John Powell
June 12th 2003, 02:03 PM
Newscientist-1
POWELL:
In the thread "The Center of the Universe" in the philosophy department of TWEB, Socrates supported claims that the Sun is special for its type with two New Scientist articles. Four of the five scientists referred to in the letter responded to my emails. I will post the New Scientist Articles, the emails, and my comments.
First, I will post the two "New Scientist" articles. I will add boldfacing.
http://www.newscientist.com/
NEWSCIENTIST:
Thank our lucky star
New Scientist vol 161 issue 2168 - 09 January 1999, page 15
A catastrophic explosion on the Sun and long-distance calls to aliens were hot news at this week's meeting of the American Astronomical Society in Austin, Texas. Charles Seife reports
COULD the Sun send out a monstrous flare powerful enough to melt the ice on Jupiter's moons, destroy much of Earth's ozone layer and obliterate all our satellites? It's possible, say astronomers who have studied other Sun-like stars in our Galaxy, which seem to produce enormous "superflares" about once a century. They are baffled by the fact that there are no records of similar solar explosions.
Our Sun often sends flares towards Earth, and more energetic explosions can spit out giant blobs of ionised gas called coronal mass ejections. Roughly once or twice a decade, the eruption of stellar material is powerful enough to send huge electric currents racing around the Earth's upper atmosphere, disrupting power grids and communications satellites. In 1989, one such explosion knocked out a power grid in northern Quebec.
But at this week's meeting, a team of three astronomers reported that this kind of solar activity is mild compared with that of the Sun's sister stars. They studied records of lone stars in our Galaxy with roughly the same brightness, size and composition as the Sun. They found that over the past century, almost all these Sun-like stars had produced superflares that made them dramatically brighter for minutes or even days.
"One of the cases I have is a star, S-Fornax, where for a 40-minute period it was seen to be three magnitudes brighter than usual," says Brad Schaefer of Yale University, a member of the team. The astronomers conclude that Sun-like stars normally produce a bright superflare about once a century.
A superflare on the Sun would be about 10 000 times as powerful as the explosion that caused the Canadian blackout. "It would melt large flood plains on the outer, icy satellites," says Schaefer. Although life on Earth would survive, the atmosphere would glow very brightly and half the ozone layer would be destroyed in the blink of an eye, not to mention spacecraft. "You'd probably lose the entire satellite fleet," says Schaefer.
Why a superflare has not occurred on the Sun in recorded history is unclear. "I think a consensus is emerging that our Sun is extraordinarily stable," suggests Galen Gisler, an astronomer at the Los Alamos National Laboratory in New Mexico. "We seem to have found a star that is extremely stable and friendly to life---or we are just on a star that happens to be stable right now and will not always be so."
Charles Seife
POWELL:
That was the New Scientist article by Charles Seife. The following is one by Marcus Chowm.
NEWSCIENTIST:
What a star!
New Scientist vol 162 issue 2192 - 26 June 1999, page 17
If the Sun is exceptional, alien life may be hard to find
DON'T believe everything you read in books---our Sun is no ordinary star. And its very uniqueness has implications for SETI, the search for extraterrestrial life, claims Guillermo Gonzalez of the University of Washington in Seattle: "Unless astronomers narrow down their search to stars as exceptional as the Sun, they are wasting much of their time."
The Sun is a single star whereas most stars are in multiple systems. But that apart, textbooks say the Sun is pretty average. However, after trawling through the data on the Sun, Gonzalez has found many idiosyncrasies. It is among the most massive 10 per cent of stars in its neighbourhood. It also has 50 per cent more heavy elements than other stars of its age and type, and about a third of the variation in brightness.
The most unusual aspects of the Sun concern its orbit around the centre of the Galaxy, says Gonzalez. Its orbit is significantly less elliptical than that of other stars of its age and type, and hardly inclined at all to the Galactic plane. What's more, the Sun is orbiting very close to the "corotation radius" for the Galaxy---the place at which the angular speed of the spiral pattern matches that of the stars.
Gonzalez argues that these exceptional characteristics made it possible for intelligent life to emerge on Earth. He points out that stable planetary orbits such as the Earth's are much more likely around single stars like the Sun. For a massive star with inhabitable planets that are relatively far away, stellar flare-ups would be little threat to the planets. Heavy elements are essential to make planets like Earth, and a star with a stable light output is essential for life.
As for the orbit of the Sun, its circularity prevents it plunging into the inner Galaxy where life-threatening supernovae are more common. And its small inclination to the Galactic plane prevents abrupt crossings of the plane that would stir up the Sun's Oort Cloud and bombard the Earth with comets. By being near the Galaxy's corotation radius, the Sun avoids crossing the spiral arms too often, an event that would expose it to supernovae, which are more common there.
Because life-bearing stars have to be close to the corotation radius, that rules out more than 95 per cent of stars in the Galaxy in one fell swoop. "There are fewer stars suitable for intelligent life than people realise," says Gonzalez, who has submitted his findings to Astronomy & Geophysics. "I'm amazed at how little thought the SETI people put into selecting their stars."
Seth Shostak of the SETI Institute in Mountain View, California, disagrees. "Our targets are all very close to the Sun. They share our Galactic neighbourhood and motions. If the Sun is the most suitable type of star to be scrutinised, then we are, indeed, looking in all the best places."
"Most astronomers disagree with Gonzalez," adds SETI researcher Dan Werthimer of the University of California at Berkeley. "Our Sun is pretty average. In any case, you don't need a star exactly like our Sun for life."
Marcus Chown
POWELL:
Next, I will post the emails.
John Powell
POWELL:
In the thread "The Center of the Universe" in the philosophy department of TWEB, Socrates supported claims that the Sun is special for its type with two New Scientist articles. Four of the five scientists referred to in the letter responded to my emails. I will post the New Scientist Articles, the emails, and my comments.
First, I will post the two "New Scientist" articles. I will add boldfacing.
http://www.newscientist.com/
NEWSCIENTIST:
Thank our lucky star
New Scientist vol 161 issue 2168 - 09 January 1999, page 15
A catastrophic explosion on the Sun and long-distance calls to aliens were hot news at this week's meeting of the American Astronomical Society in Austin, Texas. Charles Seife reports
COULD the Sun send out a monstrous flare powerful enough to melt the ice on Jupiter's moons, destroy much of Earth's ozone layer and obliterate all our satellites? It's possible, say astronomers who have studied other Sun-like stars in our Galaxy, which seem to produce enormous "superflares" about once a century. They are baffled by the fact that there are no records of similar solar explosions.
Our Sun often sends flares towards Earth, and more energetic explosions can spit out giant blobs of ionised gas called coronal mass ejections. Roughly once or twice a decade, the eruption of stellar material is powerful enough to send huge electric currents racing around the Earth's upper atmosphere, disrupting power grids and communications satellites. In 1989, one such explosion knocked out a power grid in northern Quebec.
But at this week's meeting, a team of three astronomers reported that this kind of solar activity is mild compared with that of the Sun's sister stars. They studied records of lone stars in our Galaxy with roughly the same brightness, size and composition as the Sun. They found that over the past century, almost all these Sun-like stars had produced superflares that made them dramatically brighter for minutes or even days.
"One of the cases I have is a star, S-Fornax, where for a 40-minute period it was seen to be three magnitudes brighter than usual," says Brad Schaefer of Yale University, a member of the team. The astronomers conclude that Sun-like stars normally produce a bright superflare about once a century.
A superflare on the Sun would be about 10 000 times as powerful as the explosion that caused the Canadian blackout. "It would melt large flood plains on the outer, icy satellites," says Schaefer. Although life on Earth would survive, the atmosphere would glow very brightly and half the ozone layer would be destroyed in the blink of an eye, not to mention spacecraft. "You'd probably lose the entire satellite fleet," says Schaefer.
Why a superflare has not occurred on the Sun in recorded history is unclear. "I think a consensus is emerging that our Sun is extraordinarily stable," suggests Galen Gisler, an astronomer at the Los Alamos National Laboratory in New Mexico. "We seem to have found a star that is extremely stable and friendly to life---or we are just on a star that happens to be stable right now and will not always be so."
Charles Seife
POWELL:
That was the New Scientist article by Charles Seife. The following is one by Marcus Chowm.
NEWSCIENTIST:
What a star!
New Scientist vol 162 issue 2192 - 26 June 1999, page 17
If the Sun is exceptional, alien life may be hard to find
DON'T believe everything you read in books---our Sun is no ordinary star. And its very uniqueness has implications for SETI, the search for extraterrestrial life, claims Guillermo Gonzalez of the University of Washington in Seattle: "Unless astronomers narrow down their search to stars as exceptional as the Sun, they are wasting much of their time."
The Sun is a single star whereas most stars are in multiple systems. But that apart, textbooks say the Sun is pretty average. However, after trawling through the data on the Sun, Gonzalez has found many idiosyncrasies. It is among the most massive 10 per cent of stars in its neighbourhood. It also has 50 per cent more heavy elements than other stars of its age and type, and about a third of the variation in brightness.
The most unusual aspects of the Sun concern its orbit around the centre of the Galaxy, says Gonzalez. Its orbit is significantly less elliptical than that of other stars of its age and type, and hardly inclined at all to the Galactic plane. What's more, the Sun is orbiting very close to the "corotation radius" for the Galaxy---the place at which the angular speed of the spiral pattern matches that of the stars.
Gonzalez argues that these exceptional characteristics made it possible for intelligent life to emerge on Earth. He points out that stable planetary orbits such as the Earth's are much more likely around single stars like the Sun. For a massive star with inhabitable planets that are relatively far away, stellar flare-ups would be little threat to the planets. Heavy elements are essential to make planets like Earth, and a star with a stable light output is essential for life.
As for the orbit of the Sun, its circularity prevents it plunging into the inner Galaxy where life-threatening supernovae are more common. And its small inclination to the Galactic plane prevents abrupt crossings of the plane that would stir up the Sun's Oort Cloud and bombard the Earth with comets. By being near the Galaxy's corotation radius, the Sun avoids crossing the spiral arms too often, an event that would expose it to supernovae, which are more common there.
Because life-bearing stars have to be close to the corotation radius, that rules out more than 95 per cent of stars in the Galaxy in one fell swoop. "There are fewer stars suitable for intelligent life than people realise," says Gonzalez, who has submitted his findings to Astronomy & Geophysics. "I'm amazed at how little thought the SETI people put into selecting their stars."
Seth Shostak of the SETI Institute in Mountain View, California, disagrees. "Our targets are all very close to the Sun. They share our Galactic neighbourhood and motions. If the Sun is the most suitable type of star to be scrutinised, then we are, indeed, looking in all the best places."
"Most astronomers disagree with Gonzalez," adds SETI researcher Dan Werthimer of the University of California at Berkeley. "Our Sun is pretty average. In any case, you don't need a star exactly like our Sun for life."
Marcus Chown
POWELL:
Next, I will post the emails.
John Powell