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how far will we explore?
What are the limits to space travel?
The distances between the stars are vast and are measured using a unit called “light-years.” One light-year is the distance traveled by light in one year. The speed of light is 671 million mph (299,792,458 m/s), so one light-year is the same as 5,878,625,373,183.608 miles (9,460,730,472,580.8 km)!
Our Sun is 8.3 “light-minutes” away (i.e., it takes 8.3 minutes for sunlight to reach Earth), and the Moon—the farthest place humans have ever visited—just 1.3 “light-seconds” away. So when we consider that our next nearest star is 4.2 light-years away, what chances have we got of ever reaching it? Even if we consider light as our theoretical speed limit, how far can we expect to travel from Earth? Our journey starts at bottom left of the page . . .
With current conventional rocket technology, a trip to the nearest star is out of the question. Even if we could develop an interstellar spacecraft (artist’s impression, top right), Albert Einstein has taught us that as this theoretical spacecraft approached the speed of light, it would appear to gain mass, making it increasingly difficult to accelerate.
More advanced rocket technology, such as nuclear thermal or nuclear pulse, could theoretically send a manned mission to the nearest stars at a significant fraction of the speed of light—albeit at a great cost—within a century. If anyone manages to invent sci-fi technology, such as a warp drive, it could happen much sooner!
Largest planet without a moon Of the eight major planets of the solar system, only Mercury and Venus have no natural satellite. It is possible that Venus once had a moon, which crashed into the surface. With a 7,520.8-mile (12,103.6-km) diameter, Venus is similar in size to Earth.
Largest impact crater on Venus Mead crater, north of a highland area called Aphrodite Terra, has a diameter of around 174 miles (280 km). Mead is shallow, suggesting it may have been filled by lava or impact melt after its formation.
Planet with the longest day Venus has the longest rotation period (day) of all the major planets in the solar system. While Earth takes 23 hr. 56 min. 4 sec. to complete one rotation, Venus takes 243.16 “Earth days” to spin once through 360 degrees. Because it is closer to the Sun, the length of Venus’s year is shorter than Earth’s, lasting 224.7 days, so a day on Venus is actually longer than its year!
Brightest planet seen from Earth Seen from Earth, the brightest of the five planets usually visible to the naked eye (Jupiter, Mars, Mercury, Saturn, and Venus) is Venus, with a maximum magnitude of -4.4. Venus appears so bright because around 80% of the sunlight that reaches the planet is bounced back by its reflective cloud cover (see below). At maximum elongation, it is visible for some time before and after sunrise and sunset.
Thickest planetary atmosphere Often referred to as the closest place to hell in the solar system, Venus’s atmosphere is the thickest of any planet, with a pressure nearly 100 times that of Earth’s atmospheric pressure at sea level. The gases in the thick atmosphere cause a greenhouse effect, which means the temperature on the surface reaches 896°F (480°C). Europe’s Venus Express spacecraft is currently performing the most intensive study of Venus’s atmosphere ever made (see p. zzz).
Most acidic rain in the solar system The highly reflective white clouds of Venus, which prevent direct viewing of the surface from space, are due to a layer of sulfuric acid 30–36 miles (48–58 km) above the surface. Rain of almost pure sulfuric acid falls from these clouds but never reaches the surface. At an altitude of around 18.5 miles (30 km), the rain evaporates; it is recycled into the Venusian clouds.
First successful interplanetary mission Mariner 2 (U.S.A.) performed a flyby of Venus on December 14, 1962, within 35,000 km (21,750 miles) of the planet’s surface. Results from the flyby revealed the extremely hot nature of the planet’s surface. Mariner 2, now without power, is still in orbit around the Sun.
Largest highland region on Venus Close to Venus’s equator lies Aphrodite Terra, one of two major highland “continents” on the planet. First mapped in detail by the Soviet Venera 15 and 16 orbiters in 1984, it covers an area of around 30 million km2 (11.6 million miles2), which is approximately the same size as Africa. The fractured appearance of Aphrodite suggests it has been subject to huge forces of compression in its geological history.
Tallest mountain on Venus Maxwell Montes, on the Ishtar Terra plateau, is the highest point on Venus, up to 6.8 miles (11 km) above the average surface level of the planet.
First detection of lightning on Venus On October 26, 1975, the spectrometer onboard the Soviet Venera 9 spacecraft detected optical flashes—consistent with lightning—in the Venusian atmosphere on the dark side of the planet. This represents the only time lightning has been witnessed optically by a spacecraft in the atmosphere of Venus.
On December 25, 1978, in its descent to Venus’s surface, the USSR’s Venera 11 lander picked up a sound that scientists believe to be the first thunder heard on another planet.
Longest channel in the solar system Baltis Vallis on Venus is around 4,300 miles (7,000 km) in length and has an average width of around 1 mile (1.6 km). It was discovered by the Magellan radar mapper, which orbited Venus from August 1990 to October 1994. Experts believe that the channel was originally formed by molten lava.
Fastest wind in the Solar System The solar wind is a steady stream of (mostly) electrons and protons that is emitted from the Sun in all directions. The fastest component of the solar wind travels outward at around 470 miles/sec (750 km/sec) and is thought to originate from areas of open magnetic field lines around the Sun’s poles.
Largest object in the Solar System The Sun dominates the Solar System. With a mass of 1.98 x 1030 kg, or 332,900 times that of Earth, and a diameter of 865,000 miles (1,392,000 km), it accounts for some 99.86% of the mass of the Solar System.
Largest explosions in the Solar System Coronal mass ejections are often, although not always, associated with solar flares. They are huge bubbles of plasma threaded with magnetic field lines, which erupt from the Sun over a period of several hours. They can contain up to 220.5 billion lb. (100 billion kg) of matter moving at 620 miles/sec (1,000 km/sec), with the equivalent energy of a billion hydrogen bombs. The next solar maximum, in 2013, could see several of these erupt from the Sun every day.
Largest magnetic structure in the Solar System The magnetic field of the Sun is contorted into a vast spiral shape by the Sun’s rotation and motion of the solar wind. Resembling the shape of a spinning ballerina’s skirt, and known as the “Parker spiral,” it extends all the way to the edge of the Solar System, into a region known as the “heliosheath.” The magnetic structure of the Parker spiral is approximately 160–200 AU across, or 15–18 billion miles (24–30 billion km).
Strongest magnetic fields on the Sun’s surface Sunspots can have magnetic field strengths of up to 0.4 tesla, around 1,000 times that of their surrounding areas and around 13,000 times the strength of Earth’s magnetic field at the Equator.
Longest continuous observational science data Astronomers have access to a continuous set of observational data of the number of sunspots on the Sun, dating back to 1750.
Longest solar minimum The “solar minimum” is a period during the Sun’s solar cycle when few sunspots are visible and solar activity is low. The Maunder minimum lasted from 1647 to 1715, during which it appeared as if the solar cycle had broken down altogether. This period corresponded with a period of savage winters in Earth’s northern hemisphere that became known as the “Little Ice Age.”
Largest solar granules Convection currents within the Sun cause a phenomenon known as “granulation” on the photosphere. Each granule is formed as hot hydrogen rises in its center and then falls again around its edge. A typical granule is around 620 miles (1,000 km) across and can last for less than 20 minutes. Discovered in the 1950s, supergranules measure around 18,640 miles (30,000 km) across and represent larger-scale currents in the Sun, which has several thousand of these features at any time.
Hottest place in the Solar System Scientists estimate that the temperature at the Sun’s core is around 28,000,000ºF (15,600,000ºC). The pressure there is around 250 billion times that of sea level on Earth.
living in space
First . . .
Manned spaceflight Soviet cosmonaut Yuri Gagarin was the first man in space when he orbited Earth in Vostok 1 on April 12, 1961. Gagarin ejected 108 minutes into the flight as planned and landed back on Earth 10 minutes later by parachute. The maximum altitude on the 25,394.8-mile (40,868.6-km) flight was 203 miles (327 km), with a top speed of 17,560 mph (28,260 km/h). Gagarin, invested a Hero of the Soviet Union and awarded the Order of Lenin and the Gold Star Medal, was killed in a jet plane crash in March 1968.
Flight between space stations Mir EO-1 was the first expedition to the new Soviet Mir space station. Its crew, Leonid Kizim and Vladimir Solovyov, launched from Earth on March 13, 1986, docking with Mir two days later. They remained on Mir for six weeks, changing the station’s orbit to match that of the Salyut 7 space station. On May 5, 1986, the crew undocked their Soyuz spacecraft from Mir and flew to Salyut 7, the first flight between space stations. It took 29 hours. On June 25, the crew undocked from Salyut 7 and returned to Mir, bringing equipment from the old station to the new.
Live music concert broadcast to space Paul McCartney (UK) became the first artist to broadcast live to space when he sent a “wake-up call” to the International Space Station from his concert in Anaheim, California, U.S.A., on November 12, 2005. In 2008, “Across the Universe,” by McCartney’s old band, The Beatles, became the first song to be beamed into deep space. NASA sent the song, at a speed of 186,000 miles per second (300,000 km per second), to celebrate the 50th anniversary of NASA’s founding and the 40th anniversary of the song being recorded.
Untethered space walk NASA astronaut Bruce McCandless II performed an untethered space walk from the space shuttle Challenger on February 7, 1984. His space walk was the first test of the Manned Maneuvering Unit backpack, which cost U.S. $15 million to develop.
Food smuggled into space Gemini III was an orbital mission with a duration of 4 hr. 52 min. on March 23, 1965, crewed by U.S. astronauts Gus Grissom and John Young. During the mission, Young was authorized to eat preapproved space food, while Grissom was not scheduled to eat at all during the flight. However, Young, aware of Grissom’s love of corned beef sandwiches, smuggled one onboard for his fellow astronaut. Young and Grissom were disciplined by NASA for this act.
Person to make an orbit of Earth on a bicycle Skylab 3 was the second manned mission to the U.S. Skylab space station, from July 28 to September 25, 1973. During the flight, Alan Bean, who walked on the Moon during Apollo 12’s mission, spent just over 90 minutes on a stationary bicycle, pedaling throughout a whole orbit of the Earth.
Person to vomit in space Space sickness is similar to motion sickness and is caused by the changes in gravity. The first to have it was Soviet cosmonaut Gherman Titov, who experienced nausea and vomiting on his Vostok 2 flight on August 6, 1961. Some form of space sickness is felt by around half of all people who fly in space.
Fire on a space station On February 23, 1997, a fire broke out onboard the Russian space station Mir, caused by lithium perchlorate “candles,” which supplied oxygen to the station. Although the fire was extinguished, the six-man crew came close to abandoning the station in their Soyuz “lifeboat,” which was docked with Mir.
Commercial filmed in space An advertising campaign for Tnuva Milk, showing cosmonaut Vasily Tsibliyev drinking milk onboard the Russian Mir space station, was broadcast on August 22, 1997.
Dog in space “Laika” became the first dog in space in November 1957 on board Sputnik 2, more than three years before the first human. She died early in the mission—her vehicle was not designed to return to Earth.
longest . . .
Continuous human presence in space Expedition 1’s Soyuz TM-31 was launched to the International Space Station on October 31, 2000, and its crew of three remained onboard for 136 days. This marked the longest uninterrupted human presence in space to date, with over 10 years of continuous occupation of the space station.
Mission by a spacesuit On February 3, 2006, Russian cosmonaut Valery Tokarev and U.S. astronaut Bill McArthur jettisoned an old Russian Orlan M spacesuit from the International Space Station. Equipped with a transmitter, “SuitSat-1” broadcast nearly 3,500 radio messages and data on the temperature inside the suit, which were picked up by amateur radio operators on Earth. The last transmission from SuitSat-1 was received on February 18, 2006, shortly before its battery died.
Running space grocery delivery program Russia’s Progress vehicles are unmanned spacecraft designed to resupply cosmonauts in orbit with water, food, and oxygen, as well as equipment for experiments and repairs. They have been in use since the first one was launched on January 20, 1978. Today’s Progress vehicles can carry 3,748 lb. (1,700 kg) of supplies in a 212-cu.-ft. (6-m3) space. Upon docking to the International Space Station, it remains in place for months, during which time it is filled with trash from the station before undocking and burning up in a controlled deorbit.
First gun in space Soviet cosmonaut Yuri Gagarin, the first man in space, allegedly carried a Makarov pistol on his historic Vostok 1 flight on April 12, 1961. The weapon was to be used in self-defense in case he landed back on Earth in hostile territory or amid dangerous wildlife.
First space-based submarine surveillance satellite SEASAT was a U.S. satellite designed to use synthetic aperture radar to monitor the oceans. Launched on June 27, 1978, it operated for only 105 days before malfunctioning. An unexpected feature of the radar system onboard SEASAT was its ability to detect the movement of submerged submarines by seeing their “wake” on the ocean surface. This has led some people to conjecture that the satellite’s malfunction is a cover story—they believe it was taken over by the U.S. military upon discovery of its submarine-detecting ability.