Pluto, magnanimous, whose realms profound
Are fix’d beneath the firm and solid ground,
In the Tartarian plains remote from fight,
And wrapt forever in the depths of night.
— Orphic Hymns, 6th century BC
Renowned for his legendary ability to entrance and captivate gods and mortals alike with the beauty of his divine music, Orpheus was one of the celebrated heroes of Ancient Greek mythology who was able, after a dangerous journey, to enter the Kingdom of Hades and face the god of the Underworld. In real life, following a multi-year journey through the Solar System, NASA’s New Horizons spacecraft enters the final leg of preparations for the start of its long-range reconnaissance of Pluto next January.
Staying true to the nature of its mythological namesake, Pluto is a distant and mysterious world that is currently holding the keys to the Solar System’s gates of the unknown, beyond which lies a vast expanse that we know very little about. In large part due to its great distance from the Sun, which on average is approximately 5.8 billion km, Pluto is the only planetary body from the Solar System’s total real estate that has never been examined up close by any visiting spacecraft during the 50-year history of planetary exploration, thus essentially remaining remote and exotic, ever since it was discovered by American astronomer Clyde Tombaugh in 1930. Yet, with the discovery in the 1990s of a new region of minor icy planetary bodies beyond the orbit of Neptune, known as the Kuiper Belt, the interest among the planetary science community for Pluto and the rest of the uncharted territory that laid beyond was renewed, marked as a high priority exploration target by the 2003 Planetary Science Decadal Survey.
It turns out that all this interest hasn’t been unwarranted. The highly successful Voyager, Galileo, and Cassini missions of the previous decades have put to rest in a spectacular fashion our previous notions of the outer Solar System as a collection of boring and uninteresting chunks of rock and ice. In addition, ground- and space-based telescopic observations of Pluto have revealed a world which, contrary to what the name of its mythological namesake implies, is far from a dead one. Images taken with the Hubble Space Telescope have uncovered considerable brightness variations on Pluto’s surface, while spectroscopic analysis of its thin atmosphere has shown that it is composed of gases like nitrogen, carbon monoxide, and methane, which sublimate from the ices that are present on the surface, constantly replenishing the planet’s atmosphere. More interestingly, as reported in a recent AmericaSpace article earlier this week, new studies have hinted at the possibility of Pluto sharing its atmosphere with the largest of its moons Charon, which, if confirmed, would be a unique phenomenon never before seen elsewhere in the Solar System. In addition, many scientists consider the possibility of Pluto being a geologically active body, not unlike Neptune’s moon Triton, replete with cryovolcanic activity on its surface, possibly stemming from an ocean of liquid water that could be buried deep beneath the ground.
In order to illuminate the intriguing long-standing mysteries of this far-off world, NASA launched the New Horizons mission in 2006 into a direct Sun-escape trajectory for a fast nine-year cruise toward this last unexplored frontier of the Solar System. Now, having covered most of the distance quietly passing the orbits of the outer planets, New Horizons is closing in on Pluto for its long-awaited flyby of the enigmatic world in July 2015. But before this historic event takes place, the spacecraft will come out of its long slumber to prepare for the long-range reconnaissance of the planet and its moons due to begin next January. And as with everything else in spaceflight operations, practice makes perfect.
With the exception of a few brief periods of activity, like its gravity-assist flyby of Jupiter in 2007, New Horizons has spent most of its interplanetary cruise time in hibernation, en route toward its final destination. The Johns Hopkins Applied Physics Lab in Laurel, Md., which is managing the mission, briefly activated the spacecraft for a few weeks in early 2014 to check on the overall health of its systems and prepare it for the Pluto long-range encounter activities. Wake-up tasks included checking on the spacecraft’s High-Gain Antenna, uploading of new commands to the onboard computer, and updating of the onboard star charts used for navigation. Now, New Horizons is getting ready to be reactivated again for its last dress rehearsal before finally entering the realm of Pluto later this year.
Even though the mission has been progressing quite nominally thus far with no unexpected incidents, there has nevertheless been some concern among the science team regarding New Horizons’ extended mission, following the Pluto flyby. The goal of the extended mission is the investigation of one or more large enough Kuiper Belt Objects, or KBOs, that might be located along the spacecraft’s trajectory. Yet, despite ongoing searches with some of the world’s biggest ground-based telescopes, the mission’s science team has been unable to locate a suitable KBO that fits the spacecraft’s flight profile. The team is hopeful, however, that by using the Hubble Space Telescope such an object could be found in time so that the extended mission can be successfully carried out.
With regard to these activities, we had the chance to talk with Dr. Alan Stern, Associate Vice President of the Southwest Research Institute’s Space Science and Engineering Division in Boulder, Colo., and Principal Investigator for New Horizons, about the ongoing preparations for the Pluto encounter and some of the concerns regarding the spacecraft’s extended mission.
Dr. Stern, before we start, I’d like to thank you for taking the time to talk with us about ‘New Horizons,’ that could be safely described as the most important planetary mission of the whole decade. Would you like to give us an update on the current status of the spacecraft after its short wake-up call from its hibernation in early January? What is the mission schedule for the rest of the year?
It’s my pleasure. We will be reviving the spacecraft for a short period of operations beginning later this month and lasting until late August and conduct some science observations, in order to make a full check of the spacecraft’s systems and make sure that they’re ready for the encounter with Pluto next year. Then, the spacecraft will return into hibernation, to be reactivated again in December, just prior to the beginning of the long-range reconnaissance of Pluto and its satellites.
With a growing number of moons being discovered around Pluto in recent years, scientists have expressed some fear that possible dust rings around the moons resulting from micrometeroid collisions could pose a serious threat to the spacecraft during the Pluto flyby. What are the contingencies that have been planned to better safeguard the spacecraft?
From earlier observations and through computer model calculations, the science team has determined that the actual threat from impacts with dust particles on the environment around Pluto is much lower than initially thought—less than 1 percent, we believe. Still, there are a number of contingency plans that have been drawn to ensure that New Horizons will have a safe passage through the Pluto system. There are a number of alternate trajectory flight plans that have been drawn for the spacecraft to follow, in case that a correction maneuver needs to be made—potentially as late as 10 days prior to closest approach with Pluto—to achieve a safer course than now planned. Should we determine that the dust environment poses a significant threat, we have also devised a sequence that orients the spacecraft’s communication antenna in front of the spacecraft, so that it acts as a ‘shield,’ thus protecting it from impacts with any dust particles, but sacrificing some kinds of science.
If such an alternate flight path is to be chosen that brings the spacecraft farther from Pluto, how much will the science observations be impacted?
Contrary to what is believed, some of our alternate flight trajectories will actually bring the spacecraft closer to, not farther from, Pluto, possibly even skimming above the upper layers of the atmosphere. The effects of the alternate trajectories and onboard sequences that we have planned for the spacecraft can be described in terms of the results you get in writing exams, like A, B, C, and D in order of science value. Of course, we want to get the best possible value from our observations, but even the more ‘science-limited’ alternatives that get poor or bad grades will be of a far superior science value to losing the spacecraft and its collected data altogether.
There has been some concern lately regarding the science phase of the mission following the Pluto flyby next year. Astronomers haven’t yet been able to identify a suitable Kuiper Belt Object for the spacecraft to study, following the Pluto encounter. What are the steps that are currently taken toward that goal?
That’s correct. Despite intensive searches using the largest telescopes and most talented astronomers in the world, we haven’t yet been able to identify any suitable KBO that is close enough to be within the spacecraft’s fuel supply. We have therefore submitted our request to secure search time with the Hubble Space Telescope, and we will expect to know the answer as early as next week. If we can secure some time with Hubble, computer model estimates indicate a 95 percent chance we will be able to locate a suitable KBO object for the spacecraft to study. Time is of the issue, as this needs to be done almost a year before closest approach with Pluto—or by the end of 2014. If we are unable to secure any time with Hubble, then it will really be a shame, for we will have a perfectly healthy spacecraft with more fuel than we originally expected to have for Kuiper Belt exploration, and we will not be able to make use of it. As a result, there will be no exploration of distance KBOs.
If such a KBO object cannot be found in time, how possible will it be for New Horizons to discovery such a body on its own, in the vast expanse beyond Pluto?
This simply isn’t possible. The telescopes aboard New Horizons are too small to accomplish that.
Before the Voyager missions, the outer Solar System was thought to be a vast graveyard of boring chunks of rock and ice. Since Neptune’s moon Triton has turned out to be such an interesting and geologically active object in such a great distance from the Sun, what can we expect to find on Pluto?
Something wonderful! I wouldn’t want to predict what exactly we will find, but I do think it will forever change our views of Pluto and the rest of the Solar System. After all, we have never explored this kind of planet before.
You have remarked in the past that the growing number of large KBOs that have been discovered in recent years beyond the orbit of Neptune are indicative of a third class of planets in the Solar System, besides the terrestrials like Earth and the gas giants like Jupiter. How are these discoveries affecting our definition of planet?
Before the discovery of the first KBOs in the 1990s, Pluto seemed like an oddball, because we lacked the technology to be able to probe deeper into that region and see that it was just the first of a new population of small planets and smaller bodies. With the discovery of the Kuiper Belt, however, a new realization has arisen that what we’re seeing are indeed a new class of planets, dwarf planets. And that’s how science works. You make discoveries of things that you didn’t expect to that force you to reconsider and change your views on a certain field of study. With the help of modern-day instruments, we are seeing that large terrestrial and gas giant planets are quite the minority among the planets of our Solar System.
Dr. Stern, I’d like to thank you again for taking the time to answer our questions regarding the exciting mission that is New Horizons. Before we close, do you have any final thoughts about the mission?
Well, I’d like to say that the mission’s science and engineering teams have done a tremendous job of preparing for the Pluto system flyby next year, and we’re all very excited about all the new discoveries that await us when we get there. We’re also excited to bring back first time exploration to the public’s attention—nothing like this has happened since Voyager reached Neptune in 1989!
Every new planetary mission is an exciting new step forward in our exploration of the Cosmos, advancing our understanding of the Solar System that we live in. Exactly 50 years after NASA’s Mariner 4 flyby of Mars revealed to us a completely new world that was previously unseen by human eyes, the New Horizons Pluto flyby holds the promise of completely revolutionising our entire view of the Solar System, with the exploration of its last planetary frontier and all the vast expanses that lie beyond.
That would be something wonderful indeed!
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