Starship Asterisk*

The Kepler-90 Planetary System

Explanation: Do other stars have planetary systems like our own? Yes -- one such system is Kepler-90. Cataloged by the orbiting Kepler satellite, an eighth planet has now been discovered giving Kepler-90 the same number of known planets as our Solar System. Similarities between Kepler-90 and our system include a G-type star comparable to our Sun, rocky planets comparable to our Earth, and large planets comparable in size to Jupiter and Saturn. Differences include that all of the known Kepler-90 planets orbit relatively close in -- closer than Earth's orbit around the Sun -- making them possibly too hot to harbor life. However, observations over longer time periods may discover cooler planets further out. Kepler-90 lies about 2,500 light years away, and at magnitude 14 is visible with a medium-sized telescope toward the constellation of the Dragon (Draco). Exoplanet-finding missions planned for launch in the next decade include TESS, JWST, WFIRST, and PLATO.

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WOW... all 8 orbit within Earth's orbit... WOW....well, at 2500LY... I think I'll pass....

Cold, Wet, and Cloudy here...
:---[===] *

If there are cooler rocky planets "further out" that have sentient life, they must see some hellacious and frequent occultations...

It seems the only habitable place is likely to be on any moons around the outer two planets.

I notice the Kepler-90 planets are all labeled, but 'our' planets are not. I guess we can all remember our planets by the silly sentence, "My Very Enthusiastic Mother Just Served Us Noodles!" Kepler-90's planets? Hmmm...

As I look at the chart for the Kepler-90 system here, it strikes me as a truncated version of our own planetary set. And it makes sense that the observations from transit photometry will be biased, at least at first. It will more easily find large planets and short orbits. So, if Kepler-90 actually has a planetary system that has peak masses in the "middle distance", then we have not (yet) been able to observe the smaller effects of a set of outer planets that might taper off in mass. They would have much longer orbits and much smaller occultation effects, so would be harder to detect. Indeed, we have enough trouble detecting outer planets in our own system, let alone by looking for a glimmer in a star that is about 2545 light years away.

The radial velocity detection technique would be biased in about the same way as the star dimming technique.

Of course, this is very speculative, but it would be my personal guess that Kepler 90 probably has more than 8 planets.

FLPhotoCatcher wrote:It seems the only habitable place is likely to be on any moons around the outer two planets.

I notice the Kepler-90 planets are all labeled, but 'our' planets are not. I guess we can all remember our planets by the silly sentence, "My Very Enthusiastic Mother Just Served Us Noodles!" Kepler-90's planets? Hmmm...

Sesame Street has your exoplanet systems all covered:

It seems to me that if you compress all those planets inside the orbit of one AU, then the big ones (the ones the size of Jupiter and Saturn) would fling out of their orbits the other smaller ones. Since they are all in (relative) close proximity, it doesn't seem as though stable orbits for so many members in so small a volume would be possible.

MarkBour wrote:As I look at the chart for the Kepler-90 system here, it strikes me as a truncated version of our own planetary set. And it makes sense that the observations from transit photometry will be biased, at least at first. It will more easily find large planets and short orbits. So, if Kepler-90 actually has a planetary system that has peak masses in the "middle distance", then we have not (yet) been able to observe the smaller effects of a set of outer planets that might taper off in mass. They would have much longer orbits and much smaller occultation effects, so would be harder to detect. Indeed, we have enough trouble detecting outer planets in our own system, let alone by looking for a glimmer in a star that is about 2545 light years away.

The radial velocity detection technique would be biased in about the same way as the star dimming technique.

Of course, this is very speculative, but it would be my personal guess that Kepler 90 probably has more than 8 planets.

I second your guess that this system has more than the eight planets already confirmed Mark, but I'd be even more boldly positive than what you are. (but I can't help being positive) Heck, I'm even positive that the final tally on our own system will be more than eight

Bruce

Edit to correct spelling.

Craig Willford wrote:It seems to me that if you compress all those planets inside the orbit of one AU, then the big ones (the ones the size of Jupiter and Saturn) would fling out of their orbits the other smaller ones. Since they are all in (relative) close proximity, it doesn't seem as though stable orbits for so many members in so small a volume would be possible.

The illustrations are not to scale, making it seem that the Kepler-90 planets orbit so close they might hit each other. Edit: I realize of course that this was not what lead Craig Willford to make his point. But hey, one AU is 93 million miles. Lots of room for planets IF they are properly arranged.

Wikipedia Kepler-90 wrote:The Kepler-90 system is the only eight-planet candidate system from Kepler, and the second to be discovered after the Solar System. It was also the only seven-planet candidate system from Kepler before the eighth was discovered in 2017, and one of two total seven-planet systems, along with TRAPPIST-1. Additionally, the inner six planets range in size from that of Earth to smaller than Neptune, and the outer two planets are the size of gas giants. All of the eight known planet candidates orbit within 1 AU from Kepler-90. A Hill stability test and an orbital integration of the system show that it is stable.

FLPhotoCatcher wrote:... I notice the Kepler-90 planets are all labeled, but 'our' planets are not. I guess we can all remember our planets by the silly sentence, "My Very Enthusiastic Mother Just Served Us Noodles!" Kepler-90's planets? Hmmm...

I find it even easier to remember them using this mnemonic: "Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune [and sometimes Pluto]".

Rob

MarkBour wrote:As I look at the chart for the Kepler-90 system here, it strikes me as a truncated version of our own planetary set. And it makes sense that the observations from transit photometry will be biased, at least at first. It will more easily find large planets and short orbits. So, if Kepler-90 actually has a planetary system that has peak masses in the "middle distance", then we have not (yet) been able to observe the smaller effects of a set of outer planets that might taper off in mass. They would have much longer orbits and much smaller occultation effects, so would be harder to detect. Indeed, we have enough trouble detecting outer planets in our own system, let alone by looking for a glimmer in a star that is about 2545 light years away.

The radial velocity detection technique would be biased in about the same way as the star dimming technique.

Note though that purely on a geometric basis the further out an exoplanet orbits its star, the more perfectly aligned its orbit must be for an occultation to occur at all. On this count, the radial velocity method is much less sensitive to this alignment issue.

Just as in our solar system more planets orbit outside of one AU than inside, it is entirely possible that more than eight planets orbit in the outer parts of the Kepler-90 system. 20+ planets orbiting Kepler-90 is well within reason, imo.

Bruce

Craig Willford wrote:It seems to me that if you compress all those planets inside the orbit of one AU, then the big ones (the ones the size of Jupiter and Saturn) would fling out of their orbits the other smaller ones. Since they are all in (relative) close proximity, it doesn't seem as though stable orbits for so many members in so small a volume would be possible.

No planetary systems are completely stable if they have more than one planet.