Stupid Question ™
Sept. 13, 2004
By John Ruch
© 2004
Q: How many planets are there outside of our solar system?
—anonymous, from the Internet
A: This question came in before the Sept. 10 announcement of a possible composite photograph of an “extrasolar” planet, so—one more than before, I guess.
The current count is anywhere from 124 to 140, depending on who’s counting, how and with what degree of skepticism.
They are all immensely huge. The smallest (and most recently discovered) would be about the size of Neptune—which is about 60 times the size of Earth. Most are much larger than Jupiter, our solar system’s largest planet, which is about 1,300 times the size of Earth. Like both Neptune and Jupiter, the “known” extrasolar planets are likely big balls of gas.
You wouldn’t know it from the very definitive language in astronomy textbooks and NASA and university web sites, but there is certainly room to argue the reality of any of these observations—at least, if they’re to be called “planets.”
Leaving aside the question of the possible photograph (and another similar image announced in May), none of the extrasolar planet “discoveries” involves direct observation.
At best, this is an art of interpreting “wobbles” and (most frequently and credibly) velocity shifts (sometimes also known as “wobbles”) in the movements of stars, from which it is inferred that gravitational pull from an orbiting planet is the cause. The size of the planet can be guessed from the movement.
Another mode is presuming a regular change in the beat of a pulsar—a star that emits bursts of energy rather than just glowing steadily—is due to the gravitational suction of a nearby planet. And still another is that the slight dimming of a star is due to a planet coming between it and us (a frequent “confirmation” method to other forms of detection).
The latest method is optical interferometry, which in theory will allow planets to be literally, actually seen (via infrared telescopy, usually) by using multiple images taken from various angles that cancel out the otherwise overwhelming glare of the accompanying star. If planets are out there, anyhow. It can also include adding spectrography that can determine chemical elemental makeup based on the light the object emits. (This led to the claimed discovery of a sodium-containing “atmosphere” on one “planet” in 2001.)
The Sept. 10 image of a possible planet around the star identified as 2M1207 was produced by that method by the European Southern Observatory.
The velocity-shift detection method kicked off the whole discovery boom in the early 1990s, and since then there’s essentially been an extrasolar planet discovered every month.
It’s an exciting field of observation, but there are philosophical and practical reasons for skepticism.
We’re talking about very minute, indirect observations driven by a romantic quest to, as NASA’s web site baldly puts it, be able to say we “have found another Earth.” There is a strong tea-leaf aspect to this.
And what is often left out of discussions of this field is its history of wishful-thinking errors and suspicious data. For example, as NASA again puts it, “many” of the observed planets “are bizarre,” displaying highly eccentric orbits and a proximity to their stars that doesn’t square with accepted planetary-creation theory. Why such a high degree of “bizarre” behavior? How about observer error or wishful thinking? The individual explanations become very involved.
Even more curiously, it has been determined that our Sun just so happens to have no detectable wobble from all the planets around it—this being blamed on sunspots masking the electromagnetic detection of such a shimmy. Hmm.
It’s also worth noting there is no agreement on what a “planet” is. You and I think of a ball orbiting a star; but some observing astronomers accept a definition that includes a body that is not in (stellar) orbit. They may be “failed stars,” if you will.
The earliest claimed extrasolar planet detection, in the late 1960s, was almost certainly bunk. It involved a supposed wobble of a star. Just about nobody else could detect any wobble. Instrument error and wishful thinking were likely culprits. The wobble method is not favored today.
Extrasolar excitement renewed in 1991 with a pulsar observation that was later acknowledged to be a calculation error. This did not stop a 1992 observation that claimed to find three planets around another pulsar. The observation remains controversial. (It’s also worth noting that pulsars are infamous for bizarre changes and fluctuations, and nobody has satisfactorily explained their nature in the first place.)
Wisely moving to yet another detection method, astronomers really kicked things into gear in 1995, with a flood of velocity-shift observations. Many of these are considered quite convincing and will prove to be either a watershed or a scientific fad. Things have not let up since.
I am being hyper-skeptical here because somebody has to be. Astronomers certainly put individual observations to the fire in their journals, but the overall idea of the reality of these observations is rarely questioned openly and certainly not for public consumption; quite the opposite, in fact, as misleadingly positive statements are made by highly respected sources.
The good news is that interferometry has the potential to provide direct images of some types of extrasolar planets. That could really settle some matters.
On the other hand, it may only raise more questions. Take the Sept. 10 picture, for example. The “planet” is pretty convincing as an image, but since that image is two-dimensional, there’s no way to tell the two objects’ actual relationship to each other, let alone if one is orbiting the other. The “planet” could be light-years closer or farther away from us than the star is.
Bringing most or all of the observation methods together may paint a convincing “yea” or “nay” picture of extrasolar planets. Or maybe it will take interstellar space flight to determine the question for sure.
Showing posts with label astronomy. Show all posts
Showing posts with label astronomy. Show all posts
March 29, 2008
March 28, 2008
Tides
Stupid Question ™
May 16, 2002
By John Ruch
© 2002
Q: Why are there two tides every day?
—Kris Willis
A: You probably know that tides have something to do with the Moon’s gravity yanking water upward. But when high tide is happening on the side of Earth nearest the Moon, another high tide is bulging out on the opposite side of the planet—away from the Moon. (Meanwhile, low tides occur on the points in between).
Broadly speaking, a tide is the stretching that happens to a body that’s under another body’s gravitational attraction. In principle this happens between all bodies in the universe, but the effect is only significant with large masses at close distances. That’s why the Moon exerts much stronger tides on Earth than the Sun does; it’s a lot smaller than the Sun, but a lot closer.
Tides affect Earth’s entire surface, which can bulge as much as 14 inches (not noticeable over such a large area). But in common terms, tides specifically are the bulges in ocean water which move around the planet as tidal waves, causing high tides when they meet the shore or low tides when they suck water back out to sea.
(Depending on size, depth and geography, some bodies of water have miniscule tides or none at all; the Gulf of Mexico has only one per day.)
Tides on Earth are indeed influenced by the Moon. That’s why you get two high tides every 25 hours (or usually, though not always, twice every day), coincident with the Moon’s revolution around Earth.
But it’s a mistake to imagine Earth sitting there while the Moon flies by, dragging the ocean with it. In fact, Earth and the Moon are locked together into a single gravitational system, both orbiting a common center of gravity and causing tides on each other as they go.
The Earth’s center of mass is the center of the planet. But the Earth-and-Moon system’s center of mass shifts 3,000 miles toward the Moon, to a point 1,000 miles below the Earth’s surface on the Moon side.
Both the center of Earth and the center of the Moon orbit this point—the nexus of their combined gravitational forces.
Looking at this system, we see the Moon indeed creates a tidal bulge on Earth’s near surface. We also see that the center of Earth is orbiting the system’s center of gravity, and like all orbiting bodies is in free-fall. This means it is under the Moon’s gravitational pull, but has such strong angular velocity it keeps “falling” in a circular path nearly forever.
This centripetal (“center-seeking”) force is balanced, as Newton pointed out, by a centrifugal (“center-fleeing”) force that pushes outward—in this case, creating a tidal bulge that approximately equals that of the Moon on the other side.
May 16, 2002
By John Ruch
© 2002
Q: Why are there two tides every day?
—Kris Willis
A: You probably know that tides have something to do with the Moon’s gravity yanking water upward. But when high tide is happening on the side of Earth nearest the Moon, another high tide is bulging out on the opposite side of the planet—away from the Moon. (Meanwhile, low tides occur on the points in between).
Broadly speaking, a tide is the stretching that happens to a body that’s under another body’s gravitational attraction. In principle this happens between all bodies in the universe, but the effect is only significant with large masses at close distances. That’s why the Moon exerts much stronger tides on Earth than the Sun does; it’s a lot smaller than the Sun, but a lot closer.
Tides affect Earth’s entire surface, which can bulge as much as 14 inches (not noticeable over such a large area). But in common terms, tides specifically are the bulges in ocean water which move around the planet as tidal waves, causing high tides when they meet the shore or low tides when they suck water back out to sea.
(Depending on size, depth and geography, some bodies of water have miniscule tides or none at all; the Gulf of Mexico has only one per day.)
Tides on Earth are indeed influenced by the Moon. That’s why you get two high tides every 25 hours (or usually, though not always, twice every day), coincident with the Moon’s revolution around Earth.
But it’s a mistake to imagine Earth sitting there while the Moon flies by, dragging the ocean with it. In fact, Earth and the Moon are locked together into a single gravitational system, both orbiting a common center of gravity and causing tides on each other as they go.
The Earth’s center of mass is the center of the planet. But the Earth-and-Moon system’s center of mass shifts 3,000 miles toward the Moon, to a point 1,000 miles below the Earth’s surface on the Moon side.
Both the center of Earth and the center of the Moon orbit this point—the nexus of their combined gravitational forces.
Looking at this system, we see the Moon indeed creates a tidal bulge on Earth’s near surface. We also see that the center of Earth is orbiting the system’s center of gravity, and like all orbiting bodies is in free-fall. This means it is under the Moon’s gravitational pull, but has such strong angular velocity it keeps “falling” in a circular path nearly forever.
This centripetal (“center-seeking”) force is balanced, as Newton pointed out, by a centrifugal (“center-fleeing”) force that pushes outward—in this case, creating a tidal bulge that approximately equals that of the Moon on the other side.
Meteoric Dust
Stupid Question ™
March 14, 2002
By John Ruch
© 2002
Q: I read that a trillion meteorite particles hit Earth daily. How much does this stuff weigh? Where does it all go? Does it affect the planet’s rotation?
—Rhonda
A: Earth indeed constantly attracts meteoric material, mostly debris from comets and asteroids. While the big ones get all the attention, the vast majority are in the form of microscopic dust. Even the average “shooting star” is only about as big as a sand grain.
The only real answer to “how much” is “a whole lot.” But scientists like to quantify, and they’ve made a series of educated, but nonetheless wild, guesses.
The first measurements were made in the 1950s, using magnets to draw iron-containing material out of dust. (Many meteorites contain iron.) They came up with huge figures like 14 million tons a year. But they also had a huge margin of error due to the amount of iron-containing debris we and the planet both create.
The current best guess, published in 1995, is about 44,000 tons a year, or 120 tons per day, mostly in the form of particles around 0.2 millimeters in diameter. This figure was drawn from a broad range of sources: particles from more-pure ocean and polar-ice sediments; dust collected by planes in the upper atmosphere; analysis of moon dust; and especially the debris that bombarded NASA’s Long Duration Exposure Facility satellite (in orbit from 1984 to 1990).
And even this figure was reported with an error margin of 22,000 tons.
This figure is a broad average that describes the normal influx of medium to small meteorites. It doesn’t count the rare gigantic impacts.
Also, the figure specifically describes how much material enters the atmosphere, not just what hits the ground. The smallest dust slows down so rapidly in the upper atmosphere that it actually floats there, probably for years at a time, before getting washed down by rain. An estimated 1 to 10 percent of all dust in the upper atmosphere is meteoric.
Meteoric debris eventually wears away like any other material. It tends to wear faster than terrestrial rocks because of its purer elements. A lot of the dust is eaten up in the air by sulfuric acid droplets.
Atmospherically, meteoric dust probably serves as nuclei for raindrops, and is suspected of causing noctilucent clouds (high clouds that glow after dark) and “sprites” (lightning that shoots out of the tops of clouds).
Some meteoric dust is very carbon-rich, and there are still-controversial claims that it was the basis of the rich soil called loess, of petroleum, and possibly of the organic material that was the basis for life itself.
While that would be a big deal, the sheer weight of the debris isn’t. Earth is huge—about 611,000,000,000,000,000,000 tons. The weight of all the water on the planet is less than 0.02 percent of that. And the weight of all the meteoric debris (figuring 44,000 tons a year for 4.5 billion years) would be about 0.02 percent of the water’s weight. Completely negligible.
March 14, 2002
By John Ruch
© 2002
Q: I read that a trillion meteorite particles hit Earth daily. How much does this stuff weigh? Where does it all go? Does it affect the planet’s rotation?
—Rhonda
A: Earth indeed constantly attracts meteoric material, mostly debris from comets and asteroids. While the big ones get all the attention, the vast majority are in the form of microscopic dust. Even the average “shooting star” is only about as big as a sand grain.
The only real answer to “how much” is “a whole lot.” But scientists like to quantify, and they’ve made a series of educated, but nonetheless wild, guesses.
The first measurements were made in the 1950s, using magnets to draw iron-containing material out of dust. (Many meteorites contain iron.) They came up with huge figures like 14 million tons a year. But they also had a huge margin of error due to the amount of iron-containing debris we and the planet both create.
The current best guess, published in 1995, is about 44,000 tons a year, or 120 tons per day, mostly in the form of particles around 0.2 millimeters in diameter. This figure was drawn from a broad range of sources: particles from more-pure ocean and polar-ice sediments; dust collected by planes in the upper atmosphere; analysis of moon dust; and especially the debris that bombarded NASA’s Long Duration Exposure Facility satellite (in orbit from 1984 to 1990).
And even this figure was reported with an error margin of 22,000 tons.
This figure is a broad average that describes the normal influx of medium to small meteorites. It doesn’t count the rare gigantic impacts.
Also, the figure specifically describes how much material enters the atmosphere, not just what hits the ground. The smallest dust slows down so rapidly in the upper atmosphere that it actually floats there, probably for years at a time, before getting washed down by rain. An estimated 1 to 10 percent of all dust in the upper atmosphere is meteoric.
Meteoric debris eventually wears away like any other material. It tends to wear faster than terrestrial rocks because of its purer elements. A lot of the dust is eaten up in the air by sulfuric acid droplets.
Atmospherically, meteoric dust probably serves as nuclei for raindrops, and is suspected of causing noctilucent clouds (high clouds that glow after dark) and “sprites” (lightning that shoots out of the tops of clouds).
Some meteoric dust is very carbon-rich, and there are still-controversial claims that it was the basis of the rich soil called loess, of petroleum, and possibly of the organic material that was the basis for life itself.
While that would be a big deal, the sheer weight of the debris isn’t. Earth is huge—about 611,000,000,000,000,000,000 tons. The weight of all the water on the planet is less than 0.02 percent of that. And the weight of all the meteoric debris (figuring 44,000 tons a year for 4.5 billion years) would be about 0.02 percent of the water’s weight. Completely negligible.