Interesting Science: 11 February 2007

Saturday, February 17, 2007

Mars Orbiter Sees Effects of Ancient Underground Fluids (+ Related Video)

Astronomy: Liquid or gas flowed through cracks penetrating underground rock on ancient Mars, according to a report [1] based on some of the first observations by NASA's Mars Reconnaissance Orbiter. These fluids may have produced conditions to support possible habitats for microbial life.

These ancient patterns were revealed when the most powerful telescopic camera ever sent to Mars began examining the planet last year [2]. The camera showed features as small as approximately 3 feet (one meter) across. Mineralization took place deep underground, along faults and fractures. These mineral deposits became visible after overlying layers were eroded away throughout millions of years.

Dr. Chris Okubo, a geologist at the University of Arizona, Tucson, discovered the patterns in an image of exposed layers in a Martian canyon named Candor Chasma. The image was taken in September 2006 by the High Resolution Imaging Science Experiment camera aboard the orbiter.

"What caught my eye was the bleaching or lack of dark material along the fracture. That is a sign of mineral alteration by fluids that moved through those joints," said Okubo. "It reminded me of something I had seen during field studies in Utah, that is light-tone zones, or 'haloes,' on either side of cracks through darker sandstone."

Dr. Alfred McEwen, the camera's principal investigator from the University of Arizona, Tucson, said, "This result shows how orbital observations can identify features of particular interest for future exploration on the surface or in the subsurface or by sample return. The alteration along fractures, concentrated by the underground fluids, marks locations where we can expect to find key information about chemical and perhaps biologic processes in a subsurface environment that may have been habitable."

The haloes visible along fractures seen in the Candor Chasma image appear to be slightly raised relative to surrounding, darker rock. This is evidence that the circulating fluids hardened the lining of the fractures, as well as bleaching it. The harder material would not erode away as quickly as softer material farther from the fractures.

The most likely origin for these features is that minerals that were dissolved in water came out of solution and became part of the rock material lining the fractures. Another possibility is that the circulating fluid was a gas, which may or may not have included water vapor in its composition, Okubo said.

Similar haloes adjacent to fractures show up in images that the high-resolution camera took of other places on Mars after the initial Candor Chasma image. "We are excited to be seeing geological features too small to have been noticed previously," Okubo said.

"This publication is just the first of many, many to come. The analysis is based on test observations taken even before the start of our main science phase. Since then, Mars Reconnaissance Orbiter has returned several terabits of science data, sustaining a pace greater than any other deep space mission. This flood of data will require years of study to exploit their full value, forever increasing our understanding of Mars and its history of climate change," said Dr. Richard Zurek, project scientist for Mars Reconnaissance Orbiter at NASA's Jet Propulsion Laboratory, Pasadena, Calif.

Okubo and McEwen report the findings in the February 16 2007 edition of the journal Science.

Source: NASA PR 02.15.07 (2007-017)

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[1] Based on:

Fracture-Controlled Paleo-Fluid Flow in Candor Chasma, Mars
Chris H. Okubo and Alfred S. McEwen

Science 16 February 2007:
Vol. 315. no. 5814, pp. 983 - 985
DOI: 10.1126/science.1136855

Color observations from the High Resolution Imaging Science Experiment on board the Mars Reconnaissance Orbiter reveal zones of localized fluid alteration (cementation and bleaching) along joints within layered deposits in western Candor Chasma, Mars. This fluid alteration occurred within the subsurface in the geologic past and has been exposed at the surface through subsequent erosion. These findings demonstrate that fluid flow along fractures was a mechanism by which subsurface fluids migrated through these layered deposits. Fractured layered deposits are thus promising sites for investigating the geologic history of water on Mars.

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[2] Mars Reconnaissance Orbiter Images (Images and Captions Credit: NASA)

Ridges as Evidence of Fluid Alteration
Tectonic fractures within the Candor Chasma region of Valles Marineris [3], Mars, retain ridge-like shapes as the surrounding bedrock erodes away. This points to past episodes of fluid alteration along the fractures and reveals clues into past fluid flow and geochemical conditions below the surface.

Light-Toned Bedrock Along Cracks as Evidence of Fluid Alteration
This enhanced-color image from the High Resolution Imaging Science Experiment Camera on NASA's Mars Reconnaissance Orbiter shows a landscape of sand dunes and buttes among a background of light-toned (tan-colored) bands and dark-toned (blue-colored) bands in the Candor Chasma region of Mars' Valles Marineris canyon system.

Linear Ridges at 'Victoria Crater'
This enhanced-color view of the eastern rim and floor of "Victoria Crater" in Mars' Meridiani Planum region comes from the High Resolution Imaging Science Experiment camera in NASA's Mars Reconnaissance Orbiter.

Ridges in Stereo, Candor Chasma
A stereo view shows fractures called joints. They have a ridge-like shape, standing out in positive relief as the surrounding bedrock is eroded away faster than they are. This positive relief suggests that the rock along the joints has been strengthened through chemical reactions with fluids flowing through these joints.

Halos Along Fractures Exposed in Meridiani
This image from the High Resolution Imaging Science Experiment camera on NASA's Mars Reconnaissance Orbiter shows evidence for ancient fluid flow along fractures in Mars' Meridiani Planum region.

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[3] Video: High Resolution Pictures Of Valles Marineris
(September 2006?)

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Friday, February 16, 2007

Ancient coin challenges myth of Cleopatra's beauty (+ related video)

Archaeology: Antony and Cleopatra were not the handsome General and his beautiful queen Hollywood would have us believe, according to experts at Newcastle University, who have been studying the depiction of the one of history's most tragic romantic couples found on a Roman coin.

The silver coin of Mark Antony and Cleopatra was discovered in a collection from the Society of Antiquaries of Newcastle upon Tyne, which was being researched as part of the preparations for the Great North Museum, currently under development in Newcastle upon Tyne.

Cleopatra (right) and Antony (below) are shown on either side of the small silver coin (pictured), which is about the size of a modern UK five pence piece. Cleopatra is depicted with a shallow forehead, long, pointed nose, narrow lips and a sharply pointed chin, while Mark Antony has bulging eyes, a large hooked nose and a thick neck.

Clare Pickersgill, Assistant Director of Archaeological Museums at Newcastle University, said: 'The popular image we have of Cleopatra is that of a beautiful queen who was adored by Roman politicians and generals.

'The relationship between Mark Antony and Cleopatra has long been romanticised by writers, artists and film-makers. Shakespeare wrote his tragedy 'Antony and Cleopatra' in 1608, while the Orientalist artists of the nineteenth century and the modern Hollywood depictions, such as that of Elizabeth Taylor and Richard Burton in the 1963 film have added to the idea that Cleopatra was a great beauty. Recent research would seem to disagree with this portrayal, however', said Clare.

Lindsay Allason-Jones, Director of Archaeological Museums at Newcastle University, added: 'The image on the coin is far from being that of Elizabeth Taylor and Richard Burton!

'Roman writers tell us that Cleopatra was intelligent and charismatic, and that she had a seductive voice but, tellingly, they do not mention her beauty. The image of Cleopatra as a beautiful seductress is a more recent image'.

The coin is a silver denarius of Mark Antony and Cleopatra dated to 32 BC, which would have been issued by the mint of Mark Antony. On one side is the head of Mark Antony, bearing the caption Antoni Armenia devicta meaning 'For Antony, Armenia having been vanquished'.

Cleopatra appears on the reverse of the coin with the inscription Cleopatra Reginae regum filiorumque regum, meaning 'For Cleopatra, Queen of kings and of the children of kings' (or possibly 'Queen of kings and of her children who are kings').

The coin itself is not enormously rare, but due to its depictions, it is very collectable. The collection has been owned by the Society of Antiquaries of Newcastle upon Tyne since the 1920s. Until now, it has been kept in a bank, but the development of the Great North Museum project means that other 'hidden gems' like the Antony and Cleopatra coin, will be able to go on display to the public for the first time when the GNM opens in 2009.

The coin will go on display in Newcastle University's Shefton Museum from Valentines Day, Wednesday 14 February 2007. Opening hours are Monday - Friday 10.00 am - 4.00 pm. Admission free.

Source and Images Credit: University of Newcastle (UK) PR 14 February 2007 (Part 1)

Historial note: Antony and Cleopatra

Cleopatra VII was the last ruler of Egypt before its conquest by the Roman leader Octavian in 30 BC. She was also the last Ptolemaic ruler of Egypt (See "The Ptolemaic Dynasty"). The Ptolemaic rulers, who ruled Egypt from 305 BC until 30 BC. Cleopatra was born in 70/69 BC probably in Alexandria. She became queen at the age of 17, and died when she was 38.

Mark Antony, born in 83 BC, was a Roman general and politician who had been a supporter of Julius Caesar. After the death of Julius Caesar he joined with Octavian and Lepidus to form a body of three governing people in Rome. The second triumvirate, as it is referred to, ended in 33 BC after which civil war followed. Mark Antony was also known for his fondness of wine, women and song.

Mark Antony had been interested in the support of Cleopatra and Egypt for his campaigns in Armenia, Parthia and Mesopotamia. On their meeting Cleopatra put on a show that displayed her wealth and which left Antony in awe. Antony had a relationship with Cleopatra, despite being married to Fulvia and later to Octavia. Cleopatra already had a son, Caesarion, from her relationship with Julius Caesar, but she had three more children with Antony, the twins Alexander and Cleopatra, and a son Ptolemaios.

In 31 BC the battle of Actium, between Antony and Cleopatra and Octavian, took place off the west coast of Greece. Cleopatra fled with her ships back to Egypt and Antony followed. Soon after this defeat, in 30 BC, Antony committed suicide. Shortly afterwards, Cleopatra also committed suicide, apparently by allowing asps to bite her.

Octavian, who later became the first Roman emperor Augustus, then took control of Egypt. Cleopatra's son Caesarion was killed by Octavian's troops, but the three children belonging to her and Antony were raised by Antony's wife Octavia.

After the suicide of Antony and Cleopatra the portrayal of Cleopatra as drunk and decadent and as being responsible for ensnaring Antony were circulated in Rome. Her suicide, on the other hand, was regarded as a noble act, and in Egypt she continued to be viewed as a patriotic ruler. Her suicide, often seen as a result of her love for Antony - but more likely because she did not want to be dragged into Rome as part of the victory parade of Octavian - has contributed to the romantic image we have today.

Source: University of Newcastle (UK) PR 14 February 2007 (Part 2)

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Video - Discovery Channel's "Lost Temple to the Gods":

Info from Discovery Store:

"In 20 B.C., the Egyptian city of Heracleion/Herakleion was a pleasure ground, a veritable Las Vegas of the ancient world. Famed for its handsome beaches, palatial villas and sexually charged rites, the lush city offered a paradise that seemed infinite. But with the arrival of the Romans and the suicide of Cleopatra, the region sank into a long decline, eventually mysteriously disappearing beneath the sea.

...Join French explorer, Franck Goddio, as he makes an astonishing find off the coast of modern-day Alexandria - a series of beautifully preserved statues, columns and walls that could only be the long-lost remnants of the missing city of Heracleion/Herakleion and its crowning jewel, the Temple of Hercules..."

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Thursday, February 15, 2007

Hunting behavior of Large Bioluminescent Squid (Video)

The scientists' newly developed underwater video camera system took the first live images of the deep-sea large squid, Taningia danae, between 240-940 m deep off Ogasawara Islands, western North Pacific in 2005.

The video footage includes attacking and bioluminescence behaviors and reveals that T. danae is far from the sluggish neutrally buoyant squid previously suspected. They emitted short bright light flashes from their large arm-tip photophores before final assault, which might act as a blinding flash for prey as well as a means of measuring target distance in a dark deep-sea environment. They may also use bioluminescence for attempts at communication.

The paper [1], which has been published in the journal Proceedings of the Royal Society B is available for free access on the Proceedings of the Royal Society B (Biological Sciences) website.

Source: The Royal Society PR February 14 2007

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Video clip 4 'Halogen Light Attacking':

The above video is also available at the BBC News UK story "Large squid lights up for attack":

..Deep-sea squid - once thought to be legendary monsters of the sea - are notoriously difficult to study, and little is known about their ecology and biology. Several species prowl the ocean depths..

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[1] Observations of wild hunting behavior and bioluminescence of a large deep-sea, eight-armed squid, Taningia danae by Tsunemi Kubodera, Yasuhiro Koyama and Kyoichi Mori

Proc. R. Soc. B
doi:10.1098/rspb.2006.0236

Abstract

Our newly developed underwater high definition video camera system took the first live images of adults of the mesopelagic large squid, Taningia danae, between 240 and 940 m deep off Ogasawara Islands, western North Pacific. The resulting footage includes attacking and bioluminescence behaviours, and reveals that T. danae is far from the sluggish neutrally buoyant deep-sea squid previously suspected. It can actively swim both forward and backward freely by flapping its large muscular triangular fins and changes direction quickly through bending its flexible body. It can attain speeds of 2 - 2.5 m s-1 (7.2 - 9 km h-1) when attacking bait rigs. They emitted short bright light flashes from their large arm-tip photophores before final assault, which might act as a blinding flash for prey as well as a means of measuring target distance in a dark deep-sea environment. They also emitted long and short glows separated by intervals while wandering around the double torch lights attached to the bait rig, suggestive of potential courtship behaviours during mating.

Excerpt:

As in the largest squid, Architeuthis, T. danae incorporates numerous tiny vacuoles of ammonia solution within its flesh to enable neutral buoyancy (Clarke et al. 1979). This system makes body musculature flabby and soft to touch in captured animals, leading a number of authors to propose that large ammonical squids are likely to be sluggish and relatively inactive (Hanlon and Messenger 1966; Roper and Boss 1982; Norman 2000; Nixon and Young 2003). Recent observations of live giant squid in the wild (Kubodera and Mori 2005) [2] revealed that this species is much more active predator than previously suggested. Our in situ observations also show that T. danae is an aggressive and tenacious predator rather than a sluggish, inactive squid.

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[2] First-ever observations of a live giant squid in the wild
By Kubodera T and Mori K.

Proc Biol Sci. 2005 Dec 22;272(1581):2583-6
doi:10.1098/rspb.2005.3158

Abstract

The giant squid, Architeuthis, is renowned as the largest invertebrate in the world and has featured as an ominous sea monster in novels and movies. Considerable efforts to view this elusive creature in its deep-sea habitat have been singularly unsuccessful. Our digital camera and depth recorder system recently photographed an Architeuthis attacking bait at 900m off Ogasawara Islands in the North Pacific. Here, we show the first wild images of a giant squid in its natural environment. Recovery of a severed tentacle confirmed both identification and scale of the squid (greater than 8m). Architeuthis appears to be a much more active predator than previously suspected, using its elongate feeding tentacles to strike and tangle prey.

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Wednesday, February 14, 2007

Jersusalem: Archaeological remains point to exact location of Second Temple

While scholars have put forth various assessments for the location of the Second Temple in Jerusalem, a Hebrew University of Jerusalem professor says that archaeological remains that have so far been ignored by scholars point to the exact location, which is in a spot that differs from prevailing opinion.

The location identified by Professor Joseph Patrich of the Hebrew University Institute of Archaeology places the Temple and its corresponding courtyards, chambers and gates in a more southeasterly and diagonal frame of reference than have earlier scholars.

In spotting the Temple in this way, Patrich concludes that the rock, over which the Dome of the Rock mosque was built in the 7th century C.E. is outside the confines of the Temple. The rock is considered by Moslems to be the spot from which Muhammad ascended to heaven and for Jews the place at which the binding of Isaac took place.

Patrich basis his proposal on a study of a large underground cistern on the Temple Mount that was mapped by British engineer Sir Charles Wilson (left) in 1866 on behalf of the Palestine Exploration Fund.

The giant cistern, 4.5 meters wide and 54 meters long, lay near the southeastern corner of the upper platform of the Temple Mount. It had a southeasterly orientation with branches extending north and south

Examining the location and configuration of the cistern together with descriptions of the daily rite in the Temple and its surroundings found in the Mishna (the Rabbinic Oral Tradition compiled in the 3rd century C.E.), Patrich has demonstrated that this cistern is the only one found on the Temple Mount that can tie in with the Mishna text describing elements involved in the daily purification and sacrificial duties carried out by the priests on the altar in the Temple courtyard.

On this basis, he says, one can "reconstruct" the placement of the laver (a large basin) that was used by the priests for their ritual washing, with the water being drawn by a waterwheel mechanism from the cistern. After this purification, the priests ascended the nearby ramp to the sacrificial altar. By thus locating the laver, the water wheel, the ramp and the altar, one can then finally map, again in coordination with the Mishna, the alignment of the Temple itself and its gates and chambers.

All of these considerations have led Patrich to come up with a diagram of the Temple and its surroundings that place the Temple further to the east and south than earlier thought and at a southeasterly angle relative to the eastern wall of the Temple Mount, and not perpendicular to it, as earlier assumed. It is this placement which also leaves the rock in the Dome of the Rock outside of the Temple confines (see attached drawings and caption).

Professor Patrich stressed that his research concerning the location of the Temple is strictly academic in nature, and that political connotations should not be attributed to it.

Caption: Drawing shows Professor Patrich's description of the location of the Temple compound (the rectangle defined by a solid line in the center of the drawing). The cistern upon which he basis his research is shown by a dotted line within the rectangle. The Dome of the Rock (octagonal structure) is seen in the lower left hand corner of the Temple compound. Note that given this alignment, the rock in the center of the Dome of the Rock is seen as outside the area of the Temple Compound. Credit: Drawing by Leen Ritmeyer

Source: The Hebrew University of Jerusalem Press Release 08 February, 2007

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Video depicting how King Solomon's Temple may have looked:

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Joseph Patrich is author of "Reconstructing the Magnificent Temple Herod Built" (Bible Review IV/5, pp. 16-29). Excerpt:

..The Babylonians "exiled all of Jerusalem [to Babylon]: all the commanders and all the warriors - ten thousand exiles - as well as all the craftsmen and smiths; only the poorest people in the land were left" (2 Kings 24:14).

Then in 539 B.C., in the first year of the reign of King Cyrus of Persia, an edict was issued by the king:

"All the kingdoms of the earth the Lord God of heaven has given me. And he has commanded me to build Him a house at Jerusalem which is in Judah" (Ezra 1:2).
"King Cyrus also brought out the articles of the house of the Lord, which Nebuchadnezzar had taken from Jerusalem … thirty gold platters, one thousand silver platters, twenty-nine knives, thirty gold basins, four hundred and ten silver basins … and one thousand other articles" (Ezra 1:7, 9, 10).

According to the Bible, there were successive waves of repatriations of Jews under Persian rule. The first was led by Sheshbazzar, the son of King Jehoiachin, who had been taken into captivity in 597 B.C. This first return, marking the beginning of a new era in the history of Israel - the Second Temple period - occurred not long after 539 B.C., when Cyrus issued his decree to start rebuilding the Temple in Jerusalem. Sheshbazzar was entrusted with the Temple vessels (Ezra 1:7, 5:14 - 15) and is reported to have laid the foundation for the rebuilt Temple (Ezra 5:16). The actual work of rebuilding the Temple, however, remained uncompleted.

A major wave of returning exiles was then led by Zerubbabel, grandson of Jehoiachin, and by the priest Joshua/Jehoshua, apparently during the early years of the administration of the Persian king Darius (522 - 486 B.C.). In the second year of Darius's reign, Zerubbabel and Joshua established an altar on the Temple Mount in Jerusalem and began their work of Temple construction.

"The house [Temple] was finished on the third of the month of Adar in the sixth year [516/5 B.C.] of the reign of King Darius. The Israelites, the priests, and the Levites, and all the other exiles celebrated the dedication of the House of God with joy" (Ezra 6:15 - 16)..

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Monday, February 12, 2007

NASA: Near Earth Objects - Interview, Video, Related Info

February 7 2007: A NASA podcast in which Drs. Steve Chesley and Don Yeomans of JPL and NASA's Near Earth Object office are interviewed by Jane Platt - listen to the podcast here.

Other contents:

1) Making Sure the Sky Is Not Falling - Transcript of above podcast
2) Quantifying the risk posed by potential Earth impacts - Abstract
3) NASA Scientists Use Radar to Detect Asteroid Force - Related PR
4) Asteroid 1950 DA - Video and Info

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1) Making Sure the Sky Is Not Falling - Transcript

Narrator: Making sure the sky is NOT falling. I'm Jane Platt with a podcast from JPL - NASA's Jet Propulsion Laboratory in Pasadena, California. Asteroids and comets are pretty cool, cosmic objects - as long as they keep their distance. Dr. Steve Chesley of JPL is with NASA's Near Earth Object office, which uses telescopes and radar to study objects that venture near Earth.

Chesley: Well, we have about 4,300 Near Earth objects in the catalog at the moment. That's all sizes. We're most interested in finding the large objects, what we consider to be those that could, say, threaten the climate of the Earth if they were to impact.

Narrator: Those are bigger than one kilometer, or four times the size of Pasadena's Rose Bowl. Scientists have found more than 700 of those. Most are too far away to pose any danger to Earth. On the other hand, they have identified about 120 objects - of varying sizes - that do have the potential to hit Earth. Still, no need to panic.

Yeomans: No one knows of a friend or a loved one who has been hurt by a Near Earth object, that's true. So these are very low probability events but very high consequence events. It's very unlikely that one of these large objects will hit us.

Narrator: Dr. Don Yeomans heads NASA's Near Earth Object office. His colleague, Dr. Steve Chesley, says an ounce of prevention is worth a pound of cure.

Chesley: NASA's approach to the Earth hazard problem so far, and I think rightly, has been to focus on discovery. You can not deflect an object that you haven't discovered. And so finding the asteroids, finding them early is the most important thing in this process.

Narrator: So the Near Earth Object office, with input from astronomers around the world, detects objects, tracks their location, size, speed and movement over a period of time. They rate them on the 10-point Torino scale. Sort of like the Richter scale for earthquakes.

Chesley: Torino scale zero is where 99 percent of our cases fall, which means it's just not worth any public attention, although we continue to monitor those routinely. Torino scale one means it's more than ordinary, but still not particularly alarming. We get on average a few, maybe several Torino scale one cases per year. We have had a couple of Torino scale twos. We even had one Torino scale four, which was quite extraordinary.

Narrator: Now a four is enough to worry about. But with more detailed observations, the four and the twos were downgraded.

Chesley: After an object is discovered and observations continue to arrive at our office, we continue to update and refine the orbital predictions and the impact assessments. That allows us to refine the Torino scale ratings for the object and so on.

Narrator: And so far, every single worrisome object they've tracked, with further observations, has been ruled out as a hazard to Earth. Interested in keeping tabs on these objects? Check out the Near Earth object website at http://neo.jpl.nasa.gov .

Chesley: We have the impact probabilities, and you can click on any one of the objects and get details. But at the top level, there's a summary for each object. The speed at which it passes the Earth is present there, and that of course is important for the impact energy. The size of the object, and the Torino scale.

Narrator: Again, that's http://neo.jpl.nasa.gov , and it includes a lot of links. Oh, and in case you're wondering what would happen if scientists did find an asteroid that really could threaten Earth? Researchers are scoping out different ways to handle a scenario like that.

Chesley: Probably the best and most obvious way of deflecting an asteroid is to simply slam another, a spacecraft, into it, and to slow it down, or speed it up if you overtake it from behind, and that gives it enough change in velocity to steer it off the Earth impact trajectory.

Narrator: But again, none of the known near-Earth objects have scientists staying up nights worrying. So for now, they say - the sky is not falling. Thanks for joining us for this podcast from NASA's Jet Propulsion Laboratory.

Source: NASA February 7 2007

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2) Quantifying the risk posed by potential Earth impacts - Abstract:

Steven R. Chesley (JPL), Paul W. Chodas (JPL), Andrea Milani (Univ. Pisa), Giovanni B. Valsecchi (IASF-CNR) and Donald K. Yeomans (JPL)
Icarus 159, 423-432 (2002)

Predictions of future potential Earth impacts by Near-Earth Objects (NEOs) have become commonplace in recent years, and the rate of these detections is likely to accelerate as asteroid survey efforts continue to mature. In order to conveniently compare and categorize the numerous potential impact solutions being discovered we propose a new hazard scale that will describe the risk posed by a particular potential impact in both absolute and relative terms. To this end we measure each event in two ways, first without any consideration of the event's time proximity or its significance relative to the so-called background threat, and then in the context of the expected risk from other objects over the intervening years until the impact. This approach is designed principally to facilitate communication among astronomers, and it is not intended for public communication of impact risks. The scale characterizes impacts across all impact energies, probabilities and dates, and it is useful, in particular, when dealing with those cases which fall below the threshold of public interest. The scale also reflects the urgency of the situation in a natural way, and thus can guide specialists in assessing the computational and observational effort appropriate for a given situation. In this paper we describe the metrics introduced, and we give numerous examples of their application. This enables us to establish in rough terms the levels at which events become interesting to various parties.

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3) NASA Scientists Use Radar to Detect Asteroid Force - Related PR

NASA scientists have for the first time detected a tiny but theoretically important force acting on asteroids by measuring an extremely subtle change in a near-Earth asteroid's orbital path. This force, called the Yarkovsky Effect, is produced by the way an asteroid absorbs energy from the sun and re-radiates it into space as heat. The research will impact how scientists understand and track asteroids in the future.

Asteroid 6489 Golevka is relatively inconspicuous by near- Earth asteroid standards. It is only one half-kilometer (.33 mile) across, although it weighs in at about 210 billion kilograms (460 billion pounds). But as unremarkable as Golevka is on a celestial scale it is also relatively well characterized, having been observed via radar in 1991, 1995, 1999 and this past May. An international team of astronomers, including researchers from NASA's Jet Propulsion Laboratory in Pasadena, Calif., have used this comprehensive data set to make a detailed analysis of the asteroid's orbital path. The team's report appears in the December 5 issue of Science [1].

"For the first time we have proven that asteroids can literally propel themselves through space, albeit very slowly," said Dr. Steven Chesley, a scientist at NASA's Jet Propulsion Laboratory and leader of the study.

The idea behind the Yarkovsky Effect is the simple notion that an asteroid's surface is heated by the sun during the day and then cools off during the night. Because of this the asteroid tends to emit more heat from its afternoon side, just as the evening twilight on Earth is warmer than the morning twilight. This unbalanced thermal radiation produces a tiny acceleration that has until now gone unmeasured.

"The amount of force exerted by the Yarkovsky Effect, about an ounce in the case of Golevka, is incredibly small, especially considering the asteroid's overall mass," said Chesley. "But over the 12 years that Golevka has been observed, that small force has caused a shift of 15 kilometers (9.4 miles). Apply that same force over tens of millions of years and it can have a huge effect on an asteroid's orbit. Asteroids that orbit the Sun between Mars and Jupiter can actually become near-Earth asteroids."

The Yarkovsky Effect has become an essential tool for understanding several aspects of asteroid dynamics. Theoreticians have used it to explain such phenomena as the rate of asteroid transport from the main belt to the inner solar system, the ages of meteorite samples, and the characteristics of so-called "asteroid families" that are formed when a larger asteroid is disrupted by collision. And yet, despite its profound theoretical significance, the force has never been detected, much less measured, for any asteroid until now.

"Once a near-Earth asteroid is discovered, radar is the most powerful astronomical technique for measuring its physical characteristics and determining its exact orbit," said Dr. Steven Ostro, a JPL scientist and a contributor to the paper. "To give you an idea of just how powerful - our radar observation was like pinpointing to within a half inch the distance of a basketball in New York using a softball-sized radar dish in Los Angeles."

To obtain their landmark findings, the scientists utilized an advanced model of the Yarkovsky Effect developed by Dr. David Vokrouhlicky of Charles University, Prague. Vokrouhlicky led a 2000 study that predicted the possibility of detecting the subtle force acting on Golevka during its 2003 approach to Earth.

"We predicted that the acceleration should be detectable, but we were not at all certain how strong it would be," said Vokrouhlicky. "With the radar data we have been able to answer that question."

Using the measurement of the Yarkovsky acceleration the team has for the first time determined the mass and density of a small solitary asteroid using ground-based observations. This opens up a whole new avenue of study for near-Earth asteroids, and it is only a matter of time before many more asteroids are "weighed" in this manner.

In addition to Chesley, Ostro and Vokrouhlicky, authors of the report include Jon Giorgini, Dr. Alan Chamberlin and Dr. Lance Benner of JPL; David Eapek, Charles University, Prague, Dr. Michael Nolan, Arecibo Observatory, Puerto Rico, Dr. Jean-Luc Margot, University of California, Los Angeles, and Alice Hine, Arecibo Observatory, Puerto Rico.

Arecibo Observatory is operated by Cornell University under a cooperative agreement with the National Science Foundation and with support from NASA. NASA's Office of Space Science, Washington, DC supported the radar observations. JPL is managed for NASA by the California Institute of Technology in Pasdena.

More information about NASA's planetary missions, astronomical observations, and laboratory measurements are available on the Internet at: http://neo.jpl.nasa.gov/

Information about NASA programs is available on the Internet at: www.nasa.gov

JPL is managed for NASA by the California Institute of Technology in Pasadena.

Source: NASA Press Release December 5, 2003-163

[1] Direct Detection of the Yarkovsky Effect by Radar Ranging to Asteroid 6489 Golevka
Steven R. Chesley, Steven J. Ostro, David Vokrouhlicky, David Capek, Jon D. Giorgini, Michael C. Nolan, Jean-Luc Margot, Alice A. Hine, Lance A. M. Benner, and Alan B. Chamberlin

Science 5 December 2003 302: 1739-1742 [DOI: 10.1126/science.1091452] (in Reports)

Radar ranging from Arecibo, Puerto Rico, to the 0.5-kilometer near-Earth asteroid 6489 Golevka unambiguously reveals a small nongravitational acceleration caused by the anisotropic thermal emission of absorbed sunlight. The magnitude of this perturbation, known as the Yarkovsky effect, is a function of the asteroid's mass and surface thermal characteristics. Direct detection of the Yarkovsky effect on asteroids will help constrain their physical properties, such as bulk density, and refine their orbital paths. Based on the strength of the detected perturbation, we estimate the bulk density of Golevka to be +0.4/-0.6 grams per cubic centimeter.

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4) Asteroid 1950 DA - Video and Info

History of Observation

Asteroid 1950 DA (29075) was discovered on 23 February 1950. It was observed for 17 days and then faded from view for half a century. Then, an object discovered on 31 December 2000 was recognized as being the long-lost 1950 DA. (As an aside, this was New Century's Eve and exactly 200 years to the night after the discovery of the first asteroid, Ceres.)

Radar observations were made at Goldstone and Arecibo on 3-7 March 2001, during the asteroid's 7.8 million km approach to the Earth (a distance 21 times larger than that separating the Earth and Moon). Radar echoes revealed a slightly asymmetrical spheroid with a mean diameter of 1.1 km. Optical observations showed the asteroid rotated once every 2.1 hours, the second fastest spin rate ever observed for an asteroid its size.

Detection of A Potential Hazard

When high-precision radar meaurements were included in a new orbit solution, a potentially very close approach to the Earth on March 16, 2880 was discovered to exist. Analysis performed by Giorgini et al and reported in the April 5, 2002 edition of the journal Science [2] determined the impact probability as being at most 1 in 300 and probably even more remote, based on what is known about the asteroid so far. At its greatest, this could represent a risk 50% greater than that of the average background hazard due to all other asteroids from the present era through 2880, as defined by the Palermo Technical Scale (PTS value = +0.17). 1950 DA is the only known asteroid whose hazard could be above the background level.

Understanding the Risk

However, these are maximum values. The study indicates the collision probability for 1950 DA is best described as being in the range 0 to 0.33%. The upper limit could increase or decrease as we learn more about the asteroid in the years ahead.

Expressing the risk as an interval is necessary because not enough is known about the physical properties of the asteroid. For example, radar data suggests two possible directions for the asteroid's spin pole. If one pole is correct, solar radiation acceleration could mostly cancel thermal emission acceleration. Collision probability would then be close to the maximum 0.33%. If the spin pole is instead near the other possible solution, there would be little chance of collision. There are other factors also.

The situation is similar to knowing you have a coin that is biased so one side will land up 80% of the time - but you don't know which side. You can only say that when you flip the coin, the chance of heads is 80% or 20%.

Source: NASA - Info obtained via the Near Earth Object Program's Impact Risk page ("Where is 1950 DA?")

[2] Asteroid 1950 DA's Encounter With Earth in 2880: Physical Limits of Collision Probability Prediction
J. D. Giorgini et al.

Science 5 April 2002:
Vol. 296. no. 5565, pp. 132 - 136
DOI: 10.1126/science.1068191

Abstract

Integration of the orbit of asteroid (29075) 1950 DA, which is based on radar and optical measurements spanning 51 years, reveals a 20-minute interval in March 2880 when there could be a nonnegligible probability of the 1-kilometer object colliding with Earth. Trajectory knowledge remains accurate until then because of extensive astrometric data, an inclined orbit geometry that reduces in-plane perturbations, and an orbit uncertainty space modulated by gravitational resonance. The approach distance uncertainty in 2880 is determined primarily by uncertainty in the accelerations arising from thermal re-radiation of solar energy absorbed by the asteroid. Those accelerations depend on the spin axis, composition, and surface properties of the asteroid, so that refining the collision probability may require direct inspection by a spacecraft.

Excerpt

The next radar opportunity for this asteroid is in 2032. The cumulative effect of Yarkovsky acceleration since 2001 might be detected with radar measurements obtained then, but this would be more likely during radar opportunities in 2074 or 2105. Earlier Yarkovsky detection or orbital uncertainty reduction might be possible with space-based optical astrometric systems. Ground-based photometric observations might better determine the pole direction of 1950 DA much sooner. Depending on the results of such experiments, a satisfactory assessment of the collision probability of 1950 DA may require direct physical analysis with a spacecraft mission.

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