Meteoroid
A meteoroid (/ˈmiːtiərɔɪd/ MEE-tee-ə-royd)[1] is a small rocky or metallic body in outer space. Meteoroids are distinguished as objects significantly smaller than
A meteor or shooting star[8] is the visible passage of a meteoroid, comet, or asteroid entering Earth's atmosphere. At a speed typically in excess of 20 km/s (72,000 km/h; 45,000 mph), aerodynamic heating of that object produces a streak of light, both from the glowing object and the trail of glowing particles that it leaves in its wake. Meteors typically become visible when they are about 100 km (62 mi) above sea level. A series of many meteors appearing seconds or minutes apart and appearing to originate from the same fixed point in the sky is called a meteor shower.
An estimated 25 million meteoroids, micrometeoroids and other space debris enter Earth's atmosphere each day,[9] which results in an estimated 15,000 tonnes of that material entering the atmosphere each year.[10] A meteorite is the remains of a meteoroid that has survived the ablation of its surface material during its passage through the atmosphere as a meteor and has impacted the ground.
Meteoroids
In 1961, the
Objects smaller than meteoroids are classified as micrometeoroids and interplanetary dust. The Minor Planet Center does not use the term "meteoroid".
Composition
Almost all meteoroids contain extraterrestrial nickel and iron. They have three main classifications: iron, stone, and stony-iron. Some stone meteoroids contain grain-like inclusions known as
In the Solar System
Most meteoroids come from the asteroid belt, having been perturbed by the gravitational influences of planets, but others are particles from comets, giving rise to meteor showers. Some meteoroids are fragments from bodies such as Mars or the Moon, that have been thrown into space by an impact.
Meteoroids travel around the Sun in a variety of orbits and at various velocities. The fastest move at about 42 km/s (94,000 mph) through space in the vicinity of Earth's orbit. This is
On January 17, 2013, at 05:21 PST, a one meter-sized comet from the Oort cloud entered Earth atmosphere over California and Nevada.[21] The object had a retrograde orbit with perihelion at 0.98 ± 0.03 AU. It approached from the direction of the constellation Virgo (which was in the south about 50° above the horizon at the time), and collided head-on with Earth's atmosphere at 72 ± 6 km/s (161,000 ± 13,000 mph)[21] vaporising more than 100 km (330,000 ft) above ground over a period of several seconds.
Collision with Earth's atmosphere
When meteoroids intersect with Earth's atmosphere at night, they are likely to become visible as meteors. If meteoroids survive the entry through the atmosphere and reach Earth's surface, they are called meteorites. Meteorites are transformed in structure and chemistry by the heat of entry and force of impact. A noted 4-metre (13 ft) asteroid, 2008 TC3, was observed in space on a collision course with Earth on 6 October 2008 and entered Earth's atmosphere the next day, striking a remote area of northern Sudan. It was the first time that a meteoroid had been observed in space and tracked prior to impacting Earth.[11] NASA has produced a map showing the most notable asteroid collisions with Earth and its atmosphere from 1994 to 2013 from data gathered by U.S. government sensors (see below).
Meteors
It has been suggested that this section be Meteor. (Discuss ) (May 2023) |
A meteor, known colloquially as a shooting star or falling star, is the visible passage of a glowing meteoroid, micrometeoroid, comet or asteroid through Earth's atmosphere, after being heated to incandescence by collisions with air molecules in the upper atmosphere,[11][24][25] creating a streak of light via its rapid motion and sometimes also by shedding glowing material in its wake. Although a meteor may seem to be a few thousand feet from the Earth,[26] meteors typically occur in the mesosphere at altitudes from 76 to 100 km (250,000 to 330,000 ft).[27][28] The root word meteor comes from the Greek meteōros, meaning "high in the air".[24]
Millions of meteors occur in Earth's atmosphere daily. Most meteoroids that cause meteors are about the size of a grain of sand, i.e. they are usually millimeter-sized or smaller. Meteoroid sizes can be calculated from their mass and density which, in turn, can be estimated from the observed meteor trajectory in the upper atmosphere. [29] Meteors may occur in
Meteors become visible between about 75 to 120 km (250,000 to 390,000 ft) above Earth. They usually disintegrate at altitudes of 50 to 95 km (160,000 to 310,000 ft).[31] Meteors have roughly a fifty percent chance of a daylight (or near daylight) collision with Earth. Most meteors are, however, observed at night, when darkness allows fainter objects to be recognized. For bodies with a size scale larger than 10 cm (3.9 in) to several meters meteor visibility is due to the atmospheric ram pressure (not friction) that heats the meteoroid so that it glows and creates a shining trail of gases and melted meteoroid particles. The gases include vaporised meteoroid material and atmospheric gases that heat up when the meteoroid passes through the atmosphere. Most meteors glow for about a second.
History
Although meteors have been known since ancient times, they were not known to be an astronomical phenomenon until early in the nineteenth century. Prior to that, they were seen in the West as an atmospheric phenomenon, like lightning, and were not connected with strange stories of rocks falling from the sky. In 1807, Yale University chemistry professor Benjamin Silliman investigated a meteorite that fell in Weston, Connecticut.[32] Silliman believed the meteor had a cosmic origin, but meteors did not attract much attention from astronomers until the spectacular meteor storm of November 1833.[33] People all across the eastern United States saw thousands of meteors, radiating from a single point in the sky. Careful observers noticed that the radiant, as the point is now called, moved with the stars, staying in the constellation Leo.[34]
The astronomer
Fireball
A fireball is a brighter-than-usual meteor that also becomes visible when about 100 km from sea level. The International Astronomical Union (IAU) defines a fireball as "a meteor brighter than any of the planets" (apparent magnitude −4 or greater).[36] The International Meteor Organization (an amateur organization that studies meteors) has a more rigid definition. It defines a fireball as a meteor that would have a magnitude of −3 or brighter if seen at zenith. This definition corrects for the greater distance between an observer and a meteor near the horizon. For example, a meteor of magnitude −1 at 5 degrees above the horizon would be classified as a fireball because, if the observer had been directly below the meteor, it would have appeared as magnitude −6.[37]
Fireballs reaching apparent magnitude −14 or brighter are called
A steadily growing number of fireballs are recorded at the American Meteor Society every year.[43] There are probably more than 500,000 fireballs a year,[44] but most go unnoticed because most occur over the ocean and half occur during daytime. A European Fireball Network and a NASA All-sky Fireball Network detect and track many fireballs.[45]
Year | 2008 | 2009 | 2010 | 2011 | 2012 | 2013 | 2014 | 2015 | 2016 | 2017 | 2018 | 2019 | 2020 | 2021 |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Number | 734 | 676 | 953 | 1,660 | 2,183 | 3,599 | 3,789 | 4,250 | 5,391 | 5,510 | 5,993 | 6,978 | 8,259 | 9,629 |
Effect on atmosphere
The entry of meteoroids into Earth's atmosphere produces three main effects: ionization of atmospheric molecules, dust that the meteoroid sheds, and the sound of passage. During the entry of a meteoroid or asteroid into the upper atmosphere, an ionization trail is created, where the air molecules are ionized by the passage of the meteor. Such ionization trails can last up to 45 minutes at a time.
Small,
Colours
The visible light produced by a meteor may take on various hues, depending on the chemical composition of the meteoroid, and the speed of its movement through the atmosphere. As layers of the meteoroid abrade and ionize, the colour of the light emitted may change according to the layering of minerals. Colours of meteors depend on the relative influence of the metallic content of the meteoroid versus the superheated air plasma, which its passage engenders:[49]
- Orange-yellow (sodium)
- Yellow (iron)
- Blue-green (magnesium)
- Violet (calcium)
- Red (atmospheric nitrogen and oxygen)
Acoustic manifestations
Sound generated by a meteor in the upper atmosphere, such as a
Theories on the generation of these sounds may partially explain them. For example, scientists at NASA suggested that the turbulent ionized wake of a meteor interacts with
Meteor shower
A
, some of its ice vaporizes and a certain amount of meteoroids are shed. The meteoroids spread out along the entire orbit of the comet to form a meteoroid stream, also known as a "dust trail" (as opposed to a comet's "dust tail" caused by the very small particles that are quickly blown away by solar radiation pressure).The frequency of
Notable meteors
- 1992 – Peekskill, New York
- The ground path of some 430 to 500 mi (700 to 800 km).[65] One meteorite recovered at Peekskill, New York, for which the event and object gained their name, had a mass of 27 lb (12.4 kg) and was subsequently identified as an H6 monomict breccia meteorite.[66]The video record suggests that the Peekskill meteorite had several companions over a wide area. The companions are unlikely to be recovered in the hilly, wooded terrain in the vicinity of Peekskill.
- 2009 – Bone, Indonesia
- A large fireball was observed in the skies near Bone, Sulawesi, Indonesia on October 8, 2009. This was thought to be caused by an asteroid approximately 10 m (33 ft) in diameter. The fireball contained an estimated energy of 50 kilotons of TNT, or about twice the Nagasaki atomic bomb. No injuries were reported.[67]
- 2009 – Southwestern US
- A large bolide was reported on 18 November 2009 over southeastern California, northern Arizona, Utah, Wyoming, Idaho and Colorado. At 00:07 local time a security camera at the high altitude W. L. Eccles Observatory (9,610 ft (2,930 m) above sea level) recorded a movie of the passage of the object to the north.[68][69] Of particular note in this video is the spherical "ghost" image slightly trailing the main object (this is likely a lens reflection of the intense fireball), and the bright fireball explosion associated with the breakup of a substantial fraction of the object. An object trail can be seen to continue northward after the bright fireball event. The shock from the final breakup triggered seven seismological stations in northern Utah; a timing fit to the seismic data yielded a terminal location of the object at 40.286 N, −113.191 W, altitude 90,000 ft (27 km).[citation needed] This is above the Dugway Proving Grounds, a closed Army testing base.
- 2013 – Chelyabinsk Oblast, Russia
- The superbolide, measuring about 17 to 20 m (56 to 66 ft) across, with an estimated initial mass of 11,000 tonnes, as the relatively small asteroid entered Earth's atmosphere.[70][71] It was the largest known natural object to have entered Earth's atmosphere since the Tunguska event in 1908. Over 1,500 people were injured mostly by glass from shattered windows caused by the air burst approximately 25 to 30 km (80,000 to 100,000 ft) above the environs of Chelyabinsk, Russia on 15 February 2013. An increasingly bright streak was observed during morning daylight with a large contrail lingering behind. At no less than one minute and up to at least three minutes after the object peaked in intensity (depending on distance from trail), a large concussive blast was heard that shattered windows and set-off car alarms, which was followed by a number of smaller explosions.[72]
- 2019 – Midwestern United States
- On November 11, 2019, a meteor was spotted streaking across the skies of the Midwestern United States. In the superbolide meteor was part of the South Taurids meteor shower.[73] It traveled east to west ending its visible flight path somewhere over the US state of South Carolina becoming visible once again as it entered the earth's atmosphere creating a large fireball. The fireball was brighter than the planet Venus in the night sky.[74]
Gallery of meteors
-
Orionid meteor
-
Sporadic bolide over the desert of Central Australia and a Lyrid (top edge)
-
Meteor (center) seen from the International Space Station
-
Possible meteor (center) photographed from Mars, March 7, 2004, byMER Spirit
-
Comet Shoemaker–Levy 9 colliding with Jupiter: The sequence shows fragment W turning into a fireball on the planet's dark side
Meteorites
A meteorite is a portion of a meteoroid or asteroid that survives its passage through the atmosphere and hits the ground without being destroyed.[75] Meteorites are sometimes, but not always, found in association with hypervelocity impact craters; during energetic collisions, the entire impactor may be vaporized, leaving no meteorites. Geologists use the term, "bolide", in a different sense from astronomers to indicate a very large impactor. For example, the USGS uses the term to mean a generic large crater-forming projectile in a manner "to imply that we do not know the precise nature of the impacting body ... whether it is a rocky or metallic asteroid, or an icy comet for example".[76]
Meteoroids also hit other bodies in the Solar System. On such stony bodies as the Moon or Mars that have little or no atmosphere, they leave enduring craters.
Impact craters
Meteoroid collisions with solid Solar System objects, including the Moon, Mercury, Callisto, Ganymede, and most small moons and asteroids, create impact craters, which are the dominant geographic features of many of those objects. On other planets and moons with active surface geological processes, such as Earth, Venus, Mars, Europa, Io, and Titan, visible impact craters may become eroded, buried, or transformed by tectonics over time. In early literature, before the significance of impact cratering was widely recognised, the terms cryptoexplosion or cryptovolcanic structure were often used to describe what are now recognised as impact-related features on Earth.[77] Molten terrestrial material ejected from a meteorite impact crater can cool and solidify into an object known as a tektite. These are often mistaken for meteorites.
Gallery of meteorites
-
Twometeorite impact
-
A partial slice of the Esquel pallasite
-
Willamette Meteorite, from Oregon, US
-
Meteorite, which fell in Wisconsin in 1868
-
Children posing behind the Tucson Meteorite at the Arizona Museum of Natural History
See also
Relating to meteoroids
- Interplanetary dust
- Micrometeoroid
- Near-Earth object
Relating to meteors
- American Meteor Society
- Bolide
- Desert Fireball Network
- Green fireballs
- Hydrometeor
- International Meteor Organization
- Leonids
- List of meteor showers
- Lyrids
- Meteor air burst
- North American Meteor Network
- Orionids
- Perseids
- Tollmann's hypothetical bolide
Relating to meteorites
- Baetylus – Sacred stones possibly originating as meteorites
- Impact crater
- Impact event
- Interplanetary dust cloud § Collecting interplanetary dust on Earth
- Meteorite
- Micrometeorite
- Tektite
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External links
- A History of Meteors and Other Atmospheric Phenomena
- American Meteor Society
- British Astronomical Society meteor page
- International Meteor Organization
- Live Meteor Scanner
- Meteoroids Page at NASA's Solar System Exploration
- Meteor shower predictions Archived 2011-07-03 at the Wayback Machine
- Meteor Showers and Viewing Tips
- Society for Popular Astronomy – Meteor Section
- Minor Planet Center: Asteroid Hazards, Part 2: The Challenge of Detection on YouTube(min. 7:14)
- Earth Impact Effects Program Estimates crater size and other effects of a specified body colliding with Earth.