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.