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.

A ghost of Christmas past

Five years ago I was sitting at work in that quiet week between Christmas and New Year’s Day desperately looking for the 10th planet. I had made a bet five years before that that I would find a new planet by Dec 31, 2004. Time was running out. I was about to lose. I hate losing. So I was searching and researching all of the pictures of the sky I had taken over the past two years hoping that maybe somewhere in those old pictures was something that I had missed. Maybe there was still a planet to be found after all. Maybe I wasn’t going to lose my bet.

Just 3 days after Christmas I came the closest I had ever come. There was something in the old images that had been missed the first time around, and it was bright. I sent email to Chad Trujillo and David Rabinowitz, the two other astronomers I worked with, saying that this new object was so bright that it might well be twice the size of Pluto. Or bigger! Being right after Christmas, we of course called the object Santa.
Santa, which now goes by the official name of Haumea, we now know to be only about ½ the size of Pluto, and we call it – and Pluto – a dwarf planet rather than a planet. But back in those last days of 2004 when the discovery was first made, we had no idea where all of it was heading.
Our understanding of the Kuiper belt has changed dramatically in these past five years. The best example of this change comes, I think, from the discovery of a large Kuiper belt object that was announced just a few days ago. For me it was a particularly surprising discovery. For the first time I was not at the receiving end of a telescope making the discovery, I was at the receiving end of an email asking me about this new object called 2009 YE7.

“Never heard of it,” I thought.

But, by decoding the numbers, I could tell it was something that had just been discovered a few days before. Like anyone else, my first attempt to know more was a quick trip to Google.

Ah ha! A new large Kuiper belt object found from a telescope Chile, by David Rabinowitz! Yes, the same David Rabinowitz from the Haumea discovery. He has moved on to Chile to try to make newer discoveries from there, discoveries in parts of the sky that we didn’t look at back when we were working at Palomar Observatory outside of San Diego.

Based on preliminary information, it looked likely the 9th largest Kuiper belt object ever found. David was clearly on to something good here.

I didn’t have time to delve into any more details because all of this had occurred as I was sitting in a movie theater waiting for the start of The Princess and the Frog with Lilah. She loved the part before the movie started because she could watch the on-screen ads. I checked my email and found out that there was a large Kuiper belt object that someone else had discovered. Then the movie started. I was itching to get more information about 2009 YE7, but I allowed my mind to drift down the bayou instead.

After the movie, though, my mind set to work on the implications of this new discovery. Based on its brightness it might well be a perfect size to test one of my new theories about medium-sized Kuiper belt objects. I feel like I now understand the largest objects, and I fear that I will never understand the smallest objects, but the middle ones are within grasp, if we can just find a few more to test some pet theories about them. For 2009 YE7 to be a good candidate for my theory we need to know if it has a moon, what color it is, and what materials are on its surface. Then we’ll see. I started thinking about where 2009 YE7 is in the sky, what telescopes I could use to point at it, how to time the observations.

Even as I was thinking these thoughts, my mind was drifting back to the discovery of Haumea exactly five years earlier. Back then, on the day of the discovery, we knew absolutely nothing. I had no good ideas about what Haumea would be like; I had no theories I was testing, no hypothesis to work out, no predictions to boldly claim. We were simply in the very early stages of exploration to see what was there. The exploration was going well! Soon after the discovery of Haumea, we tripled the jackpot by first discovering Eris – the one we now know to be larger than Pluto – just two weeks later, and then Makemake – the one we now know to be just a bit smaller than Pluto – a few months later. I felt the universe was exploding with new bright Kuiper belt objects and possibilities were endless. We didn’t know anything about what these objects were, how big they were, what they were made of, or what had happened to them. In April 2005 I still believed it possible that they were all 3 larger than Pluto and that they would eventually be called the 10th, 11th, and 12th planets.

In the five years since, we’ve learned a tremendous amount. We determined their sizes and gave up on any of the things in the Kuiper belt being planets (I lost my bet, too). We found Haumea’s two moons; we found that it had a surface that looks like an almost perfect glaze of ice; we found that it was white, again like ice, we found it elongated and spinning end over end every 4 hours, and we found a cloud of other smaller objects on similar orbits. We found that Makemake is covered in thick layers of frozen methane, that Eris is bigger and heavier than Pluto, and, most importantly, that things were beginning to make sense. We had moved from exploration to explanation. Haumea’s strange properties – and that cloud of objects in similar orbits – were all a consequence of a giant impact 4 billion years ago or so. Eris and Makemake were large enough that they should have methane on them.

With our new found knowledge even things that had been discovered earlier were finally being put in context. Quaoar is a weird combination of Haumea and Makemake. Orcus is what Makemake would look like if it were just a little smaller. Varuna is, well, Varuna is still confusing.

Mostly, though, now instead of each object being an individually mystery to be solved, each new object is a piece of a puzzle where many of the pieces have already been put into place. With only a little information, we can guess where the piece likely goes.

Which brings me back to 2009 YE7. Five years ago, its discovery would have been a thorough mystery to solve. But when I first heard of it two days ago, it was, instead, potentially the exact area of the puzzle I had been looking to fill in. I thought it was going to be that perfect medium-sized Kuiper belt object to try out my theories. I just needed some telescopes, some computers, and some time, and everything would fall into place. I thought it would be a fun month or two to try to collect and analyze the data quickly.

I was wrong. It took me about 2 minutes to figure out almost everything that there is to know about this object and its violent history.

When I finally got home and got a chance to look a little more closely (and “a little more closely” here doesn’t mean much; as of today still nothing is known about the object except for its position for about the past two weeks), I realized two things that told the whole story. First, 2009 is YE7 bright. In absolute terms, it is the 9th brightest object, which is what led to the reasonable assumption that it is likely the 9th largest object (by absolute brightness here, I mean the brightness things would have if they were all the same distance away; some objects are bright just by virtue of being close). Second, the orbit of 2009 YE7 is tilted relative to the planets by 29 degrees. Following the position of an object for only 2 weeks doesn’t give you a precise measurement of much about its orbit, but that tilt is one thing that is solidly known even with this limited data. An angle of 29 degrees is an unusually high angle. Not too many objects are tilted by that much. But one that is is Haumea. Ah! Haumea! Haumea with its family of shards all going around the sun on orbits just like it. Tilted by 29 degrees.

2009 YE7, the brightest object discovered in the Kuiper belt in almost 5 years, is almost certainly one of the large shards (perhaps even the largest) blasted off of the surface of Haumea 4 billion years ago. 2009 YE7 and the other shards have been circling the sun on their own ever since. It is bright not because it is particularly large, but because all of the fragments of Haumea have extremely bright, reflective, icy surfaces which make them stand out against the more common darker Kuiper belt objects. 2009 YE7 is not the 9th largest Kuiper belt object; it is probably about 440 km in diameter and so in the top 50.

 I will admit that I miss the old Kuiper belt. I miss the mystery and wonder of exploration of unknown territories. There will be nothing like it in solar system studies for a long time to come, I suspect. Perhaps ever. And yet, as much as exploration is thrilling and exhilarating, there is something deeply satisfying about learning about a new bright Kuiper belt object while sitting in a movie with your daughter and understanding most of its 4.5 billion year history soon after getting home. We’ve learned so much. We’ve come so far.


A technical aside on 2009 YE7. The tilt of the orbit alone does not prove it to be a Haumea fragment, particularly since the other parameters of the orbit are still poorly known. Above, when  I say it is “almost certainly” a fragment, the assessment is a judgment based on experience, rather than a scientific fact. But I’m pretty confident, sufficiently confident that I’d be willing to bet (I need to win back some of my loss from that old 2005 bet, right?).  The real confirmation, though, would come from an infrared spectrum that shows evidence of deep water ice absorption features, but that requires a pretty big telescope. Almost as good, though, would be optical colors showing it to be white (solar-colored, really) like all of the other Haumea fragments. Measuring these colors is actually quite easy; all you need is a ~1 meter telescope and ~1 night of observing. Any two photometric bands would be good. I would probably just try V and R. Then measure a solar colored standard star and compare. They will be the same, I predict. Go do it! Tell me the answer! It’s fun to make predictions, and even more fun for them to come true.


I don’t actually think the exploration is finished yet. The southern skies are still largely terra incognito for the Kuiper belt. David Rabinowitz has clearly just started the journey; others are scanning out there, too. Much of what they find may indeed fit into the frame of the puzzle that we already know, but I still hope some day to open up some email and read about some new discovery and sit stunned realizing that someone just found something that I didn’t expect at all.

Happy Solstice

[an encore, from a long ago Solstice. but still true today]

If you had walked out into my backyard around 4:40 the last few afternoons you would have been greeted with the orange ball of the sun setting with a final low glare over the tops of the buildings that I can see low on the horizon out across the Los Angeles basin. At this time each late afternoon I like to get out the binoculars that I keep next to the back door, and I step outside to watch the last seconds of the sun setting and to find the spot where the last glimmer of light for the day appears. Every night that glimmer has moved a little further to the south. Just a few weeks ago the last glint vanished just behind the cupola of the Pasadena city hall. By just the next day, the cupola was clear, but the sun disappeared behind the building to the left of city hall. Last night it set 4 or 5 office buildings further to the left, still, behind an anonymous office tower that I can't recognize, but through the binoculars appears impressive with the sun directly framing it and the occasional stray bit of light going through a window on the far side, rattling around on the inside, and emerging as the last bit of bit of light before a long winter night. Tonight I watched again, and the sun set behind exactly the same anonymous tower. It hadn't moved at all. Today, therefore, must be the solstice. The solstice is many things: the first day of winter, the earliest sunset, the longest night of the year, the latest sunrise. Most people notice the sunset more than anything else. But solstice comes from the latin "solstitium": sol for sun, and stitium for a stoppage ("armistice" comes from the same root: a stoppage of arms). The stoppage of the southern progression of the sun -- the turnaround to come back to the north -- was considered a big enough phenomenon to give the event its name. The sun stoppage. As the darkness tries to ascend (quickly; these winter twilights don't last) the other part of the season becomes clear. While the nearby glare of Los Angeles means that we never truly have darkness in these parts, this time of year everyone is doing their best to cut the darkness even more. I can see Christmas lights on the houses throughout Pasadena, and, with the binoculars, I can see to downtown Los Angeles where the buildings have been strung with lights. And who can blame them? With the nights so long and the sun moving further and further south, who would not want to try to do their part to make up for the absence of the light and the heat? Who would not be at least a little afraid at this time every year that the sun would somehow not decide to stop and then come back?

At our house we celebrate the solstice with our best attempt to coax back the sun. When the night is as dark as it will get, we gather with friends around our Christmas tree, turn out all of the lights in the house, and slowly refill the house with the yellowy-orange glow as we one by one light the dozens of candles hanging in the branches of the tree. Lighting candles on Christmas trees is a well known Bad Thing to Do, but we find that with a tree cut down the day before (and a fire extinguisher on hand just in case), all goes smoothly. Like the sun, the candles slowly go out. Some catch a few warm drafts and burn more quickly, some get less air and burn more slowly, but one by one they all eventually go until, with just two or three left, the house is dark again and the shadows of branches shimmer sinisterly on the ceiling. Finally the last candle sputters and dies, sometimes with a long glow and sometimes with a sudden final pop, and the longest night of the year totally envelopes us.

The night sky gets in on the act this time of year, too. Many people who claim to know no constellations in the sky can look up and identify Orion in the winter sky. With the three bright stars making the belt, the scabbard of stars hanging below, and the quartet making the shoulders and knees, Orion is truly simple to identify. But Orion is also composed of some of the brighter of the stars in the sky. In fact, look outside, and look around Orion. Bright stars are all around. The constellation of Taurus, Sirius, the brightest star around. The seasons of the sky are not created equally. Winter is a spectacular display of stars and constellations unlike any other, as if the stars, too, are trying to help us out on the longest winter nights by saving the best show for the very end of the year. None of this is true, of course. The spectacular winter skies are caused by the fact that we are looking straight in to the Milky Way galaxy, instead of out of it as we do in the spring and fall. But still, it is hard not to see the similarity between the lights strung in the town below trying to dispel the night and call back the sun, and the lights above, also seemingly strung for the same reason.

Tomorrow, if the weather holds, I'm going to go outside with my binoculars and see exactly where the sun sets again. Because I do this every year, and because I can look up the precise date and time of the solstice, and because I know that the earth will continue to go around the sun with the same tilt for my entire lifetime, I know what will happen: the sun will have moved away from the anonymous office building and finally started moving right again. The day will get imperceptibly longer. Really, there is not much suspense in what will happen, just a certain reassuring inevitability. But if I didn't know these things and didn't have confidence in the inevitable, I can imagine myself holding my breath as the last rays of the sun were shooting out and I was trying to see just where it was setting. I stopped yesterday, but is it really turning around today? Will the days really get longer again? Will my crops (well, ok, my vegetable garden) come back to life? And I'll then see the spot and it will be clearly north and I'll know. And at that point, I will say to anyone within sight: happy new year. For while the calendar claims I have another week to go, the Christmas lights and the candles and Orion and Taurus and Sirius will have done their jobs, and the sun will have started its new year already today and we should all be glad for the solstice.