# Tag Info

37

That's right. The inclination of the orbital plane around stars is considered to be random throughout the galaxy, thus the planets we can detect by the transit method is just a tiny fraction of the planets that we should expect in our stellar neighbourhood. The transit method allows for planetary detection only when the line of sight from Earth to the ...

11

One thing to keep in mind is that the Kepler instrument is not a telescope like Hubble. It is a photometer and though it uses CCDs to look at the sky, it doesn't return a picture in the usual sense. The way it operates is that you only look at the pixels around the object you're interested in because otherwise you'd never get all those pixels transmitted ...

10

Kepler's third law is that $R^3/P^2$ is a constant. However it is not a universal constant; it depends on the mass of the body that is being orbited. $$\frac{R^3}{P^2} \simeq \frac{GM}{4\pi^2},$$ where $M$ is the mass of the orbiting body (assuming that $M\gg$ the mass of the moons). Depending on your level of sophistication, you could try plotting $R^3$ ...

8

Yes. The probability of a transit taking place is something like $r/a$, where $r$ is the stellar radius and $a$ is the radius of the planetary orbit. If you assume that planet orbits are randomly inclined to our line of sight, then each detected planet corresponds to $a/r$ planets in actual fact. Note that this approximation is ok for circular orbits ...

6

There are two separate points of interest you're looking at so I'll separate this into sections. Sudden Drop at Day 1559 As near as I can tell, this is the result of a quarterly roll of the satellite, specifically the end of quarter 17. Every 90 days, which NASA calls a quarter, the space craft does a 90 degree roll to optimize the solar panel efficiency. ...

6

I'm going to try to take a stab at answering this. With our current technologies, detecting exomoons can prove hard however there are various techniques being used today such as: Analyzing data from the Kepler Spacecraft Dynamic effects – the exomoon tugs the planet, which causes deviations in the times and durations of the host planet’s transits. This is ...

5

Starting from the index you mentioned, I clicked through the links for some individual planets, which in turn link to discovery papers or other relevant observations. For planets around Kepler-23, -24, -25, -26, -27, and -28, the relevant papers are Ford et al. (2012) and Steffen et al. (2012), two out of a series of papers. Both papers used transit timing ...

5

There are many planets known which have orbits longer than the longest exoplanet orbital periods found by Kepler. These planets were discovered using the "doppler wobble" or radial velocity technique. The plot below (a few months out of date now) shows many planets orbiting with similar periods to Mars and Jupiter. The red points we discovered by transits (...

5

Changing fields breaks the timeline of the observations. If you have variation with a period similar to when you switch, you might completely miss it. Even if the periods are different, it degrades your observations and makes it harder to draw conclusions. The more uninterrupted viewing you get, the better. This mission document covers some of the ...

5

Planet "candidates" are Kepler Objects of Interest (KOIs)that have a transit-like light curve and have passed a number of observational tests. They are candidates, because although they do show a transit in the light curve of the star in question, there is no independent confirmation of a planetary mass. One problem to overcome is that of "false positives"....

5

It depends what you mean by "real position". Also, just to clarify something that should be gotten out of the way, the Earth rotates, obviously, and the night sky appears to rotate around the Earth a complete 360 degrees in a 24 hours. That's why the geocentric model lasted as long as it did. That's what it looks like, and that's what everyone believed ...

5

There is an observational bias and it is taken into account when you see inferences about planet frequency. The methods to find planets are inherently biased towards finding large, close-in planets. Both the transit and doppler-based methods suffer from this bias. The paper you reference takes into account this bias to arrive at the statistics you ...

4

The maths says that the semi-major axis is not a good measure of average distance for high eccentricity (elliptical) orbits. There are basically two ways to measure this : (1) an average over the entire orbit on a purely geometric basis, and (2) the average over time. These give quite different results - qualitatively different. Average distance on ...

4

Well "if no known astrophysical model can explain it" then nobody told Wright & Sigurdsson (2016) who, cognisant of Montet & Simon's results, explore a number of astrophysical models. They conclude by saying that the most "plausible model" is that of small scale intervening material between us and the star that may be responsible for the short-term ...

4

Go to the Kepler/K2 MAST database https://archive.stsci.edu/kepler/data_search/search.php or https://archive.stsci.edu/k2/epic/search.php Search on a temperature ($T_{\rm eff}$) range: e.g. for K-stars 4500 .. 5200 A (big) list of objects will be found and presented to you in a table. Mark the ones you want (all the Kepler objects should have available ...

4

They don't stop. The Kepler CCDs read out the signals collected during the accumulated time of 6.02 seconds. The fixed read out time is 0.52 seconds. So each CCD gets one frame every (6.02 + 0.52) = 6.54 seconds. Then Kepler sums up every 9 frames (short cadence) and 270 frames (long cadence). The time between two short cadences is (6.54 x 9) = 58.9 seconds,...

4

This can best be described by two slides from this presentation. "Forward-facing" implies looking towards Earth in the spacecraft's orbit, in the direction of the spacecraft's velocity vector: "Backward-facing" implies looking in the opposite direction, away from Earth and in the opposite direction to that of the spacecraft's velocity vector: These are ...

4

That is not correct. The area is the total area between the two radius lines, so there is a curved side. Imagine you have two points almost 180 degrees from each other. Using just a triangle, the area is close to zero. Now, two points placed closely together can have the same area in between them. Then you have an equal are, but not equal time, so your ...

4

Just to provide an analytical formula for @uhoh's correct time-averaged distance, here the derivation of $\langle r\rangle_t=1+\epsilon^2/2$: a=1 \qquad c=e\qquad b=\sqrt{1-e^2}\\ \vec{r}=(\cos \beta-e,\sqrt{1-e^2}\sin \beta)\\ \vec{r'}=(-\sin \beta,\sqrt{1-e^2}\cos \beta)\\ |r|^2=\cos^2 \beta -2e\cos \beta+e^2+\sin^2\beta-e^2\sin^2\beta=1-2e\cos \beta+e^...

3

Gyrochronology uses the rotation periods of stars, caused by rotational modulation by starspots to estimate a stellar age. In the absence of differential rotation, the rotation axis inclination has no effect on this measurement. The doppler broadening of spectral lines plays no role in gyrochronology. The rotation period of a star is just that. It is the ...

3

It's not proof that they've ejected other inner planets, because there are plenty of other explanations for why we haven't observed companions. Steffen et al. (2012) analyzed Kepler data - likely some of the same examples you've looked at - and came up with several explanations besides the no-companions-because-of-planet-planet scattering hypothesis: Inner ...

3

I do not know whether complimentary observations of the light curve are being done, but I will try to answer the rest of the question. Is it easy to observe the light curve with ground-based telescopes? No, it's quite difficult. From the Kepler homepage: Since transits only last a fraction of a day, Kepler must monitor all target stars continuously. ...

3

The prime objective of the Kepler mission was to attempt to find "Earth-like" planets using the transit technique. To establish that you definitely have a transiting planet requires, at a minimum, that you see three regularly spaced transits. The Kepler mission (originally) was planned for 4 years. Thus to ensure the detection of 3 transits for planets in ...

2

This is a well known, well researched phenomena. Yes, there certainly is a correlation between metallicity and the likelihood of observing a hot Jupiter. There are two classes of explanation. (1) The correlation is real and due to the fact that it is easier to form planetary embryos from metal-rich material in the core-accretion model of giant planet ...

2

Hohmannfan's answer is correct, but as I understand your question, you do understand the general idea correctly and the answer to your question is yes, no matter how eccentric the orbit, the planet spans equal areas over equal time, at least nearly perfectly. (more on that later) You're mistake is in calling the sectors "triangles". They're sectors of an ...

2

This was intended to be a supplemental answer to StephenG's answer. However, there appears to be a problem with the expression for time-averaged distance in that answer. I think it's great to seek a mathematical expression, but it should be confirmed numerically. I did a quick numerical double check and verified those general trends, but there may still be ...

2

One must consider the mass of the object being orbited. Kepler's third law is true for all planets orbiting the Sun, and for all moons orbiting Jupiter, but not across different gravity wells. This was not understood until Newton, and must've posed an interesting problem (I've never thought of before) already in Kepler's time since the orbital periods and ...

2

The gist of this, is that your assumption is incorrect. It's the semi-major axis that defines the period, not the average distance. Newton worked this out when he invented calculus and derived Kepler's laws. (Look up Derivation of Kepler's laws for some explanations). Here's the Wikipedia version of the Math. I should add that Kepler's three laws, ...

2

Yes, Ptolemy adopted Hipparchus's idea that epicycles and eccentric orbits could explain the irregular motion of the Sun. From David McClung's biography of Hipparchus: Hipparchus also created the first reasonably accurate model of the motion of the sun and moon. Using the idea of epicycles, probably introduced by the mathematician Apollonius of Perga, he ...

1

The Kepler Field had been covered in the near IR by the 2MASS catalog since that covered the entire northern sky. There was also a Smithsonian Institute program called the Kepler Input Catalog program that observed the Kepler field with the 48-inch telescope at the Whipple Observatory on Mount Hopkins, Arizona in the SDSS g, r, i, and z bands plus a custom ...

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