Author Topic: Dwarf planet discovery hints at a hidden Super Earth in solar system  (Read 123854 times)

Offline missinglink

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The Super-Earth that Came Home for Dinner

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. . . Over the past 20 years, surveys of planets around other stars in our galaxy have found the most common types to be "super Earths" and their somewhat larger cousins -- bigger than Earth but smaller than Neptune.


https://www.jpl.nasa.gov/news/news.php?release=2017-259&rn=news.xml&rst=6964
I thought this was due to observational bias? By which I mean, super earths closely orbiting their stars will be found preferentially because the deviations from expected behavior they cause in the stars are more easily detected from where we are.

Offline Bynaus

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The Super-Earth that Came Home for Dinner

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. . . Over the past 20 years, surveys of planets around other stars in our galaxy have found the most common types to be "super Earths" and their somewhat larger cousins -- bigger than Earth but smaller than Neptune.


https://www.jpl.nasa.gov/news/news.php?release=2017-259&rn=news.xml&rst=6964
I thought this was due to observational bias? By which I mean, super earths closely orbiting their stars will be found preferentially because the deviations from expected behavior they cause in the stars are more easily detected from where we are.

There is an observational bias, for sure. In particular, we can assume that there are many small planets which we cannot detect today. Still, the frequency of planets in size between Earth and Neptune (not known from the solar system, perhaps with the exception of P9) is surprisingly high, and higher than would have been predicted from planet formation models (which essentially assumed that early-formed planets would grow rapidly to become gas giants, while late-formed planets would not find any gas and stay rocky - Uranus and Neptun were then considered strange borderline cases - well, it turns out, they are more typical planets than all the other worlds of the solar system which we could detect with Kepler).

Offline Ben the Space Brit

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Just out of interest, is there a minimum realistic albedo below which Sol-IX, irrespective of size, would become practically unobservable at visual wavelengths?
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Offline Star One

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Has Pulsar timing killed off Planet Nine? An upcoming paper possible says so.

https://mobile.twitter.com/cosmos4u/status/923280935025610753

Offline Star One

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Mike Brown talks a little about the practicalities of the hunt for Planet Nine.

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Mike Brown
@plutokiller
Replying to @Alex997tt
most of the searching is really writing software that does the searching. and testing it. and fixing bugs. and running it and finding more bugs. repeat.

https://mobile.twitter.com/plutokiller/status/934893302536478720

Offline Star One

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Planet Nine! An Update from Konstantin Batygin
« Last Edit: 12/06/2017 08:22 PM by Star One »

Offline Star One

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Nothing new in this article but rather a summation of the evidence and arguments for and against its existence.

https://www.theatlantic.com/science/archive/2017/12/planet-nine-or-planet-nein/547907/
« Last Edit: 12/08/2017 05:14 PM by Star One »

Online KelvinZero

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I just watched a youtube clip that mentioned neptune's large hill sphere.

I guess for this super earth it would be absurdly larger? Has there been any discussion of how this could affect the sort of moon system it could have?

Online CuddlyRocket

I guess for this super earth [its Hill sphere] would be absurdly larger? Has there been any discussion of how this could affect the sort of moon system it could have?

According to Wikipedia the radius of a planet's Hill sphere is approximately a x (1-e) x cube root of m/3M, where a is the semi-major axis, e the orbital eccentricity, m the planet mass and M the mass of the Sun. For Planet Nine, a is approx 25 times that of Neptune; 1-e approximately 0.4 times and the cube root of m approximately 0.8 times. This gives a Hill radius approximately eight times that of Neptune (930 million kilometers - 6.2 AU! - versus 116 million kilometers).

As for the effect on any moon system, it would mean that a much more expansive moon system would be possible (Neptune's furthest moon (Neso) is at 50 million kilometers). However, it would seem likely that any initial moons would have been lost in the process of Planet Nine attaining its present orbit and the chances of it meeting, let alone capturing, any objects would be very low!

Offline Star One

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Online hop

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A 3pi Search for Planet Nine at 3.4 microns with WISE and NEOWISE A. M. Meisner, B. C. Bromley, S. J. Kenyon, T. E. Anderson

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The recent 'Planet Nine' hypothesis has led to many observational and archival searches for this giant planet proposed to orbit the Sun at hundreds of astronomical units. While trans-Neptunian object searches are typically conducted in the optical, models suggest Planet Nine could be self-luminous and potentially bright enough at ~3-5 microns to be detected by the Wide-field Infrared Survey Explorer (WISE). We have previously demonstrated a Planet Nine search methodology based on time-resolved WISE coadds, allowing us to detect moving objects much fainter than would be possible using single-frame extractions. In the present work, we extend our 3.4 micron (W1) search to cover more than three quarters of the sky and incorporate four years of WISE observations spanning a seven year time period. This represents the deepest and widest-area WISE search for Planet Nine to date. We characterize the spatial variation of our survey's sensitivity and rule out the presence of Planet Nine in the parameter space searched at W1 < 16.7 in high Galactic latitude regions (90% completeness).
Needless to say, the title would be different if they found it. However, the detectability of P9 at WISE wavelengths is quite model dependent, so this certainly doesn't rule it out either.

Offline jgoldader

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A 3pi Search for Planet Nine at 3.4 microns with WISE and NEOWISE A. M. Meisner, B. C. Bromley, S. J. Kenyon, T. E. Anderson

Just read it, looks like a good paper.  They seem to have done an impressive job.  As you noted, hop, the expected IR flux is highly model dependent.  That said, they seem to have thoroughly searched a large and interesting part of the parameter space and come up empty.
Recovering astronomer

Offline sanman

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So once Planet 9 is found, how long might it take a spacecraft to reach it from Earth?

Offline Alpha_Centauri

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It should be pointed out that even if it is possible for P9 to show up in WISE, dependant on its atmospheric chemistry, this search is still only sensitive to the closer regions of P9s orbit. Realistically if it does exist it is likely near aphelion and so beyond our reach. Aaron Meisner's work on the new astrometrically corrected coadds is awesome though.

Offline Star One

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It should be pointed out that even if it is possible for P9 to show up in WISE, dependant on its atmospheric chemistry, this search is still only sensitive to the closer regions of P9s orbit. Realistically if it does exist it is likely near aphelion and so beyond our reach. Aaron Meisner's work on the new astrometrically corrected coadds is awesome though.

Mike Brown has repeatedly said this so it was unlikely this search would turn up anything. Heís even made reference to the fact, I believe, that WISE data would be unlikely to show it because itís likely at the furtherest part of its orbit.
« Last Edit: 12/15/2017 11:52 AM by Star One »

Offline Alpha_Centauri

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Yeah he's right. It's a high risk, high payoff search. But his previous search using WISE was not at full sensitivity so there is room for it to have been missed. It's just not likely to be there. But the data is there and people will search because of the small chance of high payoff. I suppose I'm just saying even if it isn't found in WISE we shouldn't expect it to have been.
« Last Edit: 12/15/2017 12:19 PM by Alpha_Centauri »

Offline jebbo

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And the null result narrows the search space.

Sometimes I think there should be a Journal of Null Results :-)

--- Tony

Online KelvinZero

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So once Planet 9 is found, how long might it take a spacecraft to reach it from Earth?
Of course hugely dependent on what technology, what mass.. but just to begin with some numbers.

https://en.wikipedia.org/wiki/Planet_Nine
Implies orbit varies from 200 - 1200 AU.

https://en.wikipedia.org/wiki/Voyager_1
Has been flying for about 40 years, and has travelled 141 AU (as of Nov 22, 2017)

Im sure we can do a lot better, but I don't know what to point at as state of the art right now and if we were going to send a probe I guess it would be with technology that is best discussed in the advanced topics section.

https://en.wikipedia.org/wiki/Breakthrough_Starshot discusses 15-20% of light speed.
A lightyear is about 63,000 AU, and 20% would be more than 13,000AU / year. .. so around a month if it is at its furthest point, 1200AU?

(That would certainly be a fun little project for exploring our solar system)

Pls check my numbers yourself. I could easily have messed up.


Online hop

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Mike Brown has repeatedly said this so it was unlikely this search would turn up anything. Heís even made reference to the fact, I believe, that WISE data would be unlikely to show it because itís likely at the furtherest part of its orbit.
Context matters for these kinds of statements. "standard WISE data products go to mag X, equilibrium blackbody in at 600 AU would be Y temperature" gives a rather different impression than what was discussed in the paper. Meisner's coadds go significantly deeper than the basic WISE data products, and under some models P9 is significantly brighter at these wavelengths than a first order estimate would suggest. Again, this doesn't mean P9 ruled out, but the work being discussed did have potential to discover plausible flavors of P9 over much of the proposed orbit.

They also note there's more to be done with WISE data:
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Our methodology should be readily applicable to the WISE W2 channel. Typically, (W1−W2) ~ 0.8 corresponds
to equal signal-to-noise in W1 and W2, meaning that we should expect sensitivity to Planet Nine at W2 < 15.9. This survey limit would render the most W2-luminous model of Fortney et al. (2016) detectable at distances of up to ~1,700 AU. One operational advantage of searching in W2 rather than W1 is that W2 has a factor of ~2 fewer background sources relative to W1. A disadvantage is that scattered moonlight, one of the dominant time-dependent artifacts affecting WISE data, is more pronounced in W2 than in W1 Whereas our survey has omitted some regions, we note that the ongoing Kuchner et al. (2017) search is examining the entire sky in both W1 and W2, based on the time-resolved coadds of Meisner et al. (2017a).
Because the Kuchner et al. (2017) search employs deep W2 coadds, it can also serve as a fainter extension of the Luhman (2014) search for a roughly Jovian mass companion to the Sun.
WISE continues to collect additional data in W1 and W2, so that there will eventually be at least one additional year
of NEOWISER exposures in both bands relative to those currently available.

Offline Star One

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Iíve wanted to see if either Brown or Batygin would reply to this paper, but it looks as if they both out in Hawaii to continue their search for Planet Nine.
« Last Edit: 12/15/2017 07:01 PM by Star One »

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