Despite its long-suffering status as the ‘butt’ of many jokes, Uranus emerged from the shadows and entered the headlines this weekend, as it reached ‘opposition’: the position occupied when a celestial body is directly opposite the Sun, when viewed from Earth. Yet the prospects for future exploration of this strange, aquamarine-hued world remain shrouded in gloom and uncertainty. Last year, the National Research Council’s Planetary Science Decadal Survey for 2013-2022 identified a Uranus Orbiter and Probe as the third highest-priority exploration objective for a future flagship-type mission. NASA agreed, but the realities of the current fiscal environment have made it unlikely that such a voyage will be initiated in the near future.
More than two decades have passed since Voyager 2 flew past Uranus and revealed a bland, featureless globe, seemingly absent of major atmospheric activity. This contributed to the popular misconception that the planet was ‘boring’ and unworthy of further examination. The reality is quite different and in recent years calls from scientists from around the world to stage a dedicated mission to Uranus have intensified.
When Voyager hurtled just 50,600 miles above the planet’s cloud tops, making its closest approach on 24 January 1986, its cameras and instruments observed targets far darker than anything it had previously seen at Jupiter or Saturn. With the Sun little more than a large dot in the sky, the spacecraft’s task was likened to photographing a pile of charcoal briquettes at the foot of a Christmas tree, lit by a one-watt bulb. Clever image-compression and other techniques turned our first close-up glimpse of Uranus into a spectacular success and Voyager’s images – transmitted across the 1.8-billion-mile gulf to Earth – revealed the seventh world in our Solar System in all its splendour.
Splendour, though, was not quite the right word.
At first glance, Uranus appeared quiet and unassuming. Unlike Jupiter and Saturn, it exhibited no violent storms or zonal radiation bands or swirling spots or jumping eddies; even its rings were dark and narrow. The overall impression was so dull that members of the Voyager 2 Imaging Team wryly dubbed themselves ‘The Imagining Team’. The spacecraft’s instruments managed to pick out chemical constituents, positively identified clouds beneath a high-level hydrocarbon haze and accurately determined atmospheric temperatures and composition…but Uranus still seemed distinctly bland.
This was caused in part by an unusual 98-degree tilt in its rotational axis, which means it orbits the Sun tipped onto its side, like a beer barrel. As a consequence, Uranus’ north and south poles are aligned roughly with the ecliptic plane, where most other planets have their equators. In response to this, the planet receives more sunlight at its poles…but, due to some unknown mechanism of heat-transfer within its deep, dense atmosphere, Uranus remains hotter at its equator. During its 84-year-long orbit of the Sun, each pole is respectively subjected to 42-year periods of sunlight and darkness and at the time of Voyager 2’s arrival only the southern hemisphere and those of Uranus’ five large moons – Miranda, Ariel, Umbriel, Titania and Oberon – were in sunlight. By contrast, their northern halves were in the dead of winter.
Not for another decade or more did the Uranian north begin to stir and in 1999 the Hubble Space Telescope revealed the faint patterns of clockwise-moving winds, clipping along at more than 300 mph, together with vast, Europe-sized waves of storms. Latitudinal banding on Jupiter and Saturn is the result of strong solar heating at their equators, but Uranus’ tipped-over orientation means that it receives more heat at its poles and it was not until December 2007 that the Sun was directly above its equator. This general timeframe seems to have ushered in a new era of weather activity, including the appearance of the 800-mile-wide Uranus Dark Spot in the northern hemisphere.
The changing face of Uranus prompted much interest from scientists around the world in returning to the topsy-turvy planet. This peaked in March 2011 when the National Research Council published its Planetary Science Decadal Survey for 2013-2022. It highlighted three priorities for future ‘flagship’ missions – those in the same class as the Mars Science Laboratory, costing between $1.5 billion and $2.7 billion – and in third place, after the Mars Astrobiology Explorer-Cacher (MAX-C) and the Jupiter Europa Orbiter (JEO), was a ‘Uranus Orbiter and Probe’. Four months later, NASA’s response firmly supported the Survey’s recommendations. However, it was noted that the present budgetary situation made it “unlikely” that a Uranus voyage could be initiated alongside MAX-C and JEO.
Current fiscal predictions for the space agency – with great emphasis placed upon the development of the Space Launch System (SLS) heavy-lift booster – suggest that the budget will remain flat in the near future. Earlier this year, the Fiscal Year 2013 proposal identified a devastating 21-percent cut – amounting to around $309 million – to NASA’s planetary sciences budget. This obliged NASA to completely cancel its participation with ESA in the ExoMars mission and placed plans for future flagship-class projects on indefinite hold; a decision which garnered harsh criticism from members of the scientific community. “There is no room in the current budget proposal from the President for new flagship missions anywhere,” NASA Associate Administrator for Science and former astronaut John Grunsfeld glumly told journalists on 13 February. Meanwhile, the influential Planetary Society described its effects succinctly: “Major missions are not possible on this budget,” it noted, “and merely maintaining support for current missions would be difficult.”
With regard to Uranus, the lengthy journey time of perhaps 10-17 years – dependent upon the choice of propulsion technology used – means that humanity’s next close-up look at the planet will not occur for at least the next two or three decades…longer than we have waited since the departure of Voyager 2.
Yet despair and hope are frequently close bedfellows. A joint NASA-ESA Uranus Pathfinder mission, led by Chris Arridge of University College London, envisaged a £400 million venture to despatch a medium-class vehicle to the distant planet in 2022. It was formally proposed to ESA in December 2010, signed by 120 planetary scientists from as far afield as Argentina, Belgium, France, Germany, Greece, Hungary, Israel, Spain, Sweden, the United Kingdom and the United States, but was ultimately passed over for development funding. “Costs rear their ugly head,” Arridge remarked at the time, although he remained confident that interest in Uranus was strong and the mission was by no means dead in the water. Another proposal from the Johns Hopkins University Applied Physics Laboratory, under the impressive acronym of ‘HORUS’ – the ‘Herschel Orbital Reconnaissance of the Uranian System’ – featured plans for a nuclear-powered orbiter, equipped with cameras, spectrometers and a magnetometer to investigate the planet’s peculiarly skewed magnetic field. Still others have offered ideas for solar-electric-propelled craft, which might launch as soon as 2018.
A rock and a hard place would seem to be an accurate descriptor of NASA’s current position and Administrator Charlie Bolden explained in February 2012 that the agency was faced with “tough choices” to make. Despite renewed optimism in the human space exploration arena (as Commercial Crew moves toward fruition and the SLS advances further toward reality than its ill-fated predecessor, the Ares V, ever did) the recognition of the negative impact of ever-tightening and unfair budgets upon robotic planetary exploration is nowhere more acute than in the elusive goal of a return mission to Uranus. The discovery of ancient stream beds by the Curiosity rover – described by my colleague Jason Rhian in a recent AmericaSpace article – and President Obama’s light-hearted (but somewhat patronising) request to be called “right away” if the mission found Martian life, is indicative of an appalling level of ignorance in planetary science and exploration held by the world’s most powerful and influential man.
A Uranus Orbiter and Probe of the flagship class – the same variety which produced the Voyagers, the Galileo mission to Jupiter, the Cassini voyage to Saturn and the already enormously successful Curiosity – would set the United States back by a few hundred million dollars either side of $2 billion. A little number-crunching equates that cost to just seven or eight dollars per head of the population and when one considers that America currently devotes $115 billion annually to ongoing operations in Afghanistan – an astounding $220,000 every minute – it renders the argument that the United States cannot afford such excessive amounts for planetary exploration unpleasantly difficult to swallow. Afghanistan consumes the same sum as NASA would spend on a Uranus Orbiter and Probe in less than one week; Iraq does approximately the same. Yet both presidential candidates for 2013 seem unwilling to countenance increasing NASA’s annual coffer above its current standing of just half a single percentage point of the federal budget.
To planetary scientist Scott Hubbard of Stanford University – a former head of NASA’s Ames Research Center, a member of the Columbia Accident Investigation Board and currently on the SpaceX Safety Advisory Panel – this neglect of the space agency and planetary exploration in particular is nothing less than “a scientific tragedy and a national embarrassment”. Earlier this week, the Planetary Society announced that its members and supporters had sent 17,000 emails to the Office of Management and Budget and the Office of Science and Technology Policy, requesting the restoration of NASA’s planetary funding. According to the Casey Dreier, the Society’s technology and outreach strategist, such moves are bearing some fruit.
In whatever manner the political landscape changes in the United States in January 2013, there can be little doubt that the financial reality makes it unlikely for any substantial change in the direction of the prevailing wind. The much-anticipated ExoMars missions with ESA are gone, the Europeans are currently deep into negotiations with Russia as a potential new partner and Curiosity seems to be the last tangible flagship-class planetary mission for the foreseeable future. Even a significant budgetary shift makes it difficult to envisage the formal inauguration of a Uranus Orbiter and Probe mission and, even if it did happen, a launch would not occur for at least another decade and would not reach the mysterious planet until the latter part of the 2030s…by which time this author will be in his sixties.
Two years ago, the Obama Administration stubbornly refused to consider a human return to the Moon. The president’s infamously short-sighted summary – “We’ve been there before” – continues to echo in many ears and continues to cause more than a few toes to curl and teeth to grind. Political neglect will be one of the yardsticks by which future generations will judge our progress in space. Remarkable strides forward have been taken in the planetary science arena, on both flagship-class and shoestring budgets, and the opportunities to advance further with missions such as the Uranus Orbiter and Probe are truly limitless…for each mission plays its own critical role in improving human understanding of our Sun’s realm, our place in the cosmos and how we came to be.
Ben Evans is the author of ‘NASA’s Voyager Missions: Exploring the Outer Solar System and Beyond’, published by Springer-Praxis.