“Someday Alice!” … that day is less than 2 months away — the flyby of Pluto and Pluto’s moon Charon … and Ralph and Alice will have the last say.

New Horizons’ success at Pluto: Its all about Ralph and Alice!

by T. Reyes

NOTE: This article was originally published April 22, 2015 by Science Exploration Network (SEN) — http://sen.com/blogs/tim-reyes/new-horizons-at-pluto-its-all-about-ralph-and-alice

Like the saying, “every journey starts with a single step”, the second imaging campaign of New Horizons has commenced with a single pixel. A color imager is now in action, New Horizons’ Ralph, as in Ralph Kramden. And Ralph will soon be followed by another spectrographic imager — Alice. For a few more days, we cannot judge Pluto by its cover — by a pixel or two — but soon, one will become two pixels, two — four, then 8 and the book will truly open. Steady improvement in details are in store from Ralph and Alice as New Horizon’s approaches Pluto and Charon.

OK, it was a standing joke from a bygone era. Ralph Kramden would say, “one of these days, Alice, pow! — straight to the Moon.” Politically incorrect today, an edgy joke to times gone by, but New Horizons is heading straight to the moon — Charon and more importantly its parent - dwarf planet, Pluto. Both imaging spectrometers make a trio of cameras on New Horizons. The long range camera LORRI is performing supremely and will likely continue to do so but Ralph and Alice will tell us what these two small bodies are made of and how they interact.

Ralph’s first released image (2nd figure) is a single pixel on Pluto and another on Charon. Taken at about 110 million km distance, Pluto’s image projected on Ralph’s detector is nearly exactly the physical dimensions of one pixel. Ralph is actually two instruments sharing an optical system with an aperture (opening) very comparable to a binocular’s or a kids first telescope. The comparison ends there because Ralph is a refined instrument from Southwest Research Institute (SWRI) based on a first design for the Pluto mission which was proposed but dismissed by NASA in the 1990s.

The success of New Horizons hangs in the balance with these two instruments. NASA mission plans include a set of criteria defining full mission and partial mission success. The primary science objectives depend on the design and performance of Ralph and Alice. Unlike their comic legacy, these two are meant to work in unison, orchestrated for no conflict and not even dry humor.

Ralph is a mutli-spectral imager and also a visible and near-infrared spectrometer. It is two instruments in one — Multi-Color Visual Imaging Camera (MVIC) and Linear Etalon Visible Imaging Array (LEISA), the latter being the spectrometer. Presently, at 100 million kilometers, Ralph functions in a stare mode but on final approach to Pluto-Charon, it will use the pushbroom method of scanning; the New Horizon’s vehicle will slew so that the image pans across the 5000 x 32 pixel array. While only filling a single pixel now, Pluto at the time of closest approach, will fill the full breadth of 5000 pixels — a resolving power of less than 500 meters (1600 feet) per pixel.

Similarly, Alice is an ultraviolet imaging spectrometer. At closest approach, Alice will be able to scan the surface of Pluto and Charon but its primary purpose is to study airglow of the tenuous atmosphere of the dwarf planet. The atmosphere will be studied by viewing the Sun’s rays passing through the atmosphere during the flyby. Presently, it is used for navigational purposes but will be able to detect several molecules of interest. Alice’s spectral bandpass — ~465 to 1880 Å (Angstroms)— includes lines of CO, atomic Hydrogen, Argon, and Neon, which may be detectable as airglow, and the electronic bands of Nitrogen molecules, methane, and other hydrocarbons and nitriles (NOx). For the more technically minded reading this article, the detectors are “microchannel plate double delay line device — photon counters” in a 1024 x 32 rectangular array.

The New Horizons space probe is show in animation during closest approach to the Pluto-Charon binary system. The vehicle will slowly slew to pan the field of view of the three imaging instruments across the face of the dwarf planet Pluto. (Credit: NASA/SWRI/JHUAPL)

The New Horizons team is now in 24/7 mode working and reworking the command sequences in simulations and honing the contingency plans. There is no slowing down the space probe. It is traveling at over 1 million kilometers per day equivalent to three consecutive one-way trips to the Moon in 24 hours. New Horizons will flyby Pluto and Charon on July 14, 2015. So, thankfully, Ralph’s deputy principal investigator, Dr. Catherine Olkin of the Southwest Research Institute in Boulder, Colorado, graciously slowed down a moment to answer a few questions.

The Ralph image of Pluto and Charon appear to show a shape. The first question to Dr. Olkin — could this be revealing the shape of these small bodies? Are they oval shaped from their gravity and tidal forces? Dr. Olkin, stated, “The images do not show the oblateness of Pluto and Charon.” She explained further that without doubt, tidal forces will have shaped both bodies to oblate (oval-shaped) spheres, however, extreme deformation is unlikely. Dr. Olkin was also asked about the color — whether enhanced and how long was the exposure for a photo taken from 100 million miles away. Dr. Olkin had this to say, “The Ralph image is real color. The brightness is enhanced but the color is real. The exposure time of the image was just under 6/10ths of a seconds.”

So, followers of this great mission, will recall that until now, the Hubble images of Pluto were all we had. It is turning out that Hubble’s color image is correct and now Ralph, day by day, will return finer images and soon Hubble’s will be surpassed.

The oblateness of the two bodies remain to be determined. Theoretical work has been completed by various researchers to better understand the dynamics of a very unique binary system.

There are only three known two-body systems in the Solar System which have their center of gravity — the barycenter — above the surface of both bodies, i.e. a free point in space around which both revolve. One such pair is none other than the Sun and Jupiter. A second pair is much smaller — the Jupiter Trojan asteroid 617 Patroclus-Menoetius. These two asteroids are on the order of 150 km in width. There are certainly many smaller objects of this type but of these three, Pluto and Charon has taken it a step further.

Actually it is a final step. Pluto and Charon are the only dual synchronized tidally locked bodies in the solar system. Both objects spin such that the same sides are always facing each other as they orbit. In the Earth-Moon system, only the Moon is tidally locked to the Earth — showing one face, “the near side” towards the Earth at all times. Pluto and Charon’s condition is a final state from which they will never change unless some external force such as an impact occurs. Their state as a binary system is considered to be from a collision of two bodies such as what most scientists consider as the way our Moon came to be. Additionally, Pluto and Charon in this state, orbit around their barycenter in near perfect circles.

Eighty-five years have past since Pluto’s discovery (1930, Flagstaff, AZ) by Clyde Tombaugh. Since Clyde’s passing in 1997 at age 91, our understanding of the Pluto system has grown by leaps and bounds. Mission leader and Chief Scientist of New Horizons, Dr. Alan Stern calls Pluto a mini solar system. Within the past ten years four small moons have been discovered around Pluto, which itself is about half the size of our Moon. But the tidal forces at play between Pluto and Charon make the small bodies incredibly interesting. New Horizons will reveal how remarkable Pluto is, be it a dwarf planet or planet.

Author’s note: One of the best episodes of the Jackie Gleason Show — Honeymooners, “Mama Loves Mambo” on YouTube.

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