Main asteroid belt: The majority of known asteroids orbit within the asteroid belt between Mars and Jupiter, generally with not very elongated orbits. The belt is estimated to contain between 1.1 and 1.9 million asteroids larger than 1 kilometer (0.6 mile) in diameter, and millions of smaller ones. Early in the history of the solar system, the gravity of newly formed Jupiter brought an end to the formation of planetary bodies in this region and caused the small bodies to collide with one another, fragmenting them into the asteroids we observe today.
Trojans: These asteroids share an orbit with a larger planet, but do not collide with it because they gather around two special places in the orbit (called the L4 and L5 Lagrangian points). There, the gravitational pull from the sun and the planet are balanced by a trojan's tendency to otherwise fly out of the orbit. The Jupiter trojans form the most significant population of trojan asteroids. It is thought that they are as numerous as the asteroids in the asteroid belt. There are Mars and Neptune trojans, and NASA announced the discovery of an Earth trojan in 2011.
Near-Earth asteroids: These objects have orbits that pass close by that of Earth. Asteroids that actually cross Earth's orbital path are known as Earth-crossers. As of June 19, 2013, 10,003 near-Earth asteroids are known and the number over 1 kilometer in diameter is thought to be 861, with 1,409 classified as potentially hazardous asteroids - those that could pose a threat to Earth.
How Asteroids Get Their Names
The International Astronomical Union's Committee on Small Body Nomenclature.is a little less strict when it comes to naming asteroids than other IAU naming committees. So out there orbiting the sun we have giant space rocks named for Mr. Spock (a cat named for the character of "Star Trek" fame), rock musician Frank Zappa, regular guys like Phil Davis, and more somber tributes such as the seven asteroids named for the crew of the Space Shuttle Columbia killed in 2003. Asteroids are also named for places and a variety of other things. (The IAU discourages naming asteroids for pets, so Mr. Spock stands alone).
Asteroids are also given a number, for example (99942) Apophis. The Harvard Smithsonian Center for Astrophysics keeps a fairly current list of asteroid names.
ASTEROIDS: WHAT, WHERE AND HOW MANY?
The total mass of all asteroids is estimated at 930 miles (1,500 km) in diameter, this is less than half the size of the Moon.
Asteroids are metallic, rocky bodies without atmospheres that orbit the Sun but are too small to be classified as planets. Known as "minor planets," tens of thousands of them congregate in the main asteroid belt located between Mars and Jupiter. The orbits of these two planets are separated by a distance of 2 to 4 AU (300 million to 600 million km).
Asteroids' materials come from primordial materials not taken by the strong gravity of Jupiter. The biggest planet was formed by accretion more than 4.6 billion years ago.
In the main asteroid belt, the dwarf planet Ceres is the largest object at about 950 km in diameter, representing 25 percent of the total mass. By comparison, Pluto is tiny but still 14 times more massive.
To date, 16 asteroids are known to have diameters of at least 240 km. The majority of the main belt asteroids follow slightly elliptical and stable orbits, going in the same direction as the Earth. They take 3 to 6 years to complete the full circle of the Sun.
Even though most asteroids are located in the main belt, many exist in Earth crossing orbits that make them much more accessible, and easier to detect. These asteroids referred as Near-Earth Objects (NEOs) are defined as any asteroid with a minimum orbital radius of <1.3 AU. Because of their proximity, NEOs are seriously studied, and will probably be the first to be tapped for their resources.
The continuous process of collision and accretion that began when our solar system was formed, cannot give a predictable pattern to follow for their detection. By convention, in a given region where 100 asteroids with diameters higher than 10 km are found, it is assumed that there are about 1 million not detected with diameters of about 100 m.
No comprehensive telescopic survey has yet been conducted with the ability to detect asteroids <100 m in diameter, and the knowledge is limited to the small population that has been detected when one makes a fortuitous close pass of Earth.
THE ADVANTAGES/DISADVANTAGES TO MINE ASTEROIDS
Asteroids are formed from the same circumstellar cloud of gas and dust as inner planets, so their bulk composition is generally similar to the Earth. However, the Earth’s larger mass and gravity has allowed its interior to remain hot and geologically active, concentrating various materials through processes that never took place on asteroids.
Asteroids tend to be more homogeneous and undifferentiated. The Earth’s surface and its interior show high differentiation and can be divided into layers and geological zones. But, a sample taken from one part of an asteroid is basically the same everywhere. This asteroid's fact, provides some advantages and disadvantages for resource utilization.
In general, it is easier to characterize an asteroid's composition. Unlike Earth, any materials taken on its surface is likely present throughout its interior as the Iridium. This valuable material found deep in the Earth's iron core, is uniformly distributed throughout the asteroid.
Rare platinum group metals can also be found on Earth in locations where geologic process have brought them near the surface. But on asteroids, they are likely distributed throughout the body, and can be naturally separated while mining for other minerals.
Mining on Earth is generally a process of following veins where minerals are present in higher quantities. By contrast, mining on asteroids is likely to focus more on moving and processing large volumes of a uniformly low grade ore. So, by this lack of differentiation, much larger volumes of materials must be processed to yield the same quantity of resources.
Medium sized asteroids of 1 to 100 km in diameter have sufficient gravity to attract small rocks and regolith to their surface. But, they do not have enough gravity to develop the internal pressure or heat needed to melt or separate their interiors. Asteroids in this size range tend to resemble loose packed agglomerations with a porous structure. Mining material from these will require comparatively little breaking or mechanical processing, as an assortment of materials in a range of sizes is already available.
By contrast, asteroids less than 100 m in diameter are more likely a single continuous body, as their surface gravity is too weak to hold on to anything loosely packed.
The continuous nature of small asteroids is also evident from studies of their rotation rate. They are regularly observed to be rotating rapidly enough that centrifugal force at their surface exceeds their gravity. That means, the body must have some internal cohesion in order to remain intact.
If we want to know the period of revolution and the cycles of their magnitude, we have to make repeated observations of the asteroid. But if we want to know accurately about their diameter and mass, a spacecraft has to be sent in proximity to make the closest observations possible.
Because that fact, techniques deployed to mine it will be very different than those applied on a medium asteroid. So, as the monolithic structure can negate the need for support or reinforcement to brace the asteroid against acceleration, if it can do it, it will be able to break down large chunks before processing.
The only way to determine an asteroid’s size from ground observations is by measuring the amount of light it reflects, that is the albedo. Like with stars, this measurement is quantified with a photometric magnitude system, where a lower magnitude corresponds to a brighter source, and each step of -1 magnitude equates to a factor of 2.5 increase in the intensity of the source.
An asteroid’s apparent magnitude is not a simple function of its distance from the observer, but also of its phase angle (the angle between sun-asteroid-Earth) and its albedo. Different asteroid types will have different surface coatings, which preferentially scatter light in different directions, further complicating the estimation of an asteroid’s size from its magnitude. Asteroids tend to have dark, non-reflective surfaces with albedo values of 0.04-0.20, making them as dark as asphalt.
1801: Giuseppe Piazzi discovers the first and largest asteroid, Ceres, orbiting between Mars and Jupiter.
1898: Gustav Witt discovers Eros, one of the largest near-Earth asteroids.
1991-1994: The Galileo spacecraft takes the first close-up images of an asteroid (Gaspra) and discovers the first moon (later named Dactyl) orbiting an asteroid (Ida).
1997-2000 : The NEAR Shoemaker spacecraft flies by Mathilde and orbits and lands on Eros.
1998: NASA establishes the Near Earth Object Program Office to detect, track and characterize potentially hazardous asteroids and comets that could approach Earth.
2006: Japan's Hayabusa becomes the first spacecraft to land on, collect samples and take off from an asteroid.
2006: Ceres attains a new classification -- dwarf planet -- but retains its distinction as the largest known asteroid.
2007: The Dawn spacecraft is launched on its journey to the asteroid belt to study Vesta and Ceres.
2008: The European spacecraft Rosetta, on its way to study a comet in 2014, flies by and photographs asteroid Steins, a type of asteroid composed of silicates and basalts.
2010: Japan's Hayabusa returns its asteroid sample to Earth.
2010: Rosetta flies by asteroid Lutetia, revealing a primitive survivor from the violent birth of our solar system.
Several missions have flown by and observed asteroids. The Galileo spacecraft flew by asteroids Gaspra in 1991 and Ida in 1993; the Near-Earth Asteroid Rendezvous (NEAR-Shoemaker) mission studied asteroids Mathilde and Eros; and the Rosetta mission encountered Steins in 2008 and Lutetia in 2010. Deep Space 1 and Stardust both had close encounters with asteroids.
In 2005, the Japanese spacecraft Hayabusa landed on the near-Earth asteroid Itokawa and attempted to collect samples. On June 3, 2010, Hayabusa successfully returned to Earth a small amount of asteroid dust now being studied by scientists.
NASA's Dawn spacecraft, launched in 2007, orbited and explored asteroid Vesta for over a year. Once it left in September 2012, it headed towards the dwarf planet Ceres, with a planned arrival in2015. Vesta and Ceres are two of the largest surviving proto-planet bodies that almost became planets. By studying them with the same complement of instruments on board the same spacecraft, scientists will be able to compare and contrast the different evolutionary path each object took to help understand the early solar system overall.
By convention, the absolute magnitude of an asteroid is defined as its apparent magnitude when it is at 1 AU from the Earth and the Sun. A typical 50 m-asteroid may have an absolute magnitude of about 26, illustrating the difficulty in detecting these small objects except when they are very close to Earth.
Typical limits of telescopes dedicated to asteroid surveys are 21-24, meaning a 50 m-asteroid in a 1 AU orbit may not be detected until it is within 0.1-0.3 AU of the Earth. This further highlights the distinction between proven and unproven resources in asteroid mining. The estimated potential resources of all asteroid surveys are partial surveys only.
The vast majority of asteroids are too distant to be detected, except when they are close to Earth or at a favorable phase angle.
And, those with similar orbits to the Earth, make close passes to Earth only every few decades. Thus after detection, asteroids can go several years before being seen again.
The convention for discovery and identification of asteroids requires observing them on multiple passes (typically 4-5) before their orbit is sufficiently well characterized to not be lost again.
Once an asteroid has met this step, it is assigned a unique discovery number (e.g. 2350751). Until then, each asteroid is referred to by its discovery year and a temporary letter code (e.g. 2002 AW).
The vast majority (>90%) of asteroids have yet to be observed a sufficient number of times for a precise orbital fix, so they are most commonly referred to by the temporary discovery year and letter code.
Many factors contribute to an asteroid’s apparent magnitude. An asteroid just outside the Earth’s orbit and at low phase angle will be almost fully illuminated, and physically closer, making it easier to detect than one which is inside the Earth’s orbit and far away.
THE PHYSICAL PROPERTIES OF ASTEROIDS
Once an asteroid’s absolute magnitude (H) has been measured, and an estimate of its albedo (α) has been made (or assumed), it is possible to determine its diameter.
After repeated observations, it will be possible to measure the small changes in brightness occurring as the asteroid rotates. That variation provides an estimate of its spin rate and, approximates its shape. Also, if many images are taken in multiple color filters, the asteroid's composition can be determined, though high-resolution spectral data is still required to confirm the results.
However, observations beyond position and magnitude are not frequently collected due to telescope time and cost constraints, so the total of all “known” information about an asteroid is often limited to its approximate orbit, and a very rough estimate of its size. Nothing can be known about its shape, mass, density or composition without additional observations. Next to its diameter, the most important property of an asteroid is arguably its mass, which is impossible to measure from the ground. Until the asteroid is visited by a spacecraft, details like those can only be guessed at.
An estimate of an asteroid’s type and composition requires many measurements in multiple color bands, or detailed spectral data.
No common database of asteroid spectra exists at the moment, but a rough taxonomy of asteroids has still been developed by matching available spectral data to identify meteorites found here on Earth.The three most common types of asteroids are:
. C-cadre: More common in the main belt, less common near Earth orbit. Characterized by a darker albedo, lower density, and a higher prevalence of organic compounds, water-ice and other volatiles.
. S-cadre: The most common near Earth object type, but less common in the main belt. Characterized by a high albedo, and a stony/metallic composition with very little water-ice or volatiles.
. The M-cadres are metallic (nickel-iron). The asteroids' differences are related to how far from the Sun they formed. Some experienced high temperatures after they formed and partly melted, with iron sinking to the center and forcing basaltic (volcanic) lava to the surface. Only one such asteroid, Vesta, survives to this day.
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Asteroids are rocky remnants left over from the early formation of our solar system about 4.6 billion years ago. Most of this ancient space rubble can be found orbiting the Sun between Mars and Jupiter within the main asteroid belt. Asteroids range in size from Vesta - the largest at about 530 km in diameter - to bodies that are less than 10 m across. The total mass of all the asteroids combined is less than that of the Earth's Moon.
Most asteroids are nearly spherical, pitted and cratered. As they revolve around the Sun in elliptical orbits, the asteroids also rotate, sometimes quite erratically, tumbling as they go. More than 150 asteroids are known to have one or two small moons as companion. There are also triple asteroid systems, and binary asteroids in which two rocky bodies of roughly equal size orbit each other.
Jupiter's massive gravity and occasional close encounters with Mars or other objects change the asteroids' orbits. In fact, these encounters knock them out of the main belt and hurl them into space in all directions across the other planets' orbits.
Stray asteroids and asteroids' fragments slammed into the Earth and other planets in the past, playing a major role in altering these planets' geological history and the evolution of life on Earth.
To protect the Earth against asteroids' impacts, scientists monitor continuously those whose paths intersect the Earth's orbit and those approaching the orbital distance of about 45 million km. A radar is a valuable tool to detect and monitor potential impact hazards. The objects' signals obtained can give the orbit, the shape, as well as the asteroids' metal concentration.
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Automaton Rover for Extreme Environments (AREE) Credit: Jonathan Sauder
Like RAMA Project, Automaton Rover for VENUS Mission Will be built with mechanicals' parts to resist at High Temperature of 460°C and where the Corrosion resistance is a more nuanced problem considering the high pressure (90 bar) of the environment, i.e. CO2 is near its supercritical state.
An Automaton Rover is a mechanically-based robot that thrives in Venus' high temperatures, where electronics would quickly fail. Inspired by Strandbeests, this high temperature alloy rover extends science fiction "steampunk" to space exploration.
Credits: NASA JPL, Johathan Sauder, Jessie Kawata, Lori Nishikawa, Evan hilgemann, Katie Stack, Aaron Parness, Michael Johnson