How to reach and why Uranus, the forgotten planet
It seems that Uranus is the most neglected of planets. All the others have something
remarkable that makes them scientifically appetizing for the exploratory cravings of
our species. Mercury is the closest to the Sun, Venus the closest to Earth, Mars the most known,
Jupiter the largest, Saturn has rings, Neptune is the farthest giant, and Pluto is the most beloved.
And all these objects, except for Mercury and Venus, also have one or more large satellites,
which makes them extremely interesting to astronomers and space mission planners.
Pluto has Charon, Neptune has Triton, Saturn has Titan, Jupiter has Io, Europa, Ganymede,
and Callisto. Earth has the Moon... Uranus is the only gas giant without a
large satellite. Why, still, is not known. So what? Is Uranus forgotten just because
it has nothing particularly interesting to offer? No, of course not. Someone (joking,
but not too much) says that the planet suffers from the disadvantage of having a difficult name,
which in English is practically unpronounceable because it lends itself to bad jokes. In short,
in the English-speaking world, the pronunciation of Uranus would sound decidedly bad,
so people would avoid mentioning the planet. Something that might be true in barroom chats,
but certainly not in scientific circles. It is true, however, that space agencies
in recent decades have sent various probes to investigate the planets of the solar system. Yet,
it seems that every time new missions are proposed, Uranus is bypassed,
even ignored more than its distant twin, Neptune.
To date, only one probe has visited this planet, and it was Voyager 2,
which passed close to it in 1986, only to gain momentum and head towards Neptune.
At the time of Voyager, Uranus had a notoriously bland appearance. It was called the blue billiard
ball, and so few atmospheric features were observed that the Voyager atmospheric science
team thought to give up some of their precious observation time to other teams.
Is this perhaps why there is so little interest in exploring this planet? Is it so difficult to
reach? Or simply, does it have nothing to offer? No! Despite its bad reputation and the few
exploratory missions, we have then managed to understand that Uranus is not a boring
planet at all. On the contrary, it is one of the strangest and most exciting planets, and as we
will see at the end of this extraordinary video, its scientific importance is continually growing.
Are you curious to try to follow us to the end and
find out what has changed the minds of planetologists? OK, let's start then!
“Roll intro”
As we just said, Uranus is not a boring planet; on the contrary, it is a fascinating and unique
planet. It is the third-largest planet and the fourth by mass. It was the first planet—obviously
after Saturn—around which we discovered a ring system in 1977. And it has the unique
peculiarity of having a rotation axis inclined by 97° to the orbital plane. As if to say that
Uranus rolls on the plane of its orbit rather than turning like more or less all the other planets.
However, there's a significant reason why, in the entire history of space exploration,
only one mission has visited Uranus: getting there is a genuinely long and challenging
endeavor. The planet is located almost three billion kilometers from the Sun,
twenty times farther than Earth. But this is perhaps one of the minor problems,
especially since Neptune and Pluto are much farther away.
To understand the reason for such difficulty,
let's take a step back to the days when Voyager 2 (it was January 1986, exactly 38 years ago) was
about to reach the planet after an endless journey of 10.5 billion kilometers. Yes,
you heard it right... Although Uranus - as we just mentioned - is three billion kilometers
away from the Sun, Voyager 2 had traveled more than three times that distance by then.
This is because in space, one practically never travels in a straight line, and the probe needed
continuous gravitational assists to increase its speed and adjust its course. These assists were
obtained by stealing kinetic energy from massive planets that it could approach,
deviating from its trajectory. This increased speed, true, but it also increased the distance
to cover due to the necessary detours. So, was it really worth it? The calculations are complicated,
but we can assure you that without the assists from Jupiter and Saturn,
Voyager 2 would have taken about 12 years to reach Uranus! Instead, it took only 9 years,
saving time, fuel, and resources. This demonstrates that gravitational assistance
is a very advantageous technique for space missions, despite its disadvantages. Not
to mention that without the course changes imposed by the two fly-bys with the gas giants,
the probe would never have been able to visit all four gas giants of the solar system successively!
At this point, someone might object: Okay, Voyager 2 took 9 years to reach Uranus... but
how come the New Horizons probe reached Pluto, which is twice as far as Uranus,
in just 6 years? The difference in time between the two space missions
depends on various factors, including speed, trajectory, and probe maneuvers.
The New Horizons probe was launched in 2006 with an initial speed of about 58,000 km/h, the
highest ever achieved by a probe. Additionally, it utilized a gravitational assist from Jupiter,
which allowed it to increase its speed by about 14,000 km/h and save time and fuel on a path
that enabled it to reach Pluto in 2015 after a journey of about 5 billion kilometers. Voyager 2,
on the other hand, was launched in 1977 with an initial speed of about 35,000 km/h,
lower than that of New Horizons. Also, as we've seen, it followed a more complex trajectory.
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But it's not just a matter of speed... Another limiting factor for all spacecraft sent to
the outer reaches of the solar system is the diminishing sunlight as you move away from our
star. At certain distances, solar panels become entirely useless in generating energy. Therefore,
the mission must inevitably use a source of nuclear power, namely a
nuclear battery that would end up weighing down the spacecraft, reducing its speed.
Another problem that adds up is communication with Earth, which at the distance of Uranus
would involve receiving signals with a 2.6-hour delay and reaction times to a possible problem
of 5.2 hours. This is a delicate matter, especially considering that the insertion
of a spacecraft into orbit around the planet would have to be conducted automatically without human
intervention. Additionally, we must remember that putting a probe into orbit around Uranus would be
doubly challenging due to its axial orientation. Another significant but often overlooked obstacle
is keeping both the engineering mission teams and the operational teams together for the entire time
needed to complete the mission; in the case of Uranus, it can take up to a decade between the
launch and the arrival of the spacecraft on the planet — and even two decades if we consider the
start of the design. Although it might seem insignificant, this problem is the reason
why many missions have had to be canceled. Others have faced delays of years because the team that
began working on a mission was not the same that completed it. This is because crucial information
or codes are often lost in the transition from one generation of technicians to another.
This is precisely what happened with the Voyager probes, which used VHS-type films to send images,
and software specially made for this task was responsible for their encoding here on
Earth. The equipment that performed that task, the software, and the people who knew how to
use them no longer exist, so today it would be impossible to retrieve images from the Voyager
cameras, even if they were still operational. Another example of this problem can be seen in
the recent Artemis 1 mission aiming to bring the next generation of astronauts to the Moon. Many
people wondered why there was a need to rebuild everything from scratch, ignoring what was done
during the Apollo era. Again, the reason is that all that information has been lost — the people
who knew the computer codes, passwords, those who made the designs, and mathematical calculations,
most of them have long since passed away. No knowledge can work forever, regardless
of the passage of time. Every space mission is a case of its own, realized by technicians
and scientists who applied solutions that are now indecipherable. Sad, but that's how it is.
Today, we couldn't simply clone the missions carried out by the two Voyagers;
they would have to be redesigned from scratch, of course, improving upon them. So far,
this has been a considerable obstacle to the willingness to explore again towards
Uranus and Neptune. However, we haven't yet addressed the reason why this willingness
has been strengthening in recent years. The short answer is that in the meantime,
we've started discovering extrasolar planets, and astronomers are increasingly realizing
that planets like Uranus are the most common in the solar systems of our galaxy.
The long answer is that Uranus belongs to the class of planets that astronomers call "ice
giants" because they are formed from a large amount of volatile materials such as water,
ammonia, and methane – elements found in solid or liquid states under the atmosphere made of
hydrogen and helium. These planets differ from "gas giants" like Jupiter and Saturn,
which are predominantly composed of hydrogen and helium, and from "rocky
planets" like Earth and Mars, which have a solid core and a solid or liquid surface.
Uranus and Neptune are the only two ice giants in our solar system, but observations in recent years
have revealed that this class of planets is very common in our galaxy. Thanks to various detection
methods such as transit, radial velocity, and gravitational microlensing, astronomers have
discovered thousands of extrasolar planets, many of which have sizes and masses similar to Uranus
and Neptune. These planets are often called "mini-Neptunes" or "super-Earths," depending
on whether they are larger or smaller than Earth, but in reality, they could be ice giants.
Studying Uranus up close might be necessary to understand how these
planets, likely the most numerous in our galaxy,
form and evolve. In particular, Uranus could provide information on the following issues:
How does an ice giant form? What factors determine its composition, structure, climate,
and magnetic field? What is the role of planetary migration, i.e., the movement of planets from
their original positions due to gravitational interactions with other celestial bodies?
How does an ice giant evolve? How does its orbit, rotation axis, atmosphere, and geological activity
change over time? What are the effects of tides, collisions, radiation, and stellar disturbances?
How does a system of satellites form around an ice giant? What are the physical and dynamic
characteristics of these satellites? What are the chances that some of them
have conditions favorable for life, such as underground oceans or energy sources?
These are just some of the questions scientists have about Uranus and similar planets,
and they could potentially be answered with a dedicated space mission. A mission to Uranus
could offer us a detailed and in-depth view of this enigmatic world and its numerous satellites,
some of which might harbor underground oceans. A mission to Uranus could also help us compare
the characteristics of this planet with those of Neptune,
the other ice giant in our solar system, and with those of extrasolar planets of the same class,
to understand the similarities and differences between these worlds.
Over the years, several missions to Uranus have been proposed, later canceled in favor of other
missions deemed more scientifically valuable. But now, based on incredible discoveries in
planetary systems around other stars, it seems that NASA is convinced to take it seriously. Thus,
the Uranus Orbiter and Probe project was born, a joint proposal between NASA and ESA
to reach Uranus with an orbiter that will also release a probe into its atmosphere,
somewhat akin to what Cassini and Huygens did on Saturn and Titan in 2005. Remember that?
Experts estimate that the journey will last 12-15 years, mainly depending on the launch date,
which will determine the distance between the two planets. Uranus
and Neptune are the only planets that have never been studied with a dedicated orbital
mission, and missions to these planets have been deemed a priority for the next decade,
mainly due to the potential to produce revolutionary science on a wide range of topics.
The best launch opportunities for the mission would be in June 2031 and April 2032,
windows that could benefit from the gravitational boost of Jupiter to position the spacecraft in
orbit around Uranus after a cruise of about 13 years. But to be ready for these dates,
the mission should start in 2024. The estimated cost of the mission is around 4.2 billion dollars.
Other launch opportunities between 2032 and 2038 and beyond will have to use multiple
gravitational assists from inner planets of the Solar System (including a Venus
flyby) to position the vehicle in orbit with a cruise time of about 15 years.
The end of the ideal launch window is in 2038, which would require a 15-year journey
due to Uranus's position. Unfortunately, NASA recently postponed the launch due to
a decrease in plutonium production, meaning a launch in the mid to late '30s is more likely.
A real pity, but until we find better propulsion methods than those currently available,
we'll have to resign ourselves to aging in the hope of witnessing the conclusion
of these incredible adventures in person. Let time do its thing, and in the meantime,
let's focus on the exciting prospects of upcoming lunar and Martian missions!