Fraser Cain, Author at Universe Today

February 7, 2006March 24, 2012 by Fraser Cain

The Case of the Stolen Stars

The central part of Messier 12. Image credit: ESO Click to enlarge
Based on observations with ESO’s Very Large Telescope, a team of Italian astronomers reports that the stellar cluster Messier 12 must have lost to our Milky Way galaxy close to one million low-mass stars.

“In the solar neighbourhood and in most stellar clusters, the least massive stars are the most common, and by far”, said Guido De Marchi (ESA), lead author of the study. “Our observations with ESO’s VLT show this is not the case for Messier 12.”

The team, which also includes Luigi Pulone and Francesco Paresce (INAF, Italy), measured the brightness and colours of more than 16,000 stars within the globular cluster Messier 12 with the FORS1 multi-mode instrument attached to one of the Unit Telescopes of ESO’s VLT at Cerro Paranal (Chile). The astronomers could study stars that are 40 million times fainter than what the unaided eye can see (magnitude 25).

Located at a distance of 23,000 light years in the constellation Ophiuchus (The Serpent-holder), Messier 12 got its name by being the 12th entry in the catalogue of nebulous objects compiled in 1774 by French astronomer and comet chaser Charles Messier. It is also known to astronomers as NGC 6218 and contains about 200,000 stars, most of them having a mass between 20 and 80 percent of the mass of the Sun.

“It is however clear that Messier 12 is surprisingly devoid of low-mass stars”, said De Marchi. “For each solar-like star, we would expect roughly four times as many stars with half that mass. Our VLT observations only show an equal number of stars of different masses.”

Globular clusters move in extended elliptical orbits that periodically take them through the densely populated regions of our Galaxy, the plane, then high above and below, in the ‘halo’. When venturing too close to the innermost and denser regions of the Milky Way, the ‘bulge’, a globular cluster can be perturbed, the smallest stars being ripped away.

“We estimate that Messier 12 lost four times as many stars as it still has”, said Francesco Paresce. “That is, roughly one million stars must have been ejected into the halo of our Milky Way.”

The total remaining lifetime of Messier 12 is predicted to be about 4.5 billion years, i.e. about a third of its present age. This is very short compared to the typical expected globular cluster’s lifetime, which is about 20 billion years.

The same team of astronomers had found in 1999, another example of a globular cluster that lost a large fraction of its original content (see ESO PR 04/99).

The scientists hope to discover and study many more clusters like these, since catching clusters while being disrupted should clarify the dynamics of the process that shaped the halo of our home galaxy, the Milky Way.

High resolution images and their captions are available on this page.
A press release on this is also issued by INAF in Italian and is available at www.inaf.it/comunicati_stampa/cs070206/Inaf-04-06.html.

Original Source: ESO News Release

February 6, 2006March 24, 2012 by Fraser Cain

Young Enceladus

Saturn’s moon Enceladus. Image credit: NASA/JPL/SSI Click to enlarge
For Enceladus, wrinkles mean the opposite of old age. This view of a crescent Enceladus shows a transition zone between a wrinkled and presumably younger region of terrain and an older, more heavily cratered region. The moon’s geologically active southern polar region is seen at bottom.

The lit terrain shown here is on the side of Enceladus (505 kilometers, or 314 miles across) that faces away from Saturn. North is up and rotated 20 degrees to the right.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Dec. 24, 2005 at a distance of approximately 108,000 kilometers (67,000 miles) from Enceladus and at a Sun-Enceladus-spacecraft, or phase, angle of 102 degrees. Image scale is 646 meters (2,118 feet) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Original Source: NASA/JPL/SSI News Release

February 6, 2006June 19, 2013 by Fraser Cain

What’s Up This Week – February 6 – February 12, 2006

Download our free “What’s Up 2006” ebook, with entries like this for every day of the year.

Apollo 16. Image credit: NASA. Click to enlarge.
Monday, February 6 – On this day in 1971, astronaut Alan Shepherd became the first “lunar golfer” to tee off on the Moon’s surface. While the Apollo 14 landing site is just on the other side of the terminator tonight, we can still go “crater hopping” to catch another. Close to the terminator and about one third of the way from the southern cusp are the ancient walls of huge previous studied Albategnius. Directly to its lunar east, and about the same distance as Albategnius’ is wide, look for a trio – small western Andel, larger eastern Descartes, and larger still southern Abulfeda. Power up! Between Andel and Descartes is the small pockmark of Dolland. North of Dolland is a ruined, unnamed crater with a pronounced set of rings on its northwestern shore. On the eastern edge of the relatively smooth floor, the remains of the Apollo 16 mission still shine on!

Tonight we’ll finish up our sweep for stardust through Auriga. Start at Theta and head due south five degrees (half a fist). On most nights, M37 gives an extraordinarily dense and complex view of more than 100 stars to small scopes, but lunacy will prevent that. Power up to darken the field.

Now let’s talk about these three interesting open clusters. All were discovered by Giovanni Batista Hodierna before the year 1654 – more than a decade before Messier cataloged them. All are located roughly 4000 light years away from Earth. The smallest of the three, M36, spans 12 light years. That’s not much more than the distance between our Sun and Epsilon Eridani. Larger M37 and M38 span about 25 light years, or about the distance between us and Vega. We’ll come back for a look at all three later in the month.

Tonight observers in western North America and Hawaii should follow the progress of the Moon as it passes through the Pleiades!

Tuesday, February 7 – On this day in 1889, the first American national astronomy organization was born – the Astronomical Society of the Pacific.

Tonight, let’s return to the Moon and previous study Plato. To the south on the dark plains of Mare Imbrium, you will notice an almost star-like point of light, a singular peak named Mons Pico. Unique among lunar mountains, its highly reflective rocky composition makes it appear almost like a pyramid in the long shadows of sunrise. “Pyramid” Pico stands 8,000 feet above the lunar plane on a base some 18 miles wide!

After looking at a solitary mountain this evening, let’s have a look at a solitary star as well – Alpha Orionis. Although its designation lists it as Orion’s brightest star in Johann Bayer’s Uranometria of 1603, Betelgeuse is actually slightly fainter than Beta (Rigel). What makes it special is its color. To the eye, Betelgeuse appears a distinctive red-orange. This color relates directly to its spectral class of M2. Like many M-spectra stars, Betelgeuse truly is a “red giant” – a star approaching the end of its life. With an immensely swollen, low temperature, near-vacuum photosphere of hydrogen and helium gas, this star measures some 300 million miles in diameter. Placed at the Sun’s position, it would extend out beyond the orbit of Mars! At 430 light years away, Betelgeuse is not the farthest or bright stars of winter, but it is most certainly the largest.

Wednesday, February 8 – Today celebrates the birth of J.L.E. Dreyer. Born in 1852, the Danish Dreyer came to fame as the astronomer who compiled the New General Catalogue (NGC) published in 1878. As a professional, Dreyer began his observations of the night sky in the employ of Lord Rosse at Birr Castle Ireland. Later Dreyer moved to Armagh Observatory where he confirmed many of the deep sky studies compiled by William Herschel and other observers using the 10″ refractor he secured funds for and selected as his instrument of choice. Even with a wealth of astronomical catalogs to choose from, the NGC objects, and Dreyer’s abbreviated list of descriptions, still remain the most widely used today.

Let’s engage is some further lunar exploration as crater Copernicus again becomes visible tonight to even the most modest of optical aid. Small binoculars show Copernicus as a bright “ring” midway along the lunar dividing line of light and dark called the “terminator.” Telescopes will reveal its 97 km (60 mile) expanse and 120 meter (1200 ft.) central peak to perfection. Copernicus holds special appeal as it’s the aftermath of a huge meteoric impact. At 3800 meters (12,600 feet) deep, its walls are around 22 km (14 miles) thick and over the next few days, the impact ray system extending from this tremendous crater will become wonderfully apparent.

Now, let’s explore something special from J.L.E’s lifework. Let’s turn eyes, binoculars, and scopes on Orion’s Belt and the brightly scattered open cluster NGC 1981. On a dark, moonless night, NGC 1981 can be seen unaided as a small, fuzzy haze in Orion’s “sword.” Let’s start by using binoculars – or finderscope – to get a sense of how 1981 “fits in” with the area. Do you see those three 6th magnitude stars at the top? They’re part of the 1981 cluster. Now look south to 4.6 magnitude 42 Orionis – a tight, disparate double. You probably won’t see M43 further south, but M42 will be visible. Try observing multiple system Iota Orionus. After the low power tour, head back to the top of the list with a telescope and enjoy the dozen or so brightly scattered, hot young stars that make up number 1981 on J.L.E Dreyer’s celestial list!

Thursday, February 9 – It’s a “Moon Gazer’s” evening as our nearest astronomical neighbor continues to light up the night sky. Don’t put away your telescopes and binoculars thinking there’s nothing to view though, because one of the most “romantic” features on the lunar surface will be highlighted tonight.

The Sinus Iridium is one of the most fascinating and idyllic regions of the Moon. At 241 km (150 miles) in diameter and ringed by the Juras Mountains, it’s known by the quiet name of “The Bay of Rainbows.” Despite this serene name, the region was actually formed by cataclysm. Astronomers speculate that a minor planet of around 200 km in diameter once impacted our newly formed Moon with a glancing strike. This caused “waves” of superheated material to wash up along a “shoreline” forming this delightful C-shaped lunar feature. The effect of looking at a bay is stunning as the smooth inner sands show soft waves called “rilles,” broken only by a few small, impact craters. This picture is completed as Promentoriums Heraclides and LaPlace rise above the surface (at 1800 meters and 3000 meters respectively) appearing as distant “lighthouses” standing at the entrance.

It’s also a great time for seeing double. Before it moves too high overhead, have a look at 41 Aurigae. The pair ? one of 5th and other of the 7th magnitude – is separated by 8 arc seconds. Notice how the companion orients almost due north of its brighter primary. The result appears as two stars moving side-by-side across the field of view! 41 Aurigae and it secondary are members of the Hyades. To locate 41, start at Beta Aurigae. Use your finderscope to center on Pi – a little more than a degree north. 41 is a slightly fainter star around five degrees northeast of Pi. It’s a challenge to locate – but it means is that you can congratulate yourself when you find it! And enjoy observing it all the more…

Friday, February 10 – Let’s return to the Moon tonight and explore an area to the south around another easy and delightful lunar feature – the crater Gassendi. At 110 km in diameter and 2010 meters deep, this ancient crater contains a triple mountain peak in its center. Once one of the most “perfect circles” on the Moon, the south wall of Gassendi has been eroded by lava flows over a 48 km expanse and offers numerous detailed features to telescopic observers on its ridge and rille covered floor. Observing with binoculars? Gassendi’s bright ring stands on the north shore of Mare Humorum…an area about the size of the state of Arkansas!

Are you ready for a tough double star? Alnitak (Zeta Orionis) is the easternmost star of Orion’s belt. It’s a double just wide enough to resolve through any telescope. However, you’ll need steady skies to show the two bright stars as distinct and tiny orbs of light separated by a mere 2.3 arc seconds. While observing this tight couple, keep in mind that both stars are some 800 light-years distant and that Zeta-A has one of the hottest photospheres among all known stars. At 31,000 degrees K, its temperature is so high that it shines primarily in the ultraviolet. Look for a third, 10th magnitude star almost 1 arc minute away from the bright pair. When you can see this one plainly, you’re ready to start looking for fainter members of the famed Trapezium found in the heart of M42.

Saturday, February 11 – On this day in 1970, Lambda 4S-5, the first Japanese satellite was launched.

The waxing Moon will dominate early evening skies, but tonight is an excellent opportunity for binoculars and telescopes to explore crater Tycho.

Named for Danish astronomer, Tycho Brahe, this fantastic impact crater is very impressive in even the most modest of optical aids. Spanning 85 km, this lunar feature will be very prominent and unmistakable in the southern hemisphere of the Moon. Tycho’s highly conspicuous ray system supports its origin as an impact crater. The rays span hundreds of kilometers across the lunar surface. Tycho is also one of the youngest of the major features at an astounding age of only 50,000,000 years old!

On January 9, 1968 Surveyor 7 – the last lunar robot of its kind – landed quietly at lunar sunrise on Tycho’s slopes. Because previous Surveyor missions provided the Apollo program with all data necessary for manned missions, Surveyor 7’s presence was scientific only. Two weeks later, when the Sun set on the landing site, Surveyor 7 had provided over 21,000 photographs, determined physical and chemical properties associated with the Southern Highland area, and detected laser beams aimed at it from two separate Earth observatories.

With the Moon lighting the skies, tonight will give you and opportunity to see just how much effect it has on studies. In the spirit of investigation, have a look at the Great Nebula in Orion. Not quite the glorious sight you remember, huh? But while in M42, power up a little and have a look at those four stars in its midst. We will be back…

Sunday, February 12 – Tonight the Moon will command the skies and give naked-eye observers an opportunity to use their imaginations!

Since the dawn of mankind, we have been gazing at the Moon and seeing fanciful shapes in large lunar features. Tonight, as the Moon rises, is your chance to catch an AL lunar challenge – “The Rabbit in the Moon.” The “Rabbit” is a compilation of all the dark maria. The Oceanus Procellarum forms the “ear” while Mare Humorum makes the “nose.” The “body” is Mare Imbrium and the “front legs” appear to be Mare Nubium. Mare Serenitatis is the “backside” and the picture is complete where Mare Tranquillitatis and Mare Fecunditatis shape the “hind legs” with Crisium as the “tail.”

See the Moon with an imaginative mind and new eyes — and find the “Rabbit.” It’s already out of the hat and in the heavens…

For telescopes and binoculars, the lunar surface will provide a bright but superior view of crater Grimaldi. Named for Italian physicist and astronomer, Francesco Grimaldi, this deep grey oval is one of the darkest features on the Moon – only reflecting about 6% of the light. Approximately 430 km (140-145 miles) long, it’s easy to spot along the terminator and just slightly south of the center of the lunar limb. Tonight is the best time to view its mountained walls, for later they will disappear and Grimaldi will take on the appearance of a small mare in the light of the full Moon.

Before then, let’s look at another fine double star – Eta Orionus. Eta is the 3.4 magnitude star a little over 6 degrees north-northeast of Rigel. Like Alnitak, Eta has a bright, closely spaced companion. Look for a much fainter 9.4 magnitude star that may not be part of the system. Like Alnitak, almost any size telescope can split the pair, but it will take a still sky to fully distinguish each star clearly.

May all your journeys be at light speed… ~Tammy Plotner. Contributing writer – Jeff Barbour @ astro.geekjoy.com

February 4, 2006 by Fraser Cain

Hot Halo Surrounds Distant Galaxy

The massive spiral galaxy NGC 5746. Image credit: NASA Click to enlarge
Chandra observations of the massive spiral galaxy NGC 5746 revealed a large halo of hot gas (blue) surrounding the optical disk of the galaxy (white). The halo extends more than 60,000 light years on either side of the disk of the galaxy, which is viewed edge-on.

The galaxy shows no signs of unusual star formation, or energetic activity from its nuclear region, making it unlikely that the hot halo is produced by gas flowing out of the galaxy. Computer simulations and Chandra data show that the likely origin of the hot halo is the gradual inflow of intergalactic matter left over from the formation of the galaxy.

Spiral galaxies are thought to form from enormous clouds of intergalactic gas that collapse to form spinning disks of stars and gas. One prediction of this theory is that massive spiral galaxies should be immersed in halos of hot gas left over from the galaxy formation process.

Hot gas has been detected around spiral galaxies in which vigorous star formation is ejecting matter from the galaxy, but until now, hot halos due to infall of intergalactic matter had not been detected. Indeed, the extensive hot gas halo around NGC 5746 is faint and would be very difficult to detect without a powerful X-ray telescope such as Chandra. Also, the galaxy’s special orientation and large mass increased the chance of detection.

The discovery of a hot halo around NGC 5746 was welcome news to astronomers because it shows that the “missing” hot halos predicted by computer models in fact exist.

Original Source: Chandra X-Ray Observatory

February 4, 2006December 19, 2015 by Fraser Cain

Rough and Tumble Hyperion

Saturn’s irregularly shaped moon Hyperion. Image credit: NASA/JPL/SSI Click to enlarge
The tumbling and irregularly shaped moon Hyperion hangs before Cassini in this image taken during a distant encounter in Dec. 2005. This still image is part of a movie sequence of 40 images taken over about two hours as Cassini sped past the icy moon (see the related movie).

Hyperion (280 kilometers, or 174 miles across) is covered with closely packed and deeply etched pits. The warming action of the Sun on water ice lying beneath a darkened layer of surface material apparently has deepened and exaggerated the depressions already created by impacts.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Dec. 23, 2005 at a distance of 228,000 kilometers (142,000 miles) from Hyperion and at a Sun-Hyperion-spacecraft, or phase, angle of 77 degrees. Resolution in the original image was about 1.4 kilometers (0.9 mile) per pixel. The image was magnified by a factor of two and contrast-enhanced to aid visibility.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org.

Original Source=”http://saturn.jpl.nasa.gov/multimedia/images/image-details.cfm?imageID=1979″>NASA/JPL/SSI News Release

February 4, 2006March 29, 2013 by Fraser Cain

Claritas Fossae on Mars

The region Claritas Fossae. Image credit: ESA Click to enlarge
This image, taken by the High Resolution Stereo Camera (HRSC) on board ESA’s Mars Express spacecraft, shows the ancient tectonic region of Claritas Fossae on Mars.

This region, west of Solis Planum, is a tectonic and volcanic area located south-east of the Tharsis volcano group (the Tharsis Montes) on the Tharsis rise. It extends roughly north to south for approximately 1800 kilometres.

The scene shows an area covering roughly 200 km by 1150 km and centred approximately at 258? East and 32? South. This is a high-resolution image of Claritas Fossae further to the one which was published on 31 March 2004.

Original Source: ESA Mars Express

February 4, 2006January 24, 2021 by Fraser Cain

Astrophoto: M-81 by Tom Davis

Image credit: M-81 by Tom Davis.
Draw a line from the left bottom star through the top right star of the Big Dipper’s bowl then extend it roughly the same distance upward and you’ll see the location of this magnificent winter galaxy, the eighty first entry in Charles Messier’s catalog, known as M-81. It was first identified in the late 1700’s by German astronomer Johann Bode, so it’s also sometimes knownn as Bode’s Nebula.

Located only 12 million light years from Earth, a relative stone’s throw by intergalactic distances, M-81 is one of the brightest galaxies visible from in the night sky and can be spotted from a dark site, far from any city lights, without need for any optical assistance.

This picture was photographed by astrophotographer Tom Davis, from his Inkom, Idaho home in late January 2006 during a clear-sky break in an otherwise cloudy winter season. Tom photographed through a six inch, f/7 Astro-Physics refractor with a SBIG ST-10XME three mega-pixel camera.

M-81 exhibits beautifully symmetrical spiral arms and numerous dark lanes of dust in this 2.5 hour exposure. Some of these dusty ribbons may be evidence of interaction with its companion galaxy, M-82, which also shows signs of disturbance that is thought to be caused by M-81.

Do you have photos you’d like to share? Post them to the Universe Today astrophotography forum or email them, and we might feature one in Universe Today.

Written by R. Jay GaBany

February 2, 2006March 24, 2012 by Fraser Cain

System Maps Microfossils in 3-D

A 650-million-year-old fossil. Image credit: Dr. J. William Schopf/UCLA. Click to enlarge
UCLA paleobiologist J. William Schopf and colleagues have produced 3-D images of ancient fossils – 650 million to 850 million years old – preserved in rocks, an achievement that has never been done before.

If a future space mission to Mars brings rocks back to Earth, Schopf said the techniques he has used, called confocal laser scanning microscopy and Raman spectroscopy, could enable scientists to look at microscopic fossils inside the rocks to search for signs of life, such as organic cell walls. These techniques would not destroy the rocks.

“It’s astounding to see an organically preserved, microscopic fossil inside a rock and see these microscopic fossils in three dimensions,” said Schopf, who is also a geologist, microbiologist and organic geochemist. “It’s very difficult to get any insight about the biochemistry of organisms that lived nearly a billion years ago, and this (confocal microscopy and Raman spectroscopy) gives it to you. You see the cells in the confocal microscopy, and the Raman spectroscopy gives you the chemistry.

“We can look underneath the fossil, see it from the top, from the sides, and rotate it around; we couldn’t do that with any other technique, but now we can, because of confocal laser scanning microscopy. In addition, even though the fossils are exceedingly tiny, the images are sharp and crisp. So, we can see how the fossils have degraded over millions of years, and learn what are real biological features and what has been changed over time.”

His research is published in the January issue of the journal Astrobiology, in which he reports confocal microscopy results of the ancient fossils. (He published ancient Raman spectroscopy 3-D images of ancient fossils in 2005 in the journal Geobiology.)

Since his first year as a Harvard graduate student in the 1960s, Schopf had the goal of conducting chemical analysis of an individual microscopic fossil inside a rock, but had no technique to do so, until now.

“I have wanted to do this for 40 years, but there wasn’t any way to do so before,” said Schopf, the first scientist to use confocal microscopy to study fossils embedded in such ancient rocks. He is director of UCLA’s Institute of Geophysics and Planetary Physics Center for the Study of Evolution and the Origin of Life.

Raman spectroscopy, a technique used primarily by chemists, allows you to see the molecular and chemical structure of ancient microorganisms in three dimensions, revealing what the fossils are made of without destroying the samples. Raman spectroscopy can help prove whether fossils are biological, Schopf said. This technique involves a laser from a microscope focused on a sample; most of the laser light is scattered, but a small part gets absorbed by the fossil.

Schopf is the first scientist to use this technique to analyze ancient microscopic fossils. He discovered that the composition of the fossils changed; nitrogen, oxygen and sulfur were removed, leaving carbon and hydrogen.

Confocal microscopy uses a focused laser beam to make the organic walls of the fossils fluoresce, allowing them to be viewed in three dimensions. The technique, first used by biologists to study the inner workings of living cells, is new to geology.

The ancient microorganisms are “pond scum,” among the earliest life, much too small to be seen with the naked eye.

Schopf’s UCLA co-authors include geology graduate students Abhishek Tripathi and Andrew Czaja, and senior scientist Anatoliy Kudryavtsev. The research is funded by NASA.

Schopf is editor of “Earth’s Earliest Biosphere” and “The Proterozoic Biosphere: A Multidisciplinary Study,” companion books that provide the most comprehensive knowledge of more than 4 billion years of the earth’s history, from the formation of the solar system 4.6 billion years ago to events half‑a‑billion years ago.

Original Source: UCLA News Release

February 2, 2006December 21, 2015 by Fraser Cain

The New 10th Planet Is Larger than Pluto

The size of UB313 compared with Pluto, Charoon, Moon and Earth. Image credit: Max Planck Institute. Click to enlarge
Claims that the Solar System has a 10th planet are bolstered by the finding by a group lead by Bonn astrophysicists that this alleged planet, announced last summer and tentatively named 2003 UB313, is bigger than Pluto. By measuring its thermal emission, the scientists were able to determine a diameter of about 3000 km, which makes it 700 km larger than Pluto and thereby marks it as the largest solar system object found since the discovery of Neptune in 1846 (Nature, 2 February 2006).

Like Pluto, 2003 ub313 is one of the icy bodies in the so-called Kuiper belt that exists beyond Neptune. It is the most distant object ever seen in the Solar System. Its very elongated orbit takes it up to 97 times farther from the Sun than is the Earth – almost twice as far as the most distant point of Pluto’s orbit – so that it takes twice as long as Pluto to orbit the Sun. When it was first seen, UB313 appeared to be at least as big as Pluto. But an accurate estimate of its size was not possible without knowing how reflective it is. A team lead by Prof. Frank Bertoldi from the University of Bonn and the Max Planck Institute for Radio Astronomy (MPIfR) and the MPIfR’s Dr. Wilhelm Altenhoff has now resolved this problem by using measurements of the amount of heat UB313 radiates to determine its size, which when combined with the optical observations also allowed them to determine its reflectivity. “Since UB313 is decidedly larger than Pluto,” Frank Bertoldi remarks, “it is now increasingly hard to justify calling Pluto a planet if UB313 is not also given this status.”

UB313 was discovered in January 2005 by Prof. Mike Brown and his colleagues from the Californian Institute of Technology in a sky survey using a wide field digital camera that searches for distant minor planets at visible wavelengths. They discovered a slowly moving, spatially unresolved source, the apparent speed of which allowed them to determine its distance and orbital shape. However, they were not able to determine the size of the object, although from its optical brightness it was believed to be larger than Pluto.

Astronomers have found small planetary objects beyond the orbits of Neptune and Pluto since 1992, confirming a then 40-year old prediction by astronomers Kenneth Edgeworth (1880-1972) and Gerard P. Kuiper (1905-1973) that a belt of smaller planetary objects beyond Neptune exists. The so-called Kuiper Belt contains objects left from the formation of our planetary system some 4.5 billion years ago. In their distant orbits they were able to survive the gravitational clean-up of similar objects by the large planets in the inner solar system. Some Kuiper Belt objects are still occasionally deflected to then enter the inner solar system and may appear as short period comets.

In optically visible light, the solar system objects are visible through the light they reflect from the Sun. Thus, the apparent brightness depends on their size as well as on the surface reflectivity. Latter is known to vary between 4% for most comets to over 50% for Pluto, which makes any accurate size determination from the optical light alone impossible.

The Bonn group therefore used the IRAM 30-meter telescope in Spain, equipped with the sensitive Max-Planck Millimeter Bolometer (MAMBO) detector developed and built at the MPIfR, to measure the heat radiation of 2003 qq47 at a wavelength of 1.2 mm, where reflected sunlight is negligible and the object brightness only depends on the surface temperature and the object size. The temperature can be well estimated from the distance to the sun, and thus the observed 1.2 mm brightness allows a good size measurement. One can further conclude that the UB313 surface is such that it reflects about 60% of the incident solar light, which is very similar to the reflectivity of Pluto.

“The discovery of a solar system object larger than Pluto is very exciting,” Dr. Altenhoff exclaims, who has researched minor planets and comets for decades. “It tells us that Pluto, which should properly also be counted to the Kuiper Belt, is not such an unusual object. Maybe we can find even other small planets out there, which could teach us more about how the solar system formed and evolved. The Kuiper Belt objects are the debris from its formation, an archeological site containing pristine remnants of the solar nebula from which the sun and the planets formed.” Dr. Altenhoff made the pioneering discovery of heat radiation from Pluto in 1988 with a predecessor of the current detector at the IRAM 30-meter telescope.

The size measurement of 2003 UB313 is published in the 2 February 2006 issue of Nature. The research team includes Prof. Dr. Frank Bertoldi (Bonn University and MPIfR), Dr. Wilhelm Altenhoff (MPIfR), Dr. Axel Weiss (MPIfR), Prof. Dr. Karl M. Menten (MPIfR), and Dr. Clemens Thum (IRAM).

UB313 is a members of a ring of some 100,000 objects on the outskirts of the solar system, beyond Neptune at distances over 4 billion km from the sun, over 30 times the distance between Earth and Sun. The objects in this “Kuiper belt” circle the sun in stable orbits with periods of about 300 years. In the middle of the last century, the existence of a ring of small planetary objects was first suggested by the astronomers Kenneth Edgeworth (1880-1972) and Gerard P. Kuiper (1905-1973), but the first discovery of a “Kuiper belt object” was not until 1992. By now, over 700 such objects are known. UB313 is somewhat different from the normal Kuiper belt in that its orbit is highly excentric and 45 degrees inclined to the ecliptic plane of the planets and Kuiper Belt. It is likely that is originated in the Kuiper Belt and was deflected to its inclined orbit by Neptune.

Original Source: Max Planck Society

Update: Pluto is demoted

February 2, 2006 by Fraser Cain

Binary Icy Asteroid in Jupiter’s Orbit

An artist’s illustration of the binary asteroids Patroclus (center) and Menoetius. Image credit: W.M. Keck Observatory. Click to enlarge
A bound pair of icy comets similar to the dirty snowballs circling outside the orbit of Neptune has been found lurking in the shadow of Jupiter.

Astronomers at the University of California, Berkeley, working with colleagues in France and at the Keck Telescope in Hawaii, have calculated the density of a known binary asteroid system that shares Jupiter’s orbit, and concluded that Patroclus and its companion probably are composed mostly of water ice covered by a patina of dirt.

Because dirty snowballs are thought to have formed in the outer reaches of the solar system, from which they are occasionally dislodged and end up looping closer to the sun as comets, the team suggests that the asteroid probably formed far from the sun. It most likely was captured in one of Jupiter’s Trojan points – two eddies where debris collects in Jupiter’s orbit – during a period when the inner solar system was intensely bombarded by comets, around 650 million years after the formation of the solar system.

If confirmed, this could mean that many or most of the probably thousands of Jupiter’s Trojan asteroids are dirty snowballs that originated much farther from the sun and at the same time as the objects now occupying the Kuiper Belt.

“It’s our suspicion that the Trojans are small Kuiper Belt objects,” said study leader Franck Marchis, a research astronomer at UC Berkeley.

Marchis and colleagues from the Institut de M??bf?canique C??bf?leste et Calculs d’??bf?ph??bf?m??bf?rides (IMCCE) at the Observatoire de Paris and from the W. M. Keck Observatory report their findings in the Feb. 2 issue of Nature.

The team’s conclusion adds support to a recent hypothesis about the evolution of the orbits of our solar system’s largest planets, Jupiter, Saturn, Uranus and Neptune, put forth by a group of researchers headed by Alessandro Morbidelli, a theoretical astronomer with the Conseil National de la Recherche Scientifique laboratory of the Observatoire de la Cote d’Azur, Nice, France.
Diagram of the asteroid 617 Patroclus and its companion in the solar system

In a Nature paper last year, Morbidelli and colleagues proposed that icy comets would have been captured in Jupiter’s Trojan points during the early history of the solar system. According to their scenario, during the first few hundred million years after the birth of the solar system, the large gas planets orbited closer to the sun, enveloped in a cloud of billions of large asteroids called planetesimals, perhaps 100 kilometers (62 miles) in diameter or less. Interactions with these planetesimals caused the large gaseous planets to migrate outward until about 3.9 billion years ago, when Jupiter and Saturn entered resonant orbits and began tossing the planetesimals around like confetti, some of them leaving the solar system for good.

The bulk of the remaining planetesimals settled into orbits beyond Neptune – today’s Kuiper Belt and the source of short-period comets – but a small number were captured in the Trojan eddies of the giant planets, in particular Jupiter.

“This is the first time anyone has determined directly the density of a Trojan asteroid, and it supports the new scenario proposed by Morbidelli,” said coauthor Daniel Hestroffer, an astronomer at the IMCEE. “These asteroids would have been captured in the Trojan points at a time when the rocky planets were still forming, and this perturbation of the planetesimals about 650 million years after the birth of the solar system could have created the late bombardment of the moon and Mars.”

Though Marchis refers to the scenario as “a nice story,” he admits that more work needs to be done to provide support for it.

“We need to discover more binary Trojans and observe them to see if low density is a characteristic of all Trojans,” he said.

Trojan asteroids are those caught in the so-called Lagrange points of Jupiter’s orbit, located the same distance from Jupiter as Jupiter is from the sun – 5 astronomical units, or 465 million miles. These points, one leading and the other trailing Jupiter, are places were the gravitational attraction of the sun and Jupiter are balanced, allowing debris to collect like dust bunnies in the corner of a room. Hundreds of asteroids have been discovered in the leading (L4) and trailing (L5) points, each orbiting around that point as if in an eddy.

The asteroid 617 Patroclus, originally discovered at L5 and named in 1906, was found to have a companion in 2001, and so far is the only known Trojan binary. The discoverers were not able to estimate the orbit of the components because they had too few observations.

As experienced asteroid hunters, Marchis and his colleagues in August this year discovered the first triple asteroid system, 87 Sylvia, much closer to the sun in the main asteroid belt between Mars and Jupiter, and used a powerful 8-meter telescope of the European Southern Observatory’s Very Large Telescope in Chile to study the three objects. They were able to chart the orbits of the asteroids to estimate the density of Sylvia, from which they concluded it is a rubble-pile of loosely, packed rock.

The French and American team tried the same technique with the much more distant Patroclus, employing imaging data from the Keck II Laser Guide Star System at the W. M. Keck Observatory on Mauna Kea, which yields a sharp resolution impossible with any other ground-based telescope.

“Before, we could only look at objects near a bright reference star, limiting the use of adaptive optics to a small percentage of the heavens,” Marchis said. “Now, we can use adaptive optics to view almost any point on the sky.”

The laser guide star system uses a laser beam to excite sodium atoms within a small spot in the upper atmosphere. This artificial “star” is used to measure atmospheric turbulence, which is then removed by the movable mirrors of the Keck adaptive optics system.

With the system providing an unparalleled 58 milliarcsecond resolution, the Keck team made five observations in the infrared between November 2004 and July 2005. Marchis and his colleagues determined that the density of Patroclus and its companion, which are about the same size and circle around their center of mass every 4.3 days at a distance of 680 kilometers (423 miles), was very low: 0.8 grams per cubic centimeter, about one third that of rock and light enough to float in water. Assuming a rocky composition similar to that of Jupiter’s moons Callisto and Ganymede, the components of the system would have to be very loosely packed – about half empty space, an internal characteristic which is not expected for a same-size binary system, the researchers concluded.

The team suggests a more reasonable composition of water ice with only 15 percent open space, which makes these objects similar to comets and small Kuiper Belt objects, which have been determined to have densities less than water.

Marchis suspects that the binary system formed when a single large asteroid was torn asunder by the gravitational tug of Jupiter.

“The Patroclus system displays similar characteristics to the binary Near Earth Asteroids, which are believed to have formed during an encounter with a terrestrial planet by tidal splitting,” he said. “In the case of a Trojan asteroid, it is only when the work of our collaborators was published recently that we could suggest that this encounter was with Jupiter.”

Because in Homer’s Iliad, Patroclus was Achilles’ companion and a hero of the Trojan War, Achilles would have been an appropriate name for one of the two asteroids, which are about the same size. However, another asteroid already has the name Achilles, so Marchis and his collaborators proposed naming the smallest member of the binary system Menoetius, after the father of Patroclus. The Committee on Small Body Names of the International Astronomical Union has tentatively accepted the name. The asteroid designated Menoetius is about 112 kilometers (70 miles) in diameter, while Patroclus is about 122 kilometers (76 miles) wide.

In addition to Marchis, the team included astronomy professor Imke de Pater and postdoctoral fellow Michael H. Wong of UC Berkeley; Daniel Hestroffer, Pascal Descamps, J??bf?r??bf?me Berthier and Fr??bf?d??bf?ric Vachier of the Institut de M??bf?canique C??bf?leste et de Calculs des ??bf?ph??bf?m??bf?rides (IMCCE); and Antonin Bouchez, Randall Campbell, Jason Chin, Marcos van Dam, Scott Hartman, Erik Johansson, Robert Lafon, David Le Mignant, Paul Stomski, Doug Summers and Peter Wizinovich of the W. M. Keck Observatory.

The project was supported by grants from the National Science Foundation through the Science and Technology Center for Adaptive Optics and by the National Aeronautics and Space Administration. Most of the data were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership between the California Institute of Technology, the University of California and NASA, with additional observations obtained at the Gemini Observatory operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership.

Original Source: UC Berkeley News Release