Interstellar Travel - Science Fiction or Reality?

What is interstellar travel?

Interstellar travel is the idea of travelling between other star systems in the Milky Way beyond our own. Although it is hypothetical at best right now, over the last century, many have wondered what is beyond our solar system and scientists have put in a lot of time and research into making this somewhat of a reality someday. 

After all, if we manage to get a breakthrough, it could be the start of a new era with a multitude of new possibilities and discoveries. Space exploration beyond the Earth’s atmosphere began in 1958 and has been reaching new heights with the passing of time. 

What have we achieved so far?

Humans are evolutionarily built to explore and venture to discover new things and break records. Currently, our biggest motive to explore astronomical bodies is to potentially either find some form of extraterrestrial life or the conditions for life to flourish. The need to meet the latter motive is accelerated due to the effects of climate change on Earth.

Although strictly science fiction - the 2014 movie ‘Interstellar’ won praise from the scientific community for its research into rationalising the effects of interstellar travel for the big screen and visualising the behaviour of light (and time dilation) when travelling close to a black hole. It is based on a period in Earth’s future where climate change has killed the last food crops and humanity's only hope is to leave. Some even claimed it should be shown in schools! 

An image from the movie ‘Interstellar’ showed us what a black hole might look like using real scientific data and simulations.

We have made huge strides scientifically in monitoring space and understanding what we can see and how to navigate it, but there are a lot of technological advances needed before humans can begin thinking about traversing it. The scale of space and the travel time involved is incomprehensible to the majority of us who live and think in terms of life on Earth.

Humanity’s first big leap towards interstellar travel was initiated in 1977 with the launch of the spacecraft Voyager 1. It was launched by NASA on 5th September with the aim of exploring the four gas giants of our solar system - Jupiter, Saturn, Uranus and Neptune. 

It was launched during a special alignment in the solar system which allowed it to get accelerated, similar to a slingshot, from the planets’ gravity. This limited the fuel usage of the spacecraft. Inserted with a camera, Voyager 1 captured images of these planets for scientists to study back on Earth. In fact, one of the greatest images captured of all time was by Voyager 1! 

After the spacecraft had studied Neptune and was headed towards interstellar space, scientists commanded the camera to turn back and capture our planet for the final time. The resulting image became famously known as the ‘pale blue dot’ and was captured on 14th February 1990. 

A snapshot of voyager 1 (left) and the famously captured ‘pale blue dot’ (right).

The pale blue dot evoked fascination and emotion as at this point in time, many were beginning to realize how small and insignificant we are in the vastness of space even though the photograph was captured only 6.4 billion kilometres away from Earth when Voyager 1 was still in our solar system. 

That may seem very far away but is a minuscule amount in the grand scale of the universe. In August 2012, Voyager 1 became the first spacecraft to enter interstellar space. However, it is still in an outer boundary of our solar system called the Oort cloud after which it will truly be out of the solar system.

Shortly before Voyager 1, its twin spacecraft, Voyager 2, was launched in August 1977 with the same aim. 

Voyager 2 managed to discover the new moons of Jupiter, Uranus and Neptune. Having spent around 12 years in the solar system, Voyager 2 finally completed studying Neptune and it too headed for interstellar space but on a different trajectory than its partner. Irrespective of the pathway, both spacecraft are destined to roam within the Milky Way for the foreseeable future.

What are our limitations? 

Voyager 1 and Voyager 2 are currently travelling across the cosmos at about 17 km/s and 15 km/s respectively. This may seem extremely fast but, at this speed, it will take Voyager 1 about 30,000 years to fully exit the oort cloud! Moreover, the brightest star in the night sky, Sirius, is the star Voyager 2 is headed towards. 

Despite being 8.6 light years away from Earth, it will take Voyager 2 roughly 300,000 years to reach it! You can see what a big barrier humans have with current technology to explore other star systems. This becomes more disappointing when we consider a star system that could potentially support life. 

The closest star to us after our sun is Proxima Centauri, which is only 4.2 light years away from us. It is one of three stars and the whole star system is known as Alpha Centauri. Although it was discovered in 1915 and its discovery alone was not of much use to us, what followed very recently caused a stir in the field of space exploration. 

In 2016, an exoplanet (a planet orbiting a sun outside our solar system) called Proxima b was discovered. It is of a very similar mass to Earth. Although it sits a lot closer to its star than Earth is to the sun, what caught massive attention is the fact that it potentially sits in something called the ‘habitable zone’. 

A visual of the circumstellar habitable zone (CHZ). Also known as the habitable zone.

This is the range of distances that a planet can be from its sun in order to support life. This means that it could hold liquid water. This discovery changed the mindset of several scientists who now went from just visualizing and imagining interstellar travel to trying their best to make it a reality. 

There are still quite a few unknowns regarding Proxima B. It orbits very close to its star so scientists pose the question of whether the planet could actually hold the liquid water even if the surface temperatures allow it to exist in the liquid state. This is due to its close proximity to its star and therefore the intense radiation that could easily strip off Proxima b’s atmosphere. Nonetheless, it was too tempting not to find out more about this exoplanet.

In the scale of cosmic distances, Proxima b is delightfully close. However, humans cannot even comprehend fully how far it is when you consider the distances we are used to. Voyager 1 is currently the fastest man-made object racing through space. However, if it was headed towards Proxima b, it would take 70,000 years to reach it! We obviously don’t have that sort of time so putting humans on a spacecraft is out of the question unless you send a theoretical generation ship where several generations spend their lives in outer space.

Even if we were to consider speeding up the spacecraft that already exist, even to a small percentage of the speed of light, the energy required to do so would be phenomenal as these vessels contain an enormous amount of mass. 

Furthermore, even if we did manage to send an unmanned vessel to Proxima b, by the time it got there, there could have already been another spacecraft with humans who have colonized the planet due to technological advancements in the distant future. After all, we are talking about thousands of years here. 

How do we overcome the barriers?

In the science fiction movie ‘Interstellar’ - they skipped straight to another solar system using a wormhole, a theoretical shortcut through space and time. It’s the perfect solution to interstellar travel in theory but, in reality, one that we may never understand how to control or even how to survive the journey. 

We have several barriers which currently make it impossible for us to visit another star system. In order to hugely cut down the time taken to reach Proxima b, scientists explored the possibility of propelling spacecraft by something called antimatter rather than chemically through fuel. 

In simple terms, antimatter is the name given to the particles in an atom which have the opposite properties to the protons, neutrons and electrons that we know of. However, this method would still take around 1000 years to reach Proxima b but would be a great leap forward from the time frames today’s spacecraft would take.

The second and most anticipated attempt yet is sending not spacecraft but miniature space probes called nano-crafts into space. These would be extremely light in weight and would be attached to light sails. They would be powered through laser beams from Earth and can be accelerated to travel at a significant proportion of light speed!

This would mean that the average journey time to Alpha Centauri would take roughly 20 years and these probes could fly close enough to the star system and the exoplanet to capture images of their surfaces. This entire project is called ‘Breakthrough Starshot’ and requires an estimated $5-10 billion. It is planning to launch these probes by 2036 if all goes to plan.

A visual of the type of space probe that will be used in project ‘Breakthrough Starshot’

With the exciting, new advancements in this field, exploring other star systems could be more than just science fiction by the end of the century. After all, 100 years ago, many would have been sceptical of even going to the moon. But, we have achieved that and so much more. The main question now is - will humans ever be able to visit another star system or are we destined to be Earthlings forever?

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