- Richard Hollingham
- bbc future
image source, SPL
Space missions have rarely come close to Uranus.
Uranus is almost certainly the least appreciated planet in our solar system. When quest invites are handed out, he always seems to get ignored.
Spacecraft have been sent to Mercury, Mars, Venus, Saturn, and Jupiter. There is even one in the direction of Pluto, the dwarf planet.
Uranus has only qualified for the planetary equivalent of an official encounter when Voyager 2 sped by on its way to the edge of the solar system in 1986.
weirdo
But Uranus, in fact, is one of the most interesting, fascinating, and truly bizarre planets we know of.
«Uranus really stands out,» says Leigh Fletcher, a planetary scientist at Oxford University. «He’s the oddball in our collection of planetary types.»
image source, SPL
NASA’s Voyager 2 probe flew by Uranus in 1986.
With a volume 60 times that of Earth, Uranus is a compressed mass of toxic gases, including methane, ammonia, and hydrogen sulfide, surrounding a small, rocky core.
«There is no solid surface on any of these giant planets,» says Fletcher. «There are no sharp boundaries, nothing to stand on or navigate, but there is a continuum from gas to liquid to some kind of solid.»
‘Interesting’ atmosphere
Orbited by 26 small moons, a few faint rings, and a weak magnetic field, Uranus appears to be tipped on its side.
Each planet has a slight tilt as it spins – which gives us four seasons – but unlike every other planet in the solar system, Uranus rotates on an axis that points almost directly at the Sun. Something Fletcher describes as «really weird.» .
«Imagine a world where winter equals 42 Earth years and the sun is not seen once during that time,» he says.
«There is a situation where the atmosphere doesn’t heat up for decades and that can lead to some really interesting atmospheric properties.»
Fletcher is part of an international team that believes Uranus has been ignored for too long.
This group of engineers and space scientists from Europe, the United States and some other countries, such as Japan, is working on a US$600 million mission proposal for the European Space Agency (ESA) with the aim of to send a space probe, within the next 10 years, to find out why Uranus is so strange.
The mission will investigate the atmosphere, the magnetic field and capture detailed images of this unknown world.
image source, SPL
Uranus has a volume 60 times the size of Earth.
By comparing the ancient mix of gases held in Uranus’s atmosphere to Earth’s or Jupiter’s, they also hope to gain a better understanding of what conditions were like when the solar system began to form.
«I think of Uranus as the missing link,» says Fletcher. «A mission that can investigate the internal structure of the planet, detect atmospheric composition, and understand how the atmosphere evolves, would allow us to piece together the puzzle of how planets form.»
«I would say,» he adds, «that if we can’t understand how planets formed in our own solar system, it’s going to be even more difficult to do the same for planets circling other stars.»
epic journey
However, there is a good reason why, in the entire history of space exploration, only one mission has visited Uranus: it is extremely difficult.
For starters, the planet is almost 3 billion kilometers from the Sun, that’s 20 times farther than Earth. Consequently, any spacecraft will take up to 15 years to get there.
Because sunlight is very weak at that distance, instead of solar panels, the mission will have to use a nuclear power source, which is more difficult to build and operate.
image source, ESA Wikipedia
ESA expects to have a mission plan by January 2015.
There is also the question of how to communicate with and retrieve data from a spacecraft that is so far away. Install a giant dish on the side or build a huge receiver on Earth? Or both?
Another major hurdle is the challenge of keeping the mission, operations, and engineering teams together during the decade between launch and arrival on the planet.
And all this before analyzing what instruments are going to be put on board.
world drive
Despite space agencies considering a mission to Uranus as a priority, previous proposals from ESA and NASA have long been forgotten, including a plan by a European team in 2010 known as uranus explorer. Why is the latter different?
«In 2010 we hadn’t worked out all the details,» admits Chris Arridge of University from London, one of the leaders of the Uranus team, who spoke to the BBC from a mission planning meeting in Washington DC.
«This time we have a very well-developed understanding of the science we want to do and the instruments we want to take with us.»
image source, POT
It would take a ship 15 years to reach Uranus.
Scientists have until January 2015 to submit a detailed mission proposal to ESA.
«It takes a tremendous amount of work, as we have to work on everything from what kind of rocket we’re going to launch, what orbit we’re going to go into, and what instruments we’re going to take with us,» says Arridge. «However, there is a growing global momentum and a real sense of excitement.»
Even if the mission is accepted, it will not launch until at least 2020 and would only reach Uranus after a journey of more than a decade, in the mid-2030s.
However, for Fletcher, it will remain a dream come true.
«Today I find myself sitting in my office as a researcher in my thirties,» he says. «I hope I can be sitting in my office like a sixty-year-old researcher when the spaceship arrives.»
«Planetary exploration is not over,» adds Fletcher. «There are still interesting ideas like this on the table.»