Friday, 9 March 2012

Observing Comet Garradd (C-2009/P1) - the one that got away?

It's looking more and more as if we are not going to get any data on Comet Garradd from the Gemini Telescope. The weather over the Big Island of Hawaii is truly awful. We delayed coming up to the summit tonight until 11pm, as the situation looked more dire than ever.

And our progress up the dirt road was accompanied by a thunderstorm. It's quite cool to look down on a thunderstorm happening in the clouds below you. But it's not very encouraging in terms of being able to get good observations.

Coming up the mountain road in the winter months can be quite an experience. To the north, slopes are sprinkled with snow that sometimes drifts deep. But south across the saddle between Maunakea and Mauna Loa you can see the vent of Kilauea - Halemaumau. In the daytime, depending on how active the volcano is, steam and smoke can be seen pouring out of the vent. That's impressive enough.

But at night, and particularly from the vantage point of the road up the mountain, the view alters subtly. For now the smokestack arising from the vent is lit up by the red-hot molten lava in the pit crater. To the east of Halemaumau, the glow can be seen from lava creeping down the side of Mauna Loa from the Pu'uO'o crater. That crater started erupting on January 3, 1983, and has been erupting ever since. Recently it demolished the last house standing in a small settlement called Royal Gardens.

All night we have been monitoring the satellite images relayed by the Mauna Kea Weather Center. They show clouds building up to the west of Hawaii and drifting north-eastwards. Unfortunately for every cloud that drifts by a new one is ready to take its place. Last night, the prospects were so dire we came down from the observatory at 3am, three hours before the nominal end of our shift. It's 3am again and not looking any better, but we're going to stick it out to the end.

If Comet Garradd is going to be the one that got away, and its going to escape to the depths of the interstellar medium without having its spectrum taken, it won't be for lack of trying on our part!

Thursday, 8 March 2012

Observing Comet Garradd (C-2009/P1) - Summit sunset

Sunset watchers at the summit of Maunakea show us their tail lights as they leave and the dying colours fade from the sky, on Night Three (out of four) of our attempts to observe Comet Garradd.

Tonight we have decided to come to the summit early, ahead of our start time of midnight, because there is the possibility of ice forming on the road later and my University College London colleague Bob Barber is not so confident of getting us back down safely if he has to drive. So we are relying on our trusty telescope operator, Lucas Fuhrman, to get us safely down to the Hale Pohaku dormitories if we have to leave in a hurry.

Things are looking up, but are by no means great, as you can see by the clouds that are hovering above the Gemini North telescope dome. The relative humidity is falling and the winds are much less than the previous two nights, so we are hoping that the clouds will disperse by midnight so we can observe.

In view of what will still be tricky observing conditions, Bob and I have been discussing our observing strategies with our Gemini support scientist, the legendary Tom Geballe. Tom has been working on the mountain since 1981, first as a support scientist for the United Kingdom Infrared Telescope (UKIRT) and then as UKIRT's director. (If you want to read more about UKIRT and Tom and his achievements - or a very small selection of them - you might want to check out a book I wrote recently.)

What Tom does not know about observing at Mauna Kea probably is not worth knowing. He has helped more people than he can count, and published huge numbers of scientific papers. Indeed, he was actually kidnapped by a "cowboy" posse on his way to a conference dinner and charged with publishing too much to the "detriment" of his colleagues' careers.

Tom has advised us to observe at the longer of the two wavelength settings we have chosen, as that is less affected by high concentrations of water vapour in the atmosphere. This is one of the joys of what is now called "classical observing" where the astronomers get to go to the summit and interact directly with the telescope operator and scientific advisors. Young astronomers who only get to observe by remote polycom interfaces are missing an important and formative experience, in my view, even if they may have to suffer a little altitude sickness for the pleasure.

Shifting our observations to longer wavelengths means we will miss some key "hot" water spectral lines that we have observed in previous comets. So direct comparisons will be more difficult. But it means that we will see other "hot" water lines together with those of ammonia, hydrogen cyanide and even acetylene.

The ratio of water ice to ammonia ice in Comet Garradd is an interesting measurement, that can help us to understand how and where the comet formed, and what the Solar System was like 4.5 billion years ago. The early Sun kept the Solar System much hotter than it is now, and all of the "volatile" compounds, like water and ammonia, would have been boiled off from the proto-Earth. Not until the orbit of Jupiter was reached - five times as far from the Sun as we are - would the temperature have dropped below freezing, so that appreciable amounts of water ice have been able to form.

A lot of that would have been used up forming the core of Jupiter itself - about 20 Earth masses in total. The rest would have formed into comets and planetessimals, that would have been thrown to the outer reaches of the Solar System by the gravitational impact of Jupiter, which would have been grabbing gas from the Solar Nebula to grow to the giant ~200 Earth masses it is now. But at the orbit of Jupiter it probably would still have been too hot for ammonia ice to form, because ammonia freezes at a lower temperature than water. So a lot of the comets that formed near Jupiter would have had little ammonia ice in them. Comets rich in ammonia probably formed further out, towards or beyond the orbit of Saturn.

Depending on how much ammonia to water we find in Comet Garradd, we will have a handle on two possible scenarios. Either, we think we know when the comet formed, and the ammonia to water ratio will tell us roughly where it formed. Or we think we know where the comet formed, and the ammonia to water ratio will tell us roughly when it formed, because we know the rate at which the Sun, and hence the Solar System, cooled down. Unfortunately, there will be some ambiguity and a certain amount of "you pays yer money and takes yer choice", depending on other evidence that can be brought to bear on the problem.

But that is the joy of planetary science. It is complex, not reductive; it is synthetic as well as analytical. And so it requires minds (much better than mine) that can hold many conflicting pieces of evidence in the balance and then weigh them to makes decisions about what happened when the Solar System was forming.

Wednesday, 7 March 2012

Observing Comet Garradd - not

There is something ironic about snow and ice now on Earth preventing us from observing snow and ice from 4.5 billion years ago. But last night was a bust - snow and ice on the dome of the Gemini Telescope meant that we could not even go up the mountain, the telescope was closed.

Oh well, tonight's a new night. Oh well ...

Tuesday, 6 March 2012

Observing Comet Garradd (C-2009/P1)

The Gemini North telescope at the Mauna Kea Observatory, Hawaii

March 6, 2012

The summit of Maunakea is a cruel place. At 4,200 metres it is cruel because it is cold and sometimes very windy. But it is super-cruel because it can tease you - just above the telescope the sky can be clear with wonderfully bright stars; at the telescope itself it is too windy to open the dome and there is ridge cloud that makes the air too humid and the chance of ice forming on the telescope mirror to great to take a risk. After all, the telescope cost $90 million, and you can't take risks with that.

Oh, and I haven't introduced this properly yet.

So, I am at the Mauna Kea observatory in Hawaii with the purpose of observing Comet C-2009/P1 Garradd. This was the first comet discovered in 2009 and was thought to be on a "normal" periodic cometary orbit which would bring back close to the Sun from the icy depths of the Solar System at regular intervals. It might even have been round before it was discovered. Not so.

Garradd, which is recently past its closest approach to the Sun and just past its closest approach to Earth, is a one off. It has spent the last 4.5 billion years in what is known as the Oort Cloud, 50 thousand times further from the Sun than is our home planet Earth. Something in the environment of the outer Solar System gave it a kick and sent it crashing in towards the Sun. But it's not coming back - when the orbit was recalculated after the first discovery it was found that once past the Sun, Garradd would be hurled out of the Solar System altogether, never to be seen by humans again - or not until we get really good at space travel and surviving off-Earth for generations at a time.

Steve(left) and Bob (right) in front of the 8-metre diameter main mirror of Gemini

That makes the four nights that my colleague Bob Barber and I have been awarded on the Gemini North telescope very precious. We are here to work out how much water and ammonia the comet is giving off. Because Garradd is essentially a pristine relic of the early Solar System, finding out how much of what it has in it provides important clues into just what was in the cloud of gas, dust and ice that formed the Sun, the planets and everything else in our local space neighbourhood.

But the weather at the summit is just not cooperating, and we are closed up. And the prospects for tomorrow are not much better. Indeed, we may even get snow. The temperature outside is -7 degrees centigrade, and the wind speed is over 100 kilometres per hour, so if we do get snow there is a danger that the whole summit will be closed off. Doesn't someone up there know that if we miss this chance to view Garradd, it's not like waiting for the next bus. It's now or never (cue Elvis).

Maybe the weather forecasters are wrong and tomorrow will be better not worse. So here's a rainbow of hope over Hilo Bay, where Bob and started out from yesterday afternoon. More tomorrow, then, I hope.