KIC 8462852 has faded ~20% in brightness from 1890 to 1989

[Lorizael]

You didn't mention his paper, but you did mention "how we got our Oort cloud." Research done by Oort, Opik, and a few others are why astronomers began to hypothesize an Oort cloud. So if you have an idea about how we got the Oort cloud, I can infer that you think you have an idea about their research. If you don't know anything about their research, then you don't actually know anything about why the Oort cloud is a hypothesis astronomers take seriously.

A "swarm of comets" was not invented or invoked to explain data. New (long-period or non-periodic) comets do exist and demand an explanation. Given that these comets appear fairly regularly, there must be some population of them out there. The question is whether that population is interstellar or loosely bound to the solar system. Astronomers think they are bound because incoming comets only ever have orbits that are not quite or barely hyperbolic. If the comets were interstellar in nature, we would almost certainly see some fraction of new comets with grossly hyperbolic orbits that essentially just shoot through the solar system unperturbed. But we don't see that. Instead we see comets that are either very loosely bound or just energetic enough to escape, which heavily suggests that these comets were very far out, following along with the Sun, and nudged just enough to fall inward.

Oort's paper goes into detail about the effects that stellar perturbations would have on such a population, how those comets could be maintained over the lifetime of the solar system, and the range of inclinations and speeds they would have. Of particular note, we can observe the orbits of long-range comets and compute their semi-major axes. Oort goes through an analysis to show that comets with too large a semi-major axis would have been depleted by stellar perturbations long ago. And sure enough, we don't really see comets with semi-major axes beyond that range.

[pchang]

Perhaps a cloud of gas and dust passing between that star and us?

Light absorbed by gas or dust would then be re-emitted in the IR range, some of which would be directed at us. We don't see this IR shift.

[Dauphin]

Light absorbed by gas or dust would then be re-emitted in the IR range, some of which would be directed at us. We don't see this IR shift.

I've heard this before, but the amount of IR directed at us would be only a tiny fraction of the amount of light being absorbed by the dust. If we can't detect light reflected from a planet orbiting another star, particularly one at a more distant orbit, how can we expect to detect the IR emitted by a dust cloud orbiting another star.

I don't doubt the truthfulness of the statement, but that answer doesn't convince me unless I better understand the sensitivity of the measuring equipment (which I currently don't).

[Dauphin]

The surface area of dust answers my question....

[pchang]

Jupiter sized planet might absorb 1% of star light during transit. We are seeing between 15% and 22% drop. Earth like planets would be .1%.

[Dauphin]

I wasn't referring to the absorbed amount, I was referring to the re-emitted light. Which would constitute a direct measurement of something being there whether in transit or not.

[Lorizael]

I've heard this before, but the amount of IR directed at us would be only a tiny fraction of the amount of light being absorbed by the dust. If we can't detect light reflected from a planet orbiting another star, particularly one at a more distant orbit, how can we expect to detect the IR emitted by a dust cloud orbiting another star.

I don't doubt the truthfulness of the statement, but that answer doesn't convince me unless I better understand the sensitivity of the measuring equipment (which I currently don't).

We can actually detect the light of an exoplanet. The difficulty is that it's hard to see a planet through the glare of its star. Nevertheless, a few planets have been directly imaged.

As far as detecting the IR re-emissions of a dust cloud, that's a tricky question. It depends on the optical depth of the dust, which is an empirical measure based on the dust's temperature and optical properties.

[pchang]

Sorry - typing from phone. Was hoping you would fill in the rest.

Really 2 different problems and 2 different variables.

Problems
Planet Reflection - albedo of object
IR radiation - black body emission based upon temperature of object

Variables
Intensity
Directionality

Intensity
make math easier - say albedo and temp would equal about 1%
We can measure intensity change of .0005 (we have detected earth sized planets)
Thus 1% of 1% = intensity change of .0001 - we cannot measure accurately
But, 1% of 20% = intensity change of .002 - we would have seen this

Directionality
We cannot pinpoint the source of light to such a small angle as to distinguish between the star and a planet in close orbit (especially if the star is 10,000X brighter). There are experiments to put a shade (block just the width of that star) to see if this allows us to directly see planets, but they are not ready yet.

So - we are left with the possibility of a cold dust cloud in interstellar space in a direct line between us an KIC 8462852. It would have to be only a few pixels wide because we have not seen this type of dimming any any nearby star. The cloud would also have to be crossing our field of view relatively slowly. In addition, the structure of the cloud would have to be very irregular in a noticeable way as it crosses in front of the star (thus it could not be too far from the star - perhaps only a few thousand AU away????).

No matter what, any explanation requires a lot of low probability things to line up.

[Dauphin]

No matter what, any explanation requires a lot of low probability things to line up.

You mean one star in all observable stars kind of probability?

[pchang]

Even lower than that.

[Lorizael]

You mean one star in all observable stars kind of probability?

Kepler has only looked at ~145,000 stars.

[Berzerker]

You didn't mention his paper, but you did mention "how we got our Oort cloud."

Yes, I mentioned the cloud, not him or his paper...

A "swarm of comets" was not invented or invoked to explain data. New (long-period or non-periodic) comets do exist and demand an explanation. Given that these comets appear fairly regularly, there must be some population of them out there.

and that population was a "cloud" surrounding the solar system invoked to explain the data (long term comets)

but didn't his theory suggest long term comets might have formed near Jupiter and were subsequently tossed outward?

[Dauphin]

Kepler has only looked at ~145,000 stars.

Sorry, it was a bad attempt at humour and facts were getting in the way.

[The Mad Monk]

Apparently Jupiter had a "Grand Tack" at some point, where it danced in close to the sun and doh-si-doh'd with Saturn back out.

Lots of things got tossed around.

[Lorizael]

but didn't his theory suggest long term comets might have formed near Jupiter and were subsequently tossed outward?

At the end of the paper, Oort conjectured that gravitational interactions with Jupiter could have ejected many minor planets early in the solar system's history, but that part of his analysis is significantly less rigorous than the main argument of the paper. He admits that readily, recognizing that we needed to know more about the orbital elements of the solar system's early history. We do now, thanks in part to modern observations as well as computers powerful enough to run simulations on complicated systems that can't be solved analytically.