Starship Asterisk*

by **mollwollfumble** » Wed Dec 09, 2015 11:06 am

Based on the similarity of orbital radius distributions between Kepler planets and Kepler binaries, more than half of the Kepler planets ought to be shown with highly eccentric elliptical orbits. Fewer than half have orbits that are approximately circular.

by **Jyrki** » Mon Dec 07, 2015 10:18 pm

Thanks for the extra bits, Chris and Bystander. Looks like I need to recalibrate my impression of what Kepler can detect. Let us also recall this older APOD. In particular what Chris said about Kepler's ability to measure differences in luminosity.

by **bystander** » Mon Dec 07, 2015 2:05 pm

IA-Porto: Half of Kepler's Giant Exoplanet Candidates Are False Positives

by **Chris Peterson** » Mon Dec 07, 2015 12:48 pm

Jyrki wrote:Are you seriously saying that three transits (obviously the minimum) is enough? No room left for the chance of one of the dips in luminosity being a measurement error, or having some other explanation? I would have thought that those periods emerge from a statistical analysis, where a longer sequence of observations is used to remove whatever randomness there is. Also the durations of the transits introduce a (small) window of uncertainty.

Three transits isn't necessarily enough. As you say, it's just the minimum.

Ok. So for the most part stars are very stable (look at the Sun). But can you, or rather can Kepler, really measure the luminosity of star so accurately? Or is it so that Kepler can only detect planets of the size of Jupiter (relative to their mother stars) and up?]

Many of the stars aren't stable at all. They are rotating and contain starspots, and they have other planets around them. So you need to perform frequency analysis on the light curve to detect what are often multiple, interacting periodicities (further complicated by the fact that multiple planets can perturb each other, making the periods less regular. Kepler would be able to detect Saturn in our system just by observing the variation in Jupiter's orbit that it creates.

by **Jyrki** » Mon Dec 07, 2015 6:25 am

neufer wrote:
Wadsworth wrote:
I like Jyrki's thought experiment.

If it requires three (complete) periods, Jupiter verification would have had to start when I was born in 79..
Three transits = 2+ orbits = 2.5 (complete) periods on average.

Are you seriously saying that three transits (obviously the minimum) is enough? No room left for the chance of one of the dips in luminosity being a measurement error, or having some other explanation? I would have thought that those periods emerge from a statistical analysis, where a longer sequence of observations is used to remove whatever randomness there is. Also the durations of the transits introduce a (small) window of uncertainty.

Ok. So for the most part stars are very stable (look at the Sun). But can you, or rather can Kepler, really measure the luminosity of star so accurately? Or is it so that Kepler can only detect planets of the size of Jupiter (relative to their mother stars) and up?

by **Dale77** » Mon Dec 07, 2015 2:21 am

Why does Venus appear to be blue when seen orbiting the Sun, when from the color chart it should be approximately white? Either this is a mistake, or the cloud tops are what is being referred to, rather than the surface temp. But if that's the case, why label Venus on the color chart as being white? Is this a mistake? I think so.

I also have a comment about the question I was asked to be able to post this comment, to ensure that I was not a spam-bot, whatever that is. I was asked to "write the name of the largest object the New Horizons probe passed. Since the New Horizons probe passed near Jupiter to get a gravity assist on its way to Pluto, I responded "Jupiter". I was informed that I gave the wrong answer. So, I put "Pluto" and "got in". I think whoever wrote that question screwed up.

So, was this two mistakes?

by **bennypapa** » Sun Dec 06, 2015 3:00 pm

It would be cool to have an image of all these systems that either labeled each system or had hyperlinks attached to each system leading to some info about the system.

by **Chris Peterson** » Sat Dec 05, 2015 7:32 pm

bdx wrote:Is it reasonable to say that all stars will have planets?

Statistical analyses of radial velocity, transit, and microlensing surveys supports the hypothesis that most stars have one or more planets.

by **bdx** » Sat Dec 05, 2015 7:12 pm

Is it reasonable to say that all stars will have planets?

by **Chris Peterson** » Sat Dec 05, 2015 7:09 pm

ta152h0 wrote:I happen to be in agreement with a certain Mr Hawking. Yes, look for ET;s out there but not tell them we are here. This " serve mankind " idea could be a disaster.

That some human minds go in that direction offers much more reason for alien intelligences to avoid us than the other way around.

by **ta152h0** » Sat Dec 05, 2015 7:01 pm

I happen to be in agreement with a certain Mr Hawking. Yes, look for ET;s out there but not tell them we are here. This " serve mankind " idea could be a disaster.

by **neufer** » Sat Dec 05, 2015 4:34 pm

Wadsworth wrote:
I like Jyrki's thought experiment.

If it requires three (complete) periods, Jupiter verification would have had to start when I was born in 79..

Three transits = 2+ orbits = 2.5 (complete) periods on average.

by **Chris Peterson** » Sat Dec 05, 2015 3:51 pm

Supermoonshadow wrote:Is everything really orbiting in the same direction? The total angular momentum of this chunk of the universe seems to sum to much greater than zero.

In any system with multiple planets, they are almost certainly all orbiting in the same direction. But otherwise, the direction is random. The simulation simply normalizes all the orbits to be in the same direction as the Solar System, because there's generally no way to determine the direction of the orbit from Kepler data.

by **Wadsworth** » Sat Dec 05, 2015 2:55 pm

Hypnotic indeed.
I like Jyrki's thought experiment. If it requires three (complete) periods, Jupiter verification would have had to start when I was born in 79..

by **paulslittlebit** » Sat Dec 05, 2015 1:07 pm

Supermoonshadow wrote:Is everything really orbiting in the same direction? The total angular momentum of this chunk of the universe seems to sum to much greater than zero.

I do not believe Kepler can tell us about the orientation of the orbit, because it just see the dip in brightness as a plant orbit the star.

by **Supermoonshadow** » Sat Dec 05, 2015 12:47 pm

Is everything really orbiting in the same direction? The total angular momentum of this chunk of the universe seems to sum to much greater than zero.

by **Alex_22** » Sat Dec 05, 2015 11:54 am

A new hollywood blockbuster is under way: "Invasion of vomiting aliens".

by **Ann** » Sat Dec 05, 2015 9:19 am

Jyrki wrote:An interesting video. The observed exoplanets all seem to have relatively short orbital periods (in our Solar system -centric scale). I guess this is out of necessity...

A thought experiment: Somebody far out there wants to detect Jupiter using Kepler's method. Jupiter's diameter is one tenth of the Sun. So they would detect a one percent drop in Sun's luminosity for a brief period every 12 years. To make the observations have any kind of statistical significance those E.T.s would need to be very patient (or have very good instruments) to conclude the existence of such a period. Not forgetting that they need to live more or less on the plane of Jupiter's orbit.

Can anyone here shed some light as to how many full orbits worth of data Kepler needs in average to conclude that, yes, those periodical dips are caused by a transiting exoplanet? Or have I fundamentally misunderstood something?

I think you need three orbits. One dip in the light output of the Sun means nothing. Two dips doesn't tell you there is a period. But after three orbits, you can see that the period between the first two dips is the same as the period between the second and the third dip.

And by the way, today's APOD is quite interesting.

Ann

by **Markus Schwarz** » Sat Dec 05, 2015 9:13 am

Many of the planets are coloured dark red, meaning they have an estimated temperature of lava. Does this mean that these planets are giant balls of molten lava? Or are they hot gas giants?

by **Boomer12k** » Sat Dec 05, 2015 9:08 am

Well, that is one way of depicting all of them so far.....but they need to be labelled....

:---[===] *

by **Jyrki** » Sat Dec 05, 2015 7:38 am

An interesting video. The observed exoplanets all seem to have relatively short orbital periods (in our Solar system -centric scale). I guess this is out of necessity...

A thought experiment: Somebody far out there wants to detect Jupiter using Kepler's method. Jupiter's diameter is one tenth of the Sun. So they would detect a one percent drop in Sun's luminosity for a brief period every 12 years. To make the observations have any kind of statistical significance those E.T.s would need to be very patient (or have very good instruments) to conclude the existence of such a period. Not forgetting that they need to live more or less on the plane of Jupiter's orbit.

Can anyone here shed some light as to how many full orbits worth of data Kepler needs in average to conclude that, yes, those periodical dips are caused by a transiting exoplanet? Or have I fundamentally misunderstood something?

by **APOD Robot** » Sat Dec 05, 2015 5:06 am

Kepler Orrery IV

Explanation: The exoplanet hunting Kepler mission's total for candidate and confirmed multiple planet systems stands at 1,705 worlds in orbit around 685 distant stars. Put all of those exoplanet orbits on the same scale and follow their relative orbital motions to get Kepler Orrery IV. To make the planets visible, their sizes aren't shown to scale. But orbits of the planets in the Solar System (dashed lines) are included to scale in the hypnotic video. Of course, Kepler uses planetary transits to detect exoplanets, looking for a slight dimming of light as the planet crosses in front of its star. In the time compressed video, Kepler's multiplanet system orbits are all oriented to put observed transits at the three o'clock position. The dervish-like movements highlight a stark contrast between most Kepler-discovered exoplanetary systems and our own. Planning an interstellar vacation? Be sure to check the scale at the upper left first. The color code indicates a planet's estimated equilibrium surface temperature based on its orbit size and parent star.

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