A thoroughly sporadic column from astronomer Mike Brown on space and science, planets and dwarf planets, the sun, the moon, the stars, and the joys and frustrations of search, discovery, and life. With a family in tow. Or towing. Or perhaps in mutual orbit.



Moon shadows galore

Last spring I was extremely excited about the possibility that there was a possibility that the orbit of the satellite of the Kuiper belt object 2003 EL61 might be precisely edge-on when seen from the earth (you can re-read all about it here). As I explained then, such a thing only happens twice each orbit – so only once every 140 years in this case – and has the possibility to teach us an amazing number of things. When we finally got the data and precisely figured out the orbit we were excited – it is edge on – and dismayed – it was only going to be edge on for one more month. We had basically missed all of the action by 2 years and would have to wait 140 more years to see it again.
Things have changed since the spring.
First, 2003 EL61 is now, of course, Haumea, and the satellite with the edge-on orbit is the small inner one, Namaka. Haumea also has an outer satellite Hi’iaka. And Hi’iaka changes everything. When we did our preliminary calculations in the spring we did the comparative simple job of considering Namaka in isolation. It took us the remainder of the summer to get a solution to the full problem, where we also figured out how the orbit of Namaka changes due to the gravitational influence of Hi’iaka (“us” and “we” here is a euphemism for “my graduate student Darin Ragozzine” who actually did all of the work as part of his Ph.D. thesis). We knew there would be an effect, but we assumed early on that it would be a minor perturbation. It is, in a sense, a minor perturbation, but it makes all of the difference in the world.
Hi’iaka ever-so-slightly twists the orbit of Namaka, slowly changing the direction it is pointing. It doesn’t change by more than a degree or two a year – almost imperceptible! But, due to luck or fate or karma or cosmic design, it is changing it just enough to keep the orbit edge-on as seen from the earth for longer than usual. Normally the edge-on events would last for maybe two years. Because of Hi’iaka, they are going to last eight years! So, OK, we have missed the first two years, but we have six more years of this to go!
What are we going to see?
Namaka goes around Haumea once every 19 days. So every 9 ½ days Namaka either goes in front of or behind Haumea. We don’t have any telescopes that are good enough to see the actual event take place; it’s all much much too small. Instead, we’ll simply notice that at the moment Namaka goes behind Haumea and disappears, the whole system gets a little fainter.
Measuring a lot of these disappearances means that we will be able to reconstruct the shape of Haumea pretty precisely. Haumea is that strange object that we think is shaped like a squashed football; a precise measurement will teach us much about how and why such a crazy thing could exists.
So we need to measure a lot of these disappearances.
The problem is, they happen at specific times. It’s only nighttime over half of the earth at a time. And Haumea can only be seen by half of the earth at a time. And those two halves are not precisely the same. So there are sometimes only little slivers of the earth when it is night time and also Haumea is up in the sky. And we don’t have telescopes on all of those little slivers. So what to do?
We don’t have telescopes everywhere, but other people have them in many places. We are right now attempting to encourage a huge international collaboration to all measure these events from wherever they can best be seen (you can see the web site where we explain to astronomers what is happening). We will then all pool our data together and see what comes out. These observations are a strong case for such cooperation; a small number of measurements from just one location are almost worthless, but the full set will be priceless.
We’ve started signing people up already. First, we will be observing from our own telescopes at Palomar Observatory east of San Diego. We quickly enlisted people in Hawaii and Australia. These three telescopes cover the western US and the Pacific. We then have a huge gap of India and China and Russia and Europe until we get to a telescope that we hope to be able to use in the Canary Islands. We’ve contacted and had encouraging responses from the two largest telescopes in India and from a telescope in Armenia.
We’ve got much to do. The first good event occurs on December 7th and then they occur every 9 ½ days until about June when Haumea is too close to the sun again to see. We’re in good shape for about half of them but still struggling to get more telescopes. By next year, though, perhaps we’ll know what we’re doing a little better and we’ll get it all down smooth. And then we’ll still have 5 more years of events to go!
It’s hard to predict just how much we’ll learn about Haumea in these five years, but I think it is safe to say that Haumea, which I’ve long said is the single most interesting object out there in the Kuiper belt, will only get more and more interesting with time.

7 comments:

  1. Can you collaborate with any of the teams searching for transiting exoplanets, since it is kind of the same sort of a measurement?

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  2. Hi, Mike, this is Great News! We get to see just exactly what Haumea's diameter and albedo are.

    (As second poster I'll dispose of what will surely be commented on. Watch out for those typos).

    I can now make a falsifiable prediction. I predict that Haumea's albedo will be even higher than your previous estimates. I base this not on supernatural stuff, but on the detection of a large amount of crystalline water ice on the surface.

    I believe it is snowing on Haumea even as we speak. It doesn't take much. About a centimeter every 10 million years will keep the surface fresh and bright. It's snowing on Enceladus and that body has an amazing 99% albedo.

    The snow has the same source as at Enceladus - Namaka is getting beat up by tidal forces. Your article notes the extreme perturbation of Namaka's orbit by Hi'iaka and this should be enough to pour enough heat into Namaka to feed a slow geyser.

    I've thought Haumea was the lost moon of Triton since noticing when I flew a binary pair of equal sized objects past Neptune on the GravitySimulator, that sometimes they collided. Triton had to have been a binary to have lost enough angular momentum with respect to Neptune to be captured. I believe now that Haumea is the object that absorbed that excess angular momentum.

    Anyway it's great to be able to put out a falsifiable hypothesis. That's the difference between science and pseudoscience.

    I guess the subject of a bet might come up but I believe it is illegal to bet on the internet according to the laws of Texas and anyway I have almost no money. But a gentleman's bet is acceptable. Any takers?

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  3. Is the seperation enough to consider Haurnea and its moons as point sources for the sake of simulating their motions?

    JPL Horizons doesn't have info on TNO moons. I'd love to simulate this in Gravity Simulator. Is there any place I can get their R & V vectors, and masses?

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  4. I am glad to hear that news and read it here in your post. I also have great interests on astronomy and astrophotography like you. You may want to visit my recently discovered site and see what they are doing with tiny cheap camera. See here, http://zookland.com/

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  5. I just learned learned the Chinese characters for Haumea mean something like Rock Goddess Star. How cool is that. Joan Jett would be proud.

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  6. Hi, Mike :)

    Good luck on your observing run Saturday. I hope you can get the first observations of the dance of the moon shadows. I wish somebody had taken advantage of some of the other opportunities but they are gone now.

    I was wondering if perhaps I could ask for the locations on Earth where these events can be seen. Then perhaps if we have a friend in the area we could maybe prevail upon them to get the local institution to participate and enjoy.

    This great adventure of discovery is a treasure to watch, I can only imagine the excitement of actual participation. We who await breathlessly to see if the real facts fit out sometimes vivid imaginations are, you may rest assured, extremely appreciative of your efforts.

    Meantime those of us whose glasses are held together by string may content ourselves with playing with Wikipedia guestimates and seeing if we can do something with them. They say Haumea has a surface area of 20 X 10^7 km^2. So how much must the mass flow of any geysers in the system have to keep it painted crystalline white?

    I would guess that an accumulation of a millimeter per million years should do the job. That woud be compacted snow, I would imagine the Eskimos, who have a number of different words for snow, would have to make up a new one for this. Anyway, 2 X 10^7 km^2 X 10 ^6 m^2/km^2 X .001 m = 2 X 10^10 m^3 water, X 1000 kg/m^3 = 2 X 10^13 kg. There are about 30 million seconds in a year (1 significant figure here) so there are about 3 X 10^13 seconds in a million years. So it takes a geyser with a mass flow of about 2/3 of a kilogram per second to keep Haumea painted. That's a lot less intense than the spectacular fountains of Enceladus which spew a few hundred kilograms per second of water vapor.

    "Santa" might have been a good name after all, what with his association with snow!

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  7. Hi :)

    I was just examining Enceladus and they said it had a geometric albedo of greater than one. That was pretty confusing. Apparently what was happening there is that ice can reflect light directy back to it's source, like those highway reflectors you see in the middle of the road.

    Here is a very beaurtiful shot of Saturn at opposition, directly opposite the the Sun from the Earth, and two other shots taken with the same techniques at other times:

    http://www.astro.virginia.edu/~av4n/satfinal.jpg

    Notice the dramatic difference in the brightness of the rings.

    Haumea, of course, is not at present lined up with the Sun and the Earth.

    I was wondering how this phenomenon affects this project? Any comment?

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