Comments on Mike Brown's Planets: The shadowy hand of Eris
Were the integration times too long to learn anyth...Were the integration times too long to learn anything about the atmosphere?
C W Mageehttps://email@example.com:blogger.com,1999:blog-9094742788006644220.post-33894750309184745482010-11-13T14_46_57.615-08_002010-11-13T14_46_57.615-08_00
Could Eris be an ellipsoid?
It says in the articl...Could Eris be an ellipsoid?<br /><br />It says in the article that two chords were detected, and that "...it only takes two different chords to precisely define the size of a circle". That's true.<br /><br />Well, Eris probably isn't a Mobius Strip or a Klein's Bottle. The only other possible shape for something that massive is an ellipsoid. But there are ellipsoids known in the Kuiper belt, famously Haumea. And http://en.wikipedia.org/wiki/20000_Varuna<br />Varuna.<br /><br />"A 28-second occultation of an 11.1 magnitude star by Varuna was observed from Camalau, Paraiba, Brazil, on the night of February 19, 2010. Results of the 2010 occultation as seen from Sao Luis with a duration of 52.5 seconds corresponds with a chord of 1003 km. But Quixadá 255 km away had a negative result suggesting a significantly elongated shape is required for Varuna. Since the occultation occurred near Varuna's maximum brightness, the occultation was observing the maximum apparent surface area for an ellipsoidal shape."<br /><br />As mentioned in the article, the baseline for the Eris measurements is 700 km. That's enough room for the short axis to pass the area of observation. That would give a smaller than real size for Eris.<br /><br />I sure wish we had a third (& fourth +) chord. Some asteroid occultations have resulted in several chords. They usually pass over the United States.<br /><br />Since I think Eris is a separated binary and have done simulations of the separation of binaries, I can easily imagine Eris spinning rather rapidly. Since Eris has not shown any variation in it's light curve, for this situation to come to pass the axis of rotation would have to be pointed towards the Earth. It would help also if Eris wasn't stretched quite as radically as Haumea or Varuna.<br /><br />You might expect Dysnomia's orbit to be aligned perpendicular to the spin axis of Eris due to tidal effects. I've seen a map of Dysnomia's orbit and it's a pretty fat ellipsoid, meaning we see it close to pole-on. But it's not a cirle.<br /><br />If Eris is spinning with it's pole pointed pretty much in the direction of Earth, this will have an effect on the thermal measurements taken when IR/visual comparisons were the only method of determining it's size. Pole on would mean that the surface we see would be significantly warmer than if we were viewing it's equator. And that would account for some of the earlier oversized estimates.<br /><br />Clearly, were not done looking at the outer solar system. More stunning discoveries await us :D<br /><br />-Michael C. Emmert
Hmmm, that's a quarter billion do...Mike Brown:<br /><br />Hmmm, that's a quarter billion dollars not a billion dollars spread over a period of 20+ years. Comes to about a little over 12 million dollars annually. In comparison, about a fraction of the annual aircraft attrition write off from the USAF alone.
I would like to see a stellar occultation of Makem...I would like to see a stellar occultation of Makemake for comparison purposes (Mike would, too). We have no real idea what it's density is, it's a big mystery. I suspect Makemake is very different from the other large objects. It has no moons and is redder. Maybe Eris and Pluto have a frost/condensation cycle that keeps burying the reddish UV-baked tholins under fresh frost, and in the case of Makemake we see something very ancient.<br /><br />Pluto's atmosphere might condense into a frost a few millimeters thick, which would radically change it's appearance. I read somewhere recently that Pluto has indeed changed it's appearance since Vogt et. al's fantastic map of the object from when Charon and Pluto were undergoing mutual occultations. But what we see today is pretty fuzzy compared to that map.<br /><br />Speaking of occultations and maps, how is the Haumea mapping project coming along? I haven't heard any word on that lately.<br /><br />I had never thought to make the bet Mike was talking about concerning Eris, but I have had similar sentiments about some other objects. Unfortunately, I had no money to bet. So I missed out :(<br /><br />Mike Emmert
I like PiS hypothesis, since it predicts so much. ...I like PiS hypothesis, since it predicts so much. Now, how to test it, I come up empty.<br /><br />"This supports both of them being small planets."<br /><br />That depends on how you define a planet (and now there is a rigorous definition), but I've never seen the fraction of rock used. <br /><br />There is even speculations of all or mostly water planets out there. Still strictly exoplanets not planets, but even today the current requirements for planethood is testable in some cases so one is forced to have an open mind on these things.
Torbjörn Larsson, OMnoreply@blogger.comtag:blogger.com,1999:blog-9094742788006644220.post-33418263566213066102010-11-12T00_29_17.456-08_002010-11-12T00_29_17.456-08_00
Paolo: The occultations are rare, but there should...Paolo: The occultations are rare, but there should be attempts like this every year or so. Still, it is nice to get lucky and have telescopes right in the right place!<br /><br />Burton: I am all in favor. I'll send you the bank account to send that billion dollar check to....
Eris has a very little angular diameter and is mov...Eris has a very little angular diameter and is moving very slowly in the sky, so how rare are star's occultation? Was the previous week event the first from the Eris discovery?<br />It's nice to see that after 5 years we're here trying to figure out the exact diameter... the wicked will say "it's the curse of Pluto!" :)
How can Pluto be considered an icy comet if it is ...How can Pluto be considered an icy comet if it is 75 percent rock, as is estimated by the New Horizons mission? Eris is even more rocky since it has a higher density. This supports both of them being small planets.
Maybe someone should send a cheap probe with the N...Maybe someone should send a cheap probe with the New Horizon sensory package to get some definite measurements.<br /><br />Think a Falcon 9 Heavy rocket with a pair of tandemly stacked Centaur upper stages along with an Ion propulsion module should send a smaller refined version of the New Horizon probe to Eris in about a decade with some gravity sling shot assist from the Jovian planets. Just need a Billionaire with a quarter billion bucks handy for the 2 decade life cycle cost of an Eris encounter probe.<br /><br />Would Mike Brown have any comments of this slightly far fletch proposal?<br /><br />Burton
You're right, but what's a factor...Angela,<br /><br />You're right, but what's a factor of 2 among friends? :-)
At one point in the article you say, "...maki...At one point in the article you say, "...making it comfortably larger than Pluto, with a radius of about 2300 km", but I think you mean diameter, not radius.
We try to observe the Eris occultation...Hello Mike.<br />We try to observe the Eris occultation here ( Fortaleza city - Brazil) but the clouds did not allow us.<br /><br />Looking forward to next, :)<br /><br />Clear skies<br /><br />Dennis
What Ray said about a "frost line" got m...What Ray said about a "frost line" got me to thinking:<br /><br />In Sol's early days, wasn't it in a cluster environment where interaction with neighboring stars was much more likely? So an outer family of bodies depleted in volatiles would be much less surprising if another star or stars were present to "burn off" some of the lighter elements, particularly if these stars were a bit older or brighter than the Sun. Conveniently, this scenario is already invoked as a possible explanation for Sedna. I don't have the tools to work up the likelihood, but it's just a thought.
Pete in Spacehttps://firstname.lastname@example.org:blogger.com,1999:blog-9094742788006644220.post-38702166393396473162010-11-08T08_50_34.708-08_002010-11-08T08_50_34.708-08_00
CT has a good point. Maybe Eris was an inner rocky...CT has a good point. Maybe Eris was an inner rocky protoplanet that was scattered to the outer solar system, where-as Pluto may just be an overgrown icy comet scattered to the outer solar system when Neptune and Uranus swapped places. Besides, Jupiter can throw objects farther than Neptune can.<br /><br />-- Kevin Heider
Anyway Dysnomia is probably a potatoe shape so its...Anyway Dysnomia is probably a potatoe shape so its diameter is an estimation, which influences further mathematics on the subject. As stated, we’re looking at “preliminary results” !<br /><br /> <br /><br />Indeed a good question “What’s normal out there?”<br /><br />It seems to have an answer: Large KBOs usually have moons…<br /><br /> <br /><br />Philip
Why can't this increased density simply be the...Why can't this increased density simply be the result of Eris forming inside the protostar Sol's frost line, then being gravitationally ejected to its current elliptical orbit?<br /><br />While it may feel too convenient to invoke this explanation frequently, it seems that the only plausible outcomes of inner planetary formation are accretion (us) and ejection (them).<br /><br />We do have four gravitational giants in our outer system. This could explain the relative paucity of ice-laden planetesimals. Perhaps they were accreted at a greater rate than their inner rocky siblings.
Wikisky shows that the target star was mag 17.25 b...Wikisky shows that the target star was <a href="http://www.wikisky.org/?ra=1.6527583999999989&de=-4.353371999999999&zoom=10&show_grid=1&show_constellation_lines=1&show_constellation_boundaries=1&show_const_names=0&show_galaxies=1&show_box=1&box_ra=1.6527584&box_de=-4.353372&box_width=50&box_height=50&img_source=DSS2" rel="nofollow">mag 17.25</a> but asteroidoccultation.com seems to show the target star as <a href="http://hwww.asteroidoccultation.com/2010_11/1106_136199_25892_Summary.txt" rel="nofollow">mag 15.6</a>. Which was it?<br /><br />-- Kevin Heider
Would a primarily rocky Eris be proof it was forme...Would a primarily rocky Eris be proof it was formed much closer to the sun before being ejected out?
@Maju: really, what I would have expected is that ...@Maju: really, what I would have expected is that everything would be the same. The fact that there is SO much variation is really quite baffling. We've known Pluto's density for so long that it is easy to think of it as "normal" but you're right; I'm not even sure what normal means anymore out there.<br /><br />@nunn: Sharp eyes! What you're seeing is Eris itself. Eris is fainter than the star it occulted by not by much, so when the star disappears all that is left is Eris. If you came back a few hours later you would see the faint Eris a few pixel away still moving along.
In the Atacama animation you show I notice that ev...In the Atacama animation you show I notice that even while the star is occulted a few bright pixels continue to flicker around at it's location. What's going on? Diffraction? Atmosphere(surely not)? Some instrumental effect?
As high school students in the 1960's, we trie...As high school students in the 1960's, we tried to figure out the path of a lunar occultation of a star. We planned it and on one very cold winter evening spent a frigid night in a snow-filled corn field watching and timing the event, then sent our results in to Sky and Telescope magazine. We made the magazine story as the astronomy club that got it wrong. That would have been a lot easier than what you've just accomplished!
A most fascinating astronomy story (and lesson). T...A most fascinating astronomy story (and lesson). Thanks Mike. <br /><br />So what's the problem with different masses with same diameter? As I was reading I first thought: "well, they may be made of different minerals, say iron and carbonates" (oversimplified). But it seems you don't buy this and that your emphasis is in the different apportion of water ice they must have, with Pluto being much more icy than the others. <br /><br />So let me ask you this: why is the problem then with the "dehydrated" objects and not with Pluto? Is there any particular reason to expect these objects to have large amounts of water?