Download Studying the Universe

Studying the Universe
Scientists use a number of instruments to study various properties of the
universe.
Telescopes
There are many different types of telescopes used by scientists to study
distant objects. Some telescopes are set up on the ground. Others are
placed on satellites that transmit data back to Earth. These space-based
telescopes can gather better data because there is no interference from
Earth's atmosphere. Any telescope can help astronomers gather information
about distant objects, including what they are made of, how fast they are
moving towards or away from Earth, and even what temperature they are.
As telescopes have improved, scientists have been able to gather more
detailed information about other stars. For example, planetary systems like
that in the Solar system used to be considered rare. The first extraterrestrial
planet was discovered in 1995. Since then, more and more extrasolar
planets have been found. We now know that planets are much more
common than was originally believed.
The following image illustrates how radiation from different parts of the
spectrum may travel through or be blocked by different materials such as
air, glass, living things, and metal. The amount of light blocked by each
material is not to scale. A large portion of gamma rays and x rays are
blocked by the atmosphere, but what is left is very penetrating.
Different kinds of telescopes are designed to observe different parts of the
electromagnetic (EM) spectrum. Because different wavelengths of light are
produced and blocked by different things, each telescope can reveal unique
parts of the Universe.
X-ray telescopes are used to examine the x-ray radiation that comes from
different objects. They cannot travel far through the Earth's atmosphere.
Astronomers have identified only some of the sources of x-ray radiation in
the universe. Hot gases and the remains of supernovae are known to
produce x-rays. X-rays are produced by many high-energy objects in space.
The above image is a map of the entire sky made by x-ray telescopes. The
black streaks are places where data is missing. Blue indicates the most
energetic x-rays, and red indicates the least energetic x-rays.
Image courtesy of NASA/ROSAT Project
Light telescopes are tools used to examine objects using light in or near
the visible range. These telescopes allow people to see the objects as they
would if they were much closer to the objects.
The above image is of part of the night sky as seen with visible light.
Specifically, it is the part of the night sky through which the Milky Way runs.
The image should be packed with the bright stars that fill the center of our
galaxy, but dust obscures the view, blocking out the visible light.
Image courtesy of Goddard Space Flight Center, NASA
Radio telescopes are used to examine the radio waves that come from
different objects. Radio waves are not easily scattered, so they can travel
long distances. Radio waves are also the most likely way we would hear
from extraterrestrial civilizations, assuming they are out there. Groundbased radio telescopes can collect data during the day or night and in any
weather conditions.
It was a radio telescope that first found the cosmic microwave
background. It is a low level of microwave radiation that comes from
everywhere in the Universe. It is some of the best evidence supporting the
big bang theory, which states that all the matter and energy in the
Universe originated at a single point.
The above image is a map of the entire sky taken with radio telescopes.
Light in this part of the spectrum indicates the presence of strong magnetic
fields, much stronger than the one that causes the needle of a compass to
point north here on Earth. The Milky Way Galaxy runs along the center of
the image. The Sun is not shown here, but the Sun is the brightest radio
source in the Earth's sky.
© Max Planck Institute for Radio Astronomy (Bonn, Germany)
Satellites
A satellite is an unmanned spacecraft that is put into orbit around the Earth.
Satellites have become very common over the past 2 decades, and there
are currently about 5,000 satellites orbiting the Earth. Most of these 5,000
satellites run on solar power, but a few run on nuclear power. These
satellites have a great impact not only on space exploration but also on
technologies here on Earth. Some of the technologies that depend on
satellites are cellular phones, global positioning systems, and weather
tracking systems that can track weather on a global scale.
There are also many satellites in orbit around the Earth that are meant to
help study the universe. Some of these satellites are telescopes, the most
famous of which is the Hubble Space Telescope.
Probes
A probe is an unmanned spacecraft carrying instruments intended for use
in exploration of the physical properties of celestial bodies other than Earth.
It is launched with enough energy to escape the gravitational field of Earth.
Probes have traveled further than any other man-made object in history. As
a matter of fact, multiple probes have left our solar system. Much of the
information we have about the other planets and moons in our solar system
actually came from probes. Every planet in our solar system has been
closely observed by a space probe.
Space probes have the ability to examine many properties of planets and
moons. They can examine atmospheres, weather, magnetic fields, surface
features, and many other features of planets and moons. Some probes
have actually entered the atmosphere of other planets. We have sent
probes into the atmospheres of Venus, Mars, and Jupiter.
Composition
Different materials can emit or absorb unique sets of different colors of light.
These characteristic bands of colors are called spectra.
Hot substances emit, or radiate, light. For example, the element helium was
named after the sun because its spectrum was first found coming from the
sun. Viewed through a spectroscope, the light coming from hot helium
looks like this:
Just by looking at the spectra of glowing objects such as galaxies, stars,
and nebula, scientists can tell what they are made of.
Space Exploration
Once rockets were invented that were powerful enough to escape Earth's
gravity, humans started exploring space with a series of satellites, space
probes, and manned missions.
Humanity's exploration of space began in 1957 when the U.S.S.R. launched
Sputnik, the first artificial satellite, into orbit around the Earth. The U.S.S.R.
once again broke ground when they sent the first man into space in 1961
aboard Vostok 1. The United States followed less than a month later,
sending Alan Shepard, the first U.S. astronaut, into space. These early
milestones began a long history of space exploration, in which the United
States has played a lead role.
Apollo Missions to the Moon
The main purpose of the Apollo
missions was to put a man on the Moon and return him safely back to Earth.
This goal was reached in 1969 on the Apollo 11 mission when Neil
Armstrong and Edwin "Buzz" Aldrin set foot on the Moon and then returned
safely to Earth. There were six more Apollo missions meant to go to the
Moon after Apollo 11, and all but Apollo 13 set people on the Moon. In all,
fourteen Apollo missions were launched between 1967 and 1972.
During the Apollo missions, astronauts walked on the Moon, performed
many experiments, and collected many samples of the Moon's materials,
which were returned to Earth for study by scientists. Through these
missions, scientists learned that the Moon is lifeless, dry, and geologically
inactive today. They also learned many important things about what the
Moon is made of and the history of the solar system.
Mariner 10 Mission to Mercury
The Mariner 10 spacecraft was launched in November 1973. Its main
purpose was to study the planet Mercury. Mariner 10 flew close by Venus in
February 1974. The spacecraft used the gravity field of Venus to accelerate
itself toward Mercury. This "gravity assist" saved valuable fuel and became
an important part of many future space missions.
Mariner 10 was the first spacecraft to use the gravity of one planet to reach
another.
Image courtesy of NASA/Wikipedia.
Mariner 10 first flew by Mercury in March 1974, and it flew by the planet two
more times over the next year. The spacecraft took many photographs of
Mercury, revealing the heavily cratered nature of the planet's ancient
surface. Scientists also discovered that Mercury has a weak magnetic field
and lacks a permanent, significant atmosphere.
Magellan Mission to Venus
Launched in 1989, the Magellan spacecraft orbited the planet Venus from
1990 to 1994. Its primary purpose was to map the planet's surface using
radar, which unlike visible light can easily penetrate Venus' thick, cloudy
atmosphere.
This global topographic map of Venus was created from radar data
collected by the Magellan spacecraft. The lowest elevations are shown in
blue, while the highest elevations are shown in reddish pink.
Image courtesy of NASA/JPL/USGS.
The spacecraft also took electrical measurements and measured the
planet's surface topography and gravity. From this mission, scientists
learned that Venus' surface is mainly volcanic in nature and relatively young
compared with most other terrestrial planets' surfaces. Venus has also been
shaped by tectonic activity, but it does not have a complex plate tectonics
system like Earth.
Missions to Mars
One of the main reasons humans are so fascinated with Mars is that it is
likely the best possible site for future human colonies beyond Earth.
Humans could better cope with Mars' temperature ranges than those on
other extraterrestrial bodies. Also, evidence suggests that large volumes of
ice are present beneath the surface, which humans could use as a water
source. An artificial environment would have to be created, though, because
humans cannot breathe in Mars' thin carbon dioxide atmosphere. In the
meantime, humans have been sending spacecraft and robots to Mars for
decades. Some important missions to Mars are described below.
Viking
The Viking mission, which lasted from 1975 to 1982, had twin orbiters and
landers that studied Mars in great detail. Thousands of images were taken
from orbit and from the ground at two landing sites. The landers also
performed experiments, including soil analysis for the presence of life (none
was found).
The image on the left, taken by the Viking 2 lander, shows a thin, temporary
coating of water ice on the surface of Mars. The image on the right, taken by
the Viking 1 orbiter, shows a rampart crater (or "splosh" crater). When an
asteroid or comet struck the surface to make this crater, mixtures of rock,
dust, and melted ice flowed away from the crater. Evidence like this for
water on Mars drove scientists to send more spacecraft to Mars in later
years.
Image courtesy of NASA.
Mars Global Surveyor
Mars Global Surveyor (MGS) was on orbiter mission lasting from 1996 to
2006. MGS had a special camera (Mars Orbiter Camera, or MOC) that
captured images in detail never before seen for another planet at that time.
These images were as detailed as many images taken of Earth. The
spacecraft had several other instruments, including a laser instrument (Mars
Orbiter Laser Altimeter, or MOLA) that measured the planet's topography.
The global topography map below was created from MOLA data.
In this global topography map of Mars, low elevations are shown in blue,
and high elevations are shown in red and white. The left image shows Mars'
western hemisphere, and the right image shows the eastern hemisphere.
Image courtesy of NASA/MOLA/JPL.
Mars Exploration Rover
The Mars Exploration Rover mission (2003 to the present) has twin rovers
(Spirit and Opportunity) that have studied two different areas of Mars. These
rovers have traveled farther on an extraterrestrial body than any other
robotic rover so far. They have captured many images showing layered
rock, atmospheric events, and ice in the soil. They have also studied the
composition of many surface materials.
This image was captured by the Mars Exploration Rover Spirit. The red
arrow points to a dust devil, which is a type of sandstorm somewhat like a
tornado.
Image modified from NASA/JPL-Caltech.
Mars Reconnaissance Orbiter
Launched in 2005, the Mars Reconnaissance Orbiter has collected a wide
variety of data from Mars. Included in the spacecraft's instruments are
cameras to study the planet's surface and weather systems, a spectrometer
to study surface materials in visible and infrared wavelengths, a radiometer
that studies atmosphere conditions, and a radar instrument that detects
underground ice. In addition to providing a wealth of scientific data, the Mars
Reconnaissance Orbiter has also provided support for other missions and in
choosing landing sites for future missions.
This image was taken by the HiRISE camera on board the Mars
Reconnaissance Orbiter. The image shows an area explored by the Mars
Exploration Rover Opportunity.
Image: NASA/JPL/University of Arizona
Missions to the Outer Planets
Voyager 1 and 2
In the summer of 1977, the twin spacecraft Voyager 1 and Voyager 2 were
launched to explore Jupiter, Saturn, and some of their moons. Voyager 1
arrived at Jupiter in March 1979; Voyager 2 reached Jupiter in July of the
same year. Together, the two spacecraft captured more than 33,000 images
and took several measurements of Jupiter and its largest moons. Jupiter's
moon Io was discovered to be volcanically active. Prior to this, the Earth
was the only body in the solar system known to have current volcanic
activity. Both Voyager 1 and Voyager 2 used a gravity assist from Jupiter to
then move on to Saturn.
Voyager 1 arrived at Saturn in November 1980; Voyager 2 arrived in August
1981. The spacecraft discovered that Saturn's atmosphere, like Jupiter's, is
star-like in composition (mostly hydrogen and helium). Many images of
Saturn, its rings, and its moons, including Titan, were captured, and other
measurements such as winds speeds and temperatures were taken.
Voyager 1 left Saturn on a path to leave the solar system. As part of an
extended mission, Voyager 2 continued on to Uranus with a gravity assist
from Saturn.
Voyager 2 arrived at Uranus in January 1986. The spacecraft imaged the
planet, its moons, and its rings. Magnetic field readings and other
measurements were also taken. A gravity assist by Uranus enabled
Voyager 2 to continue its extended mission and reach Neptune in August
1989, about twelve years after its launch from Earth. The spacecraft
collected similar data as for the other gas-giant systems, including images
of the moon Triton. Voyager 2 then left the Neptune system on a path that
will take it, like Voyager 1, beyond the solar system.
As of May 14, 2010, Voyager 1 was nearly 16.9 billion km from Earth,
traveling at a velocity of about 99,320 km/hr relative to Earth. Voyager 2
was about 13.7 billion km from Earth, traveling at a relative velocity of about
85,640 km/hr. It is estimated that both spacecraft will reach the edge of the
solar system, known as the heliopause, by the year 2015. At that point, they
will enter interstellar space.
This image is an artist's conception of Voyager 1's and Voyager 2's
positions as they approach the edge of the solar system. Voyager 1 is
destined to be the first human-made object to leave the solar system.
Image courtesy of NASA/JPL.
Galileo
The Galileo spacecraft, which was launched in 1989, studied Jupiter and its
four largest moons in great detail from 1995 to 2003. The spacecraft
included an orbiter and a probe, which was sent into the atmosphere of
Jupiter. The probe revealed that Jupiter's atmosphere has less water than
previously thought, wind speeds of 450 mph, stronger but less-concentrated
lightning activity than Earth, and a composition very similar to that of the
Sun.
The Galileo orbiter measured Jupiter's magnetic field, discovered that the
planet has rings, took compositional readings, and captured thousands of
images of the the planet and its moons. Scientists learned that the moon Io
is the most volcanically active body in the solar system, and they found
more evidence that a liquid ocean likely exists beneath the icy surface of the
moon Europa. The presence of this ocean, which could possibly support life
forms, led scientists to intentionally crash Galileo into Jupiter's atmosphere
at the end of the mission to avoid a future collision with Europa.
This collage of images shows the main bodies studied by the Galileo
spacecraft. Part of Jupiter is shown at left. From top to bottom are Io,
Europa, Ganymede, and Callisto. The sizes of these bodies are shown to
scale, but their true positions and distances between them are not
represented.
Image courtesy of NASA.
Cassini-Huygens
Launched in 1997, the Cassini-Huygens spacecraft arrived at the Saturn
system in 2004. The spacecraft originally consisted of two parts—the
Cassini orbiter and the Huygens probe. The Huygens probe parachuted
through the atmosphere of the moon Titan and landed on its surface in
2005. The probe showed that Titan's atmosphere is mostly nitrogen,
methane, and argon, and it photographed Titan's surface while descending
and from the ground. Titan appears to have an icy surface, with rivers and
lakes of liquid methane and ethane. Also, like many other moons of the
outer planets, Titan may have a liquid ocean beneath the surface. In Titan's
case, the ocean is probably made of water and ammonia.
The Cassini orbiter has made many observations of Saturn, its moons, and
its rings. Images have revealed many new discoveries, such as a possible
ring system around the moon Rhea and water jets rich in organic molecules
shooting from the icy moon Enceladus. These jets suggest that warm, liquid
water might be present beneath the icy surface. As with Jupiter's moon
Europa, such an environment could be one that supports life.
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