National Geographic Society Newsroom

NG Field Notes: Chasing Pluto Across the Pacific

Pluto and its moon Charon as seen by the Hubble Space Telescope. Picture courtesy NASA, ESA The following is a brief description of an NG NASA expedition (funded in part by Nat Geo) now in the field and updates on its progress from grantee Leslie Young of the Southwest Research Institute. Team members Cathy Olkin,...

Pluto and its moon Charon as seen by the Hubble Space Telescope.
Picture courtesy NASA, ESA

The following is a brief description of an NG NASA expedition (funded in part by Nat Geo) now in the field and updates on its progress from grantee Leslie Young of the Southwest Research Institute. Team members Cathy Olkin, Harold Reitsema, Larry Wasserman, and Peter Tamblyn are also in the field (Get updates from Cathy in Majuro here). Keep up with them as they scan the skies for everyone’s favorite dwarf planet, and read more about the project on National Geographic News.  —V

Pluto and two of its moons are occulting two stars in June. An occultation is when a body passes between us and a star. By watching the starlight fade out, we measure the atmosphere on Pluto and the sizes and positions of its airless moons.

Like a solar eclipse, we need to be in just the right place at the right time. Pluto and its large moon Charon occult a star as seen from various Pacific Islands and California/Baja California on June 23. On June 27, Pluto occults a star from many of the same islands, and its small moon Hydra occults the same star as seen from Australia. We are trying to look at Pluto and Charon from about a dozen telescopes, including two portable 14-inch telescopes funded by the National Geographic Society’s Committee for Research and Exploration. The project is also being supported by NASA’s Planetary Astronomy program, NASA’s New Horizons mission, and the Southwest Research Institute.

One nifty trick is that the June 23 observations, including the NGS-funded sites, will pinpoint where in Australia to go to observe Hydra. We plan to look at Hydra with 10 to 30 amateurs in Australia with moderate-sized telescopes.


Pluto update 6/24:

All the previous posts were just to get you excited (we were all already excited). For those of you keeping track, at the time of yesterday’s post, we had three groups of telescopes. The northern ones, in Hawaii and on the West Coast of North America, were in very good shape but were outside of the very latest predicted shadow tracks. The middle ones, Majuro and Kwajalein, were in good shape and predicted to be in Charon’s shadow. The southern ones, Nauru and Cebu, were in very bad shape and the only ones predicted to be in Pluto’s shadow. (I didn’t mention Faukes Telescope South in Siding Springs yesterday, because that was well south of all the shadows).

This was a nerve-wracking situation. We had planned our deployment based on predictions from March (plus our experience of the typical uncertainty in these predictions). The March prediction was considerably north of the latest prediction, updated in June. If the shadows were even farther south than the June prediction, then only Nauru and Cebu would be in either shadow. Nauru had equipment problems. At Cebu, we watched clouds until event time, then drowned our sorrows in fish, beef, mango, yellow pineapple, and two kinds of chicken.

Our dismay was relieved after dinner. Because the star is brighter than Pluto, Dick French at San Pedro Martir was able to call the events in real-time. “Got Charon” was one email, followed quickly by “Got Pluto too!” Reading this, we immediately knew that the shadows went over all our telescopes, including all our big glass.

The score so far is:

Sedgewick 0.8-m: no data (weather)

Santa Barabara 0.4-m: no data (weather)

San Pedro Martir 0.84 and 2.1-m: Pluto and Charon.

Hale A’a 16″ and two 24″: Pluto and Charon

Faukes Telescope North 2-m: Pluto and Charon

Kauai 14″: no reports yet.

Majuro 14″: Pluto

Kwajalein two 20″: Data recorded, but it’s not trivial to get data onto visitor’s laptops.

Nauru: no data, equipment problems

Cebu: no data (weather)

Faukes Telescope South (Siding Springs, Australia): no data (weather).

Good news, right? With four occultations in two days, we have a handful of science goals. Here’s how we stand at the moment on each one:




MEASURE PLUTO’S ATMOSPHERIC TEMPERATURE AT HIGH RESOLUTION: Yes, for the upper atmosphere. For the lower atmosphere, we’re waiting on the Kwajalein reduction.


CHARACTERIZE HAZES: Maybe not. We got visible and infrared light curves at SPM and Hale A’a, but they could be too far from the shadow center to probe hazes. We can try again from Hale A’a on June 27.

MEASURE AN OCCULTATION BY HYDRA: This is the tricky one. We got enough information from this occultation to measure where Pluto is relative to the June 23 star, which should be enough to pinpoint where the Hydra occultation shadow will be on June 27. Will it be visible from Australia? The answer to that will be the main thrust of our work over the next 24 hours.


Pluto occultation update 2, 6/22 UT:

It’s 10 hours from the first occultation, and time for a full run-down for the prospects of each of our sites, East-to-West.

California, USA: The Las Campanas Las Cumbres Observatory (LCO) will be using the 0.8-m at Sedgewick, to be run by B. J. Fulton, and the 0.4-m in the LCO parking lot, to be run by Wayne Rosing.  The weather at Sedgewick has been unusually good.  Prospects:  High for equipment, moderate for being in the shadow.

Baja California, Mexico: At San Pedro Martir, the weather is good, the telescopes and instruments are working well.  There was a problem with 0.84-m telescope, but all is working now thanks to heroic efforts by the tech staff to recompile and rebuild all the telescope control software this morning.  These observers (Bob Howell using an infrared camera at the 2.1-m and Dick French using our visible camera it the 0.84-m) have been able to get on the field and take tons of test images, so their main challenge is to look through their tests and fine-tune their observations.  Prospects:  High for equipment, moderate for being in the shadow.

Hawaii (Big Island), USA: At Hale A’a, Eliot Young, Tony Vengel, Chris Erickson, Clifford Livermore, and Wayne Fukunaga will be at Hale A’a with a portable 16″, a portable 24″, and Bill Brevoort’s fixed 24″, using two of our visible CCDs and an Anacapa InGaAs short-wave infrared (SWIR) camera from NovaSensors.  Hale A’a has not gotten on field yet. Dave Tholen had planned to use the University of Hawaii 2.2-m telescope, but it was damaged by lightning last week.  We were following the progress of the repairs with great interest, but were just that it will not be running for the June 23 occultation.  Prospects for UH 2.2-m: nil. Prospects for Hale A’a:  Good for equipment, moderate for being in the shadow.

Maui, USA: Weather has prevented any imaging of the field from the 2-m Faukes Telescope North on Maui or the 2-m Faukes Telescope South in Siding Springs, Australia.  Still, these are modern telescopes and cameras, and Federica Bianco and Tim Lister should have no problems.  Prospects: High for equipment, moderate for being in the shadow.

Kauai, USA: All set to use two 14″ telescopes, one in Tom Hall’s driveway in Kehaka (Thomas Widemann observing), and one at the KEASA observatory (Hall and Merrit observing).  Marc Buie was there the previous nights, but is flying off to Alice Springs, Australia to try the Hydra occultation of July 27.  Prospects:  High for equipment, moderate for being in the shadow.

Majuro, Marshall Islands: Equipment is working fine.  Cathy Olkin and Harold Reitsema are set for tonight.  Jeff Regester was on Majuro with Cathy and Harold, and flew off to Kwajalein today.  Prospects:  High for equipment, high for being in the shadow.

Kwajalein, Marshall Islands: The telescopes were being used for another project that finished last night, so we can swap to the fast cameras we’ll be using for the occultation.  Jeff Regester, Jason Daily, and Richard Westhoff will be observing with two 20-inch telescopes. Prospects:  High for equipment, high for being in the shadow.

Nauru: This is going to be tricky.  Gears in the telescope were damaged during shipping, which affects the declination pointing.  If Larry Wasserman and Peter Tamblyn pull this off, it’ll be a real coup.  Prospects:  Very difficult for equipment, high for being in the shadow.

Cebu City, Philippines: The US travelers have yet to see a star, but we’ve done all we can under cloudy skies.  Leslie Young, Melissa Brucker, Chris Go, and Tomeo Akutsu will observe with Chris’s 14″ telescope, if the weather clears. Prospects:  High for equipment, moderate for observing circumstances (Pluto at 15 deg and rising at event time), low for weather, high for being in the shadow.


Pluto occultation update 1, 6/22 UT: It’s less than a day and a half from the first occultation, which means one more practice night before the June 23 events. We’re spread across nine time zones, so the practice night is just starting in Mexico, but it’s the morning before the practice night in Cebu City. At Hale A’a on the Big Island of Hawaii, Eliot is using three telescopes—a 16-inch, a 24-inch Dobsonian, and 24-inch fixed—using the lighter infrared camera on the Dobsonian and our heavier PHOT camera on the fixed 24-inch. The crew at Nauru is having trouble finding the field with the portable 14-inch telescope. In Cebu City, we’re glad to have a whole day to get the balance right before our last chance at a practice night tonight. It’s been very cloudy, sometimes rainy, here in the Philippines, and we have not yet put the camera on the telescope at night. If we want to get both Pluto and Charon occultations (which we do) we need to start our run only four minutes after Pluto rises above 10 degrees. Yipes! Those of us who have not yet imaged the field are feeling a little nervous, and those of us who have are feeling pretty good.


Pluto occultation update, 6/21 UT: Since the last report, more travelers have arrived on location in Majuro and Hawaii (Kauai and the Big Island). No missed flights or delayed equipment yet. Our 14-inch telescopes arrived wet in Nauru and Kauai; in Kauai, Marc Buie reports checking out the telescope, so that’s not a large concern at the moment. In Majuro, Cathy Olkin and Harold Reitsema set up the portable 14-inch telescope and imaged Pluto and the June 23 and June 27 star fields. They’re set up at the NOAA site in Majuro, a nice location to work from, as long as you pay attention to when and where they plan to launch their weather balloons. In Mexico (San Pedro Martir), the visible camera is mounted on the 0.84-meter telescope and the infrared camera is being cooled down. In Cebu City, Chris Go got a new-to-him 14-inch telescope tube just four days ago and finally had the clear skies he needed to adjust it last night and affirm that the optics are very good.


Pluto occultation update, 6/20 UT: We heard from travelers to Mexico, Majuro (Marshall Islands), Nauru, and Cebu (Philippines). All equipment is where it should be, including the shipments of the telescopes. This was not a certainty—as it happened, both the Majuro and Nauru telescopes got shipped on the latest possible flight that would still get them there on time. All observers should be in location by tomorrow. The main concerns are weather (Philippines is seeing tropical depression Egay) and the shadow track (latest prediction for 6/20 is south of Hawaii). If this holds, this will miss much of our larger telesopes, but highlights the importance of Nauru, Cebu, Majuro, and Kwajalein.

Dr. Leslie Young was lucky enough to be on Jim Elliot’s team out of MIT that discovered Pluto’s atmosphere with the stellar occultation technique in 1998 when she was a year out of college. A chance like that can warp a tender mind, and Dr. Young has been studying Pluto, tenuous atmospheres, and stellar occultations ever since. She is now the the Deputy Project Scientist for NASA’s New Horizon’s mission to the Pluto system, and she continues her observations of Pluto and its cousin, Triton.

About National Geographic Society

The National Geographic Society is a global nonprofit organization that uses the power of science, exploration, education and storytelling to illuminate and protect the wonder of our world. Since 1888, National Geographic has pushed the boundaries of exploration, investing in bold people and transformative ideas, providing more than 14,000 grants for work across all seven continents, reaching 3 million students each year through education offerings, and engaging audiences around the globe through signature experiences, stories and content. To learn more, visit or follow us on Instagram, Twitter and Facebook.