The Moon is the only natural satellite of Earth

The Moon is the only natural satellite of Earth:

        orbit:    384,400 km from Earth

        diameter: 3476 km

        mass:     7.35e22 kg

The Moon, of course, has been known since prehistoric times. It is the second brightest object in the sky after the Sun. As the Moon orbits around the Earth once per month, the angle between the Earth, the Moon and the Sun changes; we see this as the cycle of the Moon's phases. The time between successive new moons is 29.5 days (709 hours), slightly different from the Moon's orbital period (measured against the stars) since the Earth moves a significant distance in its orbit around the Sun in that time.

Due to its size and composition, the Moon is sometimes classified as a terrestrial "planet" along with Mercury, Venus, Earth and Mars.

The Moon was first visited by the Soviet spacecraft Luna 2 in 1959. It is the only extraterrestrial body to have been visited by humans. The first landing was on July 20, 1969 (do you remember where you were?); the last was in December 1972. The Moon is also the only body from which samples have been returned to Earth. In the summer of 1994, the Moon was very extensively mapped by the little spacecraft Clementine and again in 1999 by Lunar Prospector.

The gravitational forces between the Earth and the Moon cause some interesting effects. The most obvious is the tides. The Moon's gravitational attraction is stronger on the side of the Earth nearest to the Moon and weaker on the opposite side. Since the Earth, and particularly the oceans, is not perfectly rigid it is stretched out along the line toward the Moon. From our perspective on the Earth's surface we see two small bulges, one in the direction of the Moon and one directly opposite. The effect is much stronger in the ocean water than in the solid crust so the water bulges are higher. And because the Earth rotates much faster than the Moon moves in its orbit, the bulges move around the Earth about once a day giving two high tides per day. (This is a greatly simplified model; actual tides, especially near the coasts, are much more complicated.)

But the Earth is not completely fluid, either. The Earth's rotation carries the Earth's bulges slightly ahead of the point directly beneath the Moon. This means that the force between the Earth and the Moon is not exactly along the line between their centers producing a torque on the Earth and an accelerating force on the Moon. This causes a net transfer of rotational energy from the Earth to the Moon, slowing down the Earth's rotation by about 1.5 milliseconds/century and raising the Moon into a higher orbit by about 3.8 centimetres per year. (The opposite effect happens to satellites with unusual orbits such as Phobos and Triton).

The asymmetric nature of this gravitational interaction is also responsible for the fact that the Moon rotates synchronously, i.e. it is locked in phase with its orbit so that the same side is always facing toward the Earth. Just as the Earth's rotation is now being slowed by the Moon's influence so in the distant past the Moon's rotation was slowed by the action of the Earth, but in that case the effect was much stronger. When the Moon's rotation rate was slowed to match its orbital period (such that the bulge always faced toward the Earth) there was no longer an off-center torque on the Moon and a stable situation was achieved. The same thing has happened to most of the other satellites in the solar system. Eventually, the Earth's rotation will be slowed to match the Moon's period, too, as is the case with Pluto and Charon.

Actually, the Moon appears to wobble a bit (due to its slightly non-circular orbit) so that a few degrees of the far side can be seen from time to time, but the majority of the far side (left) was completely unknown until the Soviet spacecraft Luna 3 photographed it in 1959. (Note: there is no "dark side" of the Moon; all parts of the Moon get sunlight half the time (except for a few deep craters near the poles). Some uses of the term "dark side" in the past may have referred to the far side as "dark" in the sense of "unknown" (eg "darkest Africa") but even that meaning is no longer valid today!)

The Moon has no atmosphere. But evidence from Clementine suggested that there may be water ice in some deep craters near the Moon's south pole which are permanently shaded. This has now been reinforced by data from Lunar Prospector. There is apparently ice at the north pole as well.

The Moon's crust averages 68 km thick and varies from essentially 0 under Mare Crisium to 107 km north of the crater Korolev on the lunar far side. Below the crust is a mantle and probably a small core (roughly 340 km radius and 2% of the Moon's mass). Unlike the Earth, however, the Moon's interior is no longer active. Curiously, the Moon's center of mass is offset from its geometric center by about 2 km in the direction toward the Earth. Also, the crust is thinner on the near side.

There are two primary types of terrain on the Moon: the heavily cratered and very old highlands and the relatively smooth and younger maria. The maria (which comprise about 16% of the Moon's surface) are huge impact craters that were later flooded by molten lava. Most of the surface is covered with regolith, a mixture of fine dust and rocky debris produced by meteor impacts. For some unknown reason, the maria are concentrated on the near side.

Most of the craters on the near side are named for famous figures in the history of science such as Tycho, Copernicus, and Ptolemaeus. Features on the far side have more modern references such as Apollo, Gagarin and Korolev (with a distinctly Russian bias since the first images were obtained by Luna 3). In addition to the familiar features on the near side, the Moon also has the huge craters South Pole-Aitken on the far side which is 2250 km in diameter and 12 km deep making it the the largest impact basin in the solar system and Orientale on the western limb (as seen from Earth; in the center of the image at left) which is a splendid example of a multi-ring crater.

A total of 382 kg of rock samples were returned to the Earth by the Apollo and Luna programs. These provide most of our detailed knowledge of the Moon. They are particularly valuable in that they can be dated. Even today, more than 30 years after the last Moon landing, scientists still study these precious samples.

Most rocks on the surface of the Moon seem to be between 4.6 and 3 billion years old. This is a fortuitous match with the oldest terrestrial rocks which are rarely more than 3 billion years old. Thus the Moon provides evidence about the early history of the Solar System not available on the Earth.

Prior to the study of the Apollo samples, there was no consensus about the origin of the Moon. There were three principal theories: co-accretion which asserted that the Moon and the Earth formed at the same time from the Solar Nebula; fission which asserted that the Moon split off of the Earth; and capture which held that the Moon formed elsewhere and was subsequently captured by the Earth. None of these work very well. But the new and detailed information from the Moon rocks led to the impacttheory: that the Earth collided with a very large object (as big as Mars or more) and that the Moon formed from the ejected material. There are still details to be worked out, but the impact theory is now widely accepted.

The Moon has no global magnetic field. But some of its surface rocks exhibit remanent magnetism indicating that there may have been a global magnetic field early in the Moon's history.

With no atmosphere and no magnetic field, the Moon's surface is exposed directly to the solar wind. Over its 4 billion year lifetime many ions from the solar wind have become embedded in the Moon's regolith. Thus samples of regolith returned by the Apollo missions proved valuable in studies of the solar wind.

More about the Moon

more pictures of the moon

Moon calendar showing past & future moon phases

from NSSDC

a Teacher's Guide to the Moon (concentrating on lunar geology)

a Socratic Dialog about the Moon's motion

Lunar rocks and regolith

Io and Luna, a comparison from LANL

Life Under the Moon, from Phil Plait's excellent Bitsize Astronomy site

Why the Moon looks bigger near the horizon

The Lunar size illusion, why the Moon looks bigger near the horizon

a longer explanation of the tides and their causes and effects

leap seconds and the slowing of the Earth's rotation

historical info about observations of the Moon

Lunar Meteorites

Moon Phases explained

The impact theory of lunar formation

The Origin of the Moon, with nice paintings by Dr. William K. Hartmann

The Origin of the Earth and Moon, written by G. Jeffrey Taylor, Hawaii Institute of Geophysics and Planetology

Big Bang, New Moon (from Southwest Research Institute)

New theory links moon's current orbit to its formation via a giant impact (from Southwest Research Institute)

lunar exploration

Exploring the Moon from LPI, nice images from Lunar Orbiter and others plus lots of explanatory text

Apollo info and images html

Apollo Missions

Scientific Discoveries Made During Apollo

Clementine - DSPSE (including some nice images)

Lunar Prospector

SMART-1, the first European lunar mission

The Artemis Project, a private venture to establish a permanent, self-supporting community on the Moon!

LunarSat

Yes, we really did go to the Moon, debunking the Moon Hoax theories

Fraud - Books Moon Hoax

another article on lunar ice

Lunar Nomenclature Table

(Earth and) Moon Viewer

Transient Lunar Phenomena

Inconstant Moon by John Walker, info about the Moon's changing appearance

Inconstant Moon by Kevin Clarke, for amateur astronomers

Lunar Info for the Amateur Astronomer

Names of the Full Moons

The Triple Triumph of the Moon by Isaac Asimov

The Face of the Moon, an exhibit of rare books and maps from the Linda Hall Library

The Moon in landscape photography by Joe Decker

fiction

The Moon in Science Fiction, a huge bibliography

From the Earth to the Moon, fiction by Jules Verne

Chinese Moon Legends

Eugene M. Shoemaker: Obituaries

Open Issues

Why are the maria concentrated on the near side?

Why is the Moon's center of mass off center? Because of the tidal lock with the Earth?

Now that we've found water on the Moon, what are we going do to with it?

Only twelve men have ever walked on the surface of the Moon. Who will be the 13th? Who will be the first woman?

When Is the Next Doomsday (Not) Going to Happen?

Take a deep breath; Dec 21, 2012 is behind us. The Mayan calendar end-of-world debacle is over: zip, zilch, gone!

The silliness, anxiety, and paranoia leading up to the predicted end of times was so bad that on Dec. 21st — the appointed doomsday — a worried citizen left a message on my office phone that accused me of skipping town to escape Armageddon.

SLIDE SHOW: Top 5 Plans to Ensure the Continuity of our Species

If history is any example, the next cosmic doomsday prediction is always right around the corner. The Mayan blowout was just the latest in many centuries of bad calls by prognosticators who have the audacity to think they can divine the End of Everything.

So, to be a little preemptive, let’s look at just three cosmic events that might start another pop culture panic. Thankfully these aren’t born out of mythology, psychics, and misinterpreted archeoastronomy. They are real events that will inevitably be embellished by the imaginations of modern day soothsayers.

The Comet of the Century

Last September, the International Scientific Optical Network (ISON) near Kislovodsk, Russia, discovered comet C/2012 S1 (ISON). Though its closest approach to Earth is a year away, the celestial visitor is already billed as the “comet of the century.” That’s because it may be a first-time visitor to the solar system that will warm and then erupt with a lot of outgassing from pristine ices.

DNEWS VIDEO: DOOMSDAY ASTEROID

ANALYSIS: New Comet Discovered — Will It Be Spectacular?

On Nov. 28, 2013 the comet will skim above the sun’s surface at a distance slightly greater than the separation of the Earth and moon. Not doubt there will be pseudoscience predictions of the comet wreaking havoc by raising tides on the sun. The exact opposite will be the case. The sun’s tidal pull could tear apart the comet into small pieces, as has been the case for previous sungrazer-class comets.

Comet ISON is due to pass within 37 million miles of Earth in January 2014. I’m expecting to see all types of outrageous claims that the object’s feeble gravity will yank on Earth to trigger volcanoes and earthquakes.

Comet ISON has been compared with the Great Comet of 1680 (in above illustration) which, according to contemporary accounts, caused New Yorkers to be “overcome with terror at a sight in the heavens such as has seldom greeted human eyes.” A day of fasting and humiliation was set-aside in order that “the wrath of God might be assuaged.”

Likewise, soothsayers will quickly note that the comet will be at it brightest one month before Christmas 2013. “This comet, if it lives up to its billing, certainly could point to the glorious soon coming of the Lord Jesus Christ from heaven!” predicts one religious website.

The fact that the comet is anticipated to get as bright as the moon will only fuel religious and mystical speculation about its timing and significance as an omen. Chill out folks, it’s just another 4 billion year-old primeval chunk of ice from the solar system’s deep freeze, the Oort cloud.

Asteroid Apophis

NASA keeps cataloging more Earth-threatening asteroids every year. But the asteroid Apophis, named after the Egyptian spirit of evil and destruction, is legendary because it will be a record-breaker.

On April, Friday the 13th of 2029 Apophis will skim below the orbits of communication satellites and briefly be a naked-eye object scooting over the mid-Atlantic ocean.

SLIDE SHOW: Top 10 Ways to Stop an Asteroid

Earth’s gravity will deflect the comet’s trajectory. The worst-case scenario is that the chances of it striking Earth on its return on April 13, 2036 will increase to 1 in 5,500.

Apophis is the length of over three football fields. It packs enough kinetic energy to wipe out 10 million people with the power of 100,000 Hiroshima sized atomic bombs. Even in this worst case scenario a direct hit would not obliterate all life on the planet. But it certainly would not be a good day for the human race.

People will get very squeamish over the possibility of Apophisgeddon despite the best low-probability collision estimate from astronomers. Parallels no doubt will be drawn to Biblical prophecy. This is especially true because the potentially destructive path of the asteroid crosses Middle East. South America and the west coast of Africa are also along the ground track.

Congress might even debate if steps should be taken to deflect the asteroid. But given that so many legislators are tone-deaf to global warming, I wouldn’t expect any preemptive actions to be funded.

Planetary Grand Alignment

Like clockwork so-called planetary grand alignments have taken place in 1962, 1982, and 2000. This does not mean that the planets line up like pearls on a string. But they sort of gang up on one side of the sun within an angle of roughly 10 to 30 degrees — so the definition is a but mushy.

The uneventful year 1128 A.D. saw one of the tightest planetary alignments.

The doomsday best seller The Jupiter Effect in 1982 spelled out an improbable chain of events that would be triggered by the planets’ tug-of-war with the sun: tides raised on the sun’s surface would increase sunspot activity, build up the solar wind, that would effect Earth’s weather, and subsequently, Earth’s spin rate, which would then trigger earthquakes.

ANALYSIS: NoDoomsday! The Quick Reference Guide

No geological disasters happened in 1982 short of a 6.0 magnitude earthquake that killed 1,500 people in Dhamar, northern Yemen. In fact the celestial alignment allowed for NASA to pull off the Voyager 2 “grand tour” of the four outer gas giant planets from 1979 to 1989.

Jupiter contains more mass than all the other planets combined, and yet it is still less than 1 percent of the sun’s mass. Therefore Jupiter’s influence on the sun is inconsequential.

Alien astronomers could measure Jupiter’s gravitational tug as an insignificant 270 mile-per-hour cyclic change in the sun’s radial velocity over the planet’s 12-year orbital period. Only if Jupiter was moved so close to the sun that its orbital period was measured in days, would some serious tidal effects be seen. This is observed with so-called “hot Jupiters,” the exoplanet WASP-18 being the most extreme case.

Running an ephemeris forward in time, with the ease of throttling H.G. Wells’ time machine, the next closest thing to a grand alignment comes in 2163 (shown above). Unless we have bombed ourselves back to pre-Columbian society by then, people in 2163 will be too science savvy to give this any thought. They will be bemused by historical accounts of the feared Jupiter Effect by their science-illiterate ancestors.

What’s ironic is that any casual surfing of the Internet shows that a lot of people are preoccupied with doom and gloom based on mythology, psychics, and patently flaky ideas. The real Earth-threats, such as global warming, seem to be too easily shrugged off as lacking solid scientific evidence. Go figure.

Why Nothing Happened on December 21 2012 ?

Mayan End Age 12-21-2012 heralds a New Age of spiritual enlightenment.

Mayan Calender"Both the Hopis and Mayans recognize that we are approaching the end of a World Age... In both cases, however, the Hopi and Mayan elders do not prophesy that everything will come to an end. Rather, this is a time of transition from one World Age into another. The message they give concerns our making a choice of how we enter the future ahead. Our moving through with either resistance or acceptance will determine whether the transition will happen with cataclysmic changes or gradual peace and tranquility. The same theme can be found reflected in the prophecies of many other Native American visionaries from Black Elk to Sun Bear."— Joseph Robert Jochmans

"An Apocalypse (Greek: 'lifting of the veil' or 'revelation') is a disclosure of something hidden from the majority of mankind in an era dominated by falsehood and misconception, i.e. the veil to be lifted."— Wikipedia
"The 2012 phenomenon was a range of eschatological beliefs that cataclysmic or transformative events would occur around 21 December 2012.[1][2][3][4][5][6] This date was regarded as the end-date of a 5,126-year-long cycle in the Mesoamerican Long Count calendar,[7] and as such, Mayan festivities to commemorate the date took place on 21 December 2012 in the countries that were part of the Mayan empire (Mexico, Guatemala, Honduras, and El Salvador), with main events at Chichén Itzá in Mexico, and Tikal in Guatemala.[8][9][10]

Various astronomical alignments and numerological formulae were proposed as pertaining to this date, all unequivocally rejected by mainstream scholarship. A New Age interpretation held that the date marked the start of a period during which Earth and its inhabitants would undergo a positive physical or spiritual transformation, and that 21 December 2012 would mark the beginning of a new era.[11]"

Wikipedia (Web. February 27, 2013)
1. Robert K. Sitler (February 2006)."The 2012 Phenomenon: New Age Appropriation of an Ancient Mayan Calendar". Novo Religio: the Journal of Alternative and Emergent Religions (Berkeley: University of California Press)
2. Sacha Defesche (2007)."'The 2012 Phenomenon': A historical and typological approach to a modern apocalyptic mythology". skepsis. Retrieved 29 April 2011.
3. G. Jeffrey MacDonald (27 March 2007)."Does Maya calendar predict 2012 apocalypse?". USA Today. Retrieved 14 October 2009.
4. Hoopes 2011a
5. Hoopes 2011c
6. Hoopes 2011d
7. "2012 Maya Calendar Mystery and Math, Surviving Yucatan". Yucalandia.com. Retrieved 25 December 2012.
8. "Miles llegan a Chichén Itzá con la esperanza de una nueva era mejor [Thousands arrive to Chichén Itzá with the hope of a new better era]"(in Spanish). La Nación (Costa Rica). Agence France-Presse. 21 December 2012. Retrieved 22 December 2012.
9. Randal C. Archibold (21 December 2012)."As Doomsday Flops, Rites in Ruins of Mayan Empire". The New York Times. Retrieved 22 December 2012.
10. Mark Stephenson (2012)."End Of The World 2012? Not Just Yet". Huffington Post. Retrieved 22 December 2012.
11. Benjamin Anastas (1 July 2007)."The Final Days"(reproduced online, at KSU). The New York Times Magazine (New York: The New York Times Company): Section 6, p. 48. Retrieved 18 May 2009.

"All was predicted by the mathematical cycles of the Mayan calendars. It will change, everything will change. Mayan Day-keepers view the Dec. 21, 2012 date as a rebirth, the start of the World of the Fifth Sun. It will be the start of a new era resulting from and signified by the solar meridian crossing the galactic equator and the Earth aligning itself with the center of the galaxy.

At sunrise on December 21, 2012 for the first time in 26,000 years the Sun rises to conjunct the intersection of the Milky Way and the plane of the ecliptic. This cosmic cross is considered to be an embodiment of the Sacred Tree, The Tree of Life, a tree remembered in all the world's spiritual traditions."

2036 asteroid collision ‘effectively ruled out’

Asteroid Apophis

Asteroid Apophis was discovered on 19 June 2004. Credit: UH/IA

SYDNEY: The possibility that a 325-metre-wide asteroid will impact Earth in 2036 has been “effectively ruled out” based on new data leading up to yesterday’s flyby, NASA scientists announced.

When the asteroid, named Apophis after a demon from Egyptian mythology, was discovered in 2004, scientists estimated a 2.7% chance of impact in 2029 – the highest ever seen for an asteroid.

While the 2029 impact was soon ruled out, a small chance (one in 250,000) remained for a collision with Apophis in 2036 – until yesterday.

Impact odds less than one in a million

“The impact odds as they stand now are less than one in a million, which makes us comfortable saying we can effectively rule out an Earth impact in 2036,” said Don Yeomans, manager of NASA’s Near-Earth Object Program Office, in a STATEMENT. 

“Our interest in asteroid Apophis will essentially be for its scientific interest for the foreseeable future,” he said.

The scientists used updated information obtained by NASA telescopes in 2011 and 2012, as well as new data from the time leading up to Apophis’ distant Earth flyby THAT DAYS.

Next month’s close shave

When asteroid Apophis does pass Earth again in 2029, it will be the closest flyby of an asteroid of its size, at 31,300 kilometres (19,400 miles) above Earth’s surface.

However much sooner, on February 15 this year, another smaller (45 metre-wide) asteroid, called 2012 DA14, will also pass Earth at less than 30,000 km – closer than the orbit of our geostationary satellites. 2012 DA14 will not be visible to the naked eye.

More information:

Rewritten Content:

2036 asteroid collision ‘efficiently dominated out’

The possibility that a 325-metre-extensive asteroid will impact Earth in 2036 has been “successfully ruled out” based on new records leading up to the day before today’s flyby, NASA scientists announced.

The Doomsday asteroid Apophis that could hit Earth in 2036 as it whizzed past us

Pictured: The 'Doomsday' asteroid Apophis that could hit Earth in 2036 as it whizzed past us (but don't worry it was still nine million miles away)

• 1000 foot wide asteroid will brush past the Earth at a distance of 30,000km
• Scientists claim little chance of it hitting us - but scientists warn of 'tiny but real' likelihood it may in 2036
• Name inspired by two of the asteroid's co-discoverers favorite science fiction villain
• 
  

The European Space Agency's orbiting telescope has captured striking new images of the huge 'Doomsday' asteroid Apophis that could smash into Earth in 2036 - revealing it is larger than previously thought.

Long billed as a potential cause of an Extinction Level Event (ELE) for humanity, today ESA officials announced that its Herschel Space Observatory discovered that the asteroid is 1,066 feet wide, 20 percent larger than the previous estimate of 885 feet.

Whizzing past Earth at the relatively close distance of nine million miles tonight, Apophis is being closely tracked because of a 2004 study that predicted the rock has a 2.7 percent chance of hitting Earth in April 2029, which was later revised to 2036.

Scroll down for video

ESAs Herschel Space Observatory captured asteroid Apophis in its field of view during the approach to Earth on January, 5-6, 2013. This image shows the asteroid in Herschels three PACS wavelengths: 70, 100 and 160 microns

'The 20 percent increase in diameter … translates into a 75 percent increase in our estimates of the asteroid's volume or mass,' study leader Thomas Müller of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, said in a statement.

In addition to the latest findings two free webcasts will stream live views of the asteroid as it passes, filmed from telescopes in Italy and the Canary Islands.

The video streams from Slooh Space Telescope and Virtual Telescope Project will show Apophis as a moving light streaking across the sky - although scientists have said that sadly the large space rock is too small to be seen through home telescopes.

 

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• The eerie 'Phantom of the Opera' neutron star that rotates faster than a helicopter's blades
• The green, green grass of Mars: Is this how the red planet once looked?

'Alone among all these near-Earth asteroids that have passed our way in recent years, Apophis has generated the most concern worldwide because of its extremely close approach in 2029 and [chances of a] potential impact, albeit small, in 2036,' said Slooh president Patrick Paolucci.

Indeed, while scientists have ruled out any possibility of a cataclysmic collision - there remains a very real chance of the asteroid Apophis smashing into Earth in 2036.

'Apophis has been one of those celestial bodies that has captured the public's interest since it was discovered in 2004,' said Steve Chesley at NASA's Jet Propulsion Laboratory in Pasadena, California.

Jan. 8, 2013: At about 36 hours from the minimum distance (9.3 million miles from Earth), potentially hazardous asteroid Apophis was imaged again with the Virtual Telescope

'Updated computational techniques and newly available data indicate the probability of an Earth encounter on April 13, 2036, for Apophis has dropped from one-in-45,000 to about four-in-a million.'

The science of predicting asteroid orbits is based on a physical model of the solar system which includes the gravitational influence of the sun, moon, other planets and the three largest asteroids. 

The potential planet killer named after a science fiction villain

• One year after its discovery, the asteroid was given the idenitfication number of 99942 in 2005.
• This made it eligible to be be named and on July 19th 2005, the asteroid was called 'Apophis'.
• Apophis is the Greek name for the the enemy of the Ancient Egyptian sun god Ra.
• He is the Uncreator, and is characterised as an evil serpent who dwells in eternal darkness and tries to consume Ra during his nightly passage.
• Roy A. Tucker, David J. Tholen, two of the asteroids co-discoverers are also fans of the science fiction television series Stargate SG-1.
• A prominent villain in that show is called Apophis, who in the mythology of that particular series, gave rise to the myth of the Egyptian god.

NASA detects and tracks asteroids and comets passing close to Earth using both ground and space-based telescopes. 

The Near Earth-Object Observations Program, commonly called 'Spaceguard,' discovers these objects, characterizes a subset of them and plots their orbits to determine if any could be potentially hazardous to our planet.

This year Apophis, named after an Egyptian mythological demon, will not get closer than around nine million miles.

Doomsday Asteroid? An artist's rendering of the asteroid Apophis as created by the European Space Agency

Experts say the impact if Apophis struck the Earth would generate a blast equivalent to more than 500 megatons of TNT

Scientists will use the encounter to improve their estimate of just how dangerous the space rock really is to life on Earth.

In 2029, Apophis is expected to come uncomfortably close, brushing past the Earth at a distance of just 30,000 kilometres. That will put the asteroid inside the orbit of communication satellites.

Current models predict a tiny but real likelihood of Apophis colliding with the Earth in 2036.

When the asteroid was discovered in 2004 scientists calculated a one-in-45 chance of an impact in 2029.

Improved predictions later lifted the threat.

The asteroid's latest near approach will occur at midnight UK time tomorrow.

Members of the public can view the event online via the Slooh web-based sky-watching service, which collects images from observatories around the world.

'We are excited to cover this asteroid live for the general public.'

Scientists at the American space agency Nasa have calculated that if Apophis struck the Earth it would generate a blast equivalent to more than 500 megatons of TNT.

In comparison, the most powerful hydrogen bomb ever detonated, the Soviet Tsar Bomba, released 57 megatons.

 VIDEO   The 'Doomsday' huge asteroid Apophis passes by Earth 

The huge asteroid Apophis passes by Earth

Possibility of an Earth Impact in 2029 Ruled Out for Asteroid 2004 MN4

Possibility of an Earth Impact in 2029 Ruled Out for Asteroid 2004 MN4

Don Yeomans, Steve Chesley and Paul Chodas
NASA's Near Earth Object Program Office 
December 27, 2004

Over the past week, several independent efforts were made to search for pre-discovery observations of 2004 MN4. These efforts proved successful today when Jeff Larsen and Anne Descour of the Spacewatch Observatory near Tucson, Arizona, were able to detect and measure very faint images of asteroid 2004 MN4 on archival images dating to 15 March 2004. These observations extended the observed time interval for this asteroid by three months allowing an improvement in its orbit so that an Earth impact on 13 April 2029 can now be ruled out.

As is often the case, the possibility of future Earth impacts for some near-Earth objects cannot be entirely ruled out until the uncertainties associated with their trajectories are reduced as a result of either future position observations, or in this case, heretofore unrecognized, pre-discovery observations. When these additional observations were used to update the orbit of 2004 MN4, the uncertainties associated with this object's future positions in space were reduced to such an extent that none of the object's possible trajectories can impact the Earth (or Moon) in 2029.

In the accompanying diagram, the most likely position of asteroid 2004 MN4 is shown at the end of the blue line near the Earth on 13 April 2029. However, since the asteroid's position in space is not perfectly known at that time, the white dots at right angles to the blue line are possible alternate positions of the asteroid. Neither the nominal position of the asteroid, nor any of its possible alternative positions, touches the Earth, indicating that an Earth impact in 2029 is ruled out.

Updated Set of Possible Positions of 2004 MN4 on April 13, 2029

The passage of the asteroid by the Earth in 2029 alters its subsequent trajectory and expands the asteroid's position uncertainty region (i.e., the line of white dots increases in extent) so the asteroid's subsequent motion is less certain than it was prior to the 2029 close Earth approach. However, our current risk analysis for 2004 MN4 indicates that no subsequent Earth encounters in the 21st century are of any concern.

NASA - NASA Refines Asteroid Apophis' Path Toward Earth

NASA Refines Asteroid Apophis' Path Toward Earth

 

 

PASADENA, Calif. -- Using updated information, NASA scientists have recalculated the path of a large asteroid. The refined path indicates a significantly reduced likelihood of a hazardous encounter with Earth in 2036. 

The Apophis asteroid is approximately the size of two-and-a-half football fields. The new data were documented by near-Earth object scientists Steve Chesley and Paul Chodas at NASA's Jet Propulsion Laboratory in Pasadena, Calif. They will present their updated findings at a meeting of the American Astronomical Society's Division for Planetary Sciences in Puerto Rico on Oct. 8. 

"Apophis has been one of those celestial bodies that has captured the public's interest since it was discovered in 2004," said Chesley. "Updated computational techniques and newly available data indicate the probability of an Earth encounter on April 13, 2036, for Apophis has dropped from one-in-45,000 to about four-in-a million." 

A majority of the data that enabled the updated orbit of Apophis came from observations Dave Tholen and collaborators at the University of Hawaii's Institute for Astronomy in Manoa made. Tholen pored over hundreds of previously unreleased images of the night sky made with the University of Hawaii's 88-inch telescope, located near the summit of Mauna Kea. 

Tholen made improved measurements of the asteroid's position in the images, enabling him to provide Chesley and Chodas with new data sets more precise than previous measures for Apophis. Measurements from the Steward Observatory's 90-inch Bok telescope on Kitt Peak in Arizona and the Arecibo Observatory on the island of Puerto Rico also were used in Chesley's calculations. 

The information provided a more accurate glimpse of Apophis' orbit well into the latter part of this century. Among the findings is another close encounter by the asteroid with Earth in 2068 with chance of impact currently at approximately three-in-a-million. As with earlier orbital estimates where Earth impacts in 2029 and 2036 could not initially be ruled out due to the need for additional data, it is expected that the 2068 encounter will diminish in probability as more information about Apophis is acquired. 

Initially, Apophis was thought to have a 2.7 percent chance of impacting Earth in 2029. Additional observations of the asteriod ruled out any possibility of an impact in 2029. However, the asteroid is expected to make a record-setting -- but harmless -- close approach to Earth on Friday, April 13, 2029, when it comes no closer than 18,300 miles above Earth's surface. 

"The refined orbital determination further reinforces that Apophis is an asteroid we can look to as an opportunity for exciting science and not something that should be feared," said Don Yeomans, manager of the Near-Earth Object Program Office at JPL. "The public can follow along as we continue to study Apophis and other near-Earth objects by visiting us on our AsteroidWatch Web site and by following us on the @AsteroidWatch Twitter feed." 

The science of predicting asteroid orbits is based on a physical model of the solar system which includes the gravitational influence of the sun, moon, other planets and the three largest asteroids. 

NASA detects and tracks asteroids and comets passing close to Earth using both ground and space-based telescopes. The Near Earth-Object Observations Program, commonly called "Spaceguard," discovers these objects, characterizes a subset of them and plots their orbits to determine if any could be potentially hazardous to our planet. 

JPL manages the Near-Earth Object Program Office for NASA's Science Mission Directorate in Washington. Cornell University operates the Arecibo Observatory under a cooperative agreement with the National Science Foundation in Arlington, Va. 

For more information about asteroids and near-Earth objects, visit: 

http://www.jpl.nasa.gov/asteroidwatch

For more information about NASA, visit: 

http://www.nasa.gov

 

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