Asteroid Could Hit Mars in January

A recently discovered asteroid which passed close to the Earth in November is now headed toward a very close pass of Mars in late January, and there is a small chance that it could hit. There is only a 1-in-75 chance of a collision, but scientists are excited about the possibility. If it happens, the impact would occur on January 30, 2008 at around 10:55 UT (5:55 a.m. EST).

In the likely event that the asteroid misses Mars, it could come back to the vicinity of Earth years or decades later, but routine hazard monitoring shows that there is no threat of an impact with the Earth.

Designated asteroid 2007 WD5, it was discovered on November 20, 2007 by the NASA-funded Catalina Sky Survey using a 1.5-meter telescope on Mt. Lemmon, near Tucson. The object had already passed within 7.5 million km (5 million miles) of Earth on November 1, before it was discovered. Based on its magnitude (brightness), they estimate the asteroid to be about 50 meters (160 feet) across. It has already reached the halfway point between Earth and Mars. When it closes in on Mars, it will approach from the day side, and will be very difficult to observe from any of the spacecraft on or around Mars. The current best estimate predicts the asteroid will miss Mars by 50,000 km, but the miss distance is highly uncertain because the asteroid's path is not known with sufficient accuracy. As of the December 21 announcement, the uncertainty region during the Mars encounter is over a million kilometers (700,000 miles) along a very slender ellipsoid only 1200 km (700 miles) wide, but the ellipsoid does intersect Mars. The zone of potential impact on the surface of Mars is approximately 800 km wide, and sweeps across the Martian equator from southwest to northeast, crossing the equator at roughly 30 degrees W longitude. The Mars Exploration Rover "Opportunity" is close to the southern edge of this possible impact zone but clearly outside it.

The asteroid is becoming increasingly harder to observe, since it is receding from the Earth and the waxing Moon is approaching the same part of the sky. But it should become observable again early in January. These new measurements will lead to a significant improvement in the orbit accuracy, and astronomers will then be able to refine the probability that the asteroid might collide with Mars.

If the asteroid does hit Mars, it would strike with a velocity of about 13.5 km/s (8.4 miles per second), and would produce an explosion equivalent to about 3 Megatons of TNT. Scientists can only speculate as to the effects of such an impact, but it would be reasonable to expect a crater nearly a kilometer across and a significant amount of dust lifted into the atmosphere.

An impact would not be unprecedented: 21 fragments of Comet Shoemaker-Levy 9 impacted Jupiter in July, 1994. Those impacts were predicted with near certainty almost a year before the impact. But, with a 1-in-75 chance, this asteroid's possible impact with Mars is far from certain.

To learn more, visit the home page of the NASA/JPL Near-Earth Object Program: http://neo.jpl.nasa.gov


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MARS IS COMING, PART 8 (MARS IS HERE)

Here we are. Opposition has arrived, December 24. As we bask in the glow of Mars, please enjoy this installment.

The Interior, Martian Meteorites and Martian Moons

The Interior

We know little about the Martian interior. Planetary scientists have yet to conduct a successful seismic experiment via spacecraft that would provide direct information on internal structure and so must rely on indirect inferences. The moment of inertia of Mars indicates that it has a central core with a radius of 1,300–2,000 km (800–1,200 miles). Isotopic data from meteorites determined to have come from Mars (see the section Meteorites from Mars, below) demonstrate unequivocally that the planet differentiated—separated into a metal-rich core and rocky mantle—at the end of the planetary accretion period 4.5 billion years ago. The planet has no detectable magnetic field that would indicate convection (heat-induced flow) in the core today. Large regions of magnetized rock have been detected in the oldest terrains, however, which suggests that very early Mars did have a magnetic field but that it disappeared as the planet cooled and the core solidified. Martian meteorites also suggest that the core may be more sulfur-rich than Earth's core and the mantle more iron-rich.

Scientists think that Mar is probably volcanically active today, although at a very low level. Some Martian meteorites, which are all volcanic rocks, show ages as young as a few hundred million years, and some volcanic surfaces on the planet are so sparsely cratered that they must be only tens of millions of years old. So Mars was volcanically active in the geologically recent past, which implies that its mantle is warm and undergoing melting locally.

Mars's gravitational field is very different from Earth's. On Earth, excesses and deficits of mass in the surface crust, corresponding to the presence of large mountains and ocean deeps, respectively, tend to be offset by compensating masses at depth (isostatic compensation). Thus, the pull of gravity on Earth is the same on high mountains as it is over the ocean. This is also true for Mars's oldest terrains, such as the Hellas basin, the southern highlands, and the northern plains. The younger terrains, such as the Tharsis and Elysium domes, however, are only partly compensated. Associated with both of these regions are gravity highs—that is, places where the measured gravity is significantly higher than elsewhere because of the large mass of the domes. (Similar areas, called mascons, have been detected and mapped on Earth's moon.)

Because the gravity over the southern highlands is roughly the same as that over the low-lying northern plains, the southern highlands must be underlain by a thicker crust of material that is less dense than the mantle below it. Estimates of the thickness of the Martian crust range from only 3 km (2 miles) under the Isidis impact basin, which is just north of the equator and east of Syrtis Major, to more than 90 km (60 miles) at the south end of the Tharsis rise.

Martian Meteorites

By 2004 scientists had identified about 30 meteorites that came from Mars. Suspicions about their origin were first raised when meteorites that appeared to be volcanic rocks were found to have ages of about 1.3 billion years instead of the 4.5 billion years of all other meteorites. These rocks had to have come from a body that was geologically active in the comparatively recent past, and Mars was the most likely candidate. The rocks also have similar ratios of oxygen isotopes, which are distinctively different from those of Earth rocks, lunar rocks, and other meteorites. A Martian origin was finally proved when it was found that several of them contained trapped gases having a composition identical to that of the Martian atmosphere as measured by the Viking landers. The rocks are thought to have been ejected from the Martian surface by large impacts. They then went into solar orbit for several million years before falling on Earth. Claims in the mid-1990s of finding evidence for past microscopic life in one of the meteorites, called ALH84001, have been viewed skeptically by the general science community.

Martian Moons

Little was learned about the two moons of Mars, Phobos and Deimos, from their discovery in 1877 until orbiting spacecraft observed them a century later. Viking 1 flew to within 100 km (60 miles) of Phobos and Viking 2 to within 30 km (20 miles) of Deimos.

Phobos orbits Mars once every 7 hours 39 minutes. It moves in a very close orbit at a mean distance of about 6,000 km (3,700 miles) from the surface—less than twice the planet's radius. It is so near that, without internal strength, it would be torn apart by gravitational (tidal) forces. These forces also slow the motion of Phobos and may ultimately cause the satellite to collide with Mars, possibly in less than 100 million years. The opposite fate is expected for Deimos. It moves in a more distant orbit, and tidal forces are causing it to recede from the planet. Phobos and Deimos are not visible from all locations on the planet because of their small size, their closeness to Mars, and their near-equatorial orbits.

Both moons are irregular chunks of rock, roughly ellipsoidal in shape. Phobos is the larger of the two. Phobos's rugged surface is completely covered with impact craters. The largest, the crater Stickney, is about half as wide as the satellite itself. Its surface also has a widespread system of linear fractures, or grooves, many of which are geometrically related to Stickney. In contrast, the surface of Deimos appears smooth, as its many craters are almost completely buried by fine debris, and it shows no fracture system. The difference in appearance between the two moons is thought to be related to the fate of the debris created by impacts. In the case of the inner, more massive Phobos, the ejected material either fell back to the surface or, if it left the satellite with enough velocity to go into space, subsequently fell on Mars. For the more distant, smaller Deimos, debris thrown off the satellite remained in orbit until it was recaptured, sifting down to blanket its surface.

The albedo, or reflectivity, of the surfaces of both moons is very low, similar to that of the most primitive types of meteorites. One theory of the origin of the moons is that they are asteroids that were captured when Mars was forming.

Next Time, Our Final Installment: "Spacecraft Exploration, Mapping Mars, and The Question of Life"

Bibliography

Mars. (2007). In Encyclopædia Britannica. Retrieved October 26, 2007 , from Encyclopædia Britannica Online: http://www.britannica.com/eb/article-9110149

Mars (2007). In The Columbia Encyclopedia, Sixth Edition 2007. Copyright 2007 Columbia University Press. Retrieved October 26, 2007 from Encyclopedia.comhttp://www.encyclopedia.com/doc/1E1-Mars-ast.html

Planets: Mars. In NASA Solar System Exploration, Last updated October 23, 2007. Retrieved October 26, 2007, from the NASA Solar System Exploration website, maintained by NASA's Jet Propulsion Laboratory:http://solarsystem.jpl.nasa.gov/planets/profile.cfm?Object=Mars

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THE SKY THIS WEEK

Dec 23, 8:16 P.M. EST (Dec 24, 1:16 UTC) - Full Moon

Dec 23 - The planet Jupiter is in conjunction with the sun

Dec 23 - The planet Mars is 0.9° south of the moon, occultation. An occultation occurs when one object passes in front of a smaller one, temporarily obscuring all or part of the background object from view.

Dec 24 - The planet Mars is at opposition. Opposition occurs when a planet farther from the sun than Earth appears opposite the sun in the sky. It is the best time to observe a planet.

Dec 25 - The moon occults Asteroid 15 Eunomia

Dec 27 - The star Regulus is 0.6° north of the moon, occultation. An occultation occurs when one object passes in front of a smaller one, temporarily obscuring all or part of the background object from view.

Dec 28 - The planet Saturn is 3° north of the moon


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THIS WEEK IN HISTORY

Dec 23, 1672 - Giovanni Cassini's Discovery of Saturn Moon Rhea

Dec 24, 1761 - Birthday of Jean-Louis Pons

Dec 24, 1905 - Joel Metcalf's Discovery of Asteroid 581 Tauntonia

Dec 24, 1965 - Barwell Meteorite Fall (Hit Car, Buildings)

Dec 24, 1979 - 1st Ariane 1 Launch

Dec 26, 1974 - Launch of Salyut 4 Launch (Soviet Space Station)

Dec 27, 1571 - Birthday of Johannes Kepler

Dec 27, 1904 - Max Wolf's Discovery of Asteroid 553 Kundry

Dec 27, 1984 - Discovery of ALH 84001 (Mars Meteorite)

Dec 28, 1882 - Birthday of Arthur Eddington

Dec 28, 1929 - Birthday of Maarten Schmidt

Dec 29, 1977 - Discovery of ALHA 77005 Meteorite (Mars Meteorite), 30th Anniversary


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MUSICAL DIVERSION

In 1816 a young Austrian priest, Father Josef Mohr (1792 - 1848) wrote in German a beautiful six-stanza poem on the birth of the Christ child. At that time Mohr was assigned to a pilgrimage church in the Alpine town of Mariapfarr, not far from the home of his grandfather. While we do not know what inspired Mohr to write his poem, we do know he took the poem with him when he was transferred to the village of Oberndorf the following year (1817).

Early on December 24, 1818 Mohr traveled quickly from Oberndorf to nearby Arnsdorf, to the home of musician and school teacher Franz Xaver Gruber (1787 - 1863), who lived in the apartment over the town schoolhouse. In addition to his teaching in Arnsdorf, Gruber was the organist and choir director at St. Nikolaus Church where Mohr served as assistant pastor. On this day Mohr showed Gruber his poem. He may have also given Gruber a bit of melody, but we are not certain. Mohr asked Gruber to finish the song and create an arrangement for duet and chorus with guitar accompaniment. The new song had to be ready for performance at Midnight Mass that night. We are not certain why the song had to be ready for that evening, but we have some possible reasons. Some have suggested that the organ was not working, either because of mice-eaten organ bellows or because of rust and mildew caused by periodic flooding of the nearby Salzach River. Others think that Mohr, who dearly loved guitar music, just wanted a new carol for Christmas. Whatever the reason, the song had to come together quickly.

Mohr returned to Oberndorf and Gruber followed several hours later with the finished arrangement. Mohr would sing melody and Gruber would sing a bass harmony. There was not enough time for the choir to learn and rehearse the entire song, so Gruber had the choir echo the duet by repeating the last two stanzas of each verse in four-part harmony. That night, at the Midnight Mass in St. Ni­ko­laus Church, Mohr and Gruber stood in front of the main alter and sang while Mohr played his guitar and the choir echoed. And so the carol "Stille Nacht! Heilige Nacht" (Silent Night, Holy Night) was heard for the first time.

Stille Nacht, Heilige Nacht!

Stille Nacht, heilige Nacht!
Alles schläft, einsam wacht
Nur das traute hochheilige Paar,
Holder Knabe mit lockigem Haar,
Schlaf in himmlischer Ruh,
Schlaf in himmlischer Ruh.

Stille Nacht, heilige Nacht!
Gottes Sohn, o wie lacht
Lieb’ aus deinem holdseligen Mund,
Da uns schlägt die rettende Stund’,
Christ, in deiner Geburt,
Christ, in deiner Geburt!

Stille Nacht, heilige Nacht!
Die der Welt Heil gebracht,
Aus des Himmels goldenen Höhn,
Uns der Gnaden Fülle läßt sehn,
Jesum in Menschengestalt,
Jesum in Menschengestalt!

Stille Nacht, heilige Nacht!
Wo sich heut alle Macht
Väterlicher Liebe ergoß,
Und als Bruder huldvoll umschloß
Jesus die Völker der Welt,
Jesus die Völker der Welt!

Stille Nacht, heilige Nacht!
Lange schon uns bedacht,
Als der Herr vom Grimme befreit
In der Väter urgrauer Zeit
Aller Welt Schonung verhieß,
Aller Welt Schonung verhieß!

Stille Nacht, heilige Nacht!
Hirten erst kund gemacht;
Durch der Engel Halleluja
Tönt es laut von fern und nah’;
Christ der Retter ist da,
Christ der Retter ist da!

-----

Below is the literal translation of the text from German to English by Bettina Klien.


Silent Night! Holy Night!
Silent Night! Holy Night!
All is calm, all is bright
Round yon godly tender pair.
Holy infant with curly hair,
Sleep in heavenly peace,
Sleep in heavenly peace.

Silent Night! Holy Night!
Son of God, love's pure light
Radiant beams from thy holy face,
With the dawn of redeeming grace,
Jesus, Lord at thy birth
Jesus, Lord at thy birth.

Silent Night! Holy Night!
Brought the world gracious light,
Down from heaven's golden height
Comes to us the glorious sight:
Jesus, as one of mankind,
Jesus, as one of mankind.

Silent Night! Holy Night!
By his love, by his might
God our Father us has graced,
As a brother gently embraced
Jesus, all nations on earth,
Jesus, all nations on earth.

Silent Night! Holy Night!
Long ago, minding our plight
God the world from misery freed,
In the dark age of our fathers decreed:
All the world redeemed,
All the world redeemed.

Silent Night! Holy Night!
Shepherds first saw the sight
Of angels singing alleluia
Calling clearly near and far:
Christ, the Saviour is born,
Christ, the Saviour is born.

-----

Over the next few years Karl Mauracher, a master organ builder and repairman from the Ziller Valley, made several trips to Oberndorf to work on the St. Nikolaus organ. During one of these visits he either found or was given a copy of the carol and he took it home with him. The carol then began its journey around the world as a "Tyrolean Folk Song."

Two traveling families of folk singers from the Ziller Valley, named Strasser and Rainer, added the song into their performing repertoire. We know from the local newspaper that the Strassers sang the song in a concert in Leipzig in December 1832. It was during this time that several of the melody’s notes were changed, and it evolved into the melody we commonly hear. We also know from a historical plaque that the Rainer Family sang the carol before an audience which included Austrian Emperor Franz I and Russian Tsar Alexander I. In 1839, the Rainers performed "Stille Nacht" for the first time in America, at the Alexander Hamilton Monument outside Trinity Church in New York City.

Although Gruber made attempts during his life to claim authorship of the carol melody, it was thought at various times that the melody was composed by Haydn, Mozart or Beethoven. The controversy was finally put to rest when an arrangement of the song written in Mohr's own hand was found and authenticated. The authorities could also plainly see in the upper right hand corner of the first page that Mohr had written, "Melodie von Fr. Xav. Gruber."

Gruber produced a number of orchestral arrangements of the song during his life. The original guitar arrangement is missing, but five other Gruber manuscripts of the carol exist. The discovered manuscript by Joseph Mohr (ca. 1820) is for guitar accompaniment and is probably the closest to the arrangement and melody sung at Midnight Mass in 1818.
The people of Austria consider the song a national treasure. They traditionally perform it only on Christmas Eve.

Below is an English translation of the hymn found in many western hymnals. Stanzas 1 and 3 were translated from German in 1863 by John F. Young (1820 – 1885). The translator of stanzas 2 and 4 is unknown.


Silent Night, Holy Night!

Silent night, holy night,
All is calm, all is bright
Round yon virgin mother and Child.
Holy Infant, so tender and mild,
Sleep in heavenly peace,
Sleep in heavenly peace.

Silent night, holy night,
Shepherds quake at the sight;
Glories stream from heaven afar,
Heavenly hosts sing Alleluia!
Christ the Savior is born,
Christ the Savior is born!

Silent night, holy night,
Son of God, love’s pure light;
Radiant beams from Thy holy face
With the dawn of redeeming grace,
Jesus, Lord, at Thy birth,
Jesus, Lord, at Thy birth.

Silent night, holy night
Wondrous star, lend thy light;
With the angels let us sing,
Alleluia to our King;
Christ the Savior is born,
Christ the Savior is born!

-----

To see and hear more on the "Stille Nacht" visit this page of "The Cyber Hymnal" - http://www.cyberhymnal.org/non/de/stillena.htm

To see and hear more on the " Silent Night" visit this page of "The Cyber Hymnal" - http://www.cyberhymnal.org/htm/s/i/silntnit.htm

Bill Egan. “Silent Night: The Song Heard ‘Round The World.” Posted on the “SilentNightWeb” - http://silentnight.web.za/history/index.htm

Stille Nacht text in German and English, on the “SilentNightWeb” - http://silentnight.web.za/translate/deu.htm


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