P126 – Pluto Occultation

2002 July 12 (Friday)

The first night of prediction data from the US Naval Observatory was collected the previous night. These data contained the star and Pluto on the same image. Prior to this data had shown a track centered on Paranal, Chile. Other reductions from Bruno Sicardy on newer data were indicating a much more northerly track. Jim Elliot and his team were analyzing the new USNOFS data and I attempted a parallel reduction. The data reduction was not easy owing to the duplicity of both the occultation star and the Pluto-Charon system.

2002 July 13 (Saturday)

I continued the data reduction but did not reach an answer. The astrometric reduction of the images was easy but getting accurate positions for the individual components still required further work. This day saw the beginning of the exodus of the US observing teams to Chile. I had set back my departure from the others, believing that such an early arrival into Chile was not useful.

2002 July 14 (Sunday)

Ron Stone collected another night of data from USNOFS on Saturday night. The weather was not at all good and getting data at all was entirely due to a heroic effort by Ron. The data reduction for both nights of data was completed by mid afternoon. This prediction indicated a southern limit in central Peru – putting Chile completely out of the path. Both nights of data gave the same answer and the prediction seemed pretty secure. I sent out word to the general email list about my findings. Simultaneously, Jim Elliot and co. issued their prediction from the same data that gave a similar ground track. At this point, I was resigned to missing the event but determined to see the observation through. After all, there were far too many predictions all with disparate locations. I still felt that anything was possible.

2002 July 15 (Monday)

My car was in need of repair so it wasn’t available for driving to Phoenix to catch the first flight of my trip. As it happened, Ken Janes from Boston University was headed down for a flight of his own that morning. We had to leave at 8am to make his flight even though that meant a 5-hour wait in the airport before my flight left. I came in to my office a couple of hours earlier to convert my prediction information into HTML for easier access to those already in the field. Upon arrival at the Phoenix airport it was obvious that this was no normal travel day. A very vigorous monsoon storm had hit the airport Sunday night. Quite a few of the trees at the airport were uprooted and there were a huge number of displaced and delayed travelers. The American Airlines ticket counter had a huge line – bigger than any I’ve ever seen in Phoenix. Since I didn’t need to check bags, I decided to refrain from using that line to get checked in. But, I didn’t want to go through security right away. Most of the flights were in disarray and much of the morning schedule was running quite late. My own flight was still showing an on-time departure but all the rest were running late. I was debating an attempt to try and get on an earlier flight just in case. Had it not been for the huge line, I would certainly have tried. But I figured the line would take a couple of hours to get through.

As I dealt with this quandary, I got the first of many calls from Brian Taylor, already in Chile. Based on the all the new predictions, Cathy Olkin, Brian and Jay Pasachoff were all scrambling to get themselves in the newly predicted ground track. Brian had called to get my opinion and see if I wanted to modify my plans as well. At this point, Peru, Ecuador, Costa Rica, Aruba, the Azores, and the Canary Islands were all discussed as possibilities. The CTIO staff felt that they could get the equipment to Aruba and Peru. Other places weren’t so easy. I called a travel agent to see what options existed. Costa Rica and Aruba would have both been relatively easy to get to aside from the issue of getting the equipment there. In the end, it seemed as though there were only two locations that the equipment could be rerouted to. Given that there were three teams and two were already in Chile, I decided to not change my plans.

By the time this all got settled, it was too late to change my flight to Dallas. At one point I did get in the ticket line with the hope that I would figure out the travel plans just before I got to the ticket counter. As I feared, my own flight was now showing a 30-minute delay. Since I only had a 1-hour layover in Dallas this was going to make things tight, but not impossible. The aircraft I was to take came in on time and it looked like we might hold onto that delay. Not so. For some unexplained reason, all the “bumped” passengers (many from America West, apparently) had to go through a manual security inspection of their baggage at the gate. This was nearly 2/3 of the passengers on the flight. At that point, I figured that the flight schedule was doomed. Sure enough, we lost an extra 20 minutes and my already short layover was dwindling to nothing. The flight crew was able to make up about 10 minutes en route but it did no good. Our delay put us into a special category upon arrival and we had to wait nearly 20 minutes to get into a gate. Had we been 5 minutes earlier into the gate I probably would have made my flight to Santiago. As it turned out they pulled the gate on the Santiago flight at the same time I got off the first airplane. So, now I was stuck in Dallas for 23 hours and 50 minutes before the next flight could leave. The original plan called for me to arrive in La Serena mid-day on Tuesday and then begin driving north on Wednesday. That plan was clearly dead and I got word out via email about the busted schedule.

2002 July 16 (Tuesday).

I had already drained one cell phone battery and today’s activities seemed destined to drain another. I tried to use the hotel phones but for some reason no one could call the hotel. All of our phone discussions centered on repairing our deployment plans. In the end, Cathy and Brian had decided not to leave Chile and Jay set out for Aruba. But, Cathy and Brian had already sent their equipment to Santiago in preparation for redeployment. It was decided that Brian, Cathy and Oscar Saá would get one van and drive my equipment to Arica. They were to leave today and I would meet them there Wednesday night. Their equipment was to be shipped to Arica and they would hire a vehicle in Arica. So, this evening I got on a flight for Santiago and everything seemed under control again.

2002 July 17 (Wednesday)

My arrival into Santiago was uneventful, albeit early. With my flight getting changed, I had a 6.5-hour layover in Santiago and I was still cut off from everyone. My flight went as scheduled with a short stopover in Iquique. I arrived in Arica just after 6pm as planned. But, no one else was there. I waited up until midnight and still no one arrived. I finally went to sleep, hoping for the best.

2002 July 18 (Thursday)

I got up at a normal time and checked around. I discovered a van in the parking lot with all my gear but no one was around. I figured they must have arrived late and might be sleeping in a little. About 10am, Brian appeared. Cathy and Oscar showed up not too long afterward. It turns out that they got in at 4:30am. On the way north from La Serena, they had stopped in Copiapo on Tuesday night, leaving themselves a long drive for Wednesday. On Wednesday, they had problems with a leaking seal on the transmission. They encountered a 4-hour delay in Antofagasta leading to the very late arrival.

After a good breakfast, we met with the driver and his vehicle for Cathy and Brian. The picture above shows us just before heading up to the airport to get the rest of the equipment. From left to right: Cathy Olkin, Marc Buie, Oscar Saá, and Brian Taylor. After getting the equipment, we had to get gasoline containers and fuel for the generators. At 2:30 pm we were finally on our respective ways; Oscar and I headed south and Cathy and Brian to the northeast. We had a couple of possible destinations in mind but didn’t make up our mind right away.

The first part of this drive (south out of Arica) was spectacular. The canyons we drove through were enormous. The road suffered great changes in elevation as we proceeded. Oddly though, the path was not marred by incessant switchbacks as is normal when driving in mountains. Instead, we drove up and down large inclines set into the side of the canyon walls. We oscillated between 2000m and sea level as we passed each canyon. I found the structure of the walls to be amazing. From a distance, the walls appeared to be completely smooth – lacking any gullies or other erosional features. The complete and utter lack of vegetation or other signs of even simple life is additionally consistent with a total lack of precipitation in the area. The shape of the canyon walls was puzzling, though. The general cross section of the canyons looked very much like glacially carved valleys. But how can you transition from glaciated landforms to such a dry landscape without sharp erosional features?

Once we got further south we began to work out where to stop. Our first choice was Camiña. However, we found that there were very few fuel stations in that part of Chile. Just about everything away from the coast was 4 hours or more from Arica. In the end, we decided to go to Mamiña, which had the least amount of backtracking of any candidate site. This gave a larger than desired spacing from Putre but the weather prospects were improved. The drive proceeded without incident and we made it to the only relevant gas station in the area, in Pezo Almonte, before heading inland to Mamiña. The Sun set as we were refueling so that the final portion of the drive was in the dark. Mamiña is an altiplanic town, typical of the Andes – though at 3000m elevation it would be considered a lowland town.

On the way we passed a very large mine that generated a monstrous amount of light pollution. Oscar took great affront at this and immediately began considering plans for educating the mine owner on their transgressions. As an active member of the Chilean IDA (International Dark-sky Assocation), perhaps he can make a difference. The town was quite small and nestled in among hills and canyons. We checked out a couple of hotels before deciding on one in particular. The custom in this area is for all meals to be included with the hotel. That suited us just fine as it simplified things greatly. Also, this area is well known for its hot (thermal) springs and each room in the hotel had a private bath that could be supplied from the hot spring water. Oscar was quite happy with this arrangement.

After a leisurely dinner and then getting into warmer attire, we headed out to setup the equipment and practice finding the field one last time. An employee of the hotel, Marcelo, was just getting off work and he offered to guide us to a good location to setup and work. This spot was interior to a canyon but had sufficiently low horizons to permit us to work. Though we were just barely outside of town, it was quiet all night and we worked in peace. We got started on the setup at about 10:30pm. This was the start of a long night.

The equipment survived the trip just fine and the assembly of the telescope went very smoothly. Our first challenge came in doing the polar alignment. I quickly discovered that I had left the instructions for the new polar alignment scope at home so that I had to figure out how to use it without help. I did know that we had to find σ Oct (the nearest naked eye star to the south celestial pole, quite faint). I didn’t bring any printed star charts but I did have XEphem, a sky viewing program on the Linux laptop. With patience, ultimately Oscar and I found the correct star and were successful in figuring out the polar alignment tool. This part of the process took about 2 hours – considerably longer than I expected.

Once aligned, I moved on to finding P126 and Pluto. The process I had worked out was to find η Oph, a bright naked eye star. This step was trivial and also allowed tweaking up the alignment on the finder scope. The second step was to find a 7.7 mag star that is about 1.5 degrees to the NNW of η Oph. This star can be easily seen in the finder on a moonless night. We had a fairly bright moon nearby so this step was non-trivial. In fact, finding this star turned out to be very difficult. Moonlight plus the southerly latitude (20S) made for a very confusing view through the finder compared to what I remembered from my practice sessions the previous month. I had to completely reorient myself and re-determine the scale and orientation of the finder. Still, I took me nearly 3 hours to find this intermediate star. Once I had this star, finding P126 was easy using the star charts I did bring along.

I was very happy and relieved to have found P126 and we could easily see Pluto in the images on its way to encounter this star. By the time we were done, Pluto was nearly setting in the west but at this point I was confident that I could find the star again. By the time we took the sample data and packed up the equipment it was 4:30 in the morning. The weather had been perfect and the temperature was cool but not uncomfortably cold. Still, Oscar was delighted in being able to go back to his room and enjoy the thermal baths.

2002 July 19 (Friday) event night

To the chagrin of the hotel staff, Oscar and I missed breakfast. I didn’t get up until noon, exhausted from the day before. Before lunch (served at 1:30pm) I took a short hike around outside of town. The view and lay of the land was wonderful and I took lots of pictures.

Mamiña:

After lunch, we took a drive to see the spot we had worked the night before. True, it was a nice flat area to work and was located right next to a spring, but, it also is a place where a fair amount of trash had accumulated. We scouted around and found another spot that seemed to be a bit better. After scouting, we went back to the hotel to call Jim Elliot at Magellan. He had not heard anything from Cathy and Brian but we were able to relay that we were ready to go. After getting the hotel to give us sandwiches for our night’s dinner, we headed back out to set up the equipment, this time in daylight. When we got back to the site, we had a little extra time so I suggested that we continue up the road a bit to see more of the countryside. Just one more kilometer up the road was the top of a ridge with a nice flat area next to the road. This site had a much, much improved horizon, no trash, and shielded us from the meager lighting from the town and also from the much worse lighting from the mine.

Though we were setup next to the road we didn’t see any cars pass all night long — we were on our own. By sunset, we had everything put together except for the last cables to the camera head.

We had a comfortable stretch of time where there was nothing to do but sit around and have dinner before working the event. Unlike a northern hemisphere polar alignment, we had to wait until nearly an hour after sunset before we could finish the alignment. But, based on the previous wedge setting and using the GPS to get the tripod aligned to the south, we quickly found σ Oct. The alignment, once σ Oct was sighted, took just 5 minutes. From there it was on to the field.

Finding the 7.7 mag star was a challenge, entirely because of the nearby Moon. There were strong moon-glints in the finder but could be eliminated by holding a card up to shield the finder from the moon. Having found the star the previous night I had taken careful notes on where to put η Oph in the finder. With that I was able to see the intermediate star and then move on to Pluto. By 7:30pm, we were on P126 and taking data. The event was predicted for 9:44pm local time (1:44 UT), geocentric. We took turns guiding on P126 and taking data but we really didn’t need strong guiding corrections. Here’s a picture that Oscar took of me guiding on P126 just minutes before the event.

At 1:35UT I started the “official” event data that was to run for 20 minutes. I guided the telescope and Oscar watched over my shoulder. We both watched intently to see if an event would occur but given the image display stretch, neither of us saw anything definitive. There was a time when we thought that the P126 image appeared to get “sharper” but the change was very subtle. At this point, I really didn’t think we had seen the occultation; the lack of visible signs was disappointing but not unexpected. For good measure, we continued to take data until 2:05 UT and then we packed up the equipment. We got back to the hotel by 11:30pm, in time to call back to Jim and report. While Oscar made the phone call, I fired up my laptop to look at the data. I had neglected to bring along my ready made program for extracting a lightcurve so I had to settle for a visual examination of the images. I quickly found a portion of the data where P126 was clearly fainter than the rest of the time so I was pretty confident that we had seen an occultation. We reported this to Jim and then we went to bed (still not knowing what had happened to Cathy and Brian).

2002 July 20 (Saturday)

Another beautiful morning in Mamiña. I got up and packed but there was still a half hour before breakfast. So, I sat down and wrote a program to extract a lightcurve. In that time I was able to extract a crude curve but even that was sufficient to show that we had successfully observed the occultation. I could also tell right away that this would be a very interesting piece of data.

Oscar was very happy to hear that we got what we came for. At last, my 20-year drought of Pluto occultations had come to and end. We called one last time to Jim to find out what had happened at Putre and to coordinate travel with Brian. Brian and Cathy’s report was the first in a long string of negative results for the huge collection of teams that descended upon South America for this event.

Our original travel plan was for Oscar and I to drive to Arica and pick up Brian at 11am. We really didn’t like this since it meant an extra 8 hours of driving. So, we had Brian fly to Antofagasta where we would meet him this night. After breakfast we took off to the south. The drive was uneventful, nothing as spectacular as the area south of Arica. But, the extent and the extreme dryness and lack of life in the Atacama Desert is amazing. We saw roadside hieroglyphics left by the Incas more than a thousand years ago.

These figures are rock and dirt patterns on the sides of hills. Amazing that they’ve survived all this time. One thing is quite clear, they don’t get rain there or the patterns would have washed away a long time ago. We expected to get to Antofagasta somewhat after sunset. As the day wore on we started noticing problems with our car. The transmission (manual) was a bit balky. We made it to Hotel Antofagasta but I never saw the car move again. We were very, very lucky we didn’t get stranded or have a more “interesting” seizure of the transmission. Brian was there waiting for us but it soon became clear that we weren’t going anywhere real soon. The plan had been for the three of us to start driving again Sunday morning, hoping to get to La Serena late that night. All we knew that night was that it wouldn’t happen in the van we started with. So, we put our troubles aside and had a combined celebratory dinner. Brian told us all about his tales of woe in Putre, mostly driven by cloudy conditions on the practice night.

2002 July 21 (Sunday)

We explored countless scenarios for getting back to La Serena. While Brian and Oscar didn’t have time pressures, I did. I was schedule to leave Monday afternoon back to the USA. We couldn’t find another van in Antofagasta that could get all of us and the equipment to La Serena and our car wasn’t immediately repairable. The rental company sent a van north from La Serena but it couldn’t be in Antofagasta until the middle of the night, at best. So, we decided to enjoy the day in Antofagasta and I would fly to La Serena on Monday morning. Presumably, Oscar and Brian would have a car Monday morning as well and could then start to drive. I was sad to miss out on the rest of the drive but there wasn’t anything we could do about it. We went shopping in the craft markets, had lunch in a local eatery (1000 pesos for lunch! That’s about $1.60.), we hired a cab to take us to La Portada, an interesting rock feature just up the coast. The view at La Portada was beautiful. Brian setup his Hasselblad camera and I scurried around with my little camera.

To cap off the day we had a great dinner in another local restaurant. The restaurant features “La Parillada” which is a form of South American barbeque and had a wide variety of meats.

2002 July 22 (Monday)

It’s travel day. I took a morning flight from Antofagasta to La Serena where I had 4.5 hours before my next flight. Tito, the CTIO “official” taxi driver picked me up and took me to La Recova, a craft market. After that it was back to the CTIO compound where I caught up on a huge pile of email that built up while I was out of touch. At 5:45 pm I took off for Santiago. That flight went fine but the Santiago airport was a zoo. There were two flights checking in at the same time and the lines were incredibly long. For a while I was worried that 2.5 hours would not be enough. As it was, I had 20 minutes to sit around at the gate waiting for the flight to Dallas. This time I did make it and the flight proceeded to Dallas without incident.

2002 July 23 (Tuesday)

This is the end to the journey. I got into Dallas just fine, was nearly the first through the customs lines and got to my gate for the flight to Phoenix with lots of time to spare. The flight to Phoenix was fine and I just had to wait another few hours for a shuttle bus to take me up to Flagstaff. In all this, the only form of transportation I didn’t use was a train or a bicycle. A long, but for once, satisfying trip. Now begins the quest to make sense of the data I collected and see what it will tell us about Pluto’s atmosphere.

--Marc W. Buie

--Lowell Observatory

--Jul 30, 2002