SDO was launched from Cape Canaveral Air Force Station in the USA on 11 February 2010. After launch, SDO was placed into an orbit around Earth at an altitude of about 2500 km. It then underwent a series of orbit-raising maneuvers that placed it in a circular, geosynchronous orbit at altitude 36,000 km. It had a 5-year science mission but carries enough fuel to operate for an additional 5 years. At launch its mass was 3100 kg with a payload of 290 and 1450 kg of fuel. The solar panels cover an area of 6.6 m2 producing 1450 W of power. The overall length of the spacecraft along the Sun-pointing axis is 4.5 m, and each side is 2.22 m (see Fig. 2.9).
Fig. 2.9The Solar Dynamics Observatory (SDO) is the most advanced spacecraft ever designed to study the Sun (Credit: NASA/SDO).
The data from SDO is providing a lot of new information and spectacular images of the Sun. Scientists are gaining a better understanding of how even small events on the Sun can significantly effect the operation of technological infrastructure on Earth (such as GPS systems, cable TV, radio and satellite communications).
The Juno Probe
Juno is a spacecraft launched by NASA on 5 August 2011 on a mission to explore the planet Jupiter. The craft is expected to arrive at Jupiter in July 2016. It will be placed in a polar orbit to study the mass distribution, atmosphere and composition of Jupiter, as well as its gravitational and magnetic field. Juno will take 5 years to reach Jupiter. The probe’s trajectory used a gravity assist speed boost from Earth, accomplished by two Earth flybys (one in October 2013 and the second in August 2011). In August 2016 the spacecraft will perform an orbit insertion burn to slow the spacecraft enough to allow capture into an 11 day polar orbit. Once Juno enters orbit around Jupiter its infrared and microwave instruments will begin to measure the thermal radiation and convection currents within Jupiter’s atmosphere. Juno’s polar orbit is highly elliptical and takes it close to within 4300 km of the poles. This type of orbit helps the craft avoid any long-term contact with Jupiter’s radiation belts, which can cause damage to spacecraft electronics and solar panels. The craft will complete at least 33 orbits, each taking from 11 to 14 days, before being crashed into Jupiter itself.
Mars Science Laboratory
NASA launched Mars Science Laboratory (MSL) on 26 November 2011 on a mission to Mars. The probe successfully landed a rover called Curiosity in Gale crater on 6 August 2012. The objectives of the Curiosity rover include investigating the possibility of life on mars, studying the climate and geology, and collecting data for any future manned missions to Mars.
Curiosity is about twice as long and five times as heavy as the Spirit and Opportunity rovers (already on the surface of Mars), and carries over ten times the mass of scientific instruments.
The MSL spacecraft that transported Curiosity to Mars successfully carried out a more accurate landing than previous rovers, within a landing ellipse of 7 by 20 km inside Gale crater. It is designed to explore the surface for at least 2 years covering an area of 5 km by 20 km. Curiosity has been able to drill into the surface of Mars and examine sediments formed by ancient river beds.
Probing Comets
A comet is an icy small body that originates in the Kuiper belt, Scattered Disc or Oort Cloud. Sometimes the orbit of a comet brings it into the inner solar system and near the Sun. When passing the Sun, comets heat up and begin to vaporise, emitting a visible tail of gaseous material.
Comets can tell astronomers much about the history of the Solar system, but only a few space probes have been used to explore the nature of comets.
In 2001, the Deep Space 1 spacecraft obtained high-resolution images of the surface of Comet Borrelly. The surface of this comet was found to be hot and dry, with a temperature of 26–71 °C and extremely dark. This suggested that the ice had been removed by solar heating and maturation, or was hidden by soot-like material.
NASA launched the Deep Impact space probe on 12 January 2005. The probe intercepted comet Tempel 1 in July 2005 and passed within 500 km of its nucleus. The probe fired a 370 kg copper slug into the surface of the comet at 10 km/s. Earth-based telescopes and space observatories, including Hubble, Chandra, Spitzer, and XMM-Newton, photographed the entire event. Cameras and spectroscopes on board the ESA’s Rosetta spacecraft also observed the impact, which was about 80 million km from the comet at the time of impact. Rosetta determined the composition of the gas and dust cloud that was kicked up by the impact. However, the initial photographs taken of the impact site were unsatisfactory.
On 15 February 2011, NASA scientists identified the crater formed by the Deep Impact slug in images from the Stardust probe. The crater was estimated to be 150 m in diameter with a bright mound in the centre likely created when material from the impact fell back into the crater. The mission found that most of the comet’s water ice is below the surface and that reservoirs feed the jets of vaporised water that form the body of the comet.
Since its encounter with the comet Tempel 1, Deep Impact has passed by other comets, including, Boethin (2008), Hartley 2 (2010), Garradd (2012) and comet ISON (2013).
During September 2013, Deep Impact mission controllers found the computers on the spacecraft were continuously rebooting themselves and so were unable to issue any commands to the vehicles thrusters. As a result of this problem, communication to the spacecraft became more difficult as the orientation of the vehicle’s antennas was unknown. Additionally, the solar panels on the vehicle were positioned incorrectly for generating power. On 20 September 2013, NASA abandoned further attempts to contact the craft.
As previously mentioned the Rosetta probe encountered the comet Churyumov–Gerasimenko in 2014 and placed a small lander on its surface (more in Chap. 13).
Probes Leaving the Solar System
There are four probes that have passed the orbits of the major planets and are deemed to be leaving the solar system. These are, Pioneer 10 and Pioneer 11, and Voyager 1 and Voyager 2.
The United States began its exploration of more distant parts of the Solar System with its Pioneer space probes launched in 1972 and 1973. These craft were designed to survive the passage through the Asteroid Belt and Jupiter’s magnetosphere. The Asteroid Belt was relatively simple to pass through since there were many gaps, but the space probes were nearly fried by ions trapped in Jupiter’s magnetic field.
Launched in 1972, Pioneer 10 was the first spacecraft to fly by Jupiter in December 1973, passing within 130,000 km of the cloud-covered surface. Twenty-three low-resolution images were returned to Earth showing Jupiter’s turbulent atmosphere and the Great Red Spot.
Pioneer 10’s greatest achievement was the data collected on Jupiter’s moons, its strong magnetic field, and interactions with the solar wind.
About a year later, Pioneer 11 flew to within 48,000 km of Jupiter’s surface and sent back 17 images of the planet to ground crews on Earth. The space probe used the strong gravitational field of Jupiter to swing it on a path towards Saturn—a journey that was to take 5 years. In September 1979, Pioneer 11 passed within 30,000 km of Saturn’s surface and it returned 440 images and data about Saturn’s moons and its ring system.
Today Pioneer 10 and 11 are no longer sending back data, but both are still travelling at about 12 km/s and heading in opposite directions away from the solar system into deep space. Each craft carries a plaque, with a graphic message, to inform anyone out there about the Solar System, the Earth, and the human race. No further contact attempts are planned.
Voyager 1 and Voyager 2 were launched by the USA in 1977 on a mission towards Jupiter, the largest planet in the solar system. These probes flew by Jupiter in March and July of 1979 before proceeding to Saturn. Each Voyager was equipped with high-resolution cameras, three programmable computers and instruments to conduct a range of scientific experiments. Voyager 2 was actually launched 16 days before Voyager 1 but Voyager 1 took a faster, more direct route to reach Jupiter first (Fig. 2.10).
Fig. 2.10In order to track the Voyager spacecraft, NASA uses a system of deep space communication stati
ons scattered across Earth’s surface. One of these is located at Tidbinbilla near Canberra, Australia (Photo: J. Wilkinson).
On their journey through the solar system the Voyager probes discovered:22 new satellites (3 at Jupiter, 3 at Saturn, 10 at Uranus and 6 at Neptune)
Active volcanoes on Io
An atmosphere and geysers on Triton
Rings around Jupiter and spokes in Saturn’s rings
Auroral zones on Jupiter, Saturn and Neptune
Large scale storms on Neptune
Magnetospheres around Uranus and Neptune.
These two space probes provided many spectacular close-up views of the four outer planets known as the gas giants. Both space probes are still moving away from Earth at about 16 km/s and still in operation. They are returning data about cosmic rays in outer space and ultraviolet sources among the stars.
Both spacecraft also have adequate electrical power and attitude control propellant to continue operating until around 2025, after which there may not be available electrical power (from radioisotope thermoelectric generators) to support science instrument operation. At that time, science data return and spacecraft operations will cease. Interestingly, Voyager 1 has passed the Pioneer 10 space probe and is now the most distant human-made object in space.
Further Information
www.space.com/19081-solar-system-space-probes-missions.html
www.nineplanets.org/
www.hubblesite.org/
www.nasa.gov/mission_pages/hubble/main/
http://nssdc.gsfc.nasa.gov/ (check out solar system exploration)
© Springer International Publishing Switzerland 2016
John WilkinsonThe Solar System in Close-UpAstronomers' Universe10.1007/978-3-319-27629-8_3
3. The Dominant Sun
John Wilkinson1
(1)Castlemaine, Victoria, Australia
Highlights
The STEREO and the Solar Dynamics Observatory are the most technologically advanced space probes used to study the Sun.
Data obtained from the SOHO probe has shown that the strength of the magnetic fields around sunspots is thousands of times stronger than the Earth’s magnetic field.
The Ulysses space probe found that the solar wind blows faster around the Sun’s poles (750 km/s) than in equatorial regions (350 km/s).
The Japanese Hinode probe was the first to be able to measure small changes in the Sun’s magnetic field.
Solar probes have provided answers to many questions regarding the effect of the Sun on Earth’s climate.
The Sun is the dominant object in the solar system because it is by far the largest object. It is positioned at the centre of the solar system and its gravitational pull holds all the planets in orbit. The Sun is an average sized star about 4.5 billion years old. Unlike planets, stars produce their own light and heat by burning fuels like hydrogen and helium in a process known as nuclear fusion. Stars have a limited life and the Sun is no exception—it is about half way through its life cycle of about 10 billion years.
The Sun is one of over 100 billion stars that make up a galaxy called the Milky Way. The Milky Way galaxy is spiral in shape, and the Sun is positioned about halfway out from the centre. The Milky Way is about 100,000 light years in diameter and 15,000 light years thick. You can see parts of the Milky Way as a band of cloud that stretches across the night sky. Within the Milky Way, the Sun is moving at 210 km/s, and takes 225 million years to complete one revolution of the galaxy’s central mass of stars (see Fig. 3.1).
Fig. 3.1Position of the Sun in the Milky Way galaxy.
Fig. 3.2The STEREO (Ahead) spacecraft caught this spectacular eruptive prominence on the Sun (12–13th April 2010). The length of the prominence appears to stretch almost halfway across the Sun, about 800,000 km. Prominences are cooler clouds of plasma that hover above the Sun’s surface, tethered by magnetic forces. They are notoriously unstable and commonly erupt as this one did in a dramatic fashion (Credit: NASA/STEREO).
Probing the Sun
Scientists have gained much of their knowledge about the Sun from observation made on Earth over many years. However, much of our current knowledge has come from space probes that have been sent on missions to investigate the Sun. These probes have provided accurate information about the Sun’s temperature, atmosphere, composition, magnetic fields, flares, prominences, sunspots and internal dynamics.
The USA launched a number of unmanned solar probes between 1959 and 1968 as part of its Pioneer program. Many of these early probes have now completed their missions but still remain in orbit around the Sun. Missions such as Pioneer 10 and 11 showed that gravity assists were possible and that spacecraft could survive high-radiation areas in space.
America’s first space station, Skylab (launched in 1973), was used to study the Sun from Earth orbit. The space station included the Apollo Telescope Mount (ATM), which astronauts used to take more than 150,000 images of the Sun. Skylab was abandoned in February 1974 and re-entered the Earth’s atmosphere in 1979. Table 3.1 lists the more recent probes that have been used to observe and explore the Sun.Table 3.1Recent probes used to observe the Sun
Spacecraft
Country of origin
Launch date
Mission focus
SOHO
USA/Europe
Dec 1995
Solar environment
TRACE
USA
April 1998
Magnetic field, corona
Genesis
USA
Aug 2001
Solar wind
Coronas F
Russia
July 2001
Flares and interior
RHESSI
USA
February 2002
X-ray imaging
Hinode
Japan, USA, UK
September 2006
Magnetic field
Stereo A/B
USA
October 2006
CMEs
SDO
USA
February 2010
Effect of Sun on Earth
SOLO
Europe
Due 2017
Study Sun up close
Solar probe plus
USA
Due 2018
Corona and solar wind
Significant solar probes launched in the 1990s include Yohkoh (launched in 1991), Ulysses (October 1990), SOHO (December 1995), and TRACE (launched 1998). The most recently launched probes, STEREO and the Solar Dynamics Observatory (SDO), are also the most technologically advanced.
SDO was launched in 2010 and is designed to study the Sun and its dynamic behavior. This probe is providing better quality, more comprehensive science data faster than any NASA spacecraft currently studying the Sun. The probe is aimed at providing data on the processes inside the Sun, the Sun’s surface, and its atmosphere that result in solar variability. SDO is also helping scientists to better understand the Sun’s influence on Earth and near-Earth space through the use of many wavelengths simultaneously. SDO is also investigating how the Sun’s magnetic field is generated and structured.
STEREO (Solar TErrestrial RElations Observatory) was launched by NASA on 26 October 2006. It consists of two nearly identical spacecraft, one orbiting ahead of Earth (A) and the other behind Earth (B). Observations are made simultaneously of the Sun and then combined to provide a 3-D stereo image of the Sun. Spacecraft A takes 347 days to orbit the Sun while spacecraft B takes 387 days. Because the A spacecraft is moving faster than B, they are separating from each other and A is orbiting closer to the Sun than B. The images are adjusted to account for this difference.
Each of the spacecraft carries cameras (a EUV imager and two coronagraphs), particle experiments and radio detectors in four instrument packages. STEREO is used to image the inner and outer corona and the space between Sun and Earth, detect electrons and other energetic particles in the solar wind, study th
e plasma characteristics of protons, alpha particles and heavy ions, and monitor radio wave disturbances between the Sun and Earth.
By studying the Sun, scientists are gaining a better understanding of how even small solar events effect the operation of technological infrastructure on Earth (such as GPS systems, cable TV, radio and satellite communications).
Features of the Sun
The Sun is a huge ball of burning gas, which contains about 99 % of the mass of the whole solar system. This makes it over 300,000 times as massive as the Earth. The Sun’s diameter of 1.4 million km far exceeds Earth’s diameter of only 12,760 km. Even the biggest planet—Jupiter, is only one-tenth the diameter of the Sun (see Table 3.2).Table 3.2Details of the Sun
Mass
2.0 × 1030 kg
Relative to Earth
109 times larger
Diameter
1.4 million km
The Solar System in Close-Up Page 5
