polar regions, and position errors make navigation operations extremely difficult. | ||||
| S4 | Severe | Biological: unavoidable radiation hazard to astronauts on EVA; elevated radiation exposure to passengers and crew in commercial jets at high latitudes (approximately 10 chest x-rays) is possible. | 104 | 3 per cycle |
| Satellite operations: may experience memory device problems and noise on imaging systems; star-tracker problems may cause orientation problems, and solar panel efficiency can be degraded. | ||||
| Other systems: blackout of HF radio communications through the polar regions and increased navigation errors over several days are likely. | ||||
| S3 | Strong | Biological: radiation hazard avoidance recommended for astronauts on EVA; passengers and crew in commerical jets at high latitudes may receive low-level radiation exposure (approximately 1 chest x-ray). | 103 | 10 per cycle |
| Satellite operations: single-event upsets, noise in imaging systems, and slight reduction of efficiency in solar panel are likely. | ||||
| Other systems: degraded HF radio propagation through the polar regions and navigation position errors likely. | ||||
| S2 | Moderate | Biological: none. | 102 | 25 per cycle |
| Satellite operations: infrequent single-event upsets possible. | ||||
| Other systems: small effects on HF propagation through the polar regions and navigation at polar cap locations possibly affected. | ||||
| S1 | Minor | Biological: none. | 10 | 50 per cycle |
| Satellite operations: none. | ||||
| Other systems: minor impacts on HF radio in the polar regions. | ||||
| *Flux levels are 5 minute averages. Flux in particles-s-1-ster-1-cmd-2 Based on this measure, but other physical measures are also considered. | ||||
| **These events can last more than one day. | ||||
TABLE 6.5
National Oceanic and Atmospheric Administration space weather scales
| Category | Effect | |||
| Scale | Descriptor | Duration of event will influence severity of effects | Physical measure | Average frequency (1 cycle 11 years) |
| Radio blackouts | GOES X-ray peak brightness by class and by flux* | Number of events when flux level was met; (number of storm days) | ||
| R5 | Extreme | HF Radio: Complete HF (high-frequency**) radio blackout on the entire sunlit side of the Earth lasting for a number of hours. This results in no HF radio contact with mariners and en route aviators in this sector. | X20 (2x103) | Fewer than 1 per cycle |
| Navigation: Low-frequency navigation signals used by martime and general aviation systems experience outages on the sunlit side of the Earth for many hours, causing loss in positioning. Increased satellite navigation errors on the sunlit side of the Earth for many hours, causing loss in positioning. Increased satellite navigation errors in positioning for several hours on the sunlit side of Earth, which may spread into the night side. | ||||
| R4 | Severe | HF Radio: HF radio communications blackout on most of the sunlit side of Earth for one to two hours. HF radio contact lost during this time. | X10 (10-3) | 8 per cycle (8 days per cycle) |
| Navigation: Outages of low-frequency navigation signals cause increased error in positioning for one to two hours. Minor disruptions of satellite navigation possible on the sunlit side of Earth. | ||||
| R3 | Strong | HF Radio: Wide area blackout of HF radio communication, loss of radio contact for about an hour on sunlit side of the Earth. | X1 (10-4) | 175 per cycle (140 days per cycle) |
| Navigation: Low-frequency navigation signals degraded for about an hour. | ||||
| R2 | Moderate | HF Radio: Limited blackout of HF radio communciation on sunlit side, loss of radio contact for tens of minutes. | M5 (5x10-5) | 350 per cycle (300 days per cycle) |
| Navigation: Degradation of low-frequency navigation signals for tens of minutes. | ||||
| R1 | Minor | HF Radio: Weak or minor degradation of HF radio communication on sunlit side, occasional loss of radio contact. | M1 (10-5) | 2000 per cycle (950 days per cycle) |
| Navigation: Low-frequency navigation signals degraded for brief intervals. | ||||
| *Flux, measured in the 0.1–0.8 nm range, in W-m-2. Based on this measure, but other physical measures are also considered. | ||||
| **Other frequencies may also be affected by these conditions. | ||||
| SOURCE: Barbara Poppe, "NOAA Space Weather Scales," in NOAA Space Weather Scales, U.S. Department of Commerce, National Oceanic and Atmospheric Administration, Space Environment Center, Boulder, CO, October 31, 2000 [Online] http://www.sec.noaa.gov/NOAAscales/NOAAscales.pdf [accessed January 14, 2004] | ||||
The SEC uses a scale system to characterize space weather storms according to severity, effects, and frequency. The scale system is shown in Table 6.5. Geomagnetic storms are ranked from level G1 (least severe) to G5 (most severe). Solar radiation storms are similarly ranked from level S1 to level S5. Minor storms occur far more frequently than major storms. The SEC also ranks radio blackouts from level R1 to level R5. These blackouts are caused by x-ray emissions from the Sun that disturb Earth's ionosphere.
Monitoring of space weather is important. A major solar event like a coronal mass ejection can cause a tremendous inflow of electrical energy into Earth's atmosphere. This is disruptive to electrical power grids and telecommunication systems on the ground and dangerous for Earth-orbiting satellites. NASA also worries about possible harmful exposure of astronauts to excessive radiation levels during solar storms.
Ongoing Solar Exploration Missions
NASA and other space agencies operate a number of missions dedicated to studying the Sun-Earth connection. Table 6.6 describes major missions ongoing as of March 2004. NASA spacecraft support several science programs, including Explorer, Discovery, and ISTP. Most of these spacecraft are stationed in Earth orbit and study the effects of solar activity on the magnetosphere or upper atmosphere.
Some of the spacecraft are in orbits far from Earth or on other paths designed for optimal study of the Sun-Earth connection.
ACE AND SOHO.
ACE and SOHO are in halo orbits around the L1 Lagrange point. (See Figure 6.12). From its vantage point ACE collects samples of the solar wind and other particles emitted from the Sun. The spacecraft is equipped with a sophisticated communication system that allows it to transmit data very quickly. Many solar storms reach the L1 point an hour or more before hitting Earth. ACE is able to give scientists advance warning of impending storms that could disrupt Earth's magnetic field. The spacecraft has its own propulsion system and enough propellant to last until approximately 2019.
SOHO is the largest and most sophisticated solar observatory ever developed. It includes twelve instruments that collect data about the Sun's inner and outer workings and the solar wind. SOHO observes the Sun in visible light and four different wavelengths of extreme-ultraviolet radiation. This is ultraviolet radiation that lies closest to x-rays in the electromagnetic spectrum. SOHO sensors can detect waves of pressure under the Sun's surface, a process called helioseismology.
TABLE 6.6
Ongoing solar missions
| Name | Primary mission sponsors | NASA science program | Launch date | Location in space | Mission |
| ACE (Advanced Composition Explorer) | NASA, California Institute of Technology | Explorer | 8/25/1997 | L1 orbit | Samples the solar wind, particles emitted during solar flares, and high-energy galactic particles. Monitors space weather and provide s warning of impending geomagnetic storms. |
| Cluster | ESA | ISTP | 7/16/00 and 8/9/00 | Earth orbit | Includes 2 pair of two satellites that study the solar wind and its interaction with Earth's magnetospheric plasma. |
| FAST (Fast Auroral Snapshot Explorer) | NASA, University of California at Berkeley | Explorer (SMEX) | 8/21/1996 | Earth orbit | Studies Earth's aurora. Also supports ISTP. |
| Genesis | NASA, California Institute of Technology | Discovery | 8/8/2001 | Round Trip mission to L1 | Sampling ship sent to L1 to collect samples of solar wind. Expected to return to Earth in September 2004 |
| Geotail | NASA, JAXA | ISTP | 7/24/1992 | Earth orbit | Studying the dynamics of the Earth's magnetotail |
| IMAGE (Imager for Magnetopause-to-Aurora Global Exploration) | NASA, Southwest Research Institute | Explorer (MIDEX) | 3/25/2000 | Earth orbit | Satellite imaging Earth's magnetosphere. Also supports ISTP. |
| RHESSI (Reuven Ramaty High Energy Solar Spectroscopic Imager) | NASA, University California of Berkeley | Explorer (SMEX) | 2/5/2002 | Earth orbit | Explores the basic physics of particle acceleration and explosive energy release in solar flares. Named after the late NASA physicist Reuven Ramaty. |
| SAMPEX (Solar Anomalous and Magnetospheric Particle Explorer) | NASA, University of Maryland, German Universities | Explorer (SMEX) | 7/3/1992 | Earth orbit | Investigating the composition of local interstellar matter and solar material and the transport of magnetospheric charged particles into Earth's atmosphere. Also supports ISTP. |
| SOHO (Solar and Heliospheric Observatory) | NASA, ESA | ISTP | 12/2/1995 | L1 orbit | Solar observatory studying the Sun's internal structure, heating of its extensive outer atmosphere, and the origin of the solar wind |
| Stardust | NASA | Explorer | 2/7/1999 | Comet encounter | Sampling ship sent to intercept comet Wild 2 as it orbits the sun and collect particle samples. Expected to return to Earth in January 2006. |
| TIMED (Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics) | NASA, John Hopkins University Applied Physics Laboratory | Sun-Earth Connection | 12/7/2001 | Earth orbit | Studying solar influences on Earth's mesosphere and lower thermosphere/ionosphere |
| TRACE (Transition Region and Coronal Explorer) Laboratory | NASA, Lockheed-Martin Solar & Astrophysics | Explorer (SMEX) | 4/1/1998 | Earth orbit | Studies the connection between the Sun's magnetic fields and heating of its corona |
| Ulysses | NASA, ESA Connection | Sun-Earth | 10/6/1990 | Solar orbit | An observatory in polar solar orbit that studies the solar wind throughout the heliosphere |
| Wind | NASA | ISTP | 11/1/1994 | Traveling a path with multiple Loops around L1, Earth, and L2 | Investigating solar phenomena and their effects on Earth's magnetosphere. Provides almost continuous monitoring of the solar wind. |
| SOURCE: Created by the author, 2004 | |||||
SOHO has captured hundreds of images of solar events, such as solar flares and coronal mass ejections, and has discovered more than 400 comets. The spacecraft is operated by NASA and the ESA. Dozens of universities and research institutions worldwide participate in SOHO as part of the ISTP initiative. SOHO is expected to remain in orbit at least until 2013.
WIND.
Wind is an observational spacecraft that carries an array of scientific instruments. Following its launch in 1994 Wind was designed to follow a complicated path that winds back and forth between the L1 and L2 points. The path is a figure-eight shape with numerous loops around Earth in between. Wind collects data on plasma, energetic particles, and Earth's magnetic field. The spacecraft provides nearly continuous monitoring of the solar wind approaching Earth.
ULYSSES.
Ulysses is a multi-functional spacecraft on a far-flying mission. It travels around the Sun on an orbital path that reaches out near Jupiter. As shown in Figure 6.13 the Earth and Jupiter orbit the sun in the same plane.
FIGURE 6.12
Real-time prediction of global geomagnetic activity with an L1 satellite
This is called the ecliptic plane and appears as a white circle within the diagram. All of the planets except Pluto orbit the Sun in the ecliptic plane. Ulysses follows a different path that takes it high above and far below the ecliptic plane as the spacecraft circles the Sun.
This provides Ulysses with exposure to vast regions of the heliosphere. The spacecraft investigates the magnetic field and solar wind at various heliospheric altitudes. It can also detect bursts of radio and plasma waves, solar x-rays, and solar and galactic cosmic rays. During its Jupiter flybys the spacecraft studies the magnetic fields surrounding that planet. Ulysses is also unique because it flies over the polar regions of the Sun. This provides the observatory with a high-latitude view of the Sun's outer atmosphere.
Ulysses is a joint mission operated by NASA and the ESA. The spacecraft is named after a hero of Greek legend who went on a long sea journey and had many adventures along the way. The story is contained in a book called Odyssey, written by Homer, an epic poet who lived in the ninth or eighth century B.C.
GENESIS.
Genesis is a revolutionary spacecraft designed to collect samples of the solar wind and return them safely to Earth. It includes detectors to monitor the solar wind and sampling arrays to capture the charged particles. Genesis also analyzes chemical elements that may be contained in the solar wind.
In August 2001 Genesis was launched into outer space toward the L1 Lagrange point. Three months later the spacecraft reached its destination and began taking samples. Genesis was designed to assume a halo orbit around L1 for 2.5 years and then head back to Earth. The spacecraft will reenter the atmosphere and be directed toward an arrival zone in the Utah desert. During its parachute descent the spacecraft will be snagged and carried to land by a specially equipped helicopter. September 8, 2004, is the anticipated arrival date for Genesis.
If the mission is successful it will be the first time in history that solar wind samples have been returned to Earth.
FIGURE 6.13
Ulysses mission trajectory
STARDUST.
Stardust is another sampling spacecraft exploring Sun-Earth space. It was designed to collect particle samples from comet Wild 2 and return them safely to Earth. Comet Wild 2 is named after Swiss astronomer Paul Wild, who discovered it in 1978. His name is pronounced as "Vilt." Thus, comet Wild 2 is pronounced Vilt 2.
Wild 2 is a relatively small comet with a nucleus measuring about three miles in diameter. A comet nucleus is a dense core of rock and frozen gas. The coma is the thick cloud of gases and sand that surrounds a comet nucleus. Comets follow heliocentric (sun-centered) orbits.
On February 7, 1999, Stardust was launched on its journey. The spacecraft carries a particle collector about the size of a tennis racket. (See Figure 6.14 for side and bottom views of the spacecraft). The collector is made of an ultra-lightweight material called aerogel that can capture and hold tiny comet dust particles. Following capture the collector folds down into the sample return capsule for its journey back to Earth. Stardust is also equipped with special detectors for analysis of comet dust and interstellar dust.
Figure 6.15 shows the mission trajectory. Stardust collected and analyzed interstellar dust in 2000 and 2002. On January 2, 2004, it successfully sampled particles from the coma of Wild 2. These particles are believed to be more than 4.5 billion years old. The spacecraft is scheduled to return to Earth in January 2006 and make a soft landing in the Utah desert.
Stardust is the first-ever comet sample return mission.
Future Solar Missions
NASA plans to launch a number of solar missions during the late 2000s as part of its Living with a Star program. This program will focus its studies on the next solar maximum expected in 2011–2012.
FIGURE 6.14
The Stardust spacecraft
FIGURE 6.15
Stardust mission trajectory
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