Astronomers observe Pluto and its moons

Jun 28, 2011
A best-fit color image/map of Pluto generated with the Hubble Space Telescope and advanced computers. Image: NASA

(PhysOrg.com) -- A Williams College team of astronomers, headed by Bryce Babcock and Jay Pasachoff, have been in Hawaii, near Honolulu, to observe a rare double-double event about Pluto. On June 23rd, they observed an occultation, a hiding, when Pluto’s largest moon, Charon, only 755 miles across, went in front of (occulted) a star, revealing its size accurately as well as the absence of any atmosphere. About 11 minutes later, Pluto went in front of the same star, though the astronomers and their students have to analyze their observations to see if they detected that second event.

At this occasion, and at a previous Charon occultation the joint Williams-MIT team observed in 2005, the light from the star disappeared abruptly, while Pluto’s atmosphere makes the starlight disappear gradually when Pluto is occulted.

On June 27, Pluto, which is about 1750 miles across, had a second double occultation. It went in front of another star, occulting it. About 33 minutes later, its tiny moon Hydra, perhaps only 50 miles wide, was scheduled to go in front of the star, casting a shadow exactly its same size on Earth, perhaps only 40 to 100 miles across. The Williams team is allied with an MIT group that provided the continually updated calculations and that itself sent out with special cameras. Indeed, one MIT astronomer carried such a camera to Yunnan, China, to a telescope with access arranged by Pasachoff.

The Williams College team includes Babcock, Pasachoff, and students Shubpanga Pandey ’13 from Nepal as well as Wesleyan exchange student David Amrhein ’12, part of the National Science Foundation sponsored Keck Northeast Astronomy Consortium. The MIT team, founded by the late Jim Elliot, is now headed by Michael Person and Amanda Bosh in collaboration with Amanda Gulbis, who is also at the South African Astronomical Observatory in Cape Town. They also work with Stephen Levine, who works at the Lowell Observatory in flagstaff, who has been providing up-to-the-day positions of Pluto and of the stars. The consortium has the cooperation of David Tholen of the University of Hawaii’s Institute for Astronomy, who provided late corrections to the position of Hydra based on Hubble Space Telescope observations, with the tiny motions of the stars across the sky over the last few years providing the limit in accuracy.

Contrary to popular belief, the International Astronomical Union’s actions in Prague in 2006 promoted Pluto to its current state of “dwarf planet,” making it the first and a major object in its class instead of a diminutive member of a class of much larger “planets.” The measurement of a supposedly larger object in the outer solar system, now named Eris, has now been shown to have probably been in error, with Eris slightly smaller than Pluto although, thanks to a presence of a , known to be more massive.

The June 23 observations were tremendously successful, with the Williams team detecting 100 data points over 50 seconds showing the brightness of the star diminished as Charon passed in front of it. These results were obtained at Leeward Community College with its 20″ telescope, in collaboration with Mohan Kakkala, the astronomer there. Robert Lucas from Sydney, Australia, and Eric Pilger ’84, from the Hawaii Institute of Geophysics, joined in the observations. The alternative site on the other side of Oahu, Honolulu’s island, at Windward Community College with its 16″ telescope was cloudy, as it usually is. The collaboration there is with astronomer Joseph Ciotti and his students Sam Plunkett and Nathaniel Hiraoka. Pasachoff, Amrhein, and MIT undergraduate Stephanie Sallum ’12 were on site for both dates. The June 27 observations were foiled by cloudy conditions at both Windward and Leeward Community College. The Williams College and Windward Community College teams were joined each time by David Tholen and Marco Micheli of the University of Hawaii.

The observations from Hawaii were sponsored by grants from NASA’s Planetary Astronomy division to Williams College and to MIT. The cameras were provided to Williams and MIT by a previous NASA grant. Steven Souza at Williams was one of the planners of the camera systems, each of which is known as POETS, for Portable Occultation, Eclipse, and Transit System.

The successful observations from Honolulu were matched by successful observations from NASA’s Infrared Telescope Facility on Mauna Kea, operated by Gulbis. Moreover, Person and Lowell Observatory astronomer Ted Dunham flew on NASA’s new Stratospheric Observatory for Infrared Astronomy, SOFIA, in one of its first science flights after decades of development. They flew down the projected center line for Pluto’s shadow, and captured a focusing of the starlight all around Pluto’s circumference by Pluto’s atmosphere, related to a phenomenon called the “central flash.” American Astronomical Society press officer Rick Fienberg was on board to chronicle the historic flight.

Two other teams of astronomers, one from the Observatory of Paris and the other from Southwest Research Institute in Boulder, Colo., had interlocking locations of telescopes across the Pacific and adjacent countries, all to capture the double-double occultations involving , Charon, and Hydra.

Explore further: Partial solar eclipse over the U.S. on Thursday, Oct. 23

Provided by Williams College

4.3 /5 (6 votes)

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fmfbrestel
3 / 5 (6) Jun 28, 2011
I don't know why I am being such a language nazi today, but people keep writing stupid things. For example:

"Hydra, perhaps only 50 miles wide, was scheduled to go in front of the star, casting a shadow exactly its same size on Earth"

Exactly?? No, NOT exactly. Very close? yup. Tiny bit smaller? sure. Identically equal? NO.

Unless they are prepared to way that the diameter of that star is EXACTLY the same as the diameter of Hydra, then they should pick a new adverb. Words have meanings.
hooloovoo
5 / 5 (1) Jun 28, 2011
There are even more things wrong with that sentence than you've picked out. I didn't read all of the article because the rest of it is phrased just as awkwardly.

On the plus side, cool event. It'd be much cooler if the shadow were observable to the naked eye.

"What's that in the field over there?"

"Pluto."
Graeme
5 / 5 (4) Jun 28, 2011
I think the shadow was certainly observable to the naked eye, but not the star! It would have looked like dark patch of sky to the naked eye. :-)
aroc91
5 / 5 (4) Jun 28, 2011
I don't know why I am being such a language nazi today, but people keep writing stupid things. For example:

"Hydra, perhaps only 50 miles wide, was scheduled to go in front of the star, casting a shadow exactly its same size on Earth"

Exactly?? No, NOT exactly. Very close? yup. Tiny bit smaller? sure. Identically equal? NO.

Unless they are prepared to way that the diameter of that star is EXACTLY the same as the diameter of Hydra, then they should pick a new adverb. Words have meanings.


The star is far enough away for the difference in size between Hydra and its shadow to be negligible.
Sinister1811
1 / 5 (4) Jun 28, 2011
I can't wait for the New Horizons probe to finally arrive at Pluto, so we can finally learn more about it, and we'll no longer have to look at blurry images, and speculate. But unfortunately New Horizons is still four years away from reaching Pluto..

Once it's done with Pluto, it will travel further and study the Kuiper Belt. I wish were there were also plans to visit Eris, but that sounds a little too far fetched.
Sanescience
3.7 / 5 (3) Jun 29, 2011
One last chance for some kind of exotic "frozen" jungle to be found, unless there is something to be found in the Kuiper belt or Oort clout maybe, but not in our lifetime.

Sometimes I feel sad for what could have been if Venus had been a true twin of earth and inhabitable.
kevinrtrs
1 / 5 (6) Jun 29, 2011
Sometimes I feel sad for what could have been if Venus had been a true twin of earth and inhabitable

Yes, and it certainly makes you wonder sometime just why, if they were supposedly formed in the same way from the same material, how they could be so radically different. The one drenched in water and the other a veritable furnace. Really makes one wonder.
As for Pluto, I wonder just how it managed to acquire it's moons since it's such a small body with so little gravity?
LKD
1 / 5 (2) Jun 29, 2011
Unless they are prepared to way that the diameter of that star is EXACTLY the same as the diameter of Hydra, then they should pick a new adverb. Words have meanings.


They don't know how big it is exactly and eluded to that. So they are right and you are being a little unfair.
fmfbrestel
not rated yet Jun 29, 2011
I am being a little unfair, but they are not right. The shadow will NOT be the exact size of Hydra. It will be in some exact proportion of the size of Hydra. But its not like they are going to get out their yard sticks and measure the shadow directly anyway, they are going to measure the duration of the occultation and use their algebra skills to determine the diameter of Hydra.
LKD
1 / 5 (1) Jun 29, 2011
Yes, and we'll have an extraordinarily good measurement.

I'd love to hear more about them using this novel approach to measure all the large bodies in our solar system. That would be quite an achievement.
panorama
5 / 5 (1) Jun 29, 2011
As for Pluto, I wonder just how it managed to acquire it's moons since it's such a small body with so little gravity?

"Bob" did it.
kaasinees
1 / 5 (2) Jun 29, 2011
One last chance for some kind of exotic "frozen" jungle to be found, unless there is something to be found in the Kuiper belt or Oort clout maybe, but not in our lifetime.

Sometimes I feel sad for what could have been if Venus had been a true twin of earth and inhabitable.


we knows what we can do in the future.
JB85
5 / 5 (1) Jun 29, 2011
Distant occultations have been observed from land, aircraft, and space based telescopes.
Ref: Universe Today, Occultation Reveals Distant Kuiper Belt Object is Surprisingly Icy Bright
by Nancy Atkinson on June 18, 2010

Before the NASA SOFIA on a 747SP was the KAO on a C-141 which made many successful measurements. I find it amazing how many photons are generated by a star to have some arrive in a telescope after passing through a planet's atmosphere. Also how much information is transmitted by the photons relative to time and frequency. So many things had to go right on SOFIA to make this happen, and SOFIA is still in the process of taking its first science flights. The team is still learning how to use the instrument. Apparently the focus, pointing, and stabilizing systems are all working.
aroc91
5 / 5 (2) Jun 29, 2011
I am being a little unfair, but they are not right. The shadow will NOT be the exact size of Hydra. It will be in some exact proportion of the size of Hydra. But its not like they are going to get out their yard sticks and measure the shadow directly anyway, they are going to measure the duration of the occultation and use their algebra skills to determine the diameter of Hydra.


I want you to try a little experiment out for me. Grab a flashlight and a small object, like a ball for example. Put the object about 6 inches from a wall and put the flashlight a foot away and project the shadow on the wall. Now move the flashlight away. Notice how the shadow starts bigger than the object and approaches the actual size of the object as you move the light source away. You can see it for yourself on the scale of a couple feet. Guess what happens when the distance is increased to a few thousand light years and more.