Lewis Page The Register Fri, 11 Jun 2010 10:42 UTC
Most of Oort Cloud 'of extra-solar origin', say boffins
Halley's comet and other famous objects in our solar system may in fact have formed in orbit around alien suns far off across the vast gulfs of interstellar space, according to new research.
Comets, Halley's in particular, are old friends of the human race and their regular appearances in the inner solar system are thought to have been noted in humanity's earliest records. But in astronomical terms human intelligence is a very new thing - indeed, so is life on Earth.
According to top international boffins, long long before our home planet had even formed, the Sun and the various stars in our local neighbourhood were much closer together. The accretion discs of dust and space gumble from which all the planets and comets and everything originally formed were almost touching, and matter was routinely passed around among the young and excitable stars.
One wonders... Did the inhabitants of galaxy NGC 891 duck when Comet McNaught flew past the edge-on spiral on the morning of June 8th? Mike O'Connor and Tristan Dilapo took this picture of the cosmic close encounter from Colden, New York:
"The comet was only 10 degrees above the horizon," says O'Connor. "Nevertheless, we got a good picture using a 12-inch telescope and an SBIG ST9-E camera."
And, no, the denizens of that distant galaxy did not flinch, flee, duck or take notice in any way. NGC 891 is 30 million light years away, far removed from the willowy tail of Comet McNaught.
We Earthlings are having the true close encounter. Comet McNaught (C/2009 R1) is gliding through the inner solar system, due to approach our planet only 100 million miles away on June 15th and 16th. The approaching comet looks great in small telescopes, and may yet become a naked-eye object before the end of the month. Because this is Comet McNaught's first visit, predictions of future brightness are necessarily uncertain; amateur astronomers should be alert for the unexpected.
A fresh comet is swinging through the inner solar system, and it is brightening rapidly as it approaches the sun. Presenting, Comet McNaught (C/2009 R1):
Michael Jäger of Stixendorf, Austria, took the picture on June 6th using an 8-inch telescope. The comet's green atmosphere is larger than the planet Jupiter, while the long willowy ion tail stretches more than a million kilometers through space. These dimensions make the comet a fine target for backyard telescopes.
Comet McNaught can be found low in the northeastern sky before dawn gliding through the constellation Perseus. It is brightening as it approaches Earth for a 1.13 AU close encounter on June 15th and 16th. Currently, the comet is at the threshold of naked eye visibility (5th to 6th magnitude) and could become as bright as the stars of the Big Dipper (2nd magnitude) before the end of the month. Estimates are uncertain, however, because this comet is a newcomer to the inner solar system, and thus somewhat unpredictable.
This movie shows asteroids observed so far by NASA's Wide-field Infrared Survey Explorer, or WISE. As WISE scans the sky from its polar orbit, more and more asteroids and comets are caught in its infrared vision. The mission has surveyed about three-fourths of the sky; however, data for only about 50 percent of the sky has been processed for asteroids and comets at this time.
The white dots show asteroids observed by WISE - most of these are in the Main Belt between Mars and Jupiter, and some, the Trojans, orbit in front of, or behind, Jupiter. The red dots represent newfound near-Earth objects, which are asteroids and comets with orbits that come relatively close to Earth's path around the sun. The green dots are previously known near-Earth objects observed by WISE. The yellow squares show all comets seen by WISE so far.
As of May 24, 2010, WISE has seen more than 60,000 asteroids. It has observed more than 70 comets, 12 of which are new, and about 200 near-Earth objects, more than 50 of which are new.
Did a large, icy comet smash into Neptune two centuries ago? That's the picture that is emerging from the latest measurements of gases in the atmosphere of the giant blue planet.
At a meeting this week of the American Astronomical Society in Miami, Florida, Paul Hartogh, project scientist for the Herschel mission, the European Space Agency's infrared observatory satellite, described the mission's first results for the Solar System. These include measurements of abnormally high levels of carbon monoxide in Neptune's stratosphere - a possible trace of a comet impact.
Emmanuel Lellouch, an astronomer at the Paris Observatory, first published the idea five years ago, on the basis of far less certain measurements made by a 30-metre radio telescope on the mountain Pico Veleta in Spain[1]. "We are becoming more confident," says Lellouch, who is a co-author with Hartogh on a forthcoming paper concerning the Herschel results in the journal Astronomy & Astrophysics.
We rarely see a good comet when it's at its best. Most comets are brightest when nearest the Sun - just when they're most likely to be hidden in the Sun's glare or below the sunrise or sunset horizon.
That's the situation this spring with Comet C/2009 R1 (McNaught). Even so, observers in the Northern Hemisphere should be able to pick it up with telescopes, and possibly binoculars, just before dawn for at least part of June, during its runup in brightness.
And in fact, the comet is turning out to be 1 or 2 magnitudes brighter that we predicted in the June Sky & Telescope (page 60). Let's hope this behavior keeps up!
Our sun may have stolen the vast majority of its comets from other stars. The theft could explain the puzzling profusion of objects in a huge reservoir surrounding the sun called the Oort cloud.
The Oort cloud is a collection of comets thought to orbit the sun in a roughly spherical halo about 50,000 times as far from the sun as Earth - at the outer edge of the solar system. How did the comets get there? In the standard picture, they formed much closer to the sun, then migrated outward in a two-stage process.
First, the gravity of the giant planets flung them into elongated orbits to form a population called the scattered disc. Objects in the scattered disc come about as close to the sun as Neptune, but venture dozens of times further out, to more than 1000 times the Earth-sun distance. That far from the sun, the gravitational pull of the galaxy becomes significant, so many of the scattered-disc objects get pulled out to populate the Oort cloud.
There is a problem with this picture, however. Simulations have long predicted that this process could only populate the Oort cloud with 10 times as many comets as are currently in the scattered disc, while estimates based on observed comets suggest the ratio is more like 700 to 1.
Halley's Comet was last seen passing near the earth 24 years ago. The Comet passes through our inner solar system every 76 years. As most of us having an interest in astronomy know that the Halley's Comet is a huge piece of rock orbiting our sun at a very high speed. The reason that the Halley's Comet is called a Comet and not a planet is that it travels at speeds much greater than planets. Planets travel at a relatively slow speed whereas comets travel at extremely fast speeds leaving behind a trail of meteors and meteorites that are usually called the comet's cosmic dust.
There is still a long time before the Halley's Comet can be seen again, but nowadays the comet is at such a position (far away from the earth obviously) that its cosmic dust can be seen in form of some meteor showers near the earth. The shower is expected to become visible 3 to 4 days before and after May 6th.
Astronomers analyzing debris from a comet that broke apart last summer spied pieces as small as smoke-sized particles and as large as football-field-sized fragments. But it's the material they didn't see that has aroused their curiosity.
Tracking the doomed comet, named LINEAR, the Hubble telescope and the Very Large Telescope in Chile found tiny particles that made up the 2,000-mile-long dust tail and 16 large fragments, some as wide as 330 feet. But the telescopes didn't detect any intermediate-sized pieces. If they exist, then the fundamental building blocks that comprised LINEAR's nucleus may be somewhat smaller than current theories suggest.
The Hubble picture shows that that LINEAR's nucleus has been reduced to a shower of glowing "mini-comets" resembling the fiery fragments from an exploding aerial firework. This picture was taken with Hubble's Wide Field Planetary Camera 2 on August 5, 2000, when the comet was at a distance of 64 million miles (102 million kilometers) from Earth.
Scientists from the Max Planck Institute for Solar System Research identify the active regions on the surface of comets.
Studying comets can be quite dangerous - especially from close up. Because the tiny particles of dust emitted into space from the so-called active regions on a comet's surface can damage space probes. Scientists from the Max Planck Institute for Solar System Research in Germany have now developed a computer model that can locate these regions using only the information available from Earth. The new method could help calculate a safe flight route for ESA's space probe Rosetta, which is scheduled to arrive at the comet Churyumov-Gerasimenko in 2014. (Astronomy & Astrophysics, 512, A60, 2010)