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.



Showing posts with label Eris. Show all posts
Showing posts with label Eris. Show all posts

Free the dwarf planets!


 Most people will probably think of tomorrow as the 5 year anniversary of the demotion of former-planet Pluto. That seems fair; the Pluto demotion got all of the news, caused all of the fights, and promoted all of the discussion. But now that tempers have cooled and the world has come to terms with a new more scientific eight-planet solar system, it is time to remember the other important thing that happened on that day five years ago. On August 24th 2006 the International Astronomical Union (IAU) defined a new class of objects in the solar system: the dwarf planets.

As you will recall, the IAU declared that planets are the objects which go around the sun and gravitationally dominate their orbits. In our solar system, the eight planets are unique in that behavior. But there are other much smaller bodies out there – Pluto being the most famous – that look like planets (simply meaning that they are round) but are not dominant. Pluto and many of these other objects all circle the sun in similar orbits in what is called the Kuiper belt. These objects are the dwarf planets.

At the time this new class of dwarf planets was proposed, the IAU also declared that three dwarf planets were then known: Ceres (the largest asteroid), Eris (the newly discovered largest Kuiper belt object which precipitated all of this mess), and Pluto. In the entire five years since then, the IAU has declared two other objects to be dwarf planets: Makemake and Haumea.

A reasonable person might think that this means that there are five known objects in the solar system which fit the IAU definition of dwarf planet, but this reasonable person would be nowhere close to correct. By my best estimate there are possibly 390 known dwarf planets in the solar system (don’t worry, I’ll explain below).

What is going on here?

How big is Pluto, anyway?

These days, a question like that is easy to answer: type it in to Google, click on the Wikipeadia entry, and read the answer: 2306 +/- 20 km. The  +/- (to be read “plus or minus”) is important here: every measurement has limitations and an often critical  part of science is correctly quantifying those limit. The correct interpretation of 2306 +/- 20 km is that 2306 km is the most likely value, but, within a certain range of probability, the value could be as low as 2286 or as high as 2326 km. The value could still be higher or lower, but the probability is small.

So when the occultation of a start by Eris a few weeks ago lasted for such a short period of time that it was clear that Eris could be no larger 2360 km, Pluto was declared, throughout the land, the once-again largest dwarf planet and king of the Kuiper belt. Because, um, 2306 km is greater than 2360 km? [see updated size on Eris, below]

Dwarf planets are crazy

[yet another Eridian digression in lieu of continuing the Sedna story. Sorry! Plus this one is written while staying up all night and trying to run a telescope at the same time. Not the best for coherent writing or fixing typos, but I am losing sleep pondering the strange results from last week’s Eris occultation. And I have not been getting enough sleep to be able to afford the loss.]

I’m in Hawaii for a few precious nights to point the Keck telescope – one of the largest in the world – at dwarf planet Eris – one of the largest in the solar system. A week ago I would have just said “the largest in the solar system,” but as of last weekend I’m less sure.

The shadowy hand of Eris

[sorry: a brief interruption in the ongoing Sedna story for some late breaking news]

Eris, the goddess of discord and strife and the most massive dwarf planet, is up to her usual tricks.

On Friday night Eris was predicted to pass directly in front of a relatively faint star in the constellation of Cetus. You might think that this sort of thing happens all of the time, but you’d be wrong. Eris is so small in the sky and stars are such tiny points of light that, though they get close frequently, their actually intersections are rare. When they do intersect, though, something amazing happens: the star disappears. And since we know how fast Eris is moving across the sky, seeing how long the star disappears gives us a very precise measure of the size of Eris. Or, to be more exact, a very precise measure of a single chord passing through the body.

Heading South, Looking Up



For most of the past decade the last thing I would do before going to bed was to step out on to my back patio and stare up at the sky for a few minutes, checking for clouds. If the skies were clear I always slept better. In the morning, I would hop out of bed and do the same thing, to see if any unexpected weather front had passed or cirrus had snuck in while I had been sleeping. If all was well with the skies, I knew that my robotic telescope 95 miles southeast of me, likely had a successful night scanning the skies, and I was excited to get up and get to my office to see the results. I knew that any clear night we might (and eventually did!) discover something larger than anything else ever seen past Neptune. It was just a matter of time and of keeping those pesky clouds away.

Changing my world

After writing last week about a pretty major 5 year anniversary – the discovery on Dec 28th 2004 of what is now called Haumea – it seems funny to be writing once again about a 5 year anniversary. But that’s just the way that reality worked. Eight days after discovering Haumea, and just a few days into the new year of 2005, I was back in my office again. I wanted to be studying Haumea – or Santa, as we called it then – since I was certain that it had to be bigger than Pluto, but, sadly for me, we still didn’t have any new data on it. We only had those first three pictures and there was nothing new to learn. We were scheduled to get more data soon, but not soon enough for sooth my anxiousness. My fingernails were nubs.


Baby Pictures

Last night, for the second time this decade, I got to have dinner and give a talk on the floor of the dome of the famous 200-inch Hale telescope at Palomar Observatory. It’s rare for anyone to give a talk on the floor of the 200-inch telescope, because Palomar, like every other large telescope around the planet, is used night after night after night looking at everything from the nearest asteroids to the edge of the universe. Few or no pauses are allowed for frivolities such as dinners and talks (in this case we got in, had dinner, gave a talk, and vacated the floor just as the sun was setting). So it was a treat when I got invited to speak to an intimate gathering of supporters of Palomar and Caltech – the university where I work and the one which, not incidentally, owns and operates Palomar – on the floor of the dome. It was even more of a treat because I had been the speaker at the last one of these dinner 8 ½ years ago, and it was particularly interesting to reminisce about what had happened in the almost-decade since then.
When I gave that first talk, in September of 2000, I was a young assistant professor at Caltech who had embarked on what I think it is fair to say was an audacious project: I was going to go find the 10th planet. I had spent the previous two years systematically scanning a wide swath of sky using the seemingly ancient technology of manually slapping giant glass photographic plates to the back of a wide-field telescope, exposing the photographic plates to the sky for half an hour at a time, developing the photographic plates in the darkroom downstairs, and then looking at repeat exposures of the same patch of the sky to see if – perhaps! – I could find something that had moved. It was exactly what Clyde Tombaugh had done 70 years earlier that had led to the discovery of Pluto, but, no, I had the advantage of a much larger telescope and the use of computers to help analyze the final photographic plates.
At the time of the talk 8 ½ years ago I was in the third year of the project, where I was going back with a larger telescope to try to confirm anything that I thought I had detected during the first two years with the photographic survey. I told my audience sitting under the 200-inch telescope about what I was doing and about what I hoped to find. I told them about photographic technology versus the new digital cameras now widely in use. I told them about why I thought that after this third year I was going to have made that discovery I was hoping for and the 10th planet would be in our grasp. It was, I daresay, a talk full of exciting promise.
It’s a good thing I wasn’t asked to give a follow up talk right away.
By the following year it was clear that my three year survey had found a grand total of absolutely nothing.
I told that story last night at the 200-inch telescope and everyone chuckled. They chuckled, of course, only because they knew what came in the years that followed. What came next? We scraped the photographic plates, installed experimental digital cameras, roboticized the telescope, and kept scanning and scanning and scanning. With the benefit of the faster and more sensitive digital cameras we slowly surveyed the whole northern sky and blew the outer solar system open.
Last night I showed my baby pictures from the past decade. I showed Quaoar, the first large Kuiper belt object that we found, the one named for the creation force of the local Tongva Native American tribe, the harbinger of larger objects to come. I showed Orcus with its newly named moon Vanth, and talked about its odd mirror-image orbit to Pluto. I showed Sedna, far beyond the Kuiper belt, in an orbit that takes 12,000 years to go around the sun, named for the frigid Inuit goddess of the sea, a beacon pulling us even further in the distant solar system. I showed Haumea, with her two moons Hi’iiaka and Namaka, spinning her was across the sky, I showed lonely Makemake, bird god of the Rapa Nui, the runt of the litter that produced the Big Three of Makemake, Pluto, and Eris. And then, of course, I showed Eris her, in all of her discord and strife, with her tiny moon Dysnomia circling her.
I really do feel like each one of these is like a child to me. And, like children, whenever the rest of them are not in the room, I will secretly tell you that this one is my favorite. They’re all my favorites. I can tell you stories about their little quirks, their odd habits, and a funny thing that this one did the other day when it thought no one was watching (did you know that the night before Namaka went right behind Haumea playing a little hide-and-seek with us? Silly little moon.).
Something else was particularly interesting to me about my talk 8 ½ years ago at Palomar. Something happened that day that I am certain I will never forget. I was inside the telescope waiting for the group of Caltech supporters to arrive, and finally hearing the knock on the outside door, I opened the door, and, as my eyes adjusted to the blinding outside light, I was greeted by the director of the group of Caltech supporters. She had worked on the Caltech campus for years, but somehow our paths had never crossed. I had certainly never seen her before. How do I know for sure -- you might ask. Trust me -- is my answer. I would have remembered. She walked in the door, and I fumbled my words introducing myself. Her name was Diane Binney.

Diane Binney doesn’t work at Caltech anymore, but she came on the trip to Palomar last night anyway. It was her first time back to the mountain since that time 8 ½ years ago when I gave a talk up there. She came to see old friends and revisit old places. And, since she hadn’t seen many of the people in a long time, she brought baby pictures of her own. She has a 3 ½ year old daughter named Lilah. Lilah has Diane’s last name as a middle name, but she gets the last name from her father. Me. Lilah Binney Brown.