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So is it possible that the asteroid belt was once two large bodies that collided?
p.younger said:So is it possible that the asteroid belt was once two large bodies that collided?
Asteroid named
after ‘Hitchhiker’ humorist
Late British sci-fi author
honored after cosmic campaign
Douglas Adams, was the author of "The Hitchhiker's Guide to the Galaxy," a cult science-fiction comedy. He died suddenly after a heart attack in 2001 at the age of 49.
By Alan Boyle
Science editor
MSNBC
Updated: 8:55 p.m. ET Jan. 25, 2005
The week he died, science-fiction humorist Douglas Adams was honored with an asteroid named after one of the characters from his classic "Hitchhiker's Guide to the Galaxy." Now, almost four years later, Adams has his own name in the heavens as well — thanks to a campaign in which MSNBC.com played a part.
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Asteroid Douglasadams was among the 71 newly named celestial objects announced Tuesday by the International Astronomical Union's Minor Planet Center in Cambridge, Mass. Other honorees range from Ball Aerospace and the city of Las Vegas to the sometimes-overlooked co-discoverer of the DNA double helix, Rosalind Franklin.
But Adams' asteroid should hold special appeal for fans of science fiction and pop culture: His "Hitchhiker" saga, which traces the adventures of a motley interplanetary crew after Earth is destroyed to make way for a hyperspace bypass, started out as a BBC radio comedy. Eventually, the tale inspired a five-novel "trilogy" as well as a TV series, and a long-simmering movie version is due for release in May.
Asteroid tributes
When Adams died of a heart attack in 2001, at the age of 49, tributes came in from around the world — but one of the biggest tributes was actually announced just days before his death: the naming of an asteroid after Arthur Dent, the Earthling at the center of the "Hitchhiker" story.
Through the years, about 12,000 asteroids have been given proper names by the IAU's Committee on Small Body Nomenclature — including fictional characters as well as mythological names (Ceres and Quaoar) and real-life personages (Lincoln and Elvis). The names are traditionally proposed by a particular asteroid's discoverer. For example, the "Arthurdent" asteroid was so named at the suggestion of the man who actually found it, German astronomer Felix Hormuth.
But there's a backlog of not-yet-named asteroids, and so the discoverers occasionally take requests. That's where MSNBC.com enters into the story of Asteroid Douglasadams.
What's in a name?
In August 2003, we reported on the naming of seven asteroids after Columbia's fallen astronauts, and solicited readers' suggestions for future asteroid names. One reader, Sean Ferris, put Adams' name forward — and we took it a step further by seeing if there was an asteroid particularly fitting for the honor.
One prospect stood out: an asteroid given the provisional designation 2001 DA42, discovered by the Lincoln Near Earth Asteroid Research project, or LINEAR. It's a relatively unremarkable space rock, orbiting 224 million miles (358 million kilometers) from the sun in the main asteroid belt, between Mars and Jupiter. But its name held triple significance.
Not only did it memorialize the year of Adams' death (2001) and his initials (DA), but it also referenced the number 42 — which is absurdly meaningful in the "Hitchhiker" saga as the "answer to the Ultimate Question." (The problem was, no one ever knew precisely what the Ultimate Question was.)
We proposed the name to Brian Marsden, the Minor Planet Center's director and the secretary for the naming committee — and Marsden was tickled by the idea. "This was sort of made for him, wasn't it?" he recalled Tuesday.
Long process
It took almost a year and a half for the proposal to make its way through the relevant committees at LINEAR and the IAU — but Marsden finally issued the citations for Douglasadams and the 70 other named asteroids on Tuesday in Minor Planet Circular 53469.
Looking back, Marsden said the asteroid-naming process isn't always as fun as you might think. "It ought to be," he said. "But at times it can be very frustrating."
Some names had to be rejected this time around because they took the form of unpronounceable acronyms, running afoul of the IAU's rules. Another rule is that asteroids shouldn't be named after controversial historical figures such as Stalin or Hitler. That sparked a debate over a proposal to name an asteroid (1998 OU7) after the Prussian military strategist Carl von Clausewitz, Marsden said.
In the end, Asteroid Clausewitz was victorious. "It was decided he wasn't in the same class as Hitler," Marsden said.
Among the other notables on Tuesday's list:
* Rosfranklin (1997 PE6): Chemist Rosalind Franklin's work was instrumental in identifying the molecular structure of DNA, but she died without receiving due credit for her contribution.
* Ballaero (1925 BA): Recognizes Ball Aerospace and Technology Corp., which has contributed to the development of the Hubble and Spitzer space telescopes, the Deep Impact probe and other spacecraft.
* NEAT (2001 SS272): Named after the Near Earth Asteroid Tracking program. Other asteroids honor the Rome Planetarium in Italy and Kharkiv National University in Kiev.
* Wollstonecraft (2004 DA): Honors 18th-century feminist Mary Wollstonecraft. Other asteroids recognize theologians Roger Bacon and Thomas Woolston, and the recently appointed U.S. poet laureate, Ted Kooser.
* Las Vegas (2001 LV6): A celestial tribute to the Nevada city in honor of its centennial this year. Among other places newly honored by asteroid names are Sewanee in Tennessee, Bora-Bora and the Lithuanian city of Kaunas.
Asteroids Caused The Early Inner Solar System Cataclysm
Image of the lunar highlands. The new study by Strom, Malhotra, Kring and their Japanese colleagues indicates this terrain was bombarded mostly by asteroids - not comets - that were flung into the inner solar system when the asteroid belt was destabilized by migrating giant planets. The Earth was similarly bombarded but geological activity has erased most evidence of that bombardment. Credit: NASA.
Tucson (SPX) Sep 16, 2005
University of Arizona and Japanese scientists are convinced that evidence at last settles decades-long arguments about what objects bombarded the early inner solar system in a cataclysm 3.9 billion years ago.
Ancient main belt asteroids identical in size to present-day asteroids in the Mars-Jupiter belt - not comets - hammered the inner rocky planets in a unique catastrophe that lasted for a blink of geologic time, anywhere from 20 million to 150 million years, they report in the Sept. 16 issue of Science.
However, the objects that have been battering our inner solar system after the so-called Late Heavy Bombardment ended are a distinctly different population, UA Professor Emeritus Robert Strom and colleagues report in the article, "The Origin of Planetary Impactors in the Inner Solar System."
After the Late Heavy Bombardment or Lunar Cataclysm period ended, mostly near-Earth asteroids (NEAs) have peppered the terrestrial region.
Strom has been studying the size and distribution of craters across solar system surfaces for the past 35 years. He has long suspected that two different projectile populations have been responsible for cratering inner solar system surfaces. But there's been too little data to prove it.
Until now.
Now asteroid surveys conducted by UA's Spacewatch, the Sloan Digital Sky Survey, Japan's Subaru telescope and the like have amassed fairly complete data on asteroids down to those with diameters of less than a kilometer. Suddenly it has become possible to compare the sizes of asteroids with the sizes of projectiles that blasted craters into surfaces from Mars inward to Mercury.
"When we derived the projectile sizes from the cratering record using scaling laws, the ancient and more recent projectile sizes matched the ancient and younger asteroid populations smack on," Strom said. "It's an astonishing fit."
"One thing this says is that the present-day size-distribution of asteroids in the asteroid belt was established at least as far back as 4 billion years ago," UA planetary scientist Renu Malhotra, a co-author of the Science paper, said.
"Another thing it says is that the mechanism that caused the Late Heavy Bombardment was a gravitational event that swept objects out of the asteroid belt regardless of size."
Malhotra discovered in previous research what this mechanism must have been. Near the end of their formation, Jupiter and the other outer gas giant planets swept up planetary debris farther out in the solar system, the Kuiper Belt region.
In clearing up dust and pieces leftover from outer solar system planet formation, Jupiter, especially, lost orbital energy and moved inward closer to the sun. That migration greatly enhanced Jupiter's gravitational influence on the asteroid belt, flinging asteroids irrespective of size toward the inner solar system.
Evidence that main belt asteroids pummeled the early inner solar system confirms a previously published cosmochemical analysis by UA planetary scientist David A. Kring and colleagues.
"The size distribution of impact craters in the ancient highlands of the moon and Mars is a completely independent test of the inner solar system cataclysm and confirms our cosmochemical evidence of an asteroid source," Kring, a co-author of the Science paper, said.
Kring was part of a team that earlier used an argon-argon dating technique in analyzing impact melt ages of lunar meteorites - rocks ejected at random from the moon's surface and that landed on Earth after a million or so years in space.
They found from the ages of the "clasts," or melted rock fragments, in the breccia meteorites that all of the moon was bombarded 3.9 billion years ago, a true global lunar cataclysm. The Apollo lunar sample analysis said that asteroids account for at least 80 percent of lunar impacts.
Comets have played a relatively minor role in inner solar system impacts, Strom, Malhotra and Kring also conclude from their work. Contrary to popular belief, probably no more than 10 percent of Earth's water has come from comets, Strom said.
After the Late Heavy Bombardment, terrestrial surfaces were so completely altered that no surface older than 3.9 billion years can be dated using the cratering record. Older rocks and minerals are found on the moon and Earth, but they are fragments of older surfaces that were broken up by impacts, the researchers said.
Strom said that if Earth had oceans between 4.4 billion and 4 billion years ago, as other geological evidence suggests, those oceans must have been vaporized by the asteroid impacts during the cataclysm.
Kring also has developed a hypothesis that suggests that the impact events during Late Heavy Bombardment generated vast subsurface hydrothermal systems that were critical to the early development of life. He estimated that the inner solar system cataclysm produced more than 20,000 craters between 10 kilometers to 1,000 kilometers in diameter on Earth.
Inner solar system cratering dynamics changed dramatically after the Late Heavy Bombardment. From then on, the impact cratering record reflects that most objects hitting inner solar system surfaces have been near-Earth asteroids, smaller asteroids from the main belt that are nudged into terrestrial-crossing orbits by a size-selective phenomenon called the Yarkovsky Effect.
The effect has to do with the way asteroids unevenly absorb and re-radiate the sun's energy. Over tens of millions of years, the effect is large enough to push asteroids smaller than 20 kilometers across into the jovian resonances, or gaps, that deliver them to terrestrial-crossing orbits.
The smaller the asteroid, the more it is influenced by the Yarkovsky Effect.
Planetary geologists have tried counting craters and their size distribution to get absolute ages for surfaces on the planets and moons.
"But until we knew the origin of the projectiles, there has been so much uncertainty that I thought it could lead to enormous error," Strom said. "And now I know I'm right. For example, people have based the geologic history of Mars on the heavy bombardment cratering record, and it's wrong because they're using only one cratering curve, not two."
Attempts to date outer solar system bodies using the inner solar system cratering record is completely wrong, Strom said. But it should be possible to more accurately date inner solar system surfaces once researchers determine the cratering rate from the near-Earth asteroid bombardment, he added.
The authors of the Science paper are Strom, Malhotra and Kring from the University of Arizona Lunar and Planetary Laboratory, and Takashi Ito and Fumi Yoshida of National Astronomical Observatory, Tokyo, Japan.
http://www.spacedaily.com/news/asteroid-05q.html
Close-up views of asteroid Itokawa taken by Japan's Hayabusa spacecraft at the end of 2005 continue to puzzle scientists. They debated nearly every aspect of the asteroid – including its formation, age and composition – during the first major release of mission data on Friday.
Hayabusa was designed to bring the first asteroid samples back to Earth by firing pellets into the space rock and scooping up the resulting debris. But it probably failed to fire any pellets during two landings on Itokawa in November 2005, making it unlikely to have captured much – if any – rocky debris.
However, the spacecraft took high-resolution images, spectra and density measurements of the 550-metre-long space rock, and mission scientists presented the observations at the Lunar and Planetary Science Conference in Houston, Texas, US.
"We'd learn a lot more if we got samples back," says Jay Melosh, a planetary scientist at the University of Arizona in Tucson, US, who was not involved with the mission. "But it's given us a glimpse of a kind of object we've never seen before."
Shaken up
Most asteroids appear to be covered largely by fine regolith – the rock dust created by the impact of small meteorites. But Itokawa contains only small amounts – its finest-grain material appears to be gravel-sized particles. "This suggests there is some process removing fine dust or burying it under the surface," Melosh told New Scientist.
Furthermore, the gravel-like regolith is not distributed evenly but is concentrated in flat expanses that cover about one-fifth of Itokawa's surface. The rest of the surface is "rough" terrain littered with metre-sized boulders, which suggests that some process is moving the gravel into the flat zones.
One possible mechanism could be impacts by other space rocks. Melosh and his colleagues have previously shown that impacts on small asteroids could cause them to shake for several hours, moving regolith around their surfaces.
Age range
This shaking might also explain another of Itokawa's mysteries, says Hayabusa team member Naru Hirata of Kobe University in Japan, by covering up craters. Researchers see far fewer craters than they expect – just 60 candidates larger than a few metres across. Alternatively, he says, small craters may never form in the first place – a small meteoroid hitting Itokawa may simply crush one of the many boulders on its surface and not produce a crater.
Such effects imply Itokawa has been pummelled by more space rocks than its youthful appearance suggests. Assuming that this is the case, Chikatoshi Honda of the Japan Aerospace Exploration Agency (JAXA) in Kanagawa, Japan, estimates it is between 10 million and 100 million years old.
But other team members argue that the dearth of craters should be taken at face value – and that Itokawa is genuinely young. Itokawa is thought to have formed just outside the orbit of Mars in the main asteroid belt between Mars and Jupiter. Then, close encounters with Mars probably pulled it closer to the Sun into its current orbit, which crosses that of the Earth, says team member Makoto Yoshikawa of JAXA.
Rubble fusion
But its current orbit is very sensitive to the gravity of objects around it, making long-term estimates of its past or future motion difficult. Given this uncertainty, Itokawa "could have formed only one or two million years ago", says team member Andy Cheng of Johns Hopkins University in Maryland, US.
He says the asteroid may have quickly left the asteroid belt, where it would have had the highest chance of being struck by other space rocks, and spent most of its lifetime within the orbit of Mars.
Researchers are also divided over how Itokawa formed. Estimates of its density reveal it is 39% empty space. That suggests it coalesced from the debris of an ancient asteroid impact. But whether it formed as a single rubble pile or as two that later collided and stuck together remains unclear.
Hayabusa team members favour the latter scenario, pointing out that its shape resembles a sea otter, with a small head curving towards a larger body. They say these two components were once separate and at some point fused together at the "neck".
Hot and cold
But Melosh says typical collisions in the asteroid belt occur at speeds of 2 kilometres per second – too fast for objects to attach to one another. If Itokawa is a so-called "contact binary", he says, the collision would have to have been "a very special event at very, very low velocity". Instead, he says Itokawa may have been stretched into an elongated shape by an external gravity field as it passed by a massive object, such as the Earth.
The rock's composition is also unclear. Spectral observations of minerals taken from Hayabusa suggest the rock was not altered by heat in its past. But those from ground-based telescopes in Hawaii suggest it partially melted after being heated to more than 1000°C.
Pinning this history down may reveal when and where in the solar system its component rocks formed. And that would inform how to interpret the histories of meteorites that fall to Earth.
Ion engines
But the issue can only be settled definitively by studying samples returned from the asteroid, says Melosh. Mission members hope the spacecraft accidentally collected some dust from the asteroid during its two landings and are hoping to send the probe back towards Earth in early 2007.
But it is far from certain that the spacecraft can make the journey. In December, the spacecraft spun out of control after a fuel leak and was out of contact with mission managers for more than a month, with its antenna pointing in the wrong direction. During this time, its circuits may have been damaged by the cold of space, mission manager Jun'ichiro Kawaguchi told New Scientist.
Now, mission managers are turning on all of the 200 or so heaters on the spacecraft and will test the first of the spacecraft's three ion engines in about a month, with the other two engines turned on successively over the next six months. The ion engines will be used to propel the craft back to Earth, so it is crucial that they function, says Kawaguchi. "As of today, we have not been able to confirm if the ion engines operate," he says.
http://www.newscientistspace.com/articl ... kawa-.html
Two asteroids making a close approach
Within the space of less than an hour on September 5, the Mount Lemmon
Survey discovered two objects which will both pass by the Earth on September
8 at a distance closer than the Moon! This unprecedented coincidence
provides an exciting observing challenge for amateurs although those
observing from the UK will not have the best views.
The intrinsically smaller object, 2010 RF12, will be the more favourable
observing target in that it passes closest at about 0.21 lunar-distance,
i.e. about 80,000 km. Tonight from the UK (Sep 6/7) this object will be
17th magnitude but by tomorrow (Sep 7/8 ) it will be brightening rapidly from
16th to 15th magnitude and be accelerating from an apparent speed of about
30 "/min to 50 "/min. It passes closest around 2100 UT on the 8th but by
then it will be difficult from any location on the Earth.
The larger object, 2010 RX30, only approaches to within about 0.66
lunar-distances of the Earth but will be more favourably placed for UK
observers and should be able to be followed to within about 6 hours of
closest approach which takes place around 1000 UT on the 8th. It will be
visible all night on Sep 7/8 being 16th magnitude at first but then
brightening to 15th mag. The problem however is its apparent speed in that it will be racing across the sky at between 2-5 ARCSEC/SEC.
Rather garish colours on that web page!Today's Traffic: There are three objects known to be moving within ten lunar distances (LD) of our planet today, September 8th. 2010 RB12 departs from within ten LD today while two intruders are inside the Earth-Moon system.
2010 RF12 is coming its closest to Earth on this passage, reaching 0.21 LD at 2112 UTC.
2010 RX30 is moving from 1.12 to 1.46 LD, coming its closest to the Earth at 0.64 LD at 0950 UTC, and also its closest to the Moon at 0.89 LD at 1952 UTC.
No other objects are known to be coming in for a close approach to Earth until late this month.
There are five objects that recently flew past Earth at less than ten LD and remain of continuing active interest. See their details below.
This report was refreshed at 0206 UTC. New data has been posted today for one object: 2010 RL43 (new to this page).
http://www.hohmanntransfer.com/
But not necessarily good enough to pick up any Black Obelisks!At closest approach during the flyby, the resolution in Rosetta's pictures was about 60m per pixel, more than sufficient to pick out remarkable details on its surface.
Indeed, that was the launchpad for Asimov's career as a top notch SF writter.BlackRiverFalls said:Perhaps it will get Marooned off Vesta :lol:
That was a brilliant story.