New Horizons Confirms Solar Wind Slows Farther from the Sun

The SWAP instrument aboard NASA's New Horizons spacecraft has confirmed that the solar wind slows as it travels farther from the Sun. This schematic of the heliosphere shows the solar wind begins slowing at approximately 4 AU radial distance from the Sun and continues to slow as it moves toward the outer solar system and picks up interstellar material. Current extrapolations reveal the termination shock may currently be closer than found by the Voyager spacecraft. However, increasing solar activity will soon expand the heliosphere and push the termination shock farther out, possibly to the 84-94 AU range encountered by the Voyager spacecraft. (Image credit: Southwest Research Institute; background artist rendering by NASA and Adler Planetarium). Hi-res image

Research could help predict when spacecraft will cross the termination shock

Measurements taken by the Solar Wind Around Pluto (SWAP) instrument aboard NASA's New Horizons spacecraft are providing important new insights from some of the farthest reaches of space ever explored. In a paper published recently in The Astrophysical Journal, New Horizons scientists show how the solar wind — the supersonic stream of charged particles blown out by the Sun — evolves at increasing distances from the Sun.

"Previously, only the Pioneer 10 and 11 and Voyager 1 and 2 missions have explored the outer solar system and outer heliosphere, but now New Horizons is doing that with more modern scientific instruments," said Heather Elliott, a staff scientist at the Southwest Research Institute, deputy principal investigator of the SWAP instrument and lead author of the paper. "Our Sun's influence on the space environment extends well beyond the outer planets, and SWAP is showing us new aspects of how that environment changes with distance."

The solar wind fills a bubble-like region of space encompassing our solar system, called the heliosphere. From aboard New Horizons, SWAP collects detailed, daily measurements of the solar wind as well as other key components called "interstellar pickup ions" in the outer heliosphere. These interstellar pickup ions are created when neutral material from interstellar space enters the solar system and becomes ionized by light from the Sun or by charge exchange interactions with solar wind ions.

The journey New Horizons is taking through the outer heliosphere contrasts that of Voyager since this solar cycle is mild compared to the very active solar cycle explored during the Voyager passage through the outer heliosphere. In addition to measuring the solar wind, SWAP is extremely sensitive and simultaneously measures the low fluxes of interstellar pickup ions with unprecedented time resolution and extensive spatial coverage. Currently, New Horizons is the only spacecraft in the solar wind beyond Mars and consequently the only spacecraft measuring the interaction between the solar wind and interstellar material in the outer heliosphere.

As the solar wind moves farther from the Sun, it encounters an increasing amount of material from interstellar space. When interstellar material is ionized, the solar wind picks up the material and, researchers theorized, slows and heats in response. SWAP has now detected and confirmed this predicted effect.

The SWAP team compared the New Horizons solar wind speed measurements from 21 to 42 astronomical units to the speeds at 1 AU from both the Advanced Composition Explorer (ACE) and Solar TErrestrial RElations Observatory (STEREO) spacecraft. (One astronomical unit, or AU, is equal to the distance between the Sun and Earth.) By 21 AU, it appeared that SWAP could be detecting the slowing of the solar wind in response to picking up interstellar material. However, when New Horizons traveled beyond Pluto, between 33 and 42 AU, the solar wind measured 6-7% slower than at the 1 AU distance, confirming the effect.

In addition to confirming the slowing of the solar wind at great distances, the change in the solar wind temperature and density could also provide a means to estimate when New Horizons will join the Voyager spacecraft on the other side of the termination shock, the boundary marking where the solar wind slows to less than the sound speed as it approaches the interstellar medium. Voyager 1 crossed the termination shock in 2004 at 94 AU, followed by Voyager 2 in 2007 at 84 AU. Based on current lower levels of solar activity and lower solar wind pressures, the termination shock is expected to have moved closer to the Sun since the Voyager crossings.

Extrapolating current trends in the New Horizons measurements also indicates that the termination shock might now be closer than when it was intersected by Voyager. At the earliest, New Horizons will reach the termination shock in the mid-2020s. As the solar cycle activity increases, the increase in pressure will likely expand the heliosphere. This could push the termination shock to the 84-94 AU range found by the Voyager spacecraft before New Horizons has time to reach it.

"New Horizons has significantly advanced our knowledge of distant planetary objects, and it's only fitting that it is now also revealing new knowledge about our own Sun and its heliosphere," said New Horizons Principal Investigator Alan Stern, of SwRI.

New Horizons is the first mission in NASA's New Frontiers program. The Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, built and operates the New Horizons spacecraft and manages the mission for NASA's Science Mission Directorate. SwRI led the payload instrument development and leads the New Horizons science and mission teams from the Tombaugh Science Operations Center located at SwRI facilities in Boulder, Colo. For more information, go to: http://pluto.jhuapl.edu/.

The paper "Slowing of the Solar Wind in the Outer Heliosphere" by Elliott, D.J. McComas, E.J. Zirnstein, B.M. Randol, P.A. Delamere, G. Livadiotis, F. Bagenal, N.P. Barnes, S.A. Stern, L.A. Young, C.B. Olkin, J. Spencer, H.A. Weaver, K. Ennico, G.R. Gladstone, and C.W. Smith, was published November 11 in The Astrophysical Journal.

Source: New Horizons - NASA's Mission to Pluto and the Kuiper Belt/News Center

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Pluto 'Paints' its Largest Moon Red

NASA's New Horizons spacecraft captured this high-resolution, enhanced color view of Pluto’s largest moon, Charon, just before closest approach on July 14, 2015. The image combines blue, red and infrared images taken by the spacecraft's Ralph/Multispectral Visual Imaging Camera (MVIC); the colors are processed to best highlight the variation of surface properties across Charon. Scientists have learned that reddish material in the north (top) polar region – informally named Mordor Macula – is chemically processed methane that escaped from Pluto’s atmosphere onto Charon. Charon is 754 miles (1,214 kilometers) across; this image resolves details as small as 1.8 miles (2.9 kilometers). Credits: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute . Hi-res image

In June 2015, when the cameras on NASA's approaching New Horizons spacecraft first spotted the large reddish polar region on Pluto's largest moon, Charon, mission scientists knew two things: they'd never seen anything like it elsewhere in our solar system, and they couldn't wait to get the story behind it.

Over the past year, after analyzing the images and other data that New Horizons has sent back from its historic July 2015 flight through the Pluto system, the scientists think they've solved the mystery. 

As they detail this week in the international scientific journal Nature, Charon's polar coloring comes from Pluto itself - as methane gas that escapes from Pluto's atmosphere and becomes "trapped" by the moon's gravity and freezes to the cold, icy surface at Charon's pole. This is followed by chemical processing by ultraviolet light from the sun that transforms the methane into heavier hydrocarbons and eventually into reddish organic materials called tholins.

"Who would have thought that Pluto is a graffiti artist, spray-painting its companion with a reddish stain that covers an area the size of New Mexico?" asked Will Grundy, a New Horizons co-investigator from Lowell Observatory in Flagstaff, Arizona, and lead author of the paper. "Every time we explore, we find surprises. Nature is amazingly inventive in using the basic laws of physics and chemistry to create spectacular landscapes."

The team combined analyses from detailed Charon images obtained by New Horizons with computer models of how ice evolves on Charon's poles. Mission scientists had previously speculated that methane from Pluto's atmosphere was trapped in Charon's north pole and slowly converted into the reddish material, but had no models to support that theory.

The New Horizons team dug into the data to determine whether conditions on the Texas-sized moon (with a diameter of 753 miles or 1,212 kilometers) could allow the capture and processing of methane gas. The models using Pluto and Charon's 248-year orbit around the sun show some extreme weather at Charon's poles, where 100 years of continuous sunlight alternate with another century of continuous darkness. Surface temperatures during these long winters dip to -430 Fahrenheit (-257 Celsius), cold enough to freeze methane gas into a solid.

"The methane molecules bounce around on Charon's surface until they either escape back into space or land on the cold pole, where they freeze solid, forming a thin coating of methane ice that lasts until sunlight comes back in the spring," Grundy said. But while the methane ice quickly sublimates away, the heavier hydrocarbons created from it remain on the surface.

The models also suggested that in Charon's springtime the returning sunlight triggers conversion of the frozen methane back into gas. But while the methane ice quickly sublimates away, the heavier hydrocarbons created from this evaporative process remain on the surface.

Sunlight further irradiates those leftovers into reddish material - called tholins - that has slowly accumulated on Charon's poles over millions of years. New Horizons' observations of Charon's other pole, currently in winter darkness - and seen by New Horizons only by light reflecting from Pluto, or "Pluto-shine" - confirmed that the same activity was occurring at both poles.

"This study solves one of the greatest mysteries we found on Charon, Pluto's giant moon," said Alan Stern, New Horizons principal investigator from the Southwest Research Institute, and a study co-author. "And it opens up the possibility that other small planets in the Kuiper Belt with moons may create similar, or even more extensive 'atmospheric transfer' features on their moons." 

Source:  New Horizons/News Center

X-ray Detection Sheds New Light on Pluto

Pluto
Credit: X-ray: NASA/CXC/JHUAPL/R.McNutt et al; 

Optical: NASA/JHUAPL
Press Image and Caption

Scientists using NASA's Chandra X-ray Observatory have made the first detections of X-rays from Pluto. These observations offer new insight into the space environment surrounding the largest and best-known object in the solar system’s outermost regions. 

While NASA's New Horizons spacecraft was speeding toward and beyond Pluto, Chandra was aimed several times on the dwarf planet and its moons, gathering data on Pluto that the missions could compare after the flyby. Each time Chandra pointed at Pluto – four times in all, from February 2014 through August 2015 – it detected low-energy X-rays from the small planet.

Pluto is the largest object in the Kuiper Belt, a ring or belt containing a vast population of small bodies orbiting the Sun beyond Neptune. The Kuiper belt extends from the orbit of Neptune, at 30 times the distance of Earth from the Sun, to about 50 times the Earth-Sun distance. Pluto's orbit ranges over the same span as the overall Kupier Belt.

"We've just detected, for the first time, X-rays coming from an object in our Kuiper Belt, and learned that Pluto is interacting with the solar wind in an unexpected and energetic fashion,” said Carey Lisse, an astrophysicist at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland, who led the Chandra observation team with APL colleague and New Horizons Co-Investigator Ralph McNutt. “We can expect other large Kuiper Belt objects to be doing the same."

The team recently published its findings online in the journal Icarus. The report details what Lisse says was a somewhat surprising detection given that Pluto – being cold, rocky and without a magnetic field – has no natural mechanism for emitting X-rays. But Lisse, having also led the team that made the first X-ray detections from a comet two decades ago, knew the interaction between the gases surrounding such planetary bodies and the solar wind – the constant streams of charged particles from the sun that speed throughout the solar system -- can create X-rays.

New Horizons scientists were particularly interested in learning more about the interaction between the gases in Pluto's atmosphere and the solar wind. The spacecraft itself carries an instrument designed to measure that activity up-close – the aptly named Solar Wind Around Pluto (SWAP) – and scientists are using that data to craft a picture of Pluto that contains a very mild, close-in bowshock, where the solar wind first "meets" Pluto (similar to a shock wave that forms ahead of a supersonic aircraft) and a small wake or tail behind the planet. 

The immediate mystery is that Chandra's readings on the brightness of the X-rays are much higher than expected from the solar wind interacting with Pluto's atmosphere.

"Before our observations, scientists thought it was highly unlikely that we'd detect X-rays from Pluto, causing a strong debate as to whether Chandra should observe it at all," said co-author Scott Wolk, of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. "Prior to Pluto, the most distant solar system body with detected X-ray emission was Saturn's rings and disk."

The Chandra detection is especially surprising since New Horizons discovered Pluto's atmosphere was much more stable than the rapidly escaping, "comet-like" atmosphere that many scientists expected before the spacecraft flew past in July 2015. In fact, New Horizons found that Pluto's interaction with the solar wind is much more like the interaction of the solar wind with Mars, than with a comet. However, although Pluto is releasing enough gas from its atmosphere to make the observed X-rays, in simple models for the intensity of the solar wind at the distance of Pluto, there isn't enough solar wind flowing directly at Pluto to make them.

Lisse and his colleagues – who also include SWAP co-investigators David McComas from Princeton University and Heather Elliott from Southwest Research Institute – suggest several possibilities for the enhanced X-ray emission from Pluto. These include a much wider and longer tail of gases trailing Pluto than New Horizons detected using its SWAP instrument. Other possibilities are that interplanetary magnetic fields are focusing more particles than expected from the solar wind into the region around Pluto, or the low density of the solar wind in the outer solar system at the distance of Pluto could allow for the formation of a doughnut, or torus, of neutral gas centered around Pluto's orbit.

That the Chandra measurements don't quite match up with New Horizons up-close observations is the benefit – and beauty – of an opportunity like the New Horizons flyby. "When you have a chance at a once in a lifetime flyby like New Horizons at Pluto, you want to point every piece of glass – every telescope on and around Earth – at the target," McNutt says. "The measurements come together and give you a much more complete picture you couldn't get at any other time, from anywhere else."

New Horizons has an opportunity to test these findings and shed even more light on this distant region – billions of miles from Earth – as part of its recently approved extended mission to survey the Kuiper Belt and encounter another smaller Kuiper. It is unlikely to be feasible to detect X-rays from MU69, but Chandra might detect X-rays from other larger and closer objects that New Horizons will observe as it flies through the Kuiper Belt towards MU69. Belt object, 2014 MU69, on Jan. 1, 2019.

The Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland, designed, built, and operates the New Horizons spacecraft and manages the mission for NASA’s Science Mission Directorate. NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations.

An interactive image, a podcast, and a video about the findings are available at:   http://chandra.si.edu

For more Chandra images, multimedia and related materials, visit:  http://www.nasa.gov/chandra


Media contacts:

Megan Watzke
Chandra X-ray Center, Cambridge, Mass.
617-496-7998
mwatzke@cfa.harvard.edu

Source: NASA’s Chandra X-ray Observatory/Press

NASA Releases New Visualization of Space Environment at Pluto

This video shows a simulation of the space environment all the way out to Pluto in the months surrounding New Horizons’ July 2015 flyby. At the time, scientists at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, worked with the New Horizons team to test how well their models—and other models contributed by scientists around the world—predicted the space environment at Pluto. Understanding the environment through which our spacecraft travel can ultimately help protect them from radiation and other potentially damaging effects. Visualizers at Goddard recently updated the movie of the model, creating this new release. Credits: NASA's Goddard Space Flight Center Scientific Visualization Studio, the Space Weather Research Center (SWRC) and the Community-Coordinated Modeling Center (CCMC), Enlil and Dusan Odstrcil (GMU). Download this video in HD formats from NASA Goddard's Scientific Visualization Studio

This artist's concept depicts the New Horizons spacecraft during its July 2015 encounter with Pluto and one of the dwarf planet's moons, Charon.  Credits: Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.

Though the vacuum of space is about a thousand times emptier than a laboratory vacuum, it’s still not completely empty. The sun releases a constant stream of particles called the solar wind—as well as occasional denser clouds of particles known as coronal mass ejections, or CMEs—both containing embedded magnetic fields. The density, speed, and temperature of these particles, as well as the direction and strength of the embedded magnetic fields, make up the space environment.

To map the space environment at Pluto, scientists combined the predictions of several models—and looked at events that had long since passed Earth.

"We set the simulation to start in January of 2015, because the particles passing Pluto in July 2015 took some six months to make the journey from the sun," said Dusan Odstrcil, a space weather scientist at Goddard who created the Enlil model. The Enlil model, named for the Sumerian god of the wind, is one of the primary models used to simulate the space environment near Earth and is the basis for the New Horizons simulation.  

The new, combined model tracks CMEs longer than ever before. Because particles must travel for many months before reaching Pluto, the CMEs eventually spread out and merge with other CMEs and the solar wind to form larger clouds of particles and magnetic field. These combined clouds stretch out as they travel away from the sun, forming thin ring shapes by the time they reach Pluto—quite different from the typical balloon shape of CMEs seen here at Earth.


Related Links 

• Feature: “Scientists Simulate the Space Environment During NASA's New Horizons Flyby” (July 10, 2015)
• Download HD-quality multimedia related to this story from NASA Goddard’s Scientific Visualization Studio
• NASA's New Horizons mission website

Sarah Frazier
NASA’s Goddard Space Flight Center, Greenbelt, Md.

Source: NASA/New Horizons

WHT Observes Pluto in Support of NASA's New Horizons Mission

The William Herschel Telescope (WHT) has participated in 2014 and 2015 in a worldwide campaign to spectroscopically follow up Pluto from the ground in support of the encounter of NASA's New Horizons spacecraft with Pluto.

Constant monitoring of the surface of Pluto is necessary because it is known to be spectrally and photometrically variable from season to season, and probably during the whole secular calendar. By gathering data at different wavelengths astronomers are able to characterize the distribution of the materials which make up the surface and atmosphere in different ways, from the layers of volatile ices (bright, whitish areas made up of methane, nitrogen, and carbon monoxide) to the more complex organic residues, which are reddish.

Last year Pluto was already observed for six nights using the WHT. The spectra, obtained using ACAM and planned as a series of overrides, showed two principal characteristics of the surface of Pluto, the clearest being the absorption bands due to methane ice. The second characteristic is the continuum slope of the spectrum which is an indicator of the colour of the surface. This colouring agent is not uniformly distributed over Pluto's surface, but changes significantly during its rotation period, which is 6.4 Earth days. 

Images of Pluto taken from the New Horizons probe. Below, spectra from the observing campaign at the WHT in 2014. The difference between the two spectra indicates differences in the composition of the surface of the planet. The spectrum printed in yellow (dark zone) has a larger slope, which is associated with the presence of very dark complexes of organic materials, which seem to be abundant in the dark region to the left of the map. The spectrum printed in red (bright zone) has somewhat deeper absorption bands, which indicate that there is more methane ice in the bright heart-shaped zone. Credits: NASA-JHUAPL-SWRI & ORM team [ JPG ].

This year, the observations were planned in a similar way and for a period of 11 nights, from 3rd to 14th July, coinciding with the closest approach of New Horizons spacecraft with Pluto. The new spectra will provide an important independent calibration of the MVIC (Multispectral Visible Imaging Camera on board New Horizons).

More information:

• "Pluto, observed with the William Herschel Telescope", IAC press release, 13th July 2015. 

Source: Isaac Newton Group of Telescope

Pluto Wags its Tail: New Horizons Discovers a Cold, Dense Region of Atmospheric Ions Behind Pluto

Artist’s concept of the interaction of the solar wind (the supersonic outflow of electrically charged particles from the Sun) with Pluto’s predominantly nitrogen atmosphere. Some of the molecules that form the atmosphere have enough energy to overcome Pluto’s weak gravity and escape into space, where they are ionized by solar ultraviolet radiation. As the solar wind encounters the obstacle formed by the ions, it is slowed and diverted (depicted in the red region), possibly forming a shock wave upstream of Pluto. The ions are “picked up” by the solar wind and carried in its flow past the dwarf planet to form an ion or plasma tail (blue region). The Solar Wind around Pluto (SWAP) instrument on the New Horizons spacecraft made the first measurements of this region of low-energy atmospheric ions shortly after closest approach on July 14. Such measurements will enable the SWAP team to determine the rate at which Pluto loses its atmosphere and, in turn, will yield insight into the evolution of the Pluto’s atmosphere and surface. Also illustrated are the orbits of Pluto’s five moons and the trajectory of the spacecraft. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

New Horizons has discovered a region of cold, dense ionized gas tens of thousands of miles beyond Pluto — the planet’s atmosphere being stripped away by the solar wind and lost to space. Beginning an hour and half after closest approach, the Solar Wind Around Pluto (SWAP) instrument observed a cavity in the solar wind — the outflow of electrically charged particles from the Sun — between 48,000 miles (77,000 km) and 68,000 miles (109,000 km) downstream of Pluto. SWAP data revealed this cavity to be populated with nitrogen ions forming a “plasma tail” of undetermined structure and length extending behind the planet.

Similar plasma tails are observed at planets like Venus and Mars. In the case of Pluto’s predominantly nitrogen atmosphere, escaping molecules are ionized by solar ultraviolet light, “picked up” by the solar wind, and carried past Pluto to form the plasma tail discovered by New Horizons. Prior to closest approach, nitrogen ions were detected far upstream of Pluto by the Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) instrument, providing a foretaste of Pluto’s escaping atmosphere.

Plasma tail formation is but one fundamental aspect of Pluto’s solar wind interaction, the nature of which is determined by several yet poorly constrained factors. Of these, perhaps the most important is the atmospheric loss rate. “This is just a first tantalizing look at Pluto’s plasma environment,” says co-investigator Fran Bagenal, University of Colorado, Boulder, who leads the New Horizons Particles and Plasma team. “We’ll be getting more data in August, which we can combine with the Alice and Rex atmospheric measurements to pin down the rate at which Pluto is losing its atmosphere. Once we know that, we’ll be able to answer outstanding questions about the evolution of Pluto’s atmosphere and surface and determine to what extent Pluto’s solar wind interaction is like that of Mars.”

Source: Johns Hopkins University - Applied Physics Laboratory (JHUAPL)

Animated Flyover of Pluto’s Icy Mountain and Plains

This simulated flyover of Pluto’s Norgay Montes (Norgay Mountains) and Sputnik Planum (Sputnik Plain) was created from New Horizons closest-approach images. Norgay Montes have been informally named for Tenzing Norgay, one of the first two humans to reach the summit of Mount Everest. Sputnik Planum is informally named for Earth’s first artificial satellite. The images were acquired by the Long Range Reconnaissance Imager (LORRI) on July 14 from a distance of 48,000 miles (77,000 kilometers). Features as small as a half-mile (1 kilometer) across are visible. Credit: NASA/JHUAPL/SWRI. Youtube

Source: Johns Hopkins University - Applied Physics Laboratory (JHUAPL)

Views of Pluto Through the Years

This animation combines various observations of Pluto over the course of several decades. The first frame is a digital zoom-in on Pluto as it appeared upon its discovery by Clyde Tombaugh in 1930 (image courtesy Lowell Observatory Archives). The other images show various views of Pluto as seen by NASA's Hubble Space Telescope beginning in the 1990s and NASA's New Horizons spacecraft in 2015. The final sequence zooms in to a close-up frame of Pluto released on July 15, 2015.

Complete source list in order with image credits:

Clyde Tombaugh, Lowell Observatory, 1930: http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=19989
Note: This image is property of the Lowell Observatory Archives. 

Any public use requires written permission of the Lowell Observatory Archives.

Hubble Space Telescope, 1996: http://hubblesite.org/newscenter/archive/releases/solar-system/pluto/199...

Hubble Space Telescope, 1994: http://hubblesite.org/newscenter/archive/releases/solar-system/pluto/199...

Hubble Space Telescope, 2011: http://hubblesite.org/newscenter/archive/releases/solar-system/pluto/201...

Hubble Space Telescope, 2002-2003: http://hubblesite.org/newscenter/archive/releases/solar-system/pluto/201...

New Horizons, April 9, 2015: http://pluto.jhuapl.edu/Multimedia/Science-Photos/image.php?page=6&galle...

New Horizons, May 12, 2015: http://pluto.jhuapl.edu/Multimedia/Science-Photos/image.php?page=6&galle...

New Horizons, June 2, 2015: http://pluto.jhuapl.edu/Multimedia/Science-Photos/image.php?page=5&galle...

New Horizons, June 15, 2015: http://pluto.jhuapl.edu/Multimedia/Science-Photos/image.php?page=5&galle...

New Horizons, July 1, 2015: http://pluto.jhuapl.edu/Multimedia/Science-Photos/image.php?page=4&galle...

New Horizons, July 3, 2015: http://pluto.jhuapl.edu/Multimedia/Science-Photos/image.php?page=4&galle...

New Horizons, July 8, 2015: http://pluto.jhuapl.edu/Multimedia/Science-Photos/image.php?page=3&galle...

New Horizons, July 10, 2015: http://pluto.jhuapl.edu/Multimedia/Science-Photos/image.php?page=3&galle...

New Horizons, July 11, 2015: http://pluto.jhuapl.edu/Multimedia/Science-Photos/image.php?page=2&galle...

New Horizons, July 13, 2015: http://pluto.jhuapl.edu/Multimedia/Science-Photos/image.php?page=1&galle...

New Horizons, July 14, 2015: http://pluto.jhuapl.edu/Multimedia/Science-Photos/image.php?page=1&galle...

New Horizons, July 15, 2015: https://www.youtube.com/watch?v=7iyd-gh2rhM

Source: NASA/New Horizons

New Horizons Spots Pluto’s Faintest Known Moons

New Horizons Spots Pluto’s Faintest Known Moons
Download the .mov file

For the first time, NASA's New Horizons spacecraft has photographed Kerberos and Styx – the smallest and faintest of Pluto's five known moons. Following the spacecraft's detection of Pluto's giant moon Charon in July 2013, and Pluto's smaller moons Hydra and Nix in July 2014 and January 2015, respectively, New Horizons is now within sight of all the known members of the Pluto system. 

"New Horizons is now on the threshold of discovery," said mission science team member John Spencer, of the Southwest Research Institute in Boulder, Colorado. "If the spacecraft observes any additional moons as we get closer to Pluto, they will be worlds that no one has ever seen before." 

Drawing even closer to Pluto in mid-May, New Horizons will begin its first search for new moons or rings that might threaten the spacecraft on its passage through the Pluto system. The images of faint Styx and Kerberos shown here are allowing the search team to refine the techniques they will use to analyze those data, which will push the sensitivity limits even deeper. 

Kerberos and Styx were discovered in 2011 and 2012, respectively, by New Horizons team members using the Hubble Space Telescope. Styx, circling Pluto every 20 days between the orbits of Charon and Nix, is likely just 4 to 13 miles (approximately 7 to 21 kilometers) in diameter, and Kerberos, orbiting between Nix and Hydra with a 32-day period, is just 6 to 20 miles (approximately 10 to 30 kilometers) in diameter. Each is 20 to 30 times fainter than Nix and Hydra. 

The images detecting Kerberos and Styx shown here were taken with New Horizons' most sensitive camera, the Long Range Reconnaissance Imager (LORRI), from April 25-May 1. Each observation consists of five 10-second exposures that have been added together to make the image in the left panel, and extensively processed to reduce the bright glare of Pluto and Charon and largely remove the dense field of background stars (center and right panels), in order to reveal the faint satellites, whose positions and orbits, along with those of the brighter moons Nix and Hydra, are given in the right panel. 

"Detecting these tiny moons from distance of over 55 million miles is amazing, and a credit to the team that built our LORRI long-range camera and John Spencer's team of moon and ring hunters," added New Horizons Principal Investigator Alan Stern, of the Southwest Research Institute. 

Kerberos is visible in all of the images, though is partially obscured in the second image. Styx is not visible in the first image, only in subsequent ones; on April 25 it was obscured by electronic artifacts in the camera – the black and white streaks extending to the right of the extremely overexposed images of Pluto and Charon in the center of the frame. These artifacts point in different directions in different images due to the varying orientation of the spacecraft. Other unlabeled features in the processed images include the imperfectly removed images of background stars and other residual artifacts. 

Although Styx and Kerberos are more visible in some frames than others, perhaps due to brightness fluctuations as they rotate on their axes, their identity is confirmed by their positions being exactly where they are predicted to be (in the center of the circles in the right panel). 

The Johns Hopkins University Applied Physics Laboratory (APL) designed, built, and operates the New Horizons spacecraft, and manages the mission for NASA's Science Mission Directorate. SwRI leads the science team, payload operations and encounter science planning. New Horizons is part of the New Frontiers Program managed by NASA's Marshall Space Flight Center in Huntsville, Alabama. 

Source:  New Horizons/NASA's Mission to Pluto

ALMA Pinpoints Pluto to Help Guide NASA’s New Horizons Spacecraft

The cold surface of Pluto and its largest moon Charon as seen with ALMA on July 15, 2014. 

Credit: NRAO/AUI/NSF

Animated image of ALMA data showing the motion of the moon Charon around the icy dwarf planet Pluto. 

Credit: B. Saxton (NRAO/AUI/NSF)

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) are making high-precision measurements of Pluto's location and orbit around the Sun to help NASA’s New Horizons spacecraft accurately home in on its target when it nears Pluto and its five known moons in July 2015.

Though observed for decades with ever-larger optical telescopes on Earth and in space, astronomers are still working out Pluto's exact position and path around our Solar System. This lingering uncertainty is due to Pluto's extreme distance from the Sun (approximately 40 times farther out than the Earth) and the fact that we have been studying it for only about one-third of its orbit. Pluto was discovered in 1930 and takes 248 years to complete one revolution around the Sun.

“With these limited observational data, our knowledge of Pluto’s position could be wrong by several thousand kilometers, which compromises our ability to calculate efficient targeting maneuvers for the New Horizons spacecraft,” said New Horizons Project Scientist Hal Weaver, from the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland.

The New Horizons team made use of the ALMA positioning data, together with newly analyzed visible light measurements stretching back to Pluto's discovery, to determine how to perform the first such scheduled course correction for targeting, known as a Trajectory Correction Maneuver (TCM), in July. This maneuver helped ensure that New Horizons uses the minimum fuel to reach Pluto, saving as much as possible for a potential extended mission to explore Kuiper Belt objects after the Pluto system flyby is complete.

To prepare for this first TCM, astronomers needed to pinpoint Pluto's position using the most distant and most stable reference points possible. Finding such a reference point to accurately calculate trajectories of such small objects at such vast distances is incredibly challenging. Normally, stars at great distances are used by optical telescopes for astrometry (the positioning of things on the sky) since they change position only slightly over many years. For New Horizons, however, even more precise measurements were necessary to ensure its encounter with Pluto would be as on-target as possible.

The most distant and most apparently stable objects in the Universe are quasars, galaxies more than 10 billion light-years away. Though quasars appear very dim to optical telescopes, they are incredibly bright at radio wavelengths, particularly the millimeter wavelengths that ALMA can see.

“The ALMA astrometry used a bright quasar named J1911-2006 with the goal to cut in half the uncertainty of Pluto's position,” said Ed Fomalont, an astronomer with the National Radio Astronomy Observatory in Charlottesville, Virginia, and currently assigned to ALMA’s Operations Support Facility in Chile.

ALMA was able to study Pluto and its largest moon Charon by picking up the radio emission from their cold surfaces, which are about 43 degrees Kelvin (-230 degrees Celsius).

The team first observed these two icy worlds in November 2013, and then three more times in 2014 -- once in April and twice in July. Additional observations are scheduled for October 2014.

"By taking multiple observations at different dates, we allow Earth to move along its orbit, offering different vantage points in relation to the Sun," said Fomalont. "Astronomers can then better determine Pluto's distance and orbit." This astronomical technique is called measuring Pluto's parallax.

"We are very excited about the state-of-the-art capabilities that ALMA brings to bear to help us better target our historic exploration of the Pluto system," said New Horizons Principal Investigator Alan Stern of the Southwest Research Institute in Boulder, Colorado. "We thank the entire ALMA team for their support and for the beautiful data they are gathering for New Horizons."

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

ALMA, an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA construction and operations are led on behalf of Europe by the European Southern Observatory (ESO), on behalf of North America by the National Radio Astronomy Observatory (NRAO), and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

New Horizons is the first mission to the Pluto system and the Kuiper Belt of rocky, icy objects beyond. The Johns Hopkins University Applied Physics Laboratory (APL) manages the mission for NASA’s Science Mission Directorate; Alan Stern, of the Southwest Research Institute (SwRI), is the principal investigator and leads the mission. SwRI leads the science team, payload operations and encounter science planning; APL designed, built and operates the New Horizons spacecraft. New Horizons is part of the New Frontiers Program managed by NASA's Marshall Space Flight Center in Huntsville, Ala. 

For more information, visit http://pluto.jhuapl.edu.

Contact: 

Charles Blue,
NRAO Public Information Officer
(434) 296-0314;
cblue@nrao.edu

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Kerberos and Styx: Welcome to the Pluto System! Pluto's Smallest Moons Receive Official Names

 

Hubble Space Telescope image of the Pluto system, taken in July 2012  

The names of Pluto's two smallest known moons, previously referred to as "P4" and “P5,” have been formally approved by the International Astronomical Union (IAU). P4 has been named Kerberos, after the three-headed dog of Greek mythology. P5 has been named Styx, after the mythological river that separates the world of the living from the realm of the dead. They join Pluto's previously known moons Charon, Nix and Hydra. According to IAU rules, Pluto's moons are named for characters associated with the Underworld of Greek and Roman mythology.

Mark Showalter, senior research scientist at the SETI Institute in Mountain View, Calif., led the team of astronomers that discovered Kerberos and Styx. Both were first seen in lengthy exposures of the Pluto system obtained by the Hubble Space Telescope. Kerberos was discovered in 2011 and Styx in 2012. The images were obtained in support of NASA's New Horizons mission, which will fly past Pluto in July 2015.

The names were selected based on the results of an unprecedented Internet vote that was held during February 2012. The ballot at plutorocks.seti.org received almost 500,000 votes, including 30,000 write-in suggestions. "I was overwhelmed by the public response to the naming campaign," says Showalter, adding that the website received international attention and half the votes came from outside the U.S. 

Kerberos is the Greek form of the name Cerberus, which ranked second in the voting. Styx ranked third. The top vote-getter was "Vulcan," based on a suggestion from actor William Shatner of TV's “Star Trek” fame. Vulcan was the name of the home planet of Star Trek character Mr. Spock. The IAU gave serious consideration to this name, which happens to be shared by the Roman god of volcanoes. However, because the name has already been used in astronomy, and because the Roman god is not closely associated with Pluto, this proposal was rejected. "I am grateful to the IAU for giving such careful consideration to our suggestions," says Showalter.

New Horizons will provide up-close looks at Kerberos, Styx and their companion moons in 2015, when it becomes the first spacecraft to fly through the Pluto system. "The discoveries of Kerberos and Styx add to the mysteries surrounding the formation of the Pluto system,” says New Horizons Principal Investigator Alan Stern, of the Southwest Research Institute. 

During the flyby, the spacecraft will also search for additional moons, which might be too small for the Hubble telescope to detect. Afterward, New Horizons will go on to explore the more distant Kuiper Belt.

Source: New Horizon Web Site

Pluto's Undiscovered Satellites

Simulated image of the Pluto-Charon system. The Pluto-Charon binary (represented by the two largest white disks), the four small satellites -- P5, Nix, P4, and Hydra (represented by the four small white disks), and three smaller satellites (represented by the green disks) lie within an extended ensemble of solid particles shown as small blue dots. This configuration is the result after twenty years of a computer simulation with two million dust particles surrounding the known and predicted moons. On this short time scale, the small satellites clear out most of the dust particles along their orbits. On much longer time scales, satellites will clear dust from a larger fraction of their orbits.  Credit: Scott Kenyon and Ben Bromley.  Low Resolution Image (jpg)

In 2015, NASA's New Horizons spacecraft will encounter the binary planet Pluto-Charon and its coterie of small satellites. Discovered in June 2005, the satellites Nix and Hydra orbit Pluto-Charon at distances roughly 40 times (Nix) and 55 times (Hydra) larger than the radius of Pluto. Two other satellites, now known as P4 and P5, appeared on images from the Hubble Space Telescope in 2011-2012 and have similar orbits. With a planned closest approach to Pluto-Charon of only 10 Pluto radii, the New Horizons spacecraft must have a trajectory that avoids the satellites as it passes through the system. 

New computer simulations by Scott Kenyon of SAO and Ben Bromley of the University of Utah suggest New Horizons will have to dodge a few other satellites and may need to avoid a disk composed of small snowballs. Using a code developed to simulate the formation of a planetary system around a star like the Sun, Kenyon & Bromley explored whether satellites could grow in a disk of small particles surrounding Pluto-Charon. In their picture, the disk consists of icy material captured from the Kuiper Belt or left over from the giant impact thought to produce Pluto-Charon. Within this disk, small particles collide and merge into larger and larger objects which eventually become stable satellites orbiting Pluto-Charon.

The simulations typically form a few satellites with diameters of 10-30 km, similar to the sizes of Nix and Hydra, and many satellites with diameters of a few kilometers. After 10 million years of simulation time, all of the satellites orbit within a tenuous disk of very small particles with diameters of a centimeter or less. The accompanying image shows one outcome with a more massive disk and three predicted satellites lying outside the orbit of Hydra. 

Although the small sizes of the predicted satellites preclude detection with the Hubble Space Telescope, New Horizons can identify them. When the spacecraft is roughly 70 days away from Pluto, its camera will begin to search for satellites smaller than P5. A few weeks out, images might reveal a tenuous disk or an ensemble of rings outside the orbit of Hydra. The New Horizons observations will test Kenyon & Bromley's model and give us new clues about the origin of Pluto and the solar system. 

Source: Harvard-Smithsonian Center for Astrophysics

Sharpest-ever Ground-based Images of Pluto and Charon: Proves a Powerful Tool for Exoplanet Discoveries

 

Speckle image reconstruction of Pluto and Charon obtained in visible light at 692 nanometers (red) with the Gemini North 8-meter telescope using the Differential Speckle Survey Instrument (DSSI). Resolution of the image is about 20 milliarcseconds average. This is the first speckle reconstructed image for Pluto and Charon from which astronomers obtained not only the separation and position angle for Charon, but also the diameters of the two bodies. North is up, east is to the left, and the image section shown here is 1.39 arcseconds across. Credit: Gemini Observatory/NSF/NASA/AURA .  Full Resolution JPEG

Despite being infamously demoted from its status as a major planet, Pluto (and its largest companion Charon) recently posed as a surrogate extrasolar planetary system to help astronomers produce exceptionally high-resolution images with the Gemini North 8-meter telescope. Using a method called reconstructive speckle imaging, the researchers took the sharpest ground-based snapshots ever obtained of Pluto and Charon in visible light, which hint at the exoplanet verification power of a large state-of-the-art telescope when combined with speckle imaging techniques. The data also verified and refined previous orbital characteristics for Pluto and Charon while revealing the pair’s precise diameters.

 “The Pluto-Charon result is of timely interest to those of us wanting to understand the orbital dynamics of this pair for the 2015 encounter by NASA's New Horizons spacecraft,” said Steve Howell of the NASA Ames Research Center, who led the study. In addition, Howell notes that NASA’s Kepler mission, which has already proven a powerful exoplanet discovery tool, will benefit greatly from this technique.

 Kepler identifies planet candidates by repeatedly measuring the change in brightness of more than 150,000 stars to detect when a planet passes in front of, or affects the brightness of, its host star. Speckle imaging with the Gemini telescope will provide Kepler's follow-up program with a doubling in its ability to resolve objects and validate Earth-like planets. It also offers a 3- to 4-magnitude sensitivity increase for the sources observed by the team. That’s about a 50-fold increase in sensitivity in the observations Howell and his team made at Gemini. “This is an enormous gain in the effort underway to confirm small Earth-size planets,” Howell added.

 To institute this effort Howell and his team –– which included Elliott Horch (Southern Connecticut State University), Mark Everett (National Optical Astronomy Observatory), and David Ciardi (NASA Exoplanet Science Institute/Caltech) –– temporarily installed a camera, called the Differential Speckle Survey Instrument (DSSI), among the suite of instruments mounted on the Gemini telescope.

 "This was a fantastic opportunity to bring DSSI to Gemini North this past July," said Horch. "In just a little over half an hour of Pluto observations, collecting light with the large Gemini mirror, we obtained the best resolution ever with the DSSI instrument –– it was stunning!"

 The resolution obtained in the observations, about 20 milliarcseconds, easily corresponds to separating a pair of automobile headlights in Providence, Rhode Island, from San Francisco, California. To achieve this level of definition, Gemini obtained a large number of very quick “snapshots” of Pluto and Charon. The researchers then reconstructed them into a single image after subtracting the blurring effects and ever-changing speckled artifacts caused by turbulence in the atmosphere and other optical aberrations. With enough snapshots (each image was exposed for only 60 milliseconds or about 1/20 of a second) only the light from the actual objects remains constant, and the artifacts reveal their transient nature, eventually canceling each other out.

 DSSI was built at SCSU between 2007-2008 as a part of a United States National Science Foundation Astronomical Instrumentation grant and mounted on the Gemini North telescope for a limited observing run. The instrument is likely to return to Gemini North for observations in mid-2013 for general user programs from across the international Gemini partnership. Any such arrangement will be announced along with the call for proposals for Semester 13B, in February 2013.

 This work was funded in part by the National Science Foundation and NASA’s Kepler discovery mission and will be published in the journal Publications of the Astronomical Society of the Pacific in October 2012.

Science Contacts:

Steven Howell
 NASA Ames Research Center
 Moffett Field, CA
 Desk: 605-604-4238
 Cell: 520-461-6925
Steve.b.howell@nasa.gov

Elliott Horch
 Southern Connecticut State University
 New Haven, CT
 Phone: 203-392-6393
Horche2@southernct.edu

Media Contact:

Peter Michaud
 Public Information and Outreach Manager
 Gemini Observatory, Hilo, Hawai'i
 Desk: (808) 974-2510
 Cell: (808) 936-6643
pmichaud@gemini.edu

Background History of DSSI

 The Differential Speckle Survey Instrument (DSSI) was built at Southern Connecticut State University (SCSU) between 2007-2008 as a part of a NSF Astronomical Instrumentation grant on which Elliott Horch was the principal investigator. Together with student collaborators, Horch designed and assembled the instrument, and wrote the instrument control software. In 2008 DSSI was shipped to the WIYN Observatory at Kitt Peak, where it has been used since September 2008 for both Kepler follow-up observations and a NSF-funded project to study binary stars discovered by Hipparcos. In late 2009, the detectors for the instrument were upgraded from two low-noise CCDs to two electron-multiplying CCDs, one purchased by the Kepler Science Office and the other by SCSU. DSSI is the world's first two-channel speckle imaging instrument.

The PI's Perspective

New Horizons hopes to explore beyond Pluto,
into the ancient and unexplored Kuiper Belt

The Kuiper Belt at 20:
Paradigm Changes in Our Knowledge of the Solar System

New Horizons remains healthy and on course, now more than 24 times as far from the Sun as the Earth is. This summer’s spacecraft and payload checkout went extremely well, as did both major flight-software updates we loaded aboard New Horizons. And, the spacecraft’s rehearsal of the closest-approach day of the Pluto encounter went just about perfectly.

After finishing all of this at the beginning of July, we put New Horizons back into hibernation, and we’ve been cruising that way for almost eight weeks. As those who follow New Horizons on Twitter (@NewHorizons2015) know, every Monday New Horizons checks in with a beacon that tells us if all is well, or not. And almost every week we’ve been able to report a “green beacon Monday” to our 22,000-plus Twitter followers, indicating the spacecraft is in good health.

New Horizons will cruise quietly in hibernation until Jan. 6, 2013, when we wake it up for a month of complex activities, including some advance work on next summer’s checkout, and the third of the four major software upgrades needed before next summer’s on-spacecraft rehearsal of the nine days surrounding Pluto closest approach.

Since activity on New Horizons is pretty quiet right now, I’ll take this opportunity to mention that planetary science is celebrating the 20th anniversary of the discovery of the Kuiper Belt. That came in 1992, when the first Kuiper Belt Object (KBO) was discovered.

Actually, of course, the first object in the Kuiper Belt was discovered in 1930 — Pluto itself; and the second such object, Pluto’s giant moon Charon, was discovered in 1978. The Kuiper Belt was first postulated — most famously by Gerard Kuiper — by planetary scientists back in the 1930s, ‘40s and ‘50s. But it took until 1992 for technology to mature sufficiently enough to find another object (outside the Pluto system) orbiting the Sun beyond Neptune.

This plot shows one aspect of Kuiper Belt structure: Different numbers of bodies orbit at different distances. This graph includes just the known bodies, which make up a tiny fraction of the grand total. (Wikipedia)

Since 1992, more than 1,000 KBOs have been discovered. But only a tiny fraction of the sky has been surveyed for KBOs. It is estimated that more than 100,000 KBOs exist with diameters of 100 kilometers or larger, along with billions of smaller objects down to the size of cometary nuclei, just a kilometer or two across. (By comparison, Pluto is huge — its diameter is almost 2,400 kilometers, making a drive around its equator as far as from Manhattan to Moscow!)
Most of the known KBOs are just 100 to 300 kilometers across, about one-tenth of Pluto’s diameter. But some are smaller than 100 kilometers across, and some are larger than 300 kilometers across. In fact, there is great diversity among KBOs:

• Some are red and some are gray;

• The surfaces of some are covered in water ice, but others (like Pluto) have exotic volatile ices like methane and nitrogen;

• Many have moons, though none with more known moons than Pluto;

• Some are highly reflective (like Pluto), others have much darker surfaces;

• Some have much lower densities than Pluto, meaning they are primarily made of ice. Pluto’s density is so high that we know its interior is about 70% rock in its interior; a few known KBOs are more dense than Pluto, and even rockier!

Some planets of the Kuiper Belt; note that since this diagram was made, we’ve learned that Eris is actually smaller than Pluto. (http://www.sollunaterra.webs.com)

But I don’t consider this surprising assortment of KBOs to be the most important contribution to our knowledge of the solar system that has come from telescope exploration of the Kuiper Belt. In my opinion, the three greatest solar system lessons we’ve learned from the Kuiper Belt are:

• That our planetary system is much larger than we used to think. In fact, we were largely unaware of the Kuiper Belt — the largest structure in our solar system — until it was discovered 20 years ago. It’s akin to not having maps of the Earth that included the Pacific Ocean as recently as 1992!

• That the locations and orbital eccentricities and inclinations of the planets in our solar system (and other solar systems as well) can change with time. This even creates whole flocks of migration of planets in some cases. We have firm evidence that many KBOs (including some large ones like Pluto), were born much closer to the Sun, in the region where the giant planets now orbit.

• And, perhaps most surprisingly, that our solar system, and very likely very many others, was very good at making small planets, which dominate the planetary population! Today we know of more than a dozen dwarf planets in the solar system, and those dwarfs already outnumber the number of gas giants and terrestrial planets combined. But it is estimated that the ultimate number of dwarf planets we will discover in the Kuiper Belt and beyond may well exceed 10,000. Who knew? (And which class of planet is the misfit now?)

What an amazing set of paradigm shifts in our knowledge the Kuiper Belt has brought so far. Our quaint 1990s and earlier view of the solar system missed its largest structure! It didn’t know about the existence of dwarf planets, the most populous class of planet in our solar system —and very likely the galaxy. It didn’t even contemplate that dwarf planets would have such a wide range of colors, reflectivities, orbits and surface compositions. And it didn’t realize that the locations of most planets in our solar system today — even including some of the very largest planets — are different from where they were born.

Just imagine what our close flybys of the Pluto system and smaller KBOs, combined with new giant telescopes coming on line to probe the sky, will teach us about the Kuiper Belt in the next 20 years. It’s an exciting time, and its sometimes hard for me to believe after working on this since 1989, that our 2015 exploration of Pluto and its many moons is almost upon us—but it is!

Well, that’s my update for now. Thanks again for following our journey across the deep ocean of space, to a new planet and a truly new frontier.

Until I write again, I hope you’ll keep on exploring — just as we do!

Alan Stern

View The PI's Perspective Archive

Hubble Discovers a Fifth Moon Orbiting Pluto

P5, S/2012 (134340) 1

Credit:NASA,ESA, and M. Showalter (SETI Institute)

A team of astronomers using NASA's Hubble Space Telescope is reporting the discovery of another moon orbiting the icy dwarf planet Pluto.

The moon is estimated to be irregular in shape and 6 to 15 miles across. It is in a 58,000-mile-diameter circular orbit around Pluto that is assumed to be co-planar with the other satellites in the system.

"The moons form a series of neatly nested orbits, a bit like Russian dolls," said team lead Mark Showalter of the SETI Institute in Mountain View, Calif.

The discovery increases the number of known moons orbiting Pluto to five.

The Pluto team is intrigued that such a small planet can have such a complex collection of satellites. The new discovery provides additional clues for unraveling how the Pluto system formed and evolved. The favored theory is that all the moons are relics of a collision between Pluto and another large Kuiper belt object billions of years ago.

The new detection will help scientists navigate NASA's New Horizons spacecraft through the Pluto system in 2015, when it makes an historic and long-awaited high-speed flyby of the distant world.

The team is using Hubble's powerful vision to scour the Pluto system to uncover potential hazards to the New Horizons spacecraft. Moving past the dwarf planet at a speed of 30,000 miles per hour, New Horizons could be destroyed in a collision with even a BB-shot-size piece of orbital debris.

"The discovery of so many small moons indirectly tells us that there must be lots of small particles lurking unseen in the Pluto system," said Harold Weaver of the Johns Hopkins University Applied Physics Laboratory in Laurel, Md.

"The inventory of the Pluto system we're taking now with Hubble will help the New Horizons team design a safer trajectory for the spacecraft," added Alan Stern of the Southwest Research Institute in Boulder, Colo., the mission's principal investigator.

Pluto's largest moon, Charon, was discovered in 1978 in observations made at the United States Naval Observatory in Washington, D.C. Hubble observations in 2006 uncovered two additional small moons, Nix and Hydra. In 2011 another moon, P4, was found in Hubble data.

Provisionally designated S/2012 (134340) 1, the latest moon was detected in nine separate sets of images taken by Hubble's Wide Field Camera 3 on June 26, 27, and 29, 2012 and July 7 and 9, 2012.

In the years following the New Horizons Pluto flyby, astronomers plan to use the infrared vision of Hubble's planned successor, NASA's James Webb Space Telescope, for follow-up observations. The Webb telescope will be able to measure the surface chemistry of Pluto, its moons, and many other bodies that lie in the distant Kuiper Belt along with Pluto.

The Pluto team members are M. Showalter (SETI Institute), H.A. Weaver (Applied Physics Laboratory, Johns Hopkins University), and S.A. Stern, A.J. Steffl, and M.W. Buie (Southwest Research Institute).

CONTACT

Ray Villard
Space Telescope Science Institute, Baltimore, Md.
410-338-4514
villard@stsci.edu

Karen Randall
SETI Institute, Mountain View, Calif.
650-960-4537
krandall@seti.org

The PI’s Perspective: Visiting Four Moons, in Just Four Years, for All Mankind

In June and July, members of the New Horizons science team, using the Hubble Space Telescope, discovered and confirmed that Pluto has a fourth moon! The new satellite, provisionally called P4, is fainter and therefore likely much smaller, than either Nix or Hydra or Charon – Pluto’s other three known moons. For comparison, while Charon is about as wide as the U.S. state of Colorado, Nix and Hydra are closer to the width of Vermont, and P4 is likely to be no wider across than Boulder County, Colorado.

New Horizons remains healthy and on course, now approximately 21 times as far from the Sun as the Earth is – well on its way, between the orbits of Uranus and Neptune.

On July 1, we completed our 2011 checkout of the spacecraft and its payload, which went very well. During that checkout, which spanned May and June, we conducted the first of two tests of our REX radio occultation experiment, using the moon to cut off a radio signal transmitted to New Horizons from Deep Space Network (DSN) antennas on Earth. This test involved many organizations, including the REX team, our mission operations team at the Johns Hopkins Applied Physics Laboratory, and the DSN itself. And it worked perfectly!

In June, we also accomplished some cruise science for our space plasma instruments – SWAP and PEPPSI – studying the charged-particle populations of the solar system. And over May and June we completed some much-needed spacecraft tracking; from every indication, we’re so close to a perfect course toward Pluto that will not need to conduct a course correction maneuver until at least 2013.

With this checkout behind us, we’ve returned our attention to planning the Pluto encounter. More specifically, the project team is working on the four-day command loads just before and just after the core nine-day load for Pluto closest approach. These “bookend” loads are the most critical portions of our Approach Phase 3 (AP3) and Departure Phase 1 (DP1) observations. Work is also well under way on the farther-out portions of AP3 and DP1. In addition, we’re analyzing and prioritizing responses to some 280 potential contingency scenarios for the 2015 encounter – just in case.

Pluto’s newest found moon (P4) orbits between Nix and Hydra, both of which orbit well beyond Charon. Could Pluto have additional moons? Perhaps, and the New Horizons team has proposed to the Hubble Space Telescope to look even harder – so that we can best plan our encounter observations, and ensure we don’t run into something we could have avoided.

New Horizons PI Alan Stern presented a mission overview talk last month at the U.S. Space and Rocket Center’s auditorium in Huntsville, Alabama.

And if all that isn’t keeping our little mission team busy enough, we’re also planning our first encounter rehearsal on New Horizons for summer 2012.

Designed as a stress test for the spacecraft, the “24-hour rehearsal” will include an intense one-day portion of the encounter near closest approach. We’ve rehearsed this portion of the timeline (and more) on our New Horizons ground simulator at APL in Maryland, and passed with flying colors. But there is no substitute for actually going through these paces on our spacecraft, verbatim. That kind of real-world test will prove the spacecraft is up to the task, and it’ll also let us check out some aspects of the timeline that we can only do in space. A good example: New Horizons will actually perform all the timelined attitude maneuvers and turns, which our ground simulator can only pretend to do.

The 24-hour rehearsal in 2012 is a precursor to the full, nine-day-long core encounter rehearsal that we will run on New Horizons during summer 2013.

What else is coming for New Horizons? We have our usual pair of “precession wakeups” from hibernation this November and in January 2012. In these annual activities we re-point our spacecraft and its communications antenna to account for Earth’s motion around the sun, and perform some spacecraft maintenance. Also in January, we will perform our second (and final) REX radio science lunar occultation test.

On tap in the coming months will be preparations for the new fault protection/autonomy and command and data handling software we’ll send up to the spacecraft next summer, as well as the planning for a jam-packed active checkout for 2012. The “C & DH” software change will feature a key bug fix, tracked down by project engineer Steve Williams of APL, which should reduce the probability of any computer resets during the 2015 encounter.

And also in the coming months, we’ll be kicking off our extensive space plasma hibernation cruise science observations with a test in October, and if all goes well, operational data collects beginning in early 2012.

While our spacecraft and operations teams are performing all those activities, our science team is leading a search for Kuiper Belt flyby targets, conducting studies of Pluto and its moons using ground-based telescopes, and planning a major scientific conference on the Pluto system for the summer of 2013.

That conference will allow the world’s astronomers and planetary scientists to review the state of knowledge about the Pluto system before our encounter and to begin detailed planning of ground-based and space-based campaigns to observe the planet and its moons in conjunction with the New Horizons flyby. The conference will also give researchers a chance to develop educated predictions about what New Horizons may find. We are discussing a similar kind of meeting for educators in 2014.

The New Horizons project expects to propose a stamp to the U.S. Postal Service to commemorate the historic flyby of Pluto and its moons that we will accomplish in 2015. But at least one country has already issued New Horizons stamps! Can you tell which country?

Finally, I’ll close by giving a big shout out of congratulations to NASA’s Dawn mission, which is now making the first reconnaissance of Vesta – the fourth-largest asteroid – which is about 500 kilometers across. Dawn’s exploration of Vesta is just beginning, but is already yielding spectacular results and showing us a much more complex world than many scientists imagined Vesta to be. You can read more about Dawn’s exploration of Vesta here.

From those of us looking forward to exploring a world almost 2,500 kilometers in diameter to those exploring fascinating Vesta, New Horizons salutes you. First-time exploration of new worlds simply rocks!

Well, that’s my update for now. Thanks again for following our journey across the deep ocean of space to a truly new frontier. I hope you’ll keep on exploring – just as we do!

Alan Stern