Hubble Makes First Direct Measurements of Atmosphere on World Around Another Star

Hubble Telescope ^ | November 27, 2001

[The_Victor]

Hubble Makes First Direct Measurements of Atmosphere on World Around Another Star

1. How did they detect the atmosphere?

Astronomers discovered the atmosphere by watching how starlight dimmed slightly when the planet crossed in front of its star, an event known as a transit. During the transit, a small amount of starlight passed through the planet's atmosphere on its way to Earth. Hubble's spectrograph collected the light and dispersed it into the colors of the spectrum, which yielded clues about the atmosphere's chemical makeup. When astronomers analyzed the spectrum, they found the telltale "fingerprint" of sodium.

2. What does sodium reveal about the planet?

Astronomers expected to find sodium in the planet's atmosphere. Discovering sodium does not mean that life exists on the alien planet. In fact, astronomers don't think the planet can sustain life. It is a Jupiter-sized planet made up mostly of gas and is 20 times closer to its star than the Earth is to the Sun. The planet is so close to its star that its atmosphere is heated to a torrid 2000 degrees Fahrenheit (1100 degrees Celsius).

The astronomers, however, actually found less sodium than scientists had predicted for a Jupiter-class planet, leading to one interpretation that high-altitude clouds in the alien atmosphere may have blocked some of the starlight. The astronomers discovered the sodium by analyzing the starlight that passed through the planet's atmosphere.

3. What are the conditions for life?

A key ingredient for life as we know it is oxygen. The most suitable planets for life, where oxygen may be abundant, are small, rocky planets like Earth that orbit at comfortable distances away from their stars. Finding these planets and probing their atmospheres for signs of life is beyond the scope of current telescopes and detection techniques, including the transit method used in this Hubble observation. So far, astronomers have been successful at discovering a parade of alien planets. But all of them are Jupiter-sized giants that are much larger than Earth. Some of them orbit perilously close to their stars, like the planet whirling around the star HD 209458.

[RadioAstronomer]

Beat me too it! :)

[b4its2late]

Web? Is that you? :o)

[RadioAstronomer]

Forgot both of you all too. Sigh! :)

[mad_as_he$$]

very cool I have been waiting for this for years. Next warp drive to go there.

[RadioAstronomer]

I think we're moving into a 'golden age' of discovery in regards to exo-planets

Absolutely. I just might have the tiniest chance in my SETI endeavor if the universe cooperates. :)

[RadioAstronomer]

Next warp drive to go there.

If it wasn't for those pesky General Relativity equations!

[mad_as_he$$]

Ahh can't let physics bother us. Better yet if there is a Stargate there we could just dial it up. lol

[RadioAstronomer]

Ahh can't let physics bother us

I still think we are "stuck" by GR, but maybe Physicist might have a solution I do not. :)

[RadioAstronomer]

Thought you would like this. :)

[longshadow]

Thanks for the bump.

Excellent achievement!

As the founder of Faber College ("Animal House") used to say: "Knowledge is good!"

[Aurelius]

BUMP

[RadioAstronomer]

Bump :)

[blam]

Thanks for the bump. Posted an article on this myself today.

[Alamo-Girl]

Yes indeed! Thank you so much for the heads up!!!

[Neuromancer]

If it wasn't for those pesky General Relativity equations.

To the extent that we restrict our physics to special relativity and demand that the traditional order of causation is always correct, no information can travel faster than the speed c. However, special relativity is only a special case of physics within a more general theory known as general relativity.

In general relativity the vacuum speed of light is locally invariant, but not globally invariant. The vacuum speed of light remote from a given observer need not be c. It can be greater than c and can vary with direction depending on the gravitational field involved. Because this is allowed - starships that travel between the stars faster than c are not ruled out a-priori within the physics of general relativity.

[RadioAstronomer]

To the extent that we restrict our physics to special relativity and demand that the traditional order of causation is always correct, no information can travel faster than the speed c. However, special relativity is only a special case of physics within a more general theory known as general relativity.

In general relativity the vacuum speed of light is locally invariant, but not globally invariant. The vacuum speed of light remote from a given observer need not be c. It can be greater than c and can vary with direction depending on the gravitational field involved. Because this is allowed - starships that travel between the stars faster than c are not ruled out a-priori within the physics of general relativity.

I pinged an astrophysicist friend of mine who is more a gravitational physicist than I. and this is what he wrote back:

_________________________________________________

I'm not an expert on GR but there are several things wrong with this reply.

1) Even if there is some effect of GR that causes a gravitational field to allow a "vacuum speed of light" (whatever that is) to vary with direction or be greater than c it would only occur where there are strong gravitational fields. Since the claim is about travel between stars this is not relevant.
2) I don't think that that the speed of light can vary in GR anymore than it can vary in SR. I also have no idea what he means by local vs global invariance.
3) The difference between SR and GR is the treatment on non-inertial reference frames via the principle of equivalence. I don't see how this allows a change to the basic assumption of SR, the invariance of the speed of light. I could be all wet here but I've never heard of this before.

__________________________________________

I have added a few web pages that may explain this a little better:

http://www.maths.soton.ac.uk/relativity/GRExplorer/Einstein/curved.htm

http://www.astronomynotes.com/relativity/s4.htm

The only thing I can think you are referring to is using exotic matter (with imaginary mass). I found a description of what I believe you are referring to:

http://home.sunrise.ch/schatzer/space-time.html

To Physicist: If I am all wet, feel free to shoot me down! :)

[Neuromancer]

l. To be precise, what we usually call the "speed of light" is really the speed of light in a vacuum (the absence of matter). In reality, the speed of light depends on the material that light moves through. Thus, for example, light moves slower in glass than in air, and in both cases the speed is less than in a vacuum. However, the density of matter between the stars is sufficiently low that the actual speed of light through most of interstellar space is essentially the speed it would have through a vacuum.

2. The special theory of relativity assumes the existence of a unique class of global coordinate systems - called inertial coordinates - with respect to which the speed of light in vacuum is everywhere equal to the constant c. It was natural, then, to express physical laws in terms of this preferred class of coordinate systems, characterized by the global invariance of the speed of light. In addition, the special theory also strongly implied the fundamental equivalence of mass and energy, according to which light (and every other form of energy) must be regarded as possessing inertia. However, it soon became clear that the global invariance of light speed together with the idea that energy has inertia (as expressed in the famous relation E2 = m2 + |p|2) were incompatible with one of the most firmly established empirical results of physics, namely, the exact proportionality of inertial and gravitational mass, which Einstein elevated to the status of a Principle.

This incompatibility led Einstein, as early as 1907, to the belief that the global invariance of light speed, in the sense of the special theory, could not be maintained. Indeed, he concluded that we cannot assume, as do both Newtonian theory and special relativity, the existence of any global inertial systems of coordinates (although we can carry over the existence of a local system of inertial coordinates in a vanishingly small region of spacetime around any event).

[Physicist]

The speed of light through a vacuum can vary, according to a given observer, with gravitational field. But like the passage of light through matter, the light always slows down.

As the light of a distant star passes by the Sun, for example, its speed (from the point of view of an Earthbound observer) slows down as it encounters the gravitational field of the Sun. This causes an effective index of refraction, which means that the minimum-time path to Earth (i.e. the geodesic) is actually curved around the Sun.

Another way to think about it is that the gravitational field stretches space in the vicinity of the Sun. Suppose you had a long string between two fixed points that were several hundred million miles apart. If the Sun passed through the center of the string, you'd find that the string would either stretch or break--assuming it didn't burn up--because the curved spatial distance through the Sun is actually longer than the original "flat" path between the points. The reason that the speed of light close to the Sun seems slower to an outside observer is because the light has a longer distance to travel.

(You can also see why there must be a gravitational time dilation, if you take the speed of light as a standard clock.)

There is only one kind of gravitational field, and the more intense it is, the more the effective slowing of the speed of light. Gravitational lenses only have a positive index of refraction; there is no way to get a negative index of refraction. Gravitational fields can't give you a shortcut.

[RadioAstronomer]

l. To be precise, what we usually call the "speed of light" is really the speed of light in a vacuum (the absence of matter). In reality, the speed of light depends on the material that light moves through. Thus, for example, light moves slower in glass than in air, and in both cases the speed is less than in a vacuum. However, the density of matter between the stars is sufficiently low that the actual speed of light through most of interstellar space is essentially the speed it would have through a vacuum.

I am very much aware of this. We have to take into account that the speed varies with frequency also in a medium such as our atmosphere.

2. The special theory of relativity assumes the existence of a unique class of global coordinate systems - called inertial coordinates - with respect to which the speed of light in vacuum is everywhere equal to the constant c. It was natural, then, to express physical laws in terms of this preferred class of coordinate systems, characterized by the global invariance of the speed of light. In addition, the special theory also strongly implied the fundamental equivalence of mass and energy, according to which light (and every other form of energy) must be regarded as possessing inertia. However, it soon became clear that the global invariance of light speed together with the idea that energy has inertia (as expressed in the famous relation E2 = m2 + |p|2) were incompatible with one of the most firmly established empirical results of physics, namely, the exact proportionality of inertial and gravitational mass, which Einstein elevated to the status of a Principle.

Here is a very nice set of lecture notes on this very subject:

http://nedwww.ipac.caltech.edu/level5/March01/Carroll3/Carroll_contents.html

[RadioAstronomer]

There is only one kind of gravitational field, and the more intense it is, the more the effective slowing of the speed of light. Gravitational lenses only have a positive index of refraction; there is no way to get a negative index of refraction. Gravitational fields can't give you a shortcut.

I didn't think so either. And since spacetime is essentially "flat" we are still "stuck" by relativity.